I NDUSTRIAL TRAINING
SUMMER TRAINING REPORT 27/06/2016 to 26/07/2016 Submitted By:-ANKIT SAROHA
This is to certify that ANKIT SAROHA, student of 2013-2017 Batch of Electrical & Electronics Engineering Branch in Final year of Maharaja Agrasen Institute of Technology has successfully completed his industrial training at INDRAPRASTHA POWER GENERATION Corp. Ltd -PPCL-1, Bawana New Delhi for six weeks from 13 june to 24july 2016. He has completed the whole training as per the training report submitted by him.
Training In charge – Er. Sudhir Kumar
Contents
•Introduction •Combined Cycle Power Plant •Mechanical Equipment •Electrical Equipment •Protection and Switchgear •Balance of Plant •Bibliography Introduction: IPGCL-PPCL Indraprastha Power Generation Co. Ltd. (IPGCL) was incorporated on 1st July,2002 and it took over the generation activities w.e.f. 1st July,2002 from erstwhile Delhi Vidyut Board after its unbundling into six successor companies. The main functions of IPGCL is generation of electricity and its total installed capacity is 994.5 MW including of Pragati Power Station. Its associate Company is Pragati Power Corporation Limited which was incorporated on 9th January, 2001.To b r i d g e t h e g a p b e t w e e n d e ma n d a n d s u p p l y a n d t o g i v e r e l i a b l e s u p p l y t o t h e capital City a 330 MW combined cycle Gas Turbine Power Project was set up on fast track b a s i s . Th i s p l a n t c o n s i s t s o f t wo g a s b a s e d Un i t s o f 1 0 4 M W e a c h a n d o n e Wa s t e h e a t Recovery Unit of 122 MW. Gas supply has been tied up with GAIL through HBJ Pipeline. Due to paucity of water this plant was designed to operate on treated sewage water which is being supplied from Sen nursing Home and Delhi Gate Sewage Treatment plants. Pragati-III Combined Cycle Power Plant is located at Bawana Delhi, India. The power plant is one of the gas based power plants of Pragati Power Corporation Limited (PPCL). The source of water for the power plant is treated water from Rithala Sewage Treatment Plant. NEW DELHI: With both modules declared for commercial operation, the Bawana Power Plant is in full technical readiness to service 1500 MW to the national capital, Delhi government said today. The largest gas plant in Northen India, and second largest in the country, the Bawana power plant was able to produce only up to 350 MW for the city of Delhi.
Stage
Unit
Installed capacity
Date of
number
(MW)
commissioning
Turbine
1st
1
250
2010 October
Gas
1st
2
250
2011 February
Gas Turbine-2
1st
3
250
2011 October
Steam
1st
4
250
2012 July
Gas Turbine-3
1st
5
250
2014
Gas Tubine-4
Steam Turbine1st
6
250
2014
Their Vision: “TO MAKE DELHI – POWER SURPLUS”
To maximize generation from available capacity To plan & implement new generation capacity in Delhi Competitive pricing of our own generation To set ever so high standards of environment Protection. To develop competent human resources for managing the company with good standard.
2 [3]
Combined Cycle Power Plant: Gas Turbine Power Plants Gas Turbine Working Principle Gas turbine engines derive their power from burning fuel in a combustion chamber and using the fast flowing combustion gases to drive a turbine in much the same way as the high pressure steam drives a steam turbine. One major difference however is that the gas turbine has a second turbine acting as an a i r c o m p r e s s o r mo u n t e d o n t h e s a me s h a f t . T h e a i r t u r b i n e ( c o mp r e s s o r ) d r a w s i n a i r , c o mp r e s s e s i t a n d f e e d s i t a t h i g h p r e s s u r e i n t o t h e c o mb u s t i o n c h a mb e r i n c r e a s i n g
t h e intensity of the burning flame. It is a positive feedback mechanism. As the gas turbine speed su p , i t a l s o c a u s e s t h e c o mp r e s s o r t o s p e e d u p f o r c i n g mo r e a i r t h r o u g h t h e c o mb u s t i o n chamber which in turn increases the burn rate of the fuel sending more high pressure hot gases into the gas turbine increasing its speed even more. Uncontrolled runaway is prevented by controls on the fuel supply line which limit the amount of fuel fed to the turbine thus limiting its speed. The thermodynamic process used by the gas
turbine is known as the Brayton cycle. A n a l o g o u s t o t h e C a r n o t c yc l e i n w h i c h t h e e f f i c i e n c y i s ma x i mi s e d b y i n c r e a s i n g t h e temperature difference of the working fluid between the input and output of the machine, theB r a yt o n c yc l e e f f i c i e n c y i s ma x i mi s e d b y i n c r e a s i n g t h e p r e s s u r e d i f f e r e n c e a c r o s s t h e machine. The gas turbine is comprised of three main components: a compressor, a combustor, and a turbine. The working fluid, air, is compressed in the compressor (adiabatic compressionno heat gain or loss), then mixed with fuel and burned by the combustor under constant p r e s s u r e c o n d i t i o n s i n t h e c o mb u s t i o n c h a mb e r ( c o n s t a n t p r e s s u r e h e a t a d di t i o n ) . Th e resulting hot gas expands through the turbine to perform work (adiabatic expansion). Much of the power produced in the turbine is used to run the compressor and the rest is available to run auxiliary equipment and do useful work. At PPCL, when the GT reaches around 2800 RPM, all auxiliary systems supporting the turbine are shut and only the GT is used to supply power and compressed air to all these systems, thus improving efficiency. Gas turbines have a very high power to weight ratio and are lighter and smaller than internal combustion engines of the same power. Though they are mechanically simpler than reciprocating engines, their characteristics of high speed and high temperature operation require high precision components and exotic materials making them more expensive to manufacture. General Electric is a pioneer in GT manufacturing Electrical Power Generation In electricity generating applications the turbine is used to drive a synchronous generator which provides the electrical power output but because the turbine normally operates at very high rotational speeds of 3,000 RPM or more it must be connected to the generator through a high ratio reduction gear since the generators run at speeds of 1,000 or 1,200 r.p.m. depending on the AC frequency of the electricity grid. Combined Cycle Systems which are designed for maximum efficiency in which the hot exhaust gases from the gas turbine are used to raise steam to power a steam turbine with both turbines being connected to electricity generators. To minimize the size and weight of the turbine for a given output power, the output p e r p o u n d o f a i r f l o w s h o u l d b e ma x i mi z e d . Th i s i s o b t a i n e d b y ma x i mi z i n g t h e a i r f l o w through the turbine which in turn depends
