1.0 INTRODUCTION
An electric power system is a network of electrical components that generate electrical power from any source of power (such as coal, water, gas, wind, nuclear energy and oil) which then transmitted and distribute the power to nearby homes and industries. There are three main parts in electrical power system network which is generation system, transmission system and distribution system.
Figure 1.1 : Electrical Power System
Distribution systems are the link from the distribution substation to the customer which consists of transformer, feeder circuit, switches, protective equipment, primary circuits, secondary circuits and service line. Distribution feeder circuits usually consist of overhead and underground circuits in a mix of branching laterals from the station to the various customers. The circuit was designed by considering the required peak load, voltage, distance to customers, and other local conditions such as terrain, visual regulations, or customer requirements. In distribution, there are two type of system that been used that is overhead lines and underground cables. High-density urban areas are often connected in a complex distribution underground network providing a highly redundant and reliable means connecting to customers.
Figure 1.2 : Component of the Distribution System
One important part in distribution system is the distribution layout. Distribution Layout is the connection network from substation to the customers or usually been called as the distribution systems scheme of connections. Since all distribution of electrical energy is done by constant voltage system, there are several classification of connection scheme that commonly been used which are radial system, ring main system and inter-connected system. The connection scheme for DC and AC distribution system also differ whereas the DC distribution system doesn't have transformer.
2.0 PROBLEM STATEMENT
There are several problem that we've been faced in completing this project which is we are lack of knowledge in distribution system concept whereas we unable to find any information about distribution layout in internet. But then, we discover that the distribution layout is the distribution system scheme connection. We also unaware the distribution system been used in Malaysia.
3.0 OBJECTIVE
1- To identify the type of distribution layout.
2- Able to explain the distribution layout.
3- To identify main component in distribution layout.
4- To identify which distribution network system been used in Malaysia.
4.0 CHARACTERISTICS
4.1 MAIN COMPONENT
Distribution system consists of all the facilities and equipment connecting a transmission system to the customer's equipment. A typical distribution system can consist of:
4.1.1 SUBSTATIONS
A substation is a high-voltage electric system facility. It is used to switch generators, equipment, and circuits or lines in and out of a system. It also is used to change AC voltages from one level to another, and/or change alternating current to direct current or direct current to alternating current. Some substations are small with little more than a transformer and associated switches. Others are very large with several transformers and dozens of switches and other equipment. There are three aspects to substations:
Figure 4.1 : Typical substation
Substation Types: Although, there are generally four types of substations there are substations that are a combination of two or more types.
Step-up Transmission Substation
Step-down Transmission Substation
Distribution Substation
Underground Distribution Substation
Substation Functions
Substation Equipment
4.1.2. DISTRIBUTION FEEDER CIRCUIT
Distribution feeder circuits are the connections between the output terminals of a distribution substation and the input terminals of primary circuits. The distribution feeder circuit conductors leave the substation from a circuit breaker or circuit reclosed via underground cables, called substation exit cables. The underground cables connect to a nearby overhead primary circuit outside the substation. This eliminates multiple circuits on the poles adjacent to the substations thereby improving the overall appearance of the substation.
Several distribution feeder circuits can leave a substation extending in different directions to serve customers. The underground cables are connected to the primary circuit via a nearby riser pole.
The distribution feeder bay routes power from the substation to the distribution primary feeder circuits. In the photo of the distribution main feeder the primary circuit is fed underground to a nearby distribution system overhead line. The yellow cables are the primary feeder lines going underground.
Figure 4.2 : Phase Distribution Feeder Bay
Figure 4.3 : Distribution Main Feeder
Figure 4.4 : Distribution Feeder Recloser
4.1.3. SWITCHES
Distribution systems have switches installed at strategic locations to redirect or cut-off power flows for load balancing or sectionalizing. Also, this permits repairing of damaged lines or equipment or upgrading work on the system. The many types of switches include:
Circuit-breaker switches
Single-pole disconnect switches
Three-pole group-operated switches
Pad-mounted switchgear
Figure 4.5 : Air circuit-breaker switches
Figure 4.6 : Air-break isolator switch
Figure 4.7 : Circuit switchers
Figure 4.8 : Single-pole disconnect switch combined with a fuse is called a fused cut-out
Figure 4.10 Circuit breakers
Figure 4.11 Pad mounted switchgear
Figure 4.12 : Group-operated three-pole air break switch
4.1.4. PROTECTIVE EQUIPMENT
Protective equipment in a distribution system consists of protective relays, cut-out switches; disconnect switches, lightning arresters, and fuses. These work individually or may work in concert to open circuits whenever a short circuit, lightning strikes or other disruptive event occurs.
When circuit breakers open, the entire distribution circuit is de-energized. Since this can disrupt power to many customers, the distribution system is often designed with many layers of redundancy. Through redundancy, power can be shut off in portions of the system only, but not the entire system, or can be redirected to continue to serve customers. Only in extreme events, or failure of redundant systems, does an entire system become de-energized, shutting off power to large numbers of customers.
