Page 312 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Electrical supply system - transmission and distribution

Objectives: At the end of this lesson you shall be able to:
• explain the electrical supply system and layout of AC power supply scheme
• explain single line diagram of substation
• explain the types of insulator and their used
• explain transmission and distribution by online - poles and towers
• explain circuit breaker relays lighting arrestor used in HT line.

Electrical supply system

The electrical energy generated from the power plants has to be supplied to the consumers. This is large network,
which can be broadly divided into two stages, (ie.) Transmission and distribution.
The conveyance of electric power from a power station to the consumers / premises is called is Electrical supply
system.
The Electrical power supply system consists of 3 main components viz (i) The power station / plant (ii) The
transmission lines and (iii) The distribution systems. The power is produced at power plant which is away from
the consumers, It has to be transmitted over long distances to load centres by transmission and to consumers
through distribution network.

This supply system can be classified into
- DC or AC system
- Over head lines (or) underground system
Now a days, 3 phase, 3 -wire AC system is universally adopted as an economical proposition. In some places 3
phase - 4 wire AC system is adopted.
The underground system is more expensive than the over-head system, therefore in our country O.H system is
almost adopted.
Types of power transmission system
Universally, 3 - phase - 3 wire AC system is adopted in most of the places. However other systems can also be
used for transmission under special circumstances.

1 AC single phase system
i Single-phase two wire
ii Single - phase two wire with mid point earthed
iii Single phase three wire

2 AC three phase system
i Three - phase - three wire
ii Three - phase - four wire
The line network between generating station (Power station) and consumer of electric power can be divided into
two parts.
- Transmission system
- Distribution system

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CITS : Power - Electrician & Wireman - Lesson 106-116