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

4.2 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

a) Less copper is required as each part of the ring carries less current than that in radial

system.

b) Less voltage fluctuations.

c) 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

a) High cost of maintenance

b) 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