on maximizing the pressure ratio between the air inlet and exhaust outlet. System Efficiency: Thermal efficiency is important because it directly affects the fuel consumption and operating costs. Combined Cycle Turbines It is however possible to recover energy from the waste heat of simple cycle systems by using the exhaust gases in a hybrid system to raise steam to drive a steam turbine electricity generating set. In such cases the exhaust temperature may be reduced to as low as 140°C enabling efficiencies of up to 60% to be achieved in combined cycle systems. Thus simple cycle efficiency is achieved with high pressure ratios. Combined cycle efficiency is obtained with more modest pressure ratios and greater firing temperatures. Fuels One further advantage of gas turbines is their fuel flexibility. Crude and other heavy oils and can also be used to fuel gas turbines if they are first heated to reduce their viscosity to a level suitable for burning in the turbine combustion chambers. •The Open Cycle efficiency of the plant is about 31% •The Closed Cycle efficiency is around 59% HRSG(heat recovery steam generator)
is an energy recovery heat exchanger that recovers heat from a hot gas stream. It produces steam that can be used in a process or used to drive a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone. The HRSG is also an important component incogenerationp l a n t s . C o g e n e r a t i o n p l a n t s t y p i c a l l y h a v e a h i g h e r o v e r a l l e f f i c i e n c y i n comparison to a combined cycle plant. This is due to the loss of energy associated with the steam turbine The HRSG at PPCL Evaporator Section: The most important component would, of course, be the Evaporator Section. So an evaporator section may consist of one or more coils. In these coils, the effluent (water), passing through the tubes is heated to the saturation point for the pressure it is flowing. Super heater Section: The Super heater Section of the HRSG is used to dry the saturated vapor being separated in the steam drum. In some units it may only be heated to little above the saturation point where in other units it may be super-heated o a significant temperature for additional energy storage. The Super heater Section is normally located in the hotter gas stream, in front of the evaporator. Economizer Section: The Economizer Section, sometimes called a preheater or preheat coil, is used to preheat the feed water being introduced to the system to replace the steam (vapour) being removed from the system via the super heater or steam outlet and the water loss through blow down. It is normally located in the colder gas downstream of the evaporator. Since the evaporator inlet and
outlet temperatures are both close to the saturation temperature for the system pressure ,the amount of heat that may be removed from the flue gas is limited due to the approach to the evaporator, whereas the economizer inlet temperature is low, allowing the flue gas temperature to be taken lower
Block diagram of a power plant which utilizes the HRSG. The steam turbinedriven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running. To minimize the frictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated. Condenser The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shellw h e r e i t i s c o o l e d a n d c o n v e r t e d t o c o n d e n s a t e ( wa t e r ) b y f l o wi n g o v e r t h e t u b e s . S u c h condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 οC where the vapour pressure o f wa t e r i s mu c h l e s s t h a n a t mo s ph e r i c p r e s s u r e , t h e c o n d e n s e r g e n e r a l l y wo r k s u n d e r vacuum. Thus leaks of non-condensable air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning. The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean. Deaerator A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal. Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feed water. A deaerator typically includes a vertical,
domeddeaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feed water storage tank. Practical considerations demand that in a steam boiler/steam turbine/generator unit thec i r c u l a t i n g s team,condensate,andfeedwatershouldbed e v o i d o f d i s s o l v e d g a s e s , particularly corrosive ones, and dissolved or suspended solids. The gases will give rise to corrosion of the metal in contact thereby thinning them and causing rupture. The solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures due to overheating. Under some conditions it may give rise to stress corrosion cracking. Cooling Towers:
areheatremovaldevicesusedtotransferpro c e s s w a s t e h e a t t o t h e atmosphere.Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool he working fluid to near the dry-bulb air
temperature. Common applications include cooling the circulating water used in oil refineries, chemical plants, power stations and buildingc o o l i n g . T h e t o w e r s v a r y i n s i z e f r o m s m a llroof-
t o p u n i t s t o v e r y l a r g e hyperboloidstructures(as in Image 1) that can be up to 200 meters tall and 100 meters in diameter, or rectangular structures (as in Image 2) that can be over 40 meters tall and 80 meters long. Smaller towers are normally factory-built, while larger ones are constructed on site.
