Commissioning Systems, Batteries and Battery Charger

Engineering Encyclopedia Saudi Aramco DeskTop Standards

Commissioning Batteries And Battery Charger Systems

Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.

Chapter : Electrical File Reference: EEX30105

For additional information on this subject, contact W. A. Roussel on 874-1320

Engineering Encyclopedia

Electrical Commissioning Batteries and Battery Charger Systems

Contents

Page

Saudi Aramco Applications And Requirements For Batteries And Battery Charger System............................................................................

1

Evaluating Battery And Battery Charger Systems Upon Receipt ....................

36

Evaluating Battery And Battery Charger Installation And Testing ...................

38

Battery And Battery Charger System Operational Testing Requirements .......

43

Requirements For The System Operational Observation Phase ....................

45

Summary .........................................................................................................

46

Work Aid Work Aid 1: References For Evaluating Batteries And Battery Chargers Upon Receipt ..................................................................................

47

Work Aid 2: References For Evaluating Batteries And Battery Charger Installation And Testing.....................................................................

58

Glossary ..........................................................................................................

61

Saudi Aramco DeskTop Standards



SAUDI ARAMCO APPLICATIONS AND REQUIREMENTS FOR BATTERIES AND BATTERY CHARGER SYSTEMS The type and size of batteries and battery chargers that are used in Saudi Aramco installations are selected through use of a number of factors, such as the connected load, criticality of the load, and ambient conditions. Details of the selection process for batteries are provided in EEX 211. This Module will not deal with the actual selection process that occurred early in the project. This Module will be concerned with the specific items that should be verified and tested during the commissioning process. Batteries and battery chargers must meet all Saudi Aramco requirements before they are put into service. Batteries An electric cell is a device that directly converts the chemical energy that is contained in active materials into electrical energy through use of an oxidation-reduction electrochemical reaction. A battery is formed through the interconnection of one or more cells. These cells may be connected in series, which increases the voltage of the battery by the product of the cell voltage times the number of cells; or these cells may be connected in parallel, which increases the amount of current that is available. The available amp-hours are equal to the cell amp-hour rating times the number of cells. Batteries are a source of alternate energy for emergency and standby systems. Batteries may be used to power dc loads, (such as alarm and security systems) directly, or they may be used as control power for switchgear, telephone systems, and emergency lighting. Batteries also may be used indirectly to provide power through rotary or static uninterruptable power systems, which, in turn, provide power for ac loads. Batteries may also be used indirectly to provide power for lighting and industrial processes or through standby inverters. Generally, there are two types of batteries that are selected for emergency or standby service: lead-acid and nickel cadmium (Ni-Cad). The sealed lead-acid battery, also referred to as a maintenance-free battery, is a relatively new type of lead-acid battery that is sometimes specified for use in Saudi Aramco facilities. (As the text below explains, seven other types of lead-acid batteries are also used.) The specific type of battery that is selected is a result of the evaluation of many factors, such as projected lifetime, ambient conditions, criticality of load, and economics. Ni-Cad batteries are more expensive than lead-acid batteries, but they are more rugged, they require less maintenance, and they exhibit longer life than lead-acid batteries. The actual process of battery selection is outside the scope of this course, but the information can be found in the Saudi Aramco text, EEX 211, Introduction to DC/UPS Systems.


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Lead-Acid Batteries

The lead-acid battery is perhaps the most common type of battery that is used in industry to supply dc loads. The lead-acid battery consists of a group of electrochemical cells that are connected in series to generate a nominal dc voltage that is used to supply current to a specified load. The nominal voltage of the battery is determined by the total number of cells that are connected in series. The amount of active material that is contained in an individual cell is the factor that determines the discharge capacity rating of the cell. The rated capacity of the individual cells is the rated capacity of the entire battery. Although the individual cells are connected in series, the capacity amp-hour rating of the battery does not increase. The actual chemical reaction that produces a direct current is obtained through placement of a lead active material in a dilute sulfuric acid electrolyte. This electrochemical couple produces a nominal cell voltage of approximately two volts. All lead-acid cells are constructed of the following basic components that are shown in Figure 1: • • • • •

Element Cell jar Cell cover Electrolyte High and low electrolyte levels


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Basic Components of a Lead-Acid Cell Figure 1


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Figure 2 shows an exploded view of the battery element. The battery element is the key component of the cell, and it consists of an assembly of positive and negative plates that are insulated from each other through use of separators. The interaction that occurs between the battery element and the electrolyte determines the cell's performance characteristics. Each of the plates consists of a rigid lead alloy that provides physical support for the relatively porous active materials. The positive and the negative plates are sandwiched together in an alternating pattern (e.g., negative-positive-negative-positive-negative); a negative plate is placed at each end of the assembly. Each positive plate is separated from its neighboring negative plate through use of an insulating material. The insulating material typically is a thin sheet of microporous rubber or plastic that is ribbed on the side that faces the positive plate. The positive and negative terminal posts are connected to the positive and negative plates, respectively.

Battery Element Figure 2


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The cell jar, which was shown in Figure 1, is usually made of a transparent, impact-resistant plastic material. The cell jar must be large enough to enclose the element, yet it must still provide sufficient reservoir space above and below the element. The upper reservoir space is needed to allow for the gradual lowering of the electrolyte level that occurs during normal operation of the battery. The lower reservoir space serves as a collection basin for the sediment that is shed from the plates during the expected life of the battery. This sediment must be kept away from the element to prevent a short circuit between the positive and the negative plates. After the element has been lowered into the empty jar, the cell cover is placed over the top of the jar and is sealed. The terminal posts that are connected to the element protrude through holes that are located in the top of the cell cover. The cell cover also is fitted with a flame arrestor vent that allows gases to escape from inside of the cell but that prevents entry of sparks or flames. The electrolyte that is used in lead-acid batteries is a dilute solution of sulfuric acid and water. The ratio of acid weight to water is measured as specific gravity. Pure water has a specific gravity of 1.000. A typical, nominal specific gravity for a lead-acid storage battery is 1.215 at 25°C (77°F). The specific gravity of the electrolyte gradually drops as the cell is discharged. When the battery charger recharges the cell, the specific gravity gradually rises back to the nominal value. If a battery is to be operated at temperatures that exceed 29_C (85_F) for more than 30 days per year, a tropical (low) specific gravity electrolyte could be used to increase the life of the battery. A medium or a high specific gravity electrolyte is also available for special applications, such as UPS systems, that, in some cases, will reduce the overall battery size that is required. As previously stated, all lead-acid batteries contain the same basic components. The major difference between the various types of lead-acid batteries is the design of the positive plates that are used in the battery element. The remainder of this section provides information on the following specific types of lead-acid batteries: • • • •

Plante Lead calcium Lead antimony Sealed (Maintenance-Free)

Plante - The plante lead-acid battery is a lead-acid storage battery in which the active material

of the positive plates is electrochemically developed from pure metallic lead. Modern Plante lead-acid batteries are available with two types of positive plate constructions: traditional and Manchester. Both types of plates are shown in Figure3.


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The traditional positive plate starts off as a blank (slab) of pure metallic lead. Grooves are then cut into the surface of the lead blank through use of a combing process. The grooves increase the surface area of the plate, which increases the capacity of the cell. The Manchester plate is the most common type of plate that is used in Plante lead-acid batteries. The Manchester plate is constructed of a heavy antimony alloy grid that is cast with circular holes. Heavy corrugated strips of high purity lead are then rolled into spiral buttons or "rosettes" that are forced into the holes that are cast in the grid. Each of the lead buttons exposes approximately five times more surface area to the electrolyte than a comparable area on a pasted plate battery. The lead buttons also help to prolong the life of the cell by providing a reserve supply of unformed lead that is gradually converted to active material during operation of the cell. The negative plates of Plante lead-acid batteries are pasted or "flat" plates with a heavy alloy grid. The construction of these plates will be discussed in more detail in the next section of this Module.


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Positive Plates Used in Plante Lead-Acid Batteries Figure 3 The following are the major advantages and disadvantages of Plante lead-acid batteries: • • •

Advantages Long service life (20 to 25 years). Smallest amount of positive plate growth of all lead-acid cells. Very high reliability.


Disadvantages • High cost. • Poor energy density and poor power density. • Moderate self-discharge rates (3%/month).

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Plante lead-acid batteries have the highest capital cost of all types of lead-acid batteries. The cost of Plante lead-acid cells is approximately 3 to 3-1/2 times that of a comparable lead antimony cell and approximately 2-1/2 to 3 times that of a comparable lead calcium cell. However, in some applications, the high initial capital cost may be justified by the long (25 year) service life. The cyclic performance and cycle life of Plante lead-acid batteries, as is the case with all stationary lead-acid storage batteries, can only be discussed in relative terms. Stationary leadacid storage batteries are designed to provide a relatively long calendar service life (more than ten years) when they are operated under float charge conditions rather than a long cycle life. Stationary lead-acid storage batteries are normally not rated or guaranteed to deliver a specific number of equivalent full charge cycles. When any stationary lead-acid storage battery is subjected to deep and frequent discharges, its calendar service life will be reduced; however, because of the number of variables that are involved, the specific amount of calendar service life reduction cannot easily be quantified. For this reason, the cyclic performance of one type of lead-acid storage battery is generally only discussed in terms of comparison with another type of stationary lead-acid storage battery. The cyclic performance (e.g., the ability to withstand frequent and/or deep discharges) of Plante lead-acid batteries is far superior to the cyclic performance of lead calcium batteries and is approximately equivalent to the cyclic performance of lead antimony batteries. Plante lead-acid batteries are capable of withstanding a moderate amount of cycling with a minimum loss of calendar service life. Lead Calcium - The positive and the negative plates of lead calcium batteries are pasted plates.

Pasted plates are constructed by forcing a thick slurry of active material (e.g., a combination of lead oxides and sulfuric acid) into an open lattice grid. A typical pasted plate grid is shown in Figure 4. The open lattice grid is cast from an alloy of pure lead and calcium. The addition of the calcium alloying agent is necessary to increase the mechanical strength of the plate.