The redundancy consists of the many fuses and fused cu-touts throughout the system that can disable parts of the system but not the entire system. Lightning arresters also act locally to drain off electrical energy from a lightning strike so that the larger circuit breakers are not actuated.
Figure 4.13 : Substation bus lightning arresters
Figure 4.14 : Fused cut-out
Figure 4.15 Substation disconnect switch
Figure 4.16 Pole mounted type - lightning arrester
Figure 4.17 : Air-break isolator switch
Figure 4.18 : Non load-break fuse
Figure 4.19 : Load-break fuse
4.1.5. PRIMARY CIRCUIT
Primary circuits are the distribution circuits that carry power from substations to local load areas. They are also called express feeders or distribution main feeders. The distribution feeder bay routes power from the substation to the distribution primary feeder circuits.
In the photo of the distribution main feeder the primary circuit is fed underground to a nearby distribution system overhead line. The yellow cables are the primary feeder lines going underground.
Figure 4.20 : Phase distribution feeder bay
Figure 4.21 : Distribution main feeder
Figure 4.22 : Overhead primary feeder
Figure 4.23 : Distribution primary feeder under build
4.1.6. DISTRIBUTION TRANSFORMER
Distribution transformers reduce the voltage of the primary circuit to the voltage required by customers. This voltage varies and is usually:
120/240 volts single phase for residential customers,
480Y/277 or 208Y/120 for commercial or light industry customers.
Three-phase pad mounted transformers are used with an underground primary circuit and three single-phase pole type transformers for overhead service. Network service can be provided for areas with large concentrations of businesses. These are usually transformers installed in an underground vault. Power is then sent via underground cables to the separate customers.
Figure 4.24 Air Distribution transformer
Figure 4.25 : Industrial facility distribution transformer
- commercial facility
Figure 4.26 : Residential distribution transformer
Figure 4.27 : Pad-mounted residential distribution transformer
4.1.7. SECONDARIES
Secondary's are the conductors originating at the low-voltage secondary winding of a distribution transformer. Secondary's for residential service are three-wire single-phase circuits. They extend along the rear lot lines, alleys, or streets past customer's premises. The secondary's can be overhead lines or underground lines.
Overhead secondary lines are usually strung below the primary lines and typically in a vertical plane. When secondary's are strung in a vertical plane, they are directly attached to the support pole one above the other. This is in contrast to the primary lines which are often strung on a cross bar or other attachment in a horizontal or "V" shaped plane.
Figure 4.28 Cabled secondary's
Figure4.28 : Secondaries in a vertical plane
Figure 4.29 : Cabled secondaries, primaries in a "V" plane
4.1.8. SERVICES
The wires extending from the secondaries or distribution transformer to a customer's location are called a service. A service can be above or below ground. Underground services have a riser connection at the distribution pole. Commercial and residential services are much the same and can be either 120 or 220 or both.
Figure 4.30 : Distribution system lines and associated equipment
TYPE OF DISTRIBUTION NETWORK
Distribution system is a circuit of users linked to a generating station and substations that is typically arranged in either a radial or interconnected manner. Local distribution systems transport power within a building. All distribution of electrical energy is done by constant voltage system. In practice, the following distribution circuit are generally used
4.2.1 RING DISTRIBUTION SYSTEM
Figure 1 : Operation of Ring Distribution System
The loop or ring system of distribution starts at the substation and is connected to or encircles an area serving one or more distribution transformers or load centre. The conductor of the system returns to the same substation. The loop system (figure 1) is more expensive to build than the radial type, but it is more reliable. It may be justified in an area where continuity of service is of considerable importance, for example a medical centre. In the loop system, circuit breakers sectionalize the loop on both sides of each distribution transformer connected to the loop. The two primary feeder breakers and the sectionalizing breakers associated with the loop feeder are ordinarily controlled by pilot wire relaying or directional overcurrent relays. Pilot wire relaying is used when there are too many secondary substations to obtain selective timing with directional overcurrent relays.
A fault in the primary loop is cleared by the breakers in the loop nearest the fault, and power is supplied the other way around the loop without interruption to most of the connected loads. Because the load points can be supplied from two or more directions, it is possible to remove any section of the loop from service for maintenance without causing an outage at other load points.
If a fault occurs in a section adjacent to the distribution substation, the entire load may have to be fed from one side of the loop until repairs are made. Sufficient conductor capacity must be provided in the loop to permit operation without excessive voltage drop or overheating of the feeder when either side of the loop is out of service. If a fault occurs in the distribution transformer, it is cleared by the breaker in the primary leads; and the loop remains intact.
Advantages of Ring Distribution System
Less copper is required as each part of the ring carries less current than that in radial system.