WATER TREATMENT(plant layout)
Raw Water plant, capacity (250000 liters)
T h e c l a s s o f g e n e r a t o r u n d e r c o n si d e r a t i o n i s s t e a m t u r b i n e - d r i v e n g e n e r a t o r s , commonly called turbo generators. These machines are generally used in nuclear and fossil fuelled power plants, cogeneration plants, and combustion turbine units. They range from relatively small machines of a few Megawatts (MW) to very large generators with ratings up to 1900 MW. The generators particular to this category are of the two- and four-pole design employing round-rotors, with rotational operating speeds of 3600 and 1800 rpm in North America, parts of Japan, and Asia (3000 and 1500 rpm in Europe, Africa, Australia, Asia, and South America). At PPCL 3000 rpm, 50 Hz generators are used of capacities 122 MW. As the
system load demands more active power from the generator, more steam (or fuel in a combustion turbine) needs to be admitted to the turbine to increase power output. Hence more energy is transmitted to the generator from the turbine, in the form of a torque. This torque is mechanical in nature, but electromagnetically coupled to the power system through t h e g e n e r a t o r . Th e h i g h e r t h e p o we r o u t p u t , t h e h i g he r t h e t o r q u e b e t we e n t u r b i n e a n d generator. The power output of the generator generally follows the load demand from the system. Therefore the voltages and currents in the generator are continually changing based o n t h e l o a d d e ma n d . Th e g e n e r a t o r d e s i g n mu s t b e a b l e t o c o p e wi t h l a r g eandfast loadchanges,whichshowupinsidethemachineaschange s i n m e c h a n i c a l f o r c e s a n d temperatures. The design must therefore incorporate electrical current-carrying materials (i.e., copper), magnetic fluxcarrying materials (i.e., highly permeable steels), insulating materials(i.e., organic), structural members (i.e., steel and organic), and cooling media (i.e., gases and liquids), all working together under the operating conditions of a turbo generator An open Electric Generator at Power Plant Stator of a Turbo Generator S ince the turbo generator is a synchronous machine, it operates at one very specific speed to produce a constant system frequency of 50 Hz, depending on the frequency of the g r i d t o wh i c h i t i s c o n n e c t e d . As a s yn c h r o n o u s ma c h i n e , a t u r b i n e g e n e r a t o r e mp l o ys a steady magnetic flux passing radially across an air gap that exists between the rotor and the stator. (The term “air gap” is commonly used for air- and gas-cooled machines). For the machines in this discussion, this means a magnetic flux distribution of two or four poles on the rotor. This flux pattern rotates with the rotor, as it spins at its synchronous speed. The rotating magnetic field moves past a three-phase symmetrically distributed winding installedi n t h e s t a to r c ore,generatinganalternatingvoltageinthe s t a t o r wi n d i n g . Th e v o l t a g e waveform created in each of the three phases of the stator winding is very nearly sinusoidal .The output of the stator winding is the three-phase power, delivered to the power system at the voltage generated in the stator winding. In addition to the normal flux distribution in the main body of the generator, there are stray fluxes at the extreme ends of the generator that create fringing flux patterns and induces tray losses in the generator. The stray fluxes must be accounted for in the overall design. Generators are made up of two basic members, the stator and the rotor,
but the stator andr o t o r a r e e a c h c o n s t r u c t e d f r o m n u me r o u s p a r t s t h e ms e l v e s . R o t o r s a r e t h e h i gh - s p e e d rotating member of the two, and they undergo severe dynamic mechanical loading as well as the electromagnetic and thermal loads. The most critical component in the generator is the retaining rings, mounted on the rotor. These components are very carefully designed for high-stress operation. The stator is s t a t i o n a r y, a s t h e t e r m s u g g e s t s , b u t i t a l s o s e e s s i g n i f i c a n t d yn a mi c f o r c e s i n t e r ms o f v i b r a t i o n a n d t o r s i o n a l l o a d s , a s w e l l a s t h e e l e c t r o ma g n e t i c , t h e r ma l , a n d h i g h - v o l t a g e loading. The most critical component of the stator is arguably the stator winding because it is a very high cost item and it must be designed to handle all of the harsh effects described above. Most stator problems occur with the winding. STATOR The stator winding is made up of insulated