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Typical Pasted Plate Grid Figure 4 After the active material is pasted on the open lattice grid, the plates are dried and formed (activated) by an electrochemical process. The completed plate is porous so that the sulfuric acid electrolyte can circulate through the active material. The porous construction greatly increases the surface area of active material that is in contact with the electrolyte, which increases the capacity of a given sized cell. The following are the major advantages and disadvantages of lead calcium batteries: Advantages

Disadvantages

• Medium service life (12-15 years)

•

Subject to excessive positive plate grid growth.

• Better energy density and power

•

Not suitable for deep or frequent


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density than Plante batteries.

discharges.

• Low self-discharge rates (1%/month) • Low water consumption • Medium cost The cost of lead calcium batteries is more than the cost of lead antimony batteries but is considerably less than the cost of Plante batteries. On a cursory examination, this medium range cost, when coupled with the other advantages of lead calcium batteries, makes this battery appear to be more attractive for most applications than the Plante battery. However, a closer look at the disadvantages of the lead calcium battery shows that this battery is only more attractive in non-cycling applications. The cyclic performance of lead calcium batteries is extremely poor. Of the three major types of stationary lead-acid storage batteries (Plante, lead calcium, and lead antimony), the lead calcium battery suffers the greatest loss of calendar service life when it is subjected to cyclic service. Lead calcium batteries should only be used in float charge, shallow-cycle applications. Lead Antimony - The positive and the negative plates of lead antimony batteries are also pasted

plates. The only difference between the construction of lead antimony batteries and the construction of lead calcium batteries is the addition of an antimony alloying material to the grid rather than a calcium alloying material. The antimony alloying material, which is similar to the calcium alloying material, is added to increase the mechanical strength of the plate. The amount of antimony that is used in the grid varies by weight from about 1.5% to 12% antimony. The percentage of antimony that is used affects the characteristics of the battery. High antimony content provides greater grid strength; however, it also results in higher float current requirements, an increase in water usage, and an increase in the frequency of equalizing charges towards the end of the battery's service life. Low antimony content provides more desirable operating characteristics but at the sacrifice of grid strength. If the antimony content is less than 4%, small amounts of other elements, such as selenium, must be added to maintain sufficient grid strength. Saudi Aramco does not allow the use of lead antimony batteries that contain more than 3% antimony.

The following are the major advantages and disadvantages of lead antimony batteries: Advantages • Low cost.


Disadvantages • High self-discharge rates (7%/month).

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• Better energy density and power density than Plante batteries. • Can be used in cycling service.

• •

Short service life (10-12 years). High water consumption

Lead antimony batteries have the least capital cost of all lead-acid batteries. The low capital cost makes this battery an attractive choice for cycling service applications in which the high water usage is acceptable. The cyclic performance of lead antimony batteries is approximately equivalent to the cyclic performance of Plante batteries. Lead antimony batteries can withstand a moderate amount of cycling with a minimum loss of calendar service life. Sealed (Maintenance-Free) - Two different versions of sealed (maintenance-free) lead-acid batteries are available: the gelled electrolyte version and the absorbed glass mat (AGM) version. The basic technology of both versions of sealed lead-acid batteries is identical in that they are both recombinant-type batteries. Recombinant-type batteries have positive limited plate groups that operate on an oxygen cycle.

During battery recharge, oxygen is released at the positive plate, and, when the negative plate is fully charged, it releases hydrogen. These gases are formed from the decomposition of the water that is in the electrolyte. Because of the explosive nature of hydrogen, the gases must be vented out of the battery room, and they must be properly dispersed. In flooded lead-acid batteries, this electrolyte water loss must be replaced on a regular basis to prevent the battery plates from drying out. In sealed lead-acid batteries, the negative plate is designed to be what is known in the industry as "positive limited" because the battery discharge chemical reaction is stopped when the positive plate is exhausted. When a sealed lead-acid battery is recharged, the negative plate never reaches its full charge condition; therefore, hydrogen gas is not released. The oxygen is released at the positive plate, and it travels to the negative plate through the void paths that are in the plate separator. At the negative plate, the oxygen combines with the lead in the negative plate to form lead dioxide. The lead dioxide reacts with the sulfuric acid that is in the electrolyte to form lead sulfate and water. The water that is created replaces the water that was consumed at the positive plate to make the oxygen; therefore, water never needs to be added to the battery, and the battery case can be sealed to prevent evaporation.

The oxygen that is generated at the positive plate creates a positive pressure inside the battery that is two to three pounds above the ambient pressure. Because of this positive pressure, sealed lead-acid batteries must contain a relief valve to prevent overpressurization of the Saudi Aramco DeskTop Standards

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battery in the event of a malfunction, such as a runaway charger. The relief valves are designed to automatically reseal once the pressure returns to normal. The following are the major advantages and disadvantages of sealed lead-acid batteries: Advantages Disadvantages • High cost. • Long service life (15 to 20 years) in • Short service life (< 10 years) in float service. cycling • No maintenance. service • Reduced battery room/ventilation • Moderate self-discharge rates (3%/month). requirements • Not suitable for deep or frequent • Vertical or horizontal mounting. discharges. The development of sealed lead-acid batteries for large stationary storage applications is a relatively recent (within the last ten years) technology and, as such, these batteries are more expensive than their lead calcium and lead antimony flooded cell counterparts. The cost of sealed lead-acid batteries is similar to the cost of Plante lead-acid batteries. Plante lead-acid batteries are described later in the Module. Sealed lead-acid batteries do not perform well in frequent or deep-cycle applications, and they should only be used in float charge, shallowcycle applications. Nickel Cadmium (Ni-Cad)

Nickel cadmium (Ni-Cad) cells may be either sealed or vented. Some of the sealed-type incorporate a high-pressure vent as a safety measure. The vent would relieve at 100 to 300 psig. Sealed Ni-Cad battery cells are designed for applications that are lightweight and portable, and they provide a long operating life. These types of cells are generally used for small portable electrical equipment that operates on a dc source. The vented-type of Ni-Cad cell is used for emergency and standby service. The Ni-Cad cell provides a high discharge rate. Ni-Cad batteries also provide a fast recharge for emergency engine starting and for standby service. When compared to a lead-acid cell, the Ni-Cad cell is generally smaller and lighter, and it requires less maintenance than leadacid cells. If the cell is overcharged, the resealable vent allows hydrogen and oxygen gases that are generated by the electrolysis of water to escape to the atmosphere. The vent isolates the electrolyte so that it cannot pick up carbon dioxide from the atmosphere and become carbonated. As a result, deionized water must be added at regular intervals. The Ni-Cad battery also consists of a group of electrochemical cells that are connected in series to generate a nominal dc voltage that would supply power to a suitably connected electrical load. The number of cells that are connected in series determines the nominal voltage rating of the battery. Saudi Aramco DeskTop Standards

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The electrochemical couple that is used to form Ni-Cad cells is configured through placement of a nickel hydroxide positive electrode and a metallic cadmium negative electrode in a dilute potassium hydroxide electrolyte. This electrochemical couple produces a nominal cell voltage of approximately 1.2 volts. The following types of Ni-Cad stationary storage batteries will be discussed in this section: • Pocket-Plate • Sintered-Plate Pocket-Plate - Pocket-plate Ni-Cad batteries get their name from the "pocket" strip that holds

the active material of the plates. The pockets are made from very thin, finely perforated strips of steel that are formed into shallow "U" channels, as shown in Figure 5. The positive active material, which consists of hydrates of nickel oxide and graphite, and the negative active material, which consists of cadmium oxide and a small amount of iron oxide, are placed into the open "U" channel. The open "U" channel is then covered with a similar strip of perforated steel, and the two strips are crimped together to form a perforated pocket. A number of these perforated pockets are interlocked edge-to-edge and then cut to the approximate finished plate width. The interlocked pockets are then rolled to compress the active material and to form longitudinal indentations in the plate. Each plate group is then bolted or welded together. The two (positive and negative) plate groups are interleaved and insulated with plastic rod or mat separators that are inserted into the longitudinal grooves of the plates. The insulated plate group or element is then inserted into a plastic container or jar. After the mechanical assembly is complete, the cells are put through an electrochemical formation process to convert the active materials to their charged condition.


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Pocket-Plate Construction Figure 5 Figure 6 shows a cut-away view of a typical pocket-plate Ni-Cad battery. The following components are identified in Figure 6: • • • • • • •

Vent Cap/Flame Arrestor Cell Container or Jar Plate Tab Plate Group Bus Separating Grids Plate Frame Plate


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Typical Pocket-Plate Ni-Cad Battery Figure 6


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The vent cap/flame arrestor allows the gases that are generated during normal charging and discharging to escape from the battery, but it prevents the entry of sparks and foreign material. The vent cap/flame arrestor can be removed to allow access to the interior of the cell. The cell container or jar is constructed of translucent polypropylene. The cell container or jar is the enclosure that holds the individual components of the cell and that contains the liquid potassium hydroxide (KOH) electrolyte. The plate tabs are spot welded to the plate frame and to the upper edge or the pocket plates. The plate tabs provide the electrical connection between the plates and the plate group bus. The plate group bus connects the plate tabs to the terminal posts of the battery. The plate tabs and the terminal posts are welded to opposite sides of the plate group bus. The separating grids separate the plates and insulate the plate frames from each other. The separating grids are porous, and they allow the free circulation of the KOH electrolyte between the plates. The plate frames seal the plate pockets, and they serve as current collectors. The plates in Figure 6 have horizontal pockets of double-perforated steel strips. Most manufacturers make three general pocket-plate designs: thin plates, medium plates, and thick plates. The thin-plate design has a low internal resistance, and it is used in high rate, short duration (less than 30 minutes) discharge cells. The medium-plate design has an internal resistance that is similar to the internal resistance of general purpose lead-acid cells. This plate design is used in median rate, median duration (from 30 minutes to 2 hours) discharge cells. The thick-plate design has a high internal resistance, and it is used in very low rate, long duration (more than two hours) discharge cells. All vented Ni-Cad batteries have several general advantages over their flooded lead-acid counterparts. One of these advantages stems from the KOH electrolyte that is used in Ni-Cad batteries. The freezing point of the KOH electrolyte with a typical specific gravity of 1.190 is -32°C (-25°F). Because the specific gravity of the electrolyte in a Ni-Cad battery remains relatively constant from the fully-charged state to the fully-discharged state, the freezing point also remains relatively constant. In contrast, the freezing point of a fully-discharged lead-acid battery is essentially the same as the freezing point of water or 0°C (32°F); therefore, leadacid batteries are much more likely to freeze than Ni-Cad batteries. Ni-Cad batteries also make a significantly higher percentage of their current available at lower temperatures than lead-acid batteries.


