Electrical Distribution System

Electrical distribution system : The part of electrical system that distributes electrical power for local usage is known as electrical power distribution system.

Electrical power Distribution Systems

The part of electrical system that distributes electrical power for local usage is known as distribution system.

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Components of Electrical distribution system

The distribution system is constituted by following three components;

Feeders
Distributors
Service Mains

electrical distribution system — Electrical distribution system

Feeders

Feeders: These are lines or conductors that connect major station to the area where the power is to be distributed. The current remains constant in feeders and the most important parameter is their current carrying capacity.

Distributors

Distributors: These are lines or conductors to which various consumers are connected. These distribute power among these consumers.

Service mains

Service mains: It is line or a cable that connects the distributor to the consumer’s terminal.

Classification of Distribution Systems

The distribution systems may be classified based on the following criteria:

Type of construction
Nature of current
Scheme of connection

Type of construction

Type of construction: Overhead and underground distribution systems. Generally overhead
systems are cheaper and employed in preference.

However, underground cables are used where it is impractical or prohibition to use overhead lines.

Nature of current

Nature of current: AC and DC distribution system. The AC distribution system is universally
used because it is simpler and more economical.

Scheme of connection

Scheme of connection: Radial, ring main and inter-connected systems.

AC and DC Distribution Systems

The AC distribution system is for distribution for AC power, that is, AC voltage and current. It is further divided into the following two systems.

Primary distribution system
Secondary distribution system

Primary distribution system

Primary distribution system: For this system the general voltage level is 11kV, 6.6 kV and
3.3 kV, that is, higher than the voltage level used by the general consumers.

For economic considerations, this system is provided with three phase, three wire system.

Secondary distribution system

Secondary distribution system: In this case the distribution level is 230 V single phase or
415 V three phase four wire systems.

This voltage level is directly usable by the general consumers.

The DC distribution system is meant for distribution of DC voltages through the following two systems.

Two-wire DC distribution system
Three-wire DC distribution system

Two-wire DC distribution system

Two-wire DC distribution system: In this case the power is transmitted by two wires one positive (+) and then other negative (−).

The loads are connected between the two wires as shown in the Fig below.

Three-wire DC distribution system

Three-wire DC distribution system: This system consists of two outer wires and one middle
wire which is earthed in the substation.

The voltage between the outer wires is twice the voltage between one line and earth. The configuration is shown in Fig below.

Distribution system Connection Schemes

The different connection schemes in distribution system are discussed as follows;

Radial system
Ring system
Interconnected system

Radial system

Radial system: In this system separate feeders radiate from a single substation and feed the distributor one end only.

This system is used when the power is generated at low voltage and the substation
is located at the centre of the load.

Radial system Drawbacks

The drawbacks of the Radial system are:

Consumers are dependent only on single feeder and distributor, so in event of a fault, the power supply will be cut-off completely.
The distributor end nearest to the feeding point is heavily loaded.
The consumers at the distant end of the distributor (away from the feeder) will be impacted by voltage fluctuations as the load on the distributor changes.