copper conductor bars that are distributed around the inside diameter of the stator core, commonly called the stator bore, in equally spaced slots in the core to ensure symmetrical flux linkage with the field produced by rotor. Each slot contains two conductor bars, one on top of the other. These are generally referred to as top and bottom bars. Top bars are the ones nearest the slot opening (just under the wedge) and the bottom bars are the ones at the slot bottom. The core area between slots is generally called a core tooth. ROTOR The rotor winding is installed in the slots machined in the forging main body and is distributed symmetrically around the rotor between the poles. The winding itself is made up o f ma n y t u r n s o f c o p p e r t o f o r m t h e e n t i r e s e r i e s c o n n e c t e d w i n d i n g . Al l o f t h e t u r n s associated with a single slot are generally called a coil. The coils are wound into the winding slots in the forging, concentrically in corresponding positions on opposite sides of a pole. The series connection essentially creates a single multi-turn coil overall, that develops the total ampere-turns of the rotor (which is the total current flowing in the rotor winding times the total number of turns). There are numerous copperwinding designs employed in generator r o t o r s , b u t a l l r o t o r wi n d i n gs f u n c t i o n b a s i c a l l y i n t h e s a me wa y . Th e y a r e c o n f i g u r e d differently for different methods of heat removal during operation.
BEARINGS
A l l t u r b o g e n e r a t o r s r e q u i r e b e a r i n g s t o r o t a t e f r e e l y wi t h mi n i ma l f r i c t i o n a n d vibration. The main rotor body must be supported by a bearing at each end of the generator for this purpose. In some cases where the rotor shaft is very long at the excitation end of the machine to accommodate the slip/collector rings, a “steady” bearing is installed outboard of the slip-collector rings. This ensures that the excitation end of the rotor shaft does not create a wobble that transmits through the shaft and stimulates excessive vibration in the over all generator rotor or the turbo generator line. There are generally two common types of bearings employed in large generators, journal” and “tilting pad” bearings. Journal bearings are the most common. Both require lubricating and jacking oil systems. Jacking oil pumps and Lube oil pumps are used for this purpose AUXILIARY SYSTEMS All large generators require auxiliary systems to handle such things as lubricating oil for the rotor bearings, hydrogen cooling apparatus, hydrogen sealing oil, demineralized water for stator winding cooling, and excitation systems for fieldcurrent application. Not all generators require all these systems and the requirement depends on the size and nature of the machine. For instance, air cooled turbo generators do not require hydrogen for cooling and thereforenosealingoilaswell.Ontheotherhand,large g e n e r a t o r s wi t h h i g h o u t p u t s , generally above 400 MVA, have watercooled stator windings, hydrogen for cooling the s t a t o r c o r e a n d r o t o r , s e a l o i l t o c o n t a i n t h e h yd r o g e n c o o l i n g g a s u n d e r h i g h p r e s s u r e , lubricating oil for the bearings, and of course, an excitation system for field current. There are five major auxiliary systems that may be used in a generator. They are given as follows:1. Lubricating Oil System2. Hydrogen Cooling System3. Seal Oil System4. Stator Cooling Water System5. Excitation System PROTECTION: The protection system of any modern electric power grid is the most crucial functioni n t h e s y s t e m . P r o t e c t i o n i s a s y s t e m b e c a u s e i t c o m p r i s e s d i s c r e t e d e v i c e s ( r e l a y s , c o mmu n i c a t i o n me a n s , e t c . ) a n d a n a l g o r i t h m t h a t e s t a b l i s h e s a c oo r d i n a t e d me t h o d o f operation among the protective devices. This is termed coordination. The key function of any protective system is to minimize the possibility of physical damage to equipment due to a fault anywhere in the system or from abnormal operation of the equipment (over speed, under voltage, etc.). Protective systems are inherently different from other systems in a power plant. Electric power generators are most often the most critical electrical apparatus in any power plant. Protection systems can be divided into systems monitoring
current, voltage (at them a c h i n e ’ s m a i n t e r m i n a l s a n d e x c i t a t i o n s y s t e m ) , w i n d i n