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Another general advantage of Ni-Cad batteries is that they require much less maintenance than flooded lead-acid batteries. Ni-Cad batteries can last years without being watered, and they will not deteriorate when they are left in a discharged condition. Ni-Cad batteries have been successfully returned to service after being left "on-the-shelf" for 10 to 15 years. The other general advantages of Ni-Cad batteries include a more rugged and durable construction (i.e., relatively immune to vibration, shock, and overcharge currents), a long cycle life, and minimal gas generation on charge and discharge. Also, the gaseous vapors that are emitted from Ni-Cad batteries are not corrosive to ferrous metals. The only general disadvantage of Ni-Cad batteries as compared to flooded lead-acid batteries is the high cost of Ni-Cad batteries. The cost (dollars/kilowatt-hour) of Ni-Cad batteries is four to ten times the cost of flooded lead-acid batteries. Because cadmium is also more difficult and expensive to recycle or dispose of than lead, the disposal cost of expended NiCad batteries is higher than the disposal cost for expended lead-acid batteries. In North America, large Ni-Cad storage batteries are being phased out of production as a result of the disposal issues that surround cadmium. The advantages of pocket-plate Ni-Cad batteries over sintered-plate Ni-Cad batteries are that pocket-plate Ni-Cad batteries have a lower cost and a longer cycle life, and they do not suffer a "memory" effect on shallow discharges. The major disadvantage of pocket-plate Ni-Cad batteries is that they only have about 50% of the energy density of sintered-plate Ni-Cad batteries. In contrast to flooded stationary lead-acid batteries, pocket-plate Ni-Cad batteries have a long cycle life in addition to a long calendar life. Under normal operating conditions, pocket-plate Ni-Cad batteries can deliver as many as 2,000 equivalent full-charge cycles. The calendar life of pocket-plate Ni-Cad batteries ranges from 15 to 25 years. Because of the large number of cycles that this battery can withstand (more than 80 equivalent full-charge cycles per year over a 25-year calendar service life), cycling has little or no effect on the calendar service life of pocket-plate Ni-Cad batteries. Sintered-Plate - Saudi Aramco does not permit the use of sintered-plate Ni-Cad batteries;

therefore, this section is only intended for general information purposes. The primary applications of sintered-plate Ni-Cad batteries are those applications that require high-power discharge service in a lightweight compact package, such as aircraft turbine engine starting circuits. Sintered-plate Ni-Cad batteries are constructed similarly to pocket-plate Ni-Cad batteries. The major difference between the two batteries is the way in which the electrodes (positive and negative plates) are designed. In the sintered-plate design, the active materials are impregnated into a porous nickel coating that is applied to an iron grid or charge collector.


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Sintered-plate Ni-Cad batteries have nickel oxyhydroxide positive plates and cadmium hydroxide negative plates. The plates are separated by nonconductive, porous materials that act as a gas barrier and an electrical separator. The electrolyte is a dilute KOH solution, and it completely covers the plates and separators. Figure 7 shows the construction of a typical sintered-plate Ni-Cad battery. The battery consists of a plate pack that contains the positive plates, the negative plates, and the separators. A terminal comb is placed over the negative plate tabs to connect the negative plates. A separate terminal comb is placed over the positive plate tabs to connect the positive plates. The assembled plate pack is then placed in the cell container. A cell cover is placed on top of the cell container, and it is sealed to the container. A terminal is connected to the positive terminal comb and to the negative terminal comb. The terminals are used to connect the battery to the external load. The removable vent cap allows excess gases to escape and a means to add electrolyte.


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Typical Sintered-Plate Ni-Cad Battery Figure 7


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The advantages and disadvantages of sintered-plate Ni-Cad batteries are shown in Figure 8.

Advantages and Disadvantages of Sintered-Plate Ni-Cad Batteries Figure 8 As was noted in Figure 8, the sintered-plate Ni-Cad battery is more expensive than the vented pocket-plate battery and many times more expensive than the sealed lead-acid battery. The average calendar life of a sintered-plate Ni-Cad battery ranges from three to ten years, and the cycle life ranges from 500 to 2000 equivalent full charge cycles. The cycle life and calendar life are strongly influenced by the method of operation, the ambient temperature conditions, and the depth of discharge. The best battery life performance is obtained from operation at normal temperatures and at moderate (50% average) discharge depths. The life of sintered-plate Ni-Cad batteries drops when the battery is subjected to frequent deep or shallow discharges. Number of Cells


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The nominal voltage that is required by the load that is connected to a battery is the factor that determines the number of cells that are required; however, the voltage at which a battery system operates is not constant. The voltage fluctuates between minimum and maximum fixed values dependent on the state of charge. The range of voltages that lies between the minimum system voltage and the maximum system voltage is the voltage operating "window" for the battery system. The size (number of cells) of the battery is selected to ensure that the battery operates inside of the voltage window. For batteries that supply dc systems, the minimum and the maximum battery system voltages are based on the voltage rating of the most limiting load. The minimum system voltage is selected to ensure that sufficient voltage is available to operate the loads at the end of the battery duty cycle. The maximum system voltage is selected to ensure that the voltage rating of the loads will not be exceeded when the battery is being recharged. The following are the minimum and the maximum battery system voltages for Saudi Aramco dc systems: Nominal System Voltage 12 vdc 24 vdc 48 vdc 120/125 vdc 240/250 vdc 360/375 vdc

Minimum System Voltage 10.5 vdc 21.0 vdc 42.0 vdc 105 vdc 210 vdc 315 vdc

Maximum System Voltage 15.5 vdc 30.0 vdc 58 vdc 143 vdc 286 vdc 429 vdc

For batteries that supply UPS systems, the minimum and the maximum battery system voltages are based on the allowable dc input voltage ratings of the UPS system. The allowable dc input voltage ratings are specified by the manufacturer of the UPS system. For batteries that supply a combined dc and UPS system load, the minimum and the maximum system voltages for dc systems should be used. Because the battery system voltage is the product of the individual cell voltages and the number of cells that are connected in series, the minimum and the maximum battery system voltage values are used to determine the minimum and the maximum number of cells that can be used in a battery installation. The following equation, which is also included in Work Aid 2, can be used to calculate the minimum number of cells that can be used in an installation. For most applications, the final volts per cell for lead-acid batteries is 1.75, and the final volts per cell for Ni-Cad batteries is 1.1 volts. If justified by valid engineering and economic reasons, other final volts per cell values could be used. The following equation, which is also included in Work Aid 2, can be used to calculate the maximum number of cells that can be used in an installation:


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The maximum cell voltage on charge for lead-acid batteries is the equalizing voltage that is recommended by the manufacturer. If the manufacturer's data are not available, a value of 2.33 volts per cell can be assumed. The maximum cell voltage on charge for Ni-Cad batteries is the charging voltage that is recommended by the manufacturer. If the manufacturer's data are not available, a value of 1.55 volts per cell can be assumed.

After the minimum and the maximum number of cells are known, the actual number of cells can be specified. The actual number of cells that are specified can be any number that lies between the minimum and the maximum number. For consistency and ease of specification, SAES-P-103 contains the following information that lists the number of lead-acid or Ni-Cad cells that are to be specified for various nominal battery system voltages: Nominal Battery System Voltage (vdc) 12 24 48 120/125 240/250 360/375

Number of Cells Lead-Acid 6 12 24 60 120 180

Ni-Cad 10 19 37 92 184 276

The equations serve as a second check to verify that the number of cells listed is correct for the application. For example, if a new lead-acid battery is needed to supply emergency power for a dc system with a nominal voltage of 120 vdc, the number of cells that is required is determined as follows: • From the table that is in SAES-P-103, 60 lead-acid cells are required for a nominal battery system voltage of 120 vdc. The number of cells that was determined from the table can be verified as follows: The above calculations verify that 60 lead-acid cells are adequate for this installation. Duty Cycle


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The duty cycle of a battery is defined as the load currents that a battery is expected to supply for specified periods of time. This information is critical in the determination of the proper amp-hour rating of a battery. The proper size of a battery depends not only on the nominal current rating or the kW draw, but it also depends on the duration of each load (i.e., the duty cycle). Additionally, the battery size also depends on the sequence in which the load is energized. Careful scheduling of the load sequence in the duty cycle may allow the cell size to be smaller, which can reduce the cost of the installation.

Most stationary battery installations are multi-load systems rather than single-load systems. When a variety of loads are connected to a battery, sudden increases and decreases in current demands are imposed on the battery. If the high-current loads can be scheduled to energize at the beginning of the duty cycle rather than at the end of the duty cycle, a smaller-sized battery can be used. However, if the load is random in nature and could occur at any time during the duty cycle, the best practice is to assume that the load will energize at the most limiting point in the duty cycle when its effect will be the most severe. A duty cycle diagram is a tool that aids in the analysis of the duty cycle and in the determination of the required battery capacity. A duty cycle diagram shows the total required battery current at any given time in the duty cycle. To prepare such a diagram, all of the loads that are expected during the duty cycle are tabulated along with their anticipated start and stop times. The loads that have known start and stop times are plotted on the duty cycle diagram as they would occur. The remainder of the loads should be plotted through use of the following guidelines: •

If the start time for a load is known but the stop time is indefinite, the load is assumed to be continuous for the remainder of the duty cycle.

•

If the load can occur at random, the load is assumed to occur at the most critical point in the duty cycle to simulate the worst-case condition. The most critical point in the duty cycle is the point that controls the size of the battery that is needed.

