Distribution System

The system used to distribute the electrical energy to various consumers safely is known as distribution system. Generally 3-phase 4-wire a.c. system is adopted for distribution of electrical energy in industries where as single-phase two-wire system is used in home, offices and commercial purpose. There are three different systems of power distribution detailed below.

i. Single Phase Two wire System

This system of distribution is widely used in homes, offices and commercial installation having total connected load less than 5 kilowatts. Single-phase two-wire system consists of one phase and one neutral wire. The potential difference between the phase and neutral wire is 230 volts. To understand this system of distribution of electrical energy, kindly refer to circuit

Twin core PVC cable is used to energise the single-phase energy meter. The cross-sectional area of the cables depends upon the load requirement of the consumer and it varies from 4 to 10 mm 2 . This cable is supported by galvanised steel wire.The output of energy meter is controlled by I.C.D.P. (Iron Clad Double Pole) main switch. The phase wire is connected with fuse link and the neutral with neutral link,made of thick copper strip. The output of this I.C.D.P. main switch is connected to main distribution board, which may be fixed on the same iron sheet or wooden board. Then the out put of I.C.T.P. switch is sub-divided into different sub circuits and connected to different small capacity double pole switches depending upon the number of rooms and power points. It should be ensured that all the phase wires are controlled through the fuse links.

ii. Three Phase Three wire System

This distribution system is used to transfer the large quantum of electrical energy from the generating station to different sub-stations by using three-phase wire only.The generated voltage of an alternator may be 6.6, 11 and 15.7 kilovolts. This generated voltage is generally step up to 220 kv depending on distance between generating station and ultimate consumer. If the distance is too more, this generated voltage can be step-up to 440 kv. To understand three phase three wires systemkindly refers to the circuit

The working of isolators and circuit

breakers has already been described in the working of indoor and outdoor sub-station. The generated voltage is stepped-up from 11 kv to 220 kv at the generating station and then this voltage is transferred to distribution sub-station. Here, it is step down to 11 kv with the help of 220/11 kv sub-station.

iii. Three Phase Four wire System:

This system of distribution uses three Phase and one neutral wire. The out put of three phase three wire distribution system as explained above, is the input of this system. This system is most widely used for industrial and medium consumer having total connected load of less than 5 KW. However this system is explained

In this system of distribution we have only one source of electrical energy. 11/0.440 KV step-down transformer is used to step down the voltage. The voltage between any two-phase wires is 440 volts approximately whereas between any phase and neutral wire it is 230 volts. The primary winding of the transformer is delta connected whereas the secondary is star connected, to form the three phases and one neutral wire and hence the system’s name. Three phase and neutral wire is connected to three-phase energy meter to record the total energy consumed. The output of energy meter is connected to distribution panel through air circuit breaker, for effective distribution. Small domestic consumer having total connected load less than 5 KW can use one phase and neutral wire.

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