g s , a n d / o r c o o l i n g m e d i a temperature and pressure, and systems monitoring internal activity, such as partial discharge, decomposition of organic insulation materials, water content, hydrogen impurities, and flux p r o b e s . P r o t e c t i v e f u n c t i o n s a c t i n g o n t h e c u r r e n t , v o l t a g e , t e mp e r a t u r e , a n d p r e s s u r e parameters are commonly referred to as primary protection. The others are referred to as secondary protection or monitoring devices. Secondary functions tend to be monitored real time, or on demand. For instance, hydrogen purity is monitored on-line real time, while water content (for water leaks) is not. Temperature detectors (RTDs or thermocouples) on bearings( a n d s o me t i me s i n o n wi n d i ng s ) ma y b e mo n i t o r e d o n - l i ne r e a l t i me , o r t h e y ma y n o t . Furthermore these functions may more often than not result in an alarm, rather than directly trip the unit (e.g., core monitors).To the primary protective functions monitoring currents, voltages, temperatures and pressures, there can be added the mechanical protective function of vibration. Typically it will alarm, but it can also be set to trip the unit. Protections function can also be divided into Short circuit protection functions. The short-circuit protection comprises impedance, distance, and current differential protection. GENERATOR PROTECTIVE FUNCTION Protection devices are designed to monitor certain conditions, and subsequently, to alarm or trip if a specified condition is detected. The condition is represented by a function or p r o t e c t i v e f u nc t i o n c o d e . Th u s t h e r e i s a r e l a y f o r e v e r y p r o t e c t i v e f u n c t i o n . A mu l t i functionalrelaycontainingalltheprotectivefunctionsr e q u i r e d f o r t h e p r o t e c t i o n o f a generator can be combined with a few discrete relays providing backup protection for critical functions. Relays or protection devices are divided into two categories according to how they process data. The first category is that of analog relays; the second is that of numerical (also called d i g i t a l ) r e l a ys . B e a r i n mi n d t h a t a r e l a y c a n b e e l e c t r o n i c b u t s t i l l p r o c e s s t h e d a t a i n a n analog manner.
TRANSFORMER: A 400 kV Transformer at a Power PlantA N S I / I E E E d e f i n e s a t r a n s f o r m e r a s a s t a t i c e l e c t r i c a l d e v i c e , i n v o l v i n g n o continuously moving parts, used in electric power systems to transfer power between circuits through the use of electromagnetic induction. The transformer is one of the most reliable p i e c e s o f e l e c t r i c a l d i s t r i b u t i o n e q u i p me n t . I t h a s n o mo v i n g p a r t s , r e q u i r e s mi n i ma l maintenance, and is capable of withstanding overloads, surges, faults, and physical abuse that may damage or destroy other items in the circuit. Transformers are exclusively used in electric power systems to transfer power by electromagnetic induction between circuits at the same frequency, usually with changed values of voltage and current. There are numerous types of transformers used in various applications including audio, radio, instrument, and power. There are various types of transformers placed in PPCL. •Generating transformers:16.5KV to 400KV to feed into the line. •UAT: Unit Auxiliary Transformers: 16.5KV to 6.6KV for plant aux equipment(only HT equipment) •Smaller Transformers: 6.6KV to 440V for LT equipment in the plant All the positions can be noted in the single line diagram of the plan All power transformers have three basic parts, a primary winding, secondary winding, a n d a c o r e . Ev e n t h o u g h l i t t l e mo r e t h a n a n a i r s p a c e i s n e c e s s a r y t o i n s u l a t e a n “i d e a l ” transformer, when higher voltages and larger amounts of power are involved, the insulating material becomes an integral part of the transformer’s operation. Core The core, which provides the magnetic path to channel the flux, consists of thin strips of high grade steel, called laminations, which are electrically separated by a thin coating of i n s u l a t i n g ma t e r i a l . Th e s t r i p s c a n b e s t a c k e d o r wo u n d , w i t h t h e wi n d i n gs e i t h e r b u i l t integrally around the core or built separately and assembled around the core sections. J u s t l i k e o t h e r c o mp o n e n t s i n . I n l a r g e r u n i t s , c o o li n g d u c t s a r e u s e d i n s i d e t h e c o r e f o r a d d i t i o n a l c o n v e c t i v e s u r f a c e a r e a , a n d s e c t i o ns o f l a mi n a t i o n s ma y b e s p l i t t o r e d u c e localized losses.Th e g r o u n d in g p o i n t s h o u l d b e r e mo v a b l e f o r t e s t i n g p u r p o s e s , s u c h a s c h e c ki n g f o r u n i n t e n t i o n a l c o r e g r o u n d s . M u l t i p l e c o r e g r o u n d s , s u c h a s a c a s e wh e r e b y t h e c o r e i s i n a d v e r t e n t l y m a k i n gcontactwithotherwisegroundedinternalmetallicmecha