Figure 9 shows an example of the duty cycle diagram that would be plotted from the following hypothetical loads: •

L1 represents 50 amps of continuous emergency lighting load for three hours.


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•

L2 represents 100 amps of momentary switchgear operations load and 250 amps of momentary motor starting load.

•

L3 represents 50 amps of noncontinuous motor load for one and a half hours.

•

L4 represents 100 amps of noncontinuous load that starts after 30 minutes and stops after one hour of operation.

•

L5 represents 50 amps of momentary switchgear operations load that occurs during the last minute of the duty cycle.


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Duty Cycle Diagram Figure 9 Cables

Battery cables are an important link between the battery energy and the load. Cables must be selected and installed so that they will carry the anticipated current for the maximum length of time that the battery is expected to discharge into the load. Cables must be insulated with a conductor insulation that is suitable for the expected operating temperatures and corrosive effects of the battery electrolyte and gases. The cables must also be sized to provide a minimum voltage drop at the load. Excessive voltage drop could cause equipment to fail to operate or to shut down prematurely as the battery voltage decreases during a discharge cycle. If the battery cables fail to carry the current to load when required, serious consequences may result, and the function of critical equipment response might be endangered. Battery cables require only a few major considerations to ensure that their operation is reliable. Battery cables must be sized of an ampacity that is large enough to carry the load without exceeding the temperature limitations of the conductor insulation and without excessive voltage drop. The ampacity of the battery conductors is calculated through a determination of load current conditions. These conditions are the amount of load current and the maximum expected duration of the current. The actual AWG size of the conductors is determined through use of tables, such as tables 310-16 and 310-17 in the National Electrical Code, Saudi Aramco DeskTop Standards

25



NFPA-70. The battery cables that are selected must be stranded copper conductors that are insulated with a material that is suitable for the nominal battery voltage and that are resistant to corrosive atmospheres and liquids. Most thermoplastic and rubber insulated conductors are resistant to acid and caustic atmospheres that are common to battery rooms; special insulation is not required. The actual voltage drop due to the resistance of the battery cable conductors can be easily calculated. The factors that are necessary to calculate the voltage drop are the maximum load current, the one-way distance to the connected load, and the AWG or kcmil size of the battery cable conductors. The following formula is used to calculate actual voltage drop: VD = 2 x L x R x I / 1000 where: L

=

one-way length of the circuit to the farthest point

R

=

dc resistance of the conductor per 1000 linear feet

I

=

maximum expected continuous load current to the load

The dc resistance per 1000 ft. can be found in Table 8 (Conductor Properties) of the National Electrical Code. The voltage drop that is calculated from this formula must be no greater than 3% of the battery nominal voltage.

Battery cables should be connected through use of terminals that are suitable for that purpose. The cables should be run from the battery's positive and negative terminals to a battery circuit breaker. This breaker is the disconnect point for the batteries, and it should be equipped with an undervoltage trip feature that will open the battery's circuit if the battery's voltage drops to a value of 5% below the battery's final discharge voltage. The requirement for the undervoltage trip does not apply to batteries that supply emergency or life-critical loads. Battery Chargers Saudi Aramco dc systems require battery chargers that operate on constant-potential, semiconductor, static-type chargers. These chargers are designed to simultaneously supply dc power to a float-type battery and to provide power to the connected dc loads. The following two basic types of chargers are used: • •

Static Plate Rectifier Solid State Rectifier


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Static Plate Rectifier

The static plate rectifier can contain selenium discs or a group of copper or aluminum discs that contain oxidized selenium or silicon on one side. The discs are clamped together and have electrical connections on both sides. The discs are supported on an insulated shaft that is secured through use of insulator clamps at each end. The static plate rectifier is mounted in the battery charger housing through use of a mounting clasp that is connected at the ends of the static plate rectifier. Figure 10 shows a single-unit static plate rectifier. The static plate rectifier converts an ac input to a dc output. The static plate rectifier accomplishes this conversion by allowing current to flow only in one direction. When an ac voltage is applied to the static plate rectifier, current can flow from the oxidized side of the disc to the adjacent copper or aluminum side, but current cannot flow in the opposite direction. This rectification principle is known as half-wave rectification.


27



Static Plate Rectifier Figure 10 Figure 11 shows two possible ways that static plate rectifiers can be configured to produce a dc output. Figure 11A is a half-wave rectifier circuit. In this circuit, an ac voltage (EAC) is applied to the circuit through the transformer secondary winding. The static plate rectifier only allows current to flow in one direction through the load. The voltage that is applied to the load will only occur during one half of the applied ac sinewave; therefore, the shape of the resultant EDC is a series of half peaks and flat spots. Figure 11B shows a full-wave rectifier circuit. The full-wave rectifier also receives ac power from a transformer secondary winding; however, two static plate rectifiers are connected in this circuit. The load is connected between the static plate rectifiers and a center tap of the transformer. The two static plate rectifiers are electrically connected so that one rectifier conducts on the positive half-cycle of the ac supply voltage, and the other rectifier conducts on the negative half-cycle of the ac supply voltage. The output (EDC) to the dc load is a fullwave voltage.


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Static Plate Rectifier Operation Figure 11 The static plate rectifier replaced the old motor-generator systems. Because a static plate rectifier has no moving parts, it is smaller and requires less maintenance than the motorgenerator systems. One disadvantage of the static plate rectifier is the heat that is generated from the flow of current through the resistance of the oxide layer. This heat decreases the efficiency and increases the cost of operating static plate rectifiers. Solid State Rectifier


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The solid state rectifier-type of battery charger uses power diodes and/or silicon controlled rectifiers (SCR's) to convert ac to dc. Figure 12 shows a simplified diagram of a solid state rectifier. The operation of the solid state rectifier is very similar to the operation of the static plate rectifier. The diodes that make up the solid state rectifier only allow current flow in one direction. The diodes are arranged to provide a path for current flow during each half cycle of the input ac sinewave. The input ac sinewave is supplied to the solid state rectifier from the multi-tap transformer secondary. Multi-tap transformer secondaries permit a coarse mechanical adjustment of the voltage that is supplied to the dc load. During the positive half of the ac sinewave, diodes D1 and D4 conduct, which allows current flow to the system battery from negative to positive. During the negative half of the ac sinewave, diodes D2 and D3 conduct, which also allows current flow to the system battery from negative to positive. The diode pairs alternately conduct as long as an ac sinewave is applied that maintains dc current flow to the system battery from negative to positive. The resultant output wave shape that is supplied to the system battery is also shown in Figure12. The major advantages of the solid state rectifier are that it is smaller and more efficient than the static plate rectifier. The main disadvantage of the solid state rectifier is that it costs more than the static plate rectifier.


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Solid State Rectifier Figure 12 Current and Voltage Ratings

The standard continuous-duty direct current output ratings of Saudi Aramco battery chargers must be one of the following values: 1A, 3A, 6A, 12A, 15A, 20A, 25A, 35A, 50A, 75A, 100A, 150A, 200A Battery chargers that are larger than 200A must be rated in 100A increments. The ac input voltage ratings are based on the available ac voltage and the required system output voltage. The following are the nominal ac input voltages for Saudi Aramco battery chargers: • • •

120 vac 208 vac 240 vac


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•

480 vac

The output voltage ratings of a battery charger are dictated by the type of battery that the charger is intended to charge. The output voltage ratings of the battery charger are based on the float, equalizing, and final volts per cell of the battery to which it is connected. The maximum voltage output of the battery charger is equal to the following: Battery charger maximum output voltage = Equalizing voltage per cell x number of cells Figure 13 shows the typical volts per cell ratings for different types of batteries. The float, equalizing, and final volts per cell ratings are multiplied by the number of cells that are in the battery to determine the necessary battery charger output voltage rating.

Typical Volts Per Cell Ratings for Different Battery Types Figure 13 Operational Requirements

The operational requirements for Saudi Aramco battery chargers fall into the following categories: • • •

Output Regulation Controls Filters

Output Regulation

The voltage output of a battery charger must be regulated to ensure that the proper charge voltages are applied to the battery. Charge voltages that are outside of the tolerances of the battery could cause excessive gassing in the cells. The exact amount of output voltage control that is required depends on the rated size of the battery charger and the type of charge that is being performed. The following are the output voltage regulation requirements for Saudi Aramco battery chargers:


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Battery Charger Size

Float Operation Mode

< 10 kW > 10 kW

+/- 1% +/- 1%

Recharge (Equalize) Operation Mode +/- 2% +/- 1%

Battery charger output regulation also refers to the battery charger's ability to maintain the rated output during operation of the battery charger. A battery charger must be able to maintain nominal rated voltage output during load changes, battery removal, and variations in the input voltage. The battery charger output voltage must return to within the previously mentioned limits within two seconds when the load is changed or when the battery is removed, and no voltage variation should result in exceeding the rated output voltage. The battery charger also must maintain an output voltage that is within the specified voltage tolerances during variations in the battery charger input voltage. Controls - Separate and independent controls are required for the adjustment of the float and

recharge (or equalizing) voltage. The battery charger must provide the following ranges of float voltage output control at its nominal ac input voltage and half load: Lead-Acid Cells Ni-Cad

Adjustment Range Per Cell 2.15 - 2.25 VPC 1.40 - 1.47 VPC

The battery charger should also provide the following ranges of equalizing voltage control at its nominal ac input voltage and half load: Lead-Acid Cells Ni-Cad Cells

Adjustment Range Per Cell 2.25 - 2.40 VPC 1.50 - 1.65 VPC

The following formula is used to calculate the required float and equalizing voltage control ranges for battery chargers: Charger Output Voltage = VPC x Number of Cells For example, the required float and equalizing voltage control range for a 60-cell, lead-acid battery is calculated as follows: Float Voltage Adjustment Range:


33



Minimum Charger Output Voltage = Maximum Charger Output Voltage =

VPC x Number of Cells = 2.15V x 60 = 129V VPC x Number of Cells = 2.25V x 60 = 135V

Equalizing Voltage Adjustment Range: Minimum Charger Output Voltage = Maximum Charger Output Voltage =

VPC x Number of Cells = 2.25V x 60 = 135V VPC x Number of Cells = 2.40V x 60 = 144V

The battery charger must also have an input circuit breaker and an output circuit breaker or disconnect switch. The input circuit breaker must have an interrupting capacity that is equal to or greater than the available short-circuit current. The minimum capacity is 14,000 symmetrical rms amps. Current-limiting fuses may also be provided to meet the short-circuit current requirements. The output circuit breaker or disconnect switch must be able to simultaneously disconnect both output lines.