Less voltage fluctuations.
It is more reliable. In the event of fault on any one section the continuity of supply to all consumers can be maintained by isolating the faulty section
Disadvantages of Ring Distribution System
High cost of maintenance
It only used in urban place.
4.2.2 INTERCONNECTED SYSTEM
When the feeder ring is energised by two or more than two generating stations or substations, it is called inter-connected system. The Figure shows the single line diagram of interconnected system where the closed feeder ring ABCD is supplied by two substation S1 and S2 point D and C respectively. Distributors are connected to points O, P, Q and R of the feeder ring through distribution transformers.
The interconnected system has the following advantages:
(a) It increases the service reliability.
(b) Any area fed from one generating station during peak load hours can be fed from the other generating station. This reduces reserve power capacity and increases efficiency of the system.
4.2.3 RADIAL DISTRIBUTION SYSTEM
A representative schematic of a radial distribution system is shown in figure 4-1. You should note that the independent feeders branch out to several distribution centers without intermediate connections between feeders.
Figure 4-2 Radial distribution system.
The most frequently used system is the radial distribution system because it is the simplest and least expensive system to build. Operation and expansion are simple. It is not as reliable as most systems unless quality components are used. The fault or loss of a cable, primary supply, or transformer will result in an outage on all loads served by the feeder. Furthermore, electrical service is interrupted when any piece of service equipment must be de-energized to perform routine maintenance and service.
Service on this type of feeder can be improved by installing automatic circuit breakers that will reclose the service at predetermined intervals. If the fault continues after a predetermined number of closures, the breaker will lock out until the fault is cleared and service is restored by hand reset.
4.3 Distribution Network System In Malaysia
National Grid System
Primary electricity transmission network linking the electricity generation, transmission, distribution and consumption in Malaysia. It operated and owned by TNB. It have more than 420 substation in Peninsular Malaysia are linked together by the extensive network of transmission lines operating at 132kV, 275kV and 500kV.
Power generated by TNB and IPP is carried by the National Grid towards customers connected to the various distribution networks. The electrically interconnected to the transmission network of the Electricity Generating Authority of Thailand (EGAT) and also to Singapore Power.
4.3.1 Advantages of national grid system
a) Provide multiple paths between various generation sources and loads
b) Provide for power transfers from one geographic area to another to achieve overall
system operating economics.
c) Interconnect the bulk power facilities of individual power station/utilities so that they
can better withstand major disturbances.
d) Cheap and efficient
Figure 1: National Grid System in Peninsular Malaysia
Figure 2: Grid System in Sabah
Figure 3: Grid System in Sarawak
5.0 CONCLUSION
Distribution layout is very important in design in electrical system. In Malaysia, we use National Grid, Malaysia (Malay: Grid Nasional). It is the high-voltage electric power transmission network in Peninsular Malaysia. It is operated and owned by Tenaga Nasional Berhad (TNB) by its Transmission Division. There are two other electrical grids in Sabah and Sarawak operated by Sabah Electricity Sdn Bhd and Sarawak Electricity Supply Corporation respectively. The system spans the whole of Peninsular Malaysia, connecting electricity generation stations owned by TNB and Independent Power Producers (IPPs) to energy consumers. A small number of consumers, mainly steel mills and shopping malls also take power directly from the National Grid.
The distribution substation receives power from one or more transmission or sub transmission lines at the corresponding transmission or sub transmission voltage level and provides that power to one or more distribution feeders that originate in the substation and comprise the primary network. Most feeders emanate radically from the substation to supply the load. There is the main component in distribution layout, which is substation, distribution feeder circuit, switches, protective equipment, distribution transformers, secondary and services. There are five main functions of the distribution substation, Voltage transformation, Switching and protection, Voltage regulation and Metering. Most distribution substations carry between 5 and 60 MVA. In Malaysia, Distribution lines of 33 kV, 22 kV, 11 kV, 6.6 kV and 400/230 volt in the Malaysia distribution network connect to the National Grid via transmission substations where voltages are stepped down by transformers.
The distribution substation consist of Distribution Intakes (33kV, 22kV). Distribution Substations (22kV, 11kV, 6.6kV). Which is Indoor substation, Outdoor substation, Pole mounted substation, Compact substation and Underground substation. The transformer capacity will be 100kVA, 300kVA, 500kVA, 750kVA and 1000kVA.
Distribution intake.
Indoor Sub-station
Underground substation
Compact substation
Outdoor Sub-station
Pole-Mounted Sub-station
Number of consumer used
The advantages of national grid system is to provide multiple paths between various generation sources and loads, to provide for power transfers from one geographic area to another to achieve overall system operating economics, Interconnect the bulk power facilities of individual power station/utilities so that they can better withstand major disturbances. Other advantages is Stability ( Load sharing ) , Continuity of service ,Maintenance, breakdown ,Economy , Cheap and efficient