n i c a l structures, can provide a path for circulating currents induced by the main flux as well as a leakage flux, thus creating concentrations of losses that can result in localized heating. MAINTENANCE AND TESTING The oil in the transformer should be kept as pure as possible. Dirt and moisture will s t a r t c h e mi c a l r e a c t i o n s i n t h e o i l t h a t l o we r b o t h i t s e l e c t r i c a l s t r e n g th a n d i t s c o o l i n g capability. Contamination should be the primary concern any time the transformer must be opened. Most transformer oil is contaminated to some degree before it leaves the refinery. It i s i mp o r t a n t t o d e t e r mi n e h o w c o n t a mi n a t e d t h e o i l i s a n d h o w f a s t i t i s d e g e n e r a t i n g . Determining the degree of contamination is accomplished by sampling and analyzing the oil on a regular basis. T h e t e r m s wi t c h g e a r , u s e d i n a s s oc i a t i o n wi t h t h e e l e c t r i c p o w e r s ys t e m, o r g r i d , r e f e r s t o t h e c o mb i n a t i o n o f e l e c t r i c a l d i s c o n n e c t s , f u s e s a n d / o r c i r c u i t br e a k e r s u s e d t o isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. Oil-filled equipment allowed arc energy to be contained and safely controlled. By the early20thcentury,aswitchgearline-upwouldbeametal -enclosedstructurewithelectricallyo p e r a t e d s wi t c h i n g e l e me n t s , u s i n g o i l c i r c u i t b r e a k e r s . To d a y, o i l - f i l l e d equipment has largely been replaced by air-blast, vacuum, or SF6 equipment, allowing largec u r r e n t s a n d p o w e r l e v e l s t o b e s a f e l y c o n t r o l le d b y a u t o ma t i
c e q u i p me n t i n c o r p o r a t i n g digital controls, protection, metering and communications. A View of Switchgear at a Power Plant
Types of cb •O i l c i r c u i t b r e a k e r s r e l y u p o n v a p o r i z a t i o n o f s o me o f t h e o i l t o b l a s t a j e t o f o i l through the arc. •Gas (SF6) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the SF6 to quench the stretched arc. •Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount(<2-3 mm). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 35,000 volts. •Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.
•Circuit breakers are usually able to terminate all current flow very quickly: typically between 30 m s and 150 m s depending upon the age and construction of the device.
Classification Several different classifications of switchgear can be made: By the current rating: B y i n t e r r u p t i n g r a t i n g ( ma x i mu m s h o r t c i r c u i t c u r r e n t t h a t t h e d e v i c e c a n s a f e l y interrupt) Circuit breakers can open and close on fault currents Load-break/Loadmake switches can switch normal system load currents Isolators may only be operated while the circuit is dead, or the load current is very small. By voltage class: Low Tension (less than 440 volts AC) High Tension (more than 6.6 kV AC) By insulating medium: Air Gas (SF6 or mixtures)
Oil Vacuum By construction type: Indoor Outdoor Industrial Utility Marine Draw-out elements (removable without many tools) Fixed elements (bolted fasteners) Live-front Dead-front Metal-enclosed Metal-clad Metal enclose & Metal clad Arc-resistan High Tension Switchgear at a Power Plant By IEC degree of internal separation: No Separation Bus bars separated from functional units Terminals for external conductors separated from bus bars Terminals for external conductors separated from functional units but not from eachother Functional units separated from each other Terminals for external conductors separated from each other Terminals for external conductors separate from their associated functional unit By operating method: Manually-operated Motoroperated Solenoid/stored energy operated By type of current: Alternating current Direct current By application: Distribution. Transmission system One of the basic functions of switchgear is protection, which is interruption of shortcircuitandoverloadfaultcurrentswhilemaintainingservi c e t o u n a f f e c t e d c i r c u i t s . Switchgear also provides isolation of circuits
from power supplies. Switchgear also is used toenhance system availability by allowing more than one source to feed a load.