Supervisory Controls

The battery charger should be equipped with the following supervisory control circuits: •

End of Discharge Relay Circuit - The end of discharge relay senses the battery bus voltage and actuates when the battery has discharged to a predetermined level. The end of discharge relay should activate when the battery voltage equals 1.75 VPC for lead-acid batteries and 1.10 vpc for Ni-Cad batteries. The setpoint of the relay should be adjustable from +5% to -5%. Operation of this relay indicates that the battery needs to be charged.

•

Ground Detection Relay Circuit - The ground detection relay senses ground faults on the positive or the negative battery bus. Operation of this relay indicates the presence of a ground fault.


34



•

Equalizing Timer Circuit - The equalizing timer allows unsupervised control of the equalizing charge. The timer is manually set to the desired equalizing time period. When the battery charger is placed in the equalize charge mode, the timer automatically returns the battery charger to the float charge mode after the preset time has elapsed.

•

Low Voltage Relay Circuit - The low voltage relay provides an indication that the dc output voltage has dropped below a preset value. This relay must be adjustable to allow for field settings of the minimum battery output voltage.

•

Overvoltage Relay Circuit - The overvoltage relay provides an indication that the dc output voltage has increased above a preset value. The relay must be adjustable to allow for field setting of the maximum battery output voltage.

•

Charger Failure Relay Circuit - The charger failure relay provides an indication of a loss of the charger's dc output. The battery charger failure relay actuates on a charger output failure regardless of the cause. The charger failure relay is intended to alert the operator that the charger is no longer in operation, but it does not provide an exact indication as to the cause of charger output failure.

•

Low Current Relay - The low current relay provides an indication that the dc output current of the battery charger has dropped to a value that is less than two percent of the rated output.

Filters

Filters are placed on the output of a battery charger to reduce the ac ripple that is in the dc power that is supplied to the system load. The filter requirements for Saudi Aramco battery chargers vary dependent on the size of the battery charger and the type of dc load. The ac ripple voltage of battery chargers that are rated for 10 kW or less should be filtered to a maximum of 30 mV rms or 100 mV rms dependent on the requirements of the connected load. For most applications, the ripple voltage is required to be less than 1-2% of the nominal dc voltage, with a +/- 10% line voltage deviation and with a load variation of 0-100%. The battery chargers that supply dc systems that are dedicated to only emergency lighting systems do not require filters. Environmental Ratings


35



Battery chargers normally are operated inside of buildings that are air conditioned to 25°C (77°F). However, in the event of a loss of air conditioning, the battery chargers must be rated to operate for a period of eight hours in the following environment: • • •

Ambient temperatures that range from 0°C (32°F) to 50°C (122°F). Relative humidity up to 100%. Sand, salt, and dust-laden atmosphere.

Ancillary Items There are several ancillary items that are necessary to support the operation of battery systems. These items include the battery room, a ventilation system, and showers or eyewash stations. Battery rooms are constructed with features that provide isolation of the battery and its associated components from other areas of a facility. Because most batteries emit some amount of hazardous vapors, the atmosphere that surrounds the battery must be properly vented. Ventilation systems ensure that an accumulation of hazardous gases will not occur. Within battery rooms and in close proximity of the battery, emergency showers or eyewash stations are installed for the safety of personnel. Personnel must have quick access to these safety items any time that routine maintenance is performed or other work is done that involves the batteries. During the commissioning process, these items must be inspected to verify that they are correctly installed and that they will function properly. These ancillary items must be carefully scrutinized during the commissioning process to ensure that all the required components are present and that they are installed correctly and in accordance with the governing standards, such as the National Electrical Code, NEMA PE 51985, Saudi Aramco Engineering Standards, and Saudi Aramco Materials Systems Specifications.

Battery Rooms

The battery room is constructed to accommodate the battery and its associated equipment with enough area to allow easy access to the battery for routine maintenance. The actual working space is determined through use of calculations that are primarily based on the type, size, and number of cells of the battery. The minimum height of battery rooms should be no less than three meters, which allows any H2 to accumulate far away from the tops of the cells. The high ceiling also contributes to a larger overall volume of the battery room, which tends to reduce the overall concentration of H2. The battery room should be designed with sufficient working space around the battery. A minimum of 1 m (3 ft.) of work space is required on all four sides of the battery. This measurement is the distance from the exposed live electrical components and the associated Saudi Aramco DeskTop Standards

36



equipment to ground. Space in the battery room must also be provided for the easy movement of equipment in and out of the room and for ease of maintenance. Finally, the battery room should be designated as a battery room only, and it should not be used as a storage room or a supply room. The surface of battery room floors and walls are sealed to prevent the leakage of gases to adjacent rooms or spaces. The lower 150 mm (6 in.) of the wall and the floor are additionally covered with a protective paint that is resistant to acids and caustics. This protective paint ensures that a spill of electrolyte will not damage the floor or leak into adjacent areas. Penetrations through the battery room walls should not be more than 2.1 m (7 ft.) from the floor except for air conditioning and ventilation ducts. Where these types of penetrations exist, they must have vapor-tight seals around them, which ensures that any collection of H2 gas will be expelled through the ventilation system ducts. Battery rooms are equipped with doors that open out and away from the battery; in the event of an emergency, rapid exit of personnel is not impeded. Additionally, an inward opening door would tend to seal itself closed if pressure in the battery room were to suddenly increase as the result of fire or explosion. The battery room door should not contain any sort of device that would prevent the door from opening. Lighting fixtures that are located in battery rooms are suspended from the ceiling so that the fixtures will be below a level where H2 gas would accumulate. Lighting fixtures are positioned directly over the battery racks for the best illumination of the cells and battery racks. The lighting fixtures should be listed or labeled for the specific purpose, and they should be resistant to corrosion that is caused by acid fumes. Switches for lights and other similar devices are installed at least 1.5 m (5 ft.) from the battery cells. Detailed information on the method of calculating the size of the battery room can be found in EEX 211.05. Ventilation

Battery room ventilation systems are designed to prevent a concentration of H2 gas that is greater than 2%. Two percent is a concentration that is considered adequate for safety. Concentrations of less than 2% are not considered sufficient to allow an explosion. Because adequately-sized exhaust ducts permit the ventilation system to supply positive air pressure, most battery rooms in Saudi Aramco facilities will not have exhaust fans. This positive air pressure will be great enough to maintain the correct amount of air exchange in the battery room. Battery rooms that meet the battery room ventilation requirements of Saudi Aramco are not classified as hazardous locations and, therefore, are not required to include explosion-proof devices or wiring methods.


37



If the type of battery that is installed in a Saudi Aramco facility is a lead-acid battery, the battery room must be air conditioned. The air conditioning system must be able to maintain the temperature in the battery room at 25_(77_F). If the area in which the battery is located is unmanned and if air conditioning is not feasible, a Ni-Cad battery is normally selected instead of a lead-acid battery, and air conditioning is not required. Air-conditioned rooms must not contain return air ducts that would allow corrosive fumes or H2 gas to mix with the building air. Detailed information regarding the methods of determining the ventilation requirements can be found in EEX 211.05. Showers/Eyewash Stations

Battery rooms in Saudi Aramco facilities will have floor drains to accommodate eyewash and shower installations. Eyewash stations are installed within the battery room so that a worker can immediately flush his face or eyes with water in the event of an accidental splash of electrolyte into the employee's face or eyes. Large battery rooms may be outfitted with emergency showers that would allow a worker to quickly wash large spills of electrolyte from his body. If eyewash stations or shower facilities are installed, the floor of the battery room must include one or more floor drains. The drains must be installed in accordance with the requirements of SAES-P-060, Saudi Aramco Plumbing Code. This code specifically requires that the battery room be provided with a floor drain that is trapped and vented to serve eyewash facilities and washdown of electrolyte spills. Some of the particular requirements for eyewash stations and emergency showers are specified in SAES-B-069, Emergency Eyewashes and Showers. The following is a summary of those requirements as they apply to battery rooms:

•

Eyewashes and showers must be constructed of material that is resistant to corrosion from the effects of the battery room atmosphere. The plumbing that is connected directly to the eyewash station or shower must be constructed of galvanized pipe, and the other piping from the supply may be PVC, CPVC, or copper. The connection branch may also be galvanized pipe if it supplies only the eyewash and shower.

•

The eyewash station and shower must be supplied from a suitable potable water supply that is certified to be suitable for the purpose by Saudi Aramco's Medical Service Division.


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•

The eyewash and shower must be able to provide a continuous flow rate for at least 15 minutes at a pressure that is no greater than 207 kPa (30 psig) and at a temperature that is not greater than 37.8_(100_F) except for the short period of time where water is naturally heated from the environment by above-ground piping. The pressure must be maintained through use of pressure controllers or self-regulating orifices that prevent the pressure from being greater than 207 kPa if the system is capable of delivering higher pressure at the eyewash and shower outlets.

•

The shower and eyewash stations must be located no closer than 3 m (10 ft.) and no further than 15.2 m (50 ft.) from the nearest battery cell. The shower and eyewash stations must also be easily accessible without going through doors or up or down stairs, and it must be adjacent to the normal exit from the battery room and in a well-lit area.

•

The eyewash and shower area must be indicated by a background area that is painted with alternate green and white diagonal stripes that are approximately 152mm wide and that cover an area 1 m wide by 2 m high. A sign that indicates both stations and the emergency procedures for each must be posted.

•

The eyewash and shower stations may be equipped with an alarm that is activated whenever either facility is operated. The determination of whether an alarm is needed is made by the Industrial Hygiene Unit of the Medical Services.

•

During the commissioning of battery systems, the installation of showers and eyewash stations must be carefully inspected to ensure that they meet the requirements of SAES-B-069 and that they function properly.


39



EVALUATING BATTERY AND BATTERY CHARGER SYSTEMS UPON RECEIPT The components of battery systems must be evaluated upon receipt to ensure that they meet the relevant Saudi Aramco Material Standards and Specifications. This verification should be performed as soon as receipt of the equipment occurs so that any discrepancies that are noted can be resolved before the equipment is installed. The primary focus of this verification is to ensure that the equipment is not damaged and that the nameplate data and manufacturer's information that are provided correspond to the electrical drawings and material and equipment specifications. Verify Against Specification Many items should be verified and inspected during the receipt inspection of battery systems. These items include the battery cells, the battery racks, the interconnecting links, the battery charger, and ancillary items, such as ventilation equipment. Battery cells must be verified against the information that is provided on the data schedule to ensure that the type of battery that was received is the type of battery that was specified on the data schedule. This verification includes a careful review of the manufacture's literature, which should accompany the battery and associated hardware, for compliance with the Saudi Aramco specifications. The information that is contained in the manufacturer's data should indicate that the battery will meet the load requirements as described on the data schedule. This information is normally provided by the manufacturer in the form of a load vs. time graph of battery cell performance. The battery charger should be inspected in a manner that is similar to the inspection for battery cells. That is, the battery charger should be verified against the data specification sheet to ensure that it meets all the requirements that are listed, as well as compliance with Saudi Aramco Materials Systems Specifications 17-SAMSS-514 and NEMA PE 5-1985. The battery charger receipt inspection should include a verification of hardware and accessory equipment to ensure that all the components are on hand before installation begins. Verification of all accessory equipment that is specified in the data schedule, such as relays, alarms and indicating devices, and protective devices must be completed. The battery charger enclosure must also be inspected upon receipt to verify that is meets the requirements that are specified in 17-SAMSS-514 and the requirements of NEMA ICS 6, Type 1 enclosure. Other items that are associated with the battery and battery charger system must be accounted for during the receipt inspection. The material and equipment schedule that accompanies the electrical drawings for the battery system installation should be the reference that is checked when this receipt inspection is performed. Any missing or damaged items should be


40



identified as soon as possible so that corrective action can be taken and the project progress is not delayed. A complete and detailed description of these inspections and verifications is contained in Work Aid 1. Physical Inspection At the same time that the verification of the battery and battery charger system is confirmed against specification, a complete physical inspection should be performed. The items that should be visually and physically inspected are briefly described in the following paragraphs. Details of this physical inspection are included in Work Aid 1. The battery cells must be visually inspected to ensure that the manufacturer took the proper steps to prevent damage and contamination of the cells during shipment. Proper documentation that explains the shipping and storage procedures should accompany the batteries and associated equipment. A physical inventory of all the major items of the accessory equipment must be performed. Battery hardware, such as intercell connectors, terminal connectors, and rack hardware must be accounted for and inspected for compliance with specifications and for indication of damage. The battery rack and associated hardware should be visually inspected to verify that they are of the correct size and material composition in accordance with the drawings and specifications. This inspection includes verification that the rack framework is properly coated with the specified protective material to prevent corrosion. Physical inspection includes verification of the inventory of all required accessories, such as shower and eyewash equipment, safety protective gear, tools, and test equipment, as well as the battery charger accessory devices.


41



EVALUATING BATTERY AND BATTERY CHARGER INSTALLATION AND TESTING The commissioning of batteries and battery chargers must include a series of installation checks and tests to confirm that the battery system will function as designed. The Engineer should evaluate the results of these tests and check points, and he should reconcile any discrepancies that are identified. A battery system that has not met commissioning criteria but that is allowed into service can lead to a catastrophe. Batteries The battery cells should be inspected to verify that they are correctly installed on the battery racks. The intercell connectors, battery cables, and connection to the battery disconnect switch should be inspected to verify that these components are properly installed. The bolts for the intercell connectors and battery cable terminals should have been applied to the specified torque for the given size bolt. When battery cells are inspected, the inspection personnel should verify that the battery cells have been filled with the correct type electrolyte at the correct specific gravity. The inspection personnel should also verify that the electrolyte level is within the upper and lower indicating lines on the cell jar. The inspection personnel should also verify that the battery rack has been properly assembled and that all metal parts are manufacturer. Prior to the battery cell installation, the inspection personnel should ensure that battery cell covered with the protective coating that is supplied by the internal resistance measurements have been taken and recorded. Electrolyte

The battery electrolyte for lead-acid batteries consists of a dilute solution of sulfuric acid. For Ni-Cad batteries, the battery electrolyte consists of potassium hydroxide. After lead-acid battery cells have been filled with electrolyte, and after the battery receives its "freshening charge," the specific gravity of each cell must be read and recorded. The freshening charge must not be applied to the battery unless the electrolyte level is above the low-level line on the cell jar. The freshening charge must be applied for a period of time that is specific for each type of lead-acid battery and the required specific gravity. Figure 14 shows the charging time and per cell voltage that are required to obtain the desired specific gravity that is specified by the battery manufacturer.


42



Charging Time and VPC to Obtain Desired Specific Gravity Figure 14 During the freshening charge process, the electrolyte temperature must be monitored, and it should not be allowed to exceed 110°F (43°C). The charging should be interrupted and the battery should be permitted to stand open circuited if the temperature exceeds 110°F (43°C). When the cells cool down to 100°F (38°C), the charging may be resumed. When the battery has been properly filled and charged in accordance with manufacturer's recommended procedures, the battery is then placed on the float voltage. This voltage should be provided by the battery manufacturer; Figure 15 provides the average volts per cell for float charge based on the nominal specific gravity for lead-acid cells. After the battery has been initially charged and has been on float charge for at least 72 hours, specific gravity readings can be taken. The specific gravity readings should be corrected for temperature. For every 3°F (1.67°C) above 77°F (25°C), one point (.001) should be added to the specific gravity reading. For every 3°F (1.67°C) below 77°F (25°C), one point (.001) should be subtracted from the hydrometer reading.


43



Average Float Volts Per Cell for Nominal Specific Gravities Listed Figure 15 Chargers After the installation is complete, battery chargers should be checked for the following items: •

The battery charger wiring from the ac supply to the charger and the dc output conductors (battery cables) should be checked for correct wiring practices.

•

The size of conductors and type of insulation should be verified.

•

The conductors should be checked to verify that they are insulated stranded copper conductors with a thermoplastic insulation that is suitable for battery room installation.

•

The battery charger should be checked to verify that it is attached to the equipment ground circuit of the ac supply in accordance with Article 250 of the NEC.

Figure 16, NEC Table 250-95, provides the required size of the equipment grounding conductors for battery chargers.


44



NEC Table 250-95: Sizes of Equipment Grounding Conductors for Battery Chargers Figure 16 The charger output is checked for proper operation through verification of the output conditions. The settings for the float voltage and for the equalize voltage should be verified against the data schedule and battery manufacturer's requirements. An accurate voltmeter should be used to measure the voltage at the output terminals of the battery charger and then across the positive and negative terminals of the battery. The difference of these two voltages will indicate the voltage drop of the battery charger input circuit. This voltage drop should be minimal. The voltage output of the battery charger must checked to verify that the charger voltage will be regulated within the specified limits listed on the data schedule. A guide for the percent voltage regulation requirements is provided below. Battery Charger Size

Float Operation Mode

< 10 kW > 10 kW

+/- 1% +/- 1%


Recharge (Equalize) Operation Mode +/- 2% +/- 1%

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BATTERY AND BATTERY CHARGER SYSTEM OPERATIONAL TESTING REQUIREMENTS The battery charger should be tested to ensure that the battery charger is capable of delivering the specified current output to the battery for the specified time as indicated on the data schedule. The battery should be load tested to confirm that it will deliver the specified value of current to the load for the specified length of time without reaching the final discharge voltage. These tests are best accomplished through use of a load bank of sufficient rating. The float and equalize settings should be verified, and the actual value of these settings should be measured under various conditions of charge rate and load. When the charger is operated within the specified current capability, the charger voltage regulation should maintain output voltage under all conditions. Charging Rate The charging rate of the battery charger can be verified by connecting the charger to the load bank and adjusting the load to a value that will cause the charger to deliver the specified output current. The charging rate verification test should be run for the length of time that is required on the data schedule. During this test, the battery charger output voltage should be continuously monitored to ensure that it is maintained within the specified limits. Discharge Rate The battery must be tested for its ability to discharge into the load and provide the rated value of current for the specified length of time without reaching the final voltage. This test is accomplished through use of a load bank. The battery output is connected to the load bank, and the load bank is adjusted to cause the battery discharge current to equal the discharge capability that is listed on the data schedule. An accurate voltmeter should be connected to the battery output so that voltage readings can be monitored and recorded at regular intervals during the test. Float/Equalize Settings After all the charger and battery testing is complete, a final check of the float setting and the equalize setting should be confirmed. The float and equalize settings should provide a constant voltage output through battery cycles of charging and discharging.


46



Charging Capacity (Amp-Hour Rating) The battery charger ampere output is listed on the nameplate, and it can be calculated through use of the following formula A = ( SF * L + (BIF * AH/RT) ) /Kt Where: SF L BIF

A = = =

= Ampere rating of the charger. Service factor: 1.1. Sum of continuous dc loads (amperes). Battery inefficiency factor: 1.15 for lead-acid batteries and 1.14 Ni-Cad batteries.

AH RT Kt

= = =

Battery ampere-hour. Recharge time. Temperature compensation: Kt = 1.00 at or below 40_C. Kt = 0.83 from 40_C to 50_C.

for

This rating of the battery charger is verified during the charger charging rate verification that was described above.