HIGH TENSION SWITCHGEAR High voltage switchgear is any switchgear and switchgear assembly of rated voltage h i g h e r t h a n 1 0 0 0 v o l ts . Hi g h v o l t a g e s w i t c h g e a r i s a n y s wi t c h g e a r u s e d t o c o n n e c t o r t o disconnect a part of a high voltage power system. These switchgears are essential elements for the protection and for a safety operating mode without interruption of a high voltage power system. This type of equipment is really important because it is directly linked to the quality of the electricity supply. The high voltage is a voltage above 1000 V for alternating current and above 1500 V for direct current. Disconnectors/Isolators and Earthing Switches
They are above all safety devices used to open or to close a circuit when there is no c u r r e n t t h r o u g h t h e m . Th e y a r e u s e d t o i s o l a t e a p a r t o f a c i r c u i t , a ma c hi n e , a p a r t o f a n overhead-line or an underground line for the operating staff to access it without any danger. The opening of the line isolator or busbar section isolator is necessary for the safety but it is not enough. Grounding must be done at the upstream sector and the downstream sector on thed e v i c e w h i c h t h e y w a n t t o i n t e r v e n e t h a n k s t o t h e e a r t h i n g s w i t c h e s . I n p r i n c i p l e , disconnecting switches do not have to interrupt currents, but some of them can interrupt currents (up to 1600 A under 10 to 300V) and some earthing switches must interrupt inducedc u r r e n t s wh i c h a r e g e n e r a t e d i n a n o n - c u r r e n t c a r r yi n g l i n e b y i n d u c t i v e a n d c a p a c i t i v e coupling with nearby lines (up to 160 A under 20 kV).A Vacuum Circuit Breaker (High Tension Switchgear)
Contactor Their functions are similar to the high-current switching mechanism, but they can be used at higher rates. They have a high electrical endurance and a high mechanical endurance. Contactors are used to frequently operate device like electric furnaces, high voltage motors. They cannot be used as a disconnecting switch. They are used only in the band 30 kV to 100kV. Fuses The fuses can interrupt automatically a circuit with an over current flowing in it for a fixed time. The current interrupting is got by the fusion of an electrical conductor which is graded. They are mainly used to protect against the short-circuits. They limit the peak value
of the fault current. In three-phase electric power, they only eliminate the phases where the fault current is flowing, which is a risk for the devices and the people. Against this trouble, the fuses can be associated with high-current switches or contactors. They are used only in the band 30 kV to 100 kV. A high voltage circuit breaker is capable of making, carrying and breaking currents under the rated voltage (the maximal voltage of the power system which it is protecting):Under normal circuit conditions, for example to connect or disconnect a line in a power system. Underspecified abnormal circuit conditions especially to eliminate a short circuit. From its characteristics, a circuit breaker is the protection device essential for a high voltage power system, because it is the only one able to interrupt a short circuit current and so to avoid the others devices to be damaged by this short circuit. The international
standard IEC62271-100 defines the demands linked to the characteristics of a
high voltage circuit breaker. The circuit breaker can be equipped with electronic devices in order to know at any momenttheir states (wear, gas pressure etc) and possibly to detec t faults from characteristicsderivatives and it can permit to plan maintenance operations and to avoid failures. To operateo l o n g l i n t h e c i r c u i t b r e a k e r s a r e e q u i p n es, pedwith a c l o s i r e s i s t o r l i m i t t h e overvoltage. They can be ng to equipp ed with devices to synchronize the closing and/or theopening to limit the overvoltage and the inrush currents from the lines, the unloaded transformers, the shunt reactance and the capacitor banks. Switchyard: High-voltage circuit breakers Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV or higher, according to a recent definition by the International Electro technical Commission(IEC). High-voltage breakers are nearly always solenoidoperated,w i t h c u r r e n t s e n s i n g p r o t e c t i v e relayso p eratedthroughcurrenttransformers.
In substations the protection scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault .High-voltage breakers are broadly classified by the medium used to extinguish the arc. Bus Coupler
Bus couplers are used in distribution system to provide better isolation and protection from electrical arcs. They are used on Transformers to connect it to the distribution system. It has it advantage over direct coupling w.r.t arc suppression as they provide greater impedance to the path of the load. So, they provide better
arc protection especially, during the transient or switching period. Even if only one non-terminated coupler acts as the bus because all devices (bus controller, remote terminals, etc. ) are connected to the coupler’s stubs, the external bus connections of the coupler must be terminated. A dualterminated coupler (with or without non-functional bus connectors) can be employed where the coupler acts as the bus without other couplers. Isolator/ Diconnector: Isolators are devices used to isolate a certain portion of the circuit in case of a fault. The isolator can clip off a certain portion of the circuit if it Busbar: In electrical power distribution, a busbar is a thick strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus. Busbars are used to carry very large currents, or to distribute current to multiple devices within switchgear or equipment. For example, a household circuit breaker panel board will have bus bars at the back, arranged for the connection of multiple branch circuit breakers. An aluminum smelter will have very large bus bars used to carry tens of thousands of amperes to the electrochemical cells that produce aluminum from molten salts. The size of the busbar is important in determining the maximum amount of current that can be safely carried. Busbars can have a cross-sectional area of as little as 10 mm² but electrical substations may use metal tubes of 50 mm in diameter (1,963 mm²) or more as busbars. A busbar may either be supported on insulators, or else insulation may completely surround it. Busbars are protected from accidental contact either by a metal enclosure or by elevation out of normal reach. Neutral busbars may also be