47



REQUIREMENTS FOR THE SYSTEM OPERATIONAL OBSERVATION PHASE After all tests and inspections of the battery system have been completed, and after the commissioning process has resulted in the battery being placed in service, the battery system should be monitored at frequent intervals for several weeks. The purpose of this observation phase is to carefully monitor the battery and charger under all conditions of service for any signs of improper or erratic operation. The items that should be observed include all parts of the battery system. The charger output should be monitored by observing and recording the output voltage and current. The charger wiring should be inspected to note any signs of poor connections, overheating, or other similar problems. The battery should be observed for any signs of cell overheating, excessive loss of electrolyte, leaking cell jars, and loose battery connections. Specific gravity tests should be conducted and recorded after the battery has been in normal service for a period of time. The specific gravity of all cells should be within a small percentage of each other. If ac power is lost to the battery charger, the battery will be the sole source of dc power. When a loss of ac power occurs, the battery voltage and discharge rate should be noted.


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SUMMARY As mentioned in the Introduction, commissioning of batteries and battery charger systems is part of the overall process by which a facility is commissioned. The actions explained below are required to bring commissioning of batteries and battery chargers to completion. After the battery has completed the testing and operational observance phase, after all items have been verified as satisfactory, the battery system should be accepted as having completed the commissioning process. Maintenance intervals should be established so that all components of the battery system that require routine maintenance are placed on a periodic maintenance schedule. All the commissioning documents, including data schedules, commissioning form P-003, manufacturers' technical manuals, system drawings, and any other related paperwork should be turned over to the appropriate authority for proper custody. A spare parts inventory should be maintained that is based on the charger and battery manufacturer's recommendations. This spare parts inventory would include items, such as spare hardware for the battery intercell connectors, battery rack hardware, and spare parts for the charger internal circuits. Battery rooms receive a final inspection to ensure that all the items, such as the ventilation or air conditioning system and eyewash and shower facilities, function properly. The inspection should include verification that all the accessories that are necessary to maintain the battery are properly located in the battery room.


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WORK AID 1: REFERENCES FOR EVALUATING BATTERIES AND BATTERY CHARGERS UPON RECEIPT The following information is to be used as a guide for performing Exercise 1. The information that is provided should be used in addition to the Saudi Aramco Battery PreCommissioning Form P-003, sheets 1 through 4. (This form is obtained from the Instrumentation unit of the Consulting Services Department.) Criteria for Evaluating Batteries Upon Receipt 1. Verify that the battery cells are of the type that is indicated on the data schedule. The type of battery should be one of the following: • • • • •

Ni-Cad (pocket-plate) Plante Lead-Calcium Lead-Antimony (maximum 3% antimony) Tubular Lead (maximum 3% antimony)

Note: Ni-Cad cells must be of the vented pocket-plate construction. Sintered-plate cells are not permitted. 2. Verify that the recharge period is as specified on the data sheet. 3. Verify that the number of cells corresponds to the battery nominal voltage. Nominal Battery System Voltage (vdc) 12 24 48 120/125 240/250 360/375

Number of Cells Lead-Acid 6 12 24 60 120 180

Ni-Cad 10 19 37 92 184 276

4. Verify that the battery manufacturer's design float voltage is as indicated on the data schedule. 5. Verify that the maintenance interval is as indicated on the data schedule, both standard and extended. 6. Verify that the battery design ambient temperature is in accordance with the data schedule. Saudi Aramco DeskTop Standards

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7. Verify that the electrolyte density corresponds to the data schedule. 8. Verify that the battery load is per the data schedule information or that the battery will accommodate the load profile that is attached to the data schedule. Criteria for Evaluating Battery Chargers Upon Receipt 1. The battery charger's nameplate data should be verified against the data schedule through comparison of the nameplate data to the following information that is indicated on the data schedule. AC Input Nominal Voltage Frequency

= or - 10%

phases

60 Hz + or - 5 %

Available short-circuit current

rms symmetrical amperes

Battery Load Type: Ni-Cad Lead Calcium Plante Lead-Antimony Charging capacity

for

hours to

final volts per cell.

External dc load (excluding battery) Amperes Maximum Duty Cycle Description Output Voltage Range Floating Equalizing

volts minimum to volts minimum to

volts maximum volts maximum

Ambient Temperature Maximum Saudi Aramco DeskTop Standards

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Minimum

2. The battery chargers for Saudi Aramco dc systems should be constant-potential, semiconductor, static-type chargers that are designed to simultaneously supply dc power to a float-type battery and to the connected dc loads. The battery charger that is received should be one of the two types that are listed below as specified on the material data sheet: • •

Static Plate Rectifier Solid State Rectifier

3. Verify that the battery charger meets the requirements of NEMA PE 5-1983 with the additions and exceptions that are listed in 17-SAMSS-514. The following information should be as specified on the data schedule and is an exception to NEMA PE 5-1985: "Input supply voltage and frequency are as specified on the data schedule." 4. The following items are in addition to the requirements of NEMA PE 5-1985: •

Panel meters that are furnished on the battery charger must have an accuracy of +/- 2% of full scale accuracy, and designed in accordance with ANSI C39.1. Each battery charger must be supplied with a dc ammeter and voltmeter.

•

Printed circuit boards that are contained within the battery charger must meet the requirements of UL 796 and several additional requirements as listed in 17-SAMSS514.

•

The battery charger must be equipped with an end of discharge relay that operates when the battery discharges to a voltage of 1.75 volts for lead-acid cells and 1.10 volts for Ni-Cad cells.

•

The charger should come equipped with a ground detection relay for the dc bus that is capable of detecting grounds on either the positive or negative bus.

•

Battery charger alarm relays must have form "C" single-pole, double-throw relay contacts.

•

The battery charger output voltage regulation must be designed to maintain voltage regulation when the battery is disconnected from the charger (battery elimination feature).

•

The battery charger is equipped with a filter that meets "limit B" requirements for output ripple.


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•

The battery charger must be equipped with an input circuit breaker that has an interrupting rating that is equal to or greater than the available short-circuit currents that are listed on the data schedule (14,000 rms symmetrical amps minimum). This requirement may be alternately met through use of current limiting fuses of the required interrupting rating. The circuit breaker must be designed and tested in accordance with UL 489.

•

The charger must be equipped with an output breaker or disconnect switch that will simultaneously open both output lines.

Enclosures for the battery charger must meet the following requirements: •

Enclosures must be either carbon steel or aluminum, and they must meet the requirements of NEMA ICS 6, Type 1.

•

Enclosures must be naturally or force ventilated. If the enclosure is force ventilated, it must be equipped with removable, easily-cleaned air filters.

•

The enclosure must be designed for front access to all components, and it must have double or full-length, hinged doors.

•

Handles, hinges, and screws must be corrosion resistant.

•

Terminal blocks must be provided for connection to external alarm circuits and must be of a phenolic, one-piece, barrier-type with pan head screws.

•

Insulated compression-type terminals must be provided for all wiring that terminates on terminal blocks. Solder terminals are not permitted for connection to terminal blocks.

•

Power cable terminations (lugs) must be the copper-bodied, compression-type (crimped-type) that are suitable for use with ASTM Class B and C stranded conductors.

•

All wiring must be stranded copper conductors only.

•

Wiring terminal blocks must be identified with thermoplastic slip-on wire markers with permanently printed characters. The wiring markers must directly correspond to the numbering found on the schematic.

•

Nameplates on the charger must be written in the English language.


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•

Exterior nameplates are to be attached with stainless steel or brass screws, and internal compartment nameplates may be attached with permanent adhesive. All devices that are located within a panel must be identified with a suitable nameplate that identifies the item and its function.

The following accessory devices must be provided on the battery charger: • • • • •

Equalizing timer Low voltage alarm relay Overvoltage alarm relay Charger failure relay Low current alarm relay

Physical Inspection The battery, battery charger, and associated equipment should be physically inspected for the following: •

Lead-acid cells are shipped in a "dry-charged" condition. Each cell should be sealed with a moisture-proof vent cap. Ni-Cad cells should be shipped dry, discharged, and sealed with moisture-proof vent caps.

•

Individual cells should arrive wrapped and sealed against moisture with a desiccant. There should be instructions contained in each cell shipping container that instructs how to correctly lift the cell.

•

The shipping information sheet should indicate that the cells should be stored in a cool, dry location. The label on the outer wrapping of the cell should include the manufacturer's warranty statement, which includes the storage conditions, date of shipment, and maximum storage time from date of manufacture.

•

The cell accessories should be included with each cell, and they should not be shipped in bulk in a separate package.

•

Battery plate material is of the type that is specified in the data schedule. The NiCad cells must be of the vented pocket-plate construction. Sintered-plate Ni-Cad cells are not permitted to be used in Saudi Aramco battery systems.


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•

The battery containers should be constructed of a heat- and impact-resistant plastic material that is either transparent or translucent. Adequate space must be provided above the cells to meet the manufacturer's maintenance schedule. The cell jars should also have clearly-marked level lines on the sides of the container.

•

The cell cover and the container must be sealed properly at the joint between these two parts, which provides a gas-tight seal.

•

The cells should be equipped with explosion-proof vent caps that meet the requirements of NEMA-IB-7. These vent caps are designed to allow gases to escape from the cells, but they prevent any flame or sparks from entering the cell.

•

The intercell connectors and battery cable terminals should be checked to ensure they are of the proper size and material to carry the design current and not permit excessive voltage drop. Ensure that the intercell connectors are of the correct type for the particular battery. If copper links are used, they must be coated with a homogeneous lead or lead alloy coating that is no less than 50 micrometers (0.002 in.) thick. If the battery is a Ni-Cad-type, the intercell connectors must be nickel plated. Connector bolts, nuts, and washers must be either lead-plated brass or stainless steel (ANSI type 316). The polarity of each cell terminal must be clearly marked as positive or negative.

•

Battery racks should be inspected and verified for the following conditions: -

The racks should be a one- or two-row stepped arrangement that is large enough to accommodate the number of cells.

-

The racks should be no more than two tiers in height.

-

The width of the racks must be at least as wide as the battery cell width.

-

The racks should be constructed of welded structural steel frames with boltedon steel runners and braces and with provision for anchoring the racks to the floor.

-

The metal frame of the racks should be coated with an acid-resistant plastic or equivalent material.

•

Additionally, a sufficient quality of the battery rack coating material should be supplied by the vendor to take care of nicks and to cover exposed hardware and bolt threads after the racks have been installed.

•

A verification of the required accessories should include:


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-

Battery cell thermometer

-

Hydrometer with temperature correction scale (for lead-acid cells)

-

Insulated wrenches to fit battery hardware

-

Bottle with pour spout for adding distilled water

-

Spare intercell connecting hardware and extra rack bolts and nuts that are equal to 10% of the total hardware

-

Supply of NO-OX terminal grease (lead-acid only)

-

Cell lifting straps or apparatus for cells over 34Kg (75lb)

-

Cell voltmeter

All components must be inspected for any visual signs of damage or deterioration during shipment. This inspection should include items that are broken, bent, cracked, or other obvious signs of damage. All of the battery cell containers must also be checked. Any effects of corrosion or moisture damage that often occur during shipping should also be noted. Saudi Aramco Pre-Commissioning Form P-003, Battery System The Saudi Aramco Pre-Commissioning Form P-003, Battery System, provides a field installation checklist for batteries and battery chargers. The pre-commissioning form has a broad checklist of visual and mechanical inspections, as well as the listed electrical tests that are required for battery and battery charger installations. Space is also provided on the form for test data. This form is obtained from the Instrumentation Unit of the Consulting Services Department.


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Saudi Aramco Pre-Commissioning Form, P-003, Battery System Figure 22


57



Saudi Aramco Pre-Commissioning Form, P-003, Battery System Figure 22 (Cont'd)


58



Saudi Aramco Pre-Commissioning Form, P-003, Battery System Figure 22 (Cont'd)


59



Saudi Aramco Pre-Commissioning Form, P-003, Battery System Figure 22 (Cont'd) WORK AID 2: REFERENCES FOR EVALUATING BATTERY AND BATTERY CHARGER INSTALLATION AND TESTING The Participant should use Work Aid 2 as necessary to complete Exercise 2. Procedure for Evaluating Battery and Battery Charger Installation and Testing 1. Verify that the battery and battery rack have been installed correctly. Inspect for proper equipment grounding of battery rack, battery charger enclosure, and all non-currentcarrying metal parts of the system. Ensure that these components are properly connected to the equipment grounding circuit. Ensure that all parts of the battery rack have been painted with appropriate coating after installation of all rack hardware. 2. Eyewash and Shower Stations 2a. The eyewash and shower stations may be equipped with an alarm that is activated whenever either facility is operated. The determination of an alarm is made by the Industrial Hygiene Unit of the Medical Services. If an alarm is installed, verify that it operates correctly by operating the eyewash and the emergency shower. 2b. During the commissioning of battery systems, the installation of showers and eyewash stations should be carefully inspected to ensure that they meet the requirements of SAES-B-069 and that they function properly. 2c. Verify that the eyewash and shower can provide a continuous flow rate for at least 15 minutes at a pressure that is no greater than 207 kPa (30 psig) and at a temperature that is no greater than 37.8_C (100_F) except for the short period of time where water is naturally heated from the environment by above-ground piping. If the system is capable of delivering higher pressure at the eyewash and shower outlets, the pressure Saudi Aramco DeskTop Standards

60



must be maintained through use of pressure controllers or self-regulating orifices to prevent the pressure from exceeding 207 kPa. 3. Verify that all accessory equipment is in place, including: • • • • • • • • •

Safety protective clothing Hydrometer (for lead-acid cells) Cell voltmeter Cell thermometer Insulated wrenches to fit battery hardware Bottle with pour spout for battery water Spare intercell connecting hardware, 10% of total amount Supply of NO-OX terminal grease (lead acid only) Cell lifting straps for cells over 34 kg (75 lb.)

4. Verify that the battery intercell connectors are properly torqued and that non-corrosive protective coating has been applied to terminal connections. 5. Verify the battery charger operating conditions: •

Float voltage is between 2.25 volts to 2.30 volts per cell for lead-acid cells, or +/- 1.0 % of the nominal voltage, or as recommended by the battery manufacturer.

•

Equalize voltage should be within +/- 1.0% of the specified equalize voltage that is recommended by the battery manufacturer. If the battery charger is 10 kW or less, the acceptable value is +/- 2 % of nominal voltage (cell open circuit voltage).

6. Battery Cells 6a.

Verify that the battery cell terminal resistance has been measured and that no cell has a resistance greater than 10% or 5 micro-ohms, whichever is greater over the average of all the cell terminal resistances.

6b. Cell Specific Gravity (Lead-Acid Only) After the battery has been fully charged with the freshening charge and allowed to remain on float charge for no less than 72 hours, specific gravity readings can be taken. The specific gravity readings should be corrected for temperature. For every 3°F (1.67°C) above 77°F (25°C), add one point (.001) to the specific gravity reading. For every 3° (1.67°C) below 77°F (25°C), subtract one point (.001) from the hydrometer reading.


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The specific gravity readings should be such that no cell has a specific gravity that is more than ten points (0.010) below the average of the specific gravity of all cells after corrections for temperature have been made. 6c. Cell Voltage The acceptable value for cell voltage is that no cell voltage should have a value that is lower than 2.10 volts (1.215 specific gravity) for lead-acid cells and 1.29 volts (1.300 specific gravity) for Ni-Cad cells. 6d. Battery Discharge Rate The acceptable value for battery discharge rate is that the battery meets the requirements that are specified on the data schedule and that the battery is in accordance with the battery manufacturer's specifications.

Unless 100% battery capacity is specified upon delivery, batteries may be less than rated capacity when received from the manufacturer. Verify the battery discharge duration by testing. This testing involves discharging the battery at a pre-determined value of current (based on the battery rating) and measuring the time it takes the battery to reach its final voltage per cell (1.75 volts for lead-acid) times the number of cells. 7. Check and Verify the Following Battery Charger Setpoints: 7a. End of charge condition alarm is +/- 5% of the 1.75 volts per cell for lead-acid cells and +/- 5% of the 1.10 volts per cell for Ni-Cad cells. 7b. Low charger output voltage alarm setpoint is 2.2 volts per cell for lead-acid cells and 1.4 volts per cell for Ni-Cad cells. 7c. Ground detection alarm operates when the leakage current exceeds 10.0 milliamps, which is a fixed value that is set by the equipment manufacturer. 7d. The charger overvoltage alarm setpoint should operate at +/- 10% of the nominal cell voltage, as recommended by the charger manufacturer. 7e. The enclosure overtemperature alarm is + 10% , - 0% of the manufacturer's stated operating temperature.


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8. Inspect the battery room door and ensure that it opens outward and away from the batteries to facilitate easy exit in the event of an emergency. 9. Verify that battery cables are installed in accordance with the NEC NFPA 70. Battery cables should be installed neatly and properly. Verify that the cable AWG size and insulation are in accordance with the ampacity of the battery system. 10. The battery output circuit breaker should be equipped with a low voltage shunt trip device that will cause the circuit breaker to open if the battery voltage drops to a value 5% below the battery final voltage. This circuit breaker undervoltage device should be tested to confirm that it operates properly.


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GLOSSARY battery

One or more electrochemical cells that are lined together to provide a direct current output. Several cells are normally connected in series to provide the desired nominal voltage of a dc system.

battery charger

An electrical device that is designed to convert an ac input to a DC output for the purpose of charging electrochemical cells.

cell

A container that is constructed to house the active plates and electrolyte solution that are necessary to maintain an electrochemical reaction that delivers direct current at its terminals.

cell voltage

The voltage that is measured at the terminals of an electrochemical cell. The cell voltage can be an indication of the state of charge of some types of cells.

cycle service

A duty cycle that is characterized by frequent and usually deep discharge sequences, such as motive power applications.

electrolyte

A liquid mixture that is used in electrochemical cells to conduct the migration of charges between the plates of the cells. The electrolyte for lead-acid cells consists of a solution of sulfuric acid and water; the electrolyte for Ni-Cad cells consists of a solution of potassium hydroxide and water.

energy density

A ratio of the energy that is available from a battery or cell to its volume (Wh/L) or weight (Wh/kg).

equalize charge

An amount of charging voltage and current that are sufficient to restore all the cells of a battery to an equal state of charge.

flame arrestor

A device that is used to allow generated gases to escape from electrochemical cells and to prevent a spark or flame from entering the cell and possibly causing an explosion.

float service

A method of maintaining a cell or battery in a charged condition by continuous, long-term, constant voltage charging at a level sufficient to balance self-discharge.


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freshening charge

The charge that is applied to a new battery after it has been received and filled with electrolyte. Flooded-plate-types of battery cells are typically shipped in a dry charged condition.

hydrometer

A device that is used to measure the specific gravity of an electrolyte in an electrochemical cell.

intercell connectors

Rectangular metallic links that are designed to connect adjacent cells to one another in a battery. These links are commonly made of lead-plated copper for lead-acid cells or of stainless steel for Ni-Cad cells.

memory effect

A phenomenon in which a cell is operated in successive cycles to the same but less than full depth of discharge. When a battery is repeatedly cycled to less than full depth, it temporarily loses the rest of its capacity at normal voltage levels. This phenomenon normally applies to Ni-Cad cells only.

Plante cell

A specific type of lead-acid cell in which the active materials are formed directly from a lead substrate by electrochemical processing. Cells of the Plante design provide long service life, low positive plate growth, and very high reliability when compared to other types of lead-acid cells.

power density

The ratio of the power that is available from a battery or cell to its weight (W/kg) or volume (W/L).

specific gravity

The ratio of the weight of an electrolyte solution compared to water. For example, an electrolyte solution that has a specific gravity of 1.215 has 1.215 times the density of water. The specific gravity is an indication of the state of charge of certain types of electrochemical cells, such as lead-acid cells.

VPC (voltage per cell)

This term is used to indicate the average voltage that is available at the terminals of an individual cell. VPC may be determined by dividing the total battery voltage by the number of cells in the battery.


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Commissioning Systems, Batteries and Battery Charger

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