insulated. Earth busbars are typically bolted directly onto any metal chassis of their enclosure. Busbars may be enclosed in a metal housing, in the form of bus duct or busway, segregatedphase bus, or isolated- phase bus. Busbars may be connected to each other and to electrical apparatus by bolted or clamp
connections. Often joints between high-current bus sections have matching surfaces that are silver-plated to reduce the contact resistance. At extra-high voltages (more than 300 kV) inoutdoor buses,coronaa r o u n d t h e c o n n e c t i o n s b e c o m e s a s o u r c e o f r a d i o - f r e q u e n c y interference and power loss, so connection fittings designed for these voltages are used. Lightning arrester A lightning arrester is a device used on electrical power systems toprotectthe insulationo n t h e s y s t e m f r o m t h e d a m a g i n g e f f e c t o f lightning.Met al oxide varistors (MOVs) have been used for power system protection since the mid 1970s. The typical lightning arrester also known as surge arrester has a high voltage terminal and a ground
terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth. Disconnectors and earthing switches Disconnectors and earthing switches are safety devices used to open or to close a circuit when there is no current through them. They are used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted. The opening of the line isolator or busbar section isolator is necessary for safety, but not sufficient. Grounding must be conducted at both the upstream and downstream sections of the device under maintenance. This is accomplished by earthing switches. In principle, disconnecting switches do not have to interrupt currents, as they aredesigned
for use on de - energized circuits. In practice, some are capable of interruptingc urrents (as much as 1,600ampereunder 300 V but only if current is drawn via a same circuit half breaker bypass system), and some earthing switches
must interrupt induced currents which are generated in a noncurrent-carrying line by inductive and capacitive coupling with nearby lines (up to 160 A under 20 kV). Fuses A fuse can automatically interrupt a circuit with an overcurrent flowing in it for a fixed time. This is accomplished by the fusion of an electrical conductor which is graded. Fuses are mainly used to protect against short circuits. They limit the peak value of the fault current .In three-phase electric power , they only eliminate the phases where the fault current is flowing, which can pose a risk for both the malfunctioning devices and the people. Toalleviate this problem, fuses can be used in conjunction with h igh - current switches or contactors.Like contactors, high-voltage fuses are used only in the band 30 kV to 100 kV Balance of plant: Demineralised Water: Purified water is water from any source that is physically processed to remove impurities. Distilled water and deionized water have been the most common forms of purified water, but water can also be purified by other processes including reverse osmosis,carbonfiltration,microporous filtration ,ultrafiltration, u l t r a v i o l e t o x i d a t i o n , or electrodialysis.In recent decades, a combination of th e above processes have come intouse to produce water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt). Purified water has many uses, largely in science and engineering laboratories and industries, and is produced in a range o
terminal. When a lightning surge or switching surge travels down the power system to the arrester, the current from the surge is diverted around the protected insulation in most cases to earth. Disconnectors and earthing switches Disconnectors and earthing switches are safety devices used to open or to close a circuit when there is no current through them. They are used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted. The opening of the line isolator or busbar section isolator is necessary for safety, but not sufficient .Grounding must be conducted at both the upstream and downstream sections of the device under maintenance. This is accomplished by earthing switches .In principle, disconnecting switches do not have to interrupt currents, as they aredesigned for use on de - energized circuits. In practice, some are capable of interruptingc urrents (as much as 1,600ampereunder 300 V but only if current is drawn via a same circuit half breaker bypass system), and some earthing switches must interrupt induced currents which are generated in a non-current-carrying line by inductive and capacitive coupling with nearby lines (up to 160 A under 20 kV). And engineering laboratories and industries, and is produced in a range of purities. Deionization RODM: Reverse osmosis and De-minerelisation plant in PPCl is used to carry out the conversion of soft water to DM water. DM water is expensive and is only used in critical machinery
It should be noted that deionization does not remove the hydroxide or hydronium ions from water; as water self-ionizes to equilibrium, this would lead to the removal of the water itself. Cyclo-Separators: To separate sludge from
the water through centrifugal action Lime Softening Plant: Lime dosing to treat hard water and converting it to soft water. Gravity Filters: Gravity filters separating out dust and dirt particles. Deionized water which is also known as demineralized water (DI water or de-ionized water; can also be spelled deionised water, seespelling differences) iswater that has had its mineral ions removed, such as cations from sodium ,calcium, iron, copper and anions such as chloride and bromide. Deionization is a physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup. However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except by incidental trapping in the resin. Specially made strong base anion resinsc a n r e m o v e Gramnegative b a c t e r i a . D e i o n i z a t i o n c a n b e d o n e c o n t i n u o u s l y a n d inexpensively usingelectrodeionization.DM Water is used in a closed-loop steam generation cycle to drive the turbines that produce electricity. After passing through the turbine, the steam will eventually be condensed into water to be fed back to the boiler to repeat the cycle. Demineralization will protect the boiler from the formation of salt deposits on its inner surfaces Bibliography: •www.ipgcl-ppcl.gov.in •www.google.com •www.wikipedia.com •www.scribd.com
