D.C. DISTRIBUTION

 D.C. DISTRIBUTION

It is a common knowledge that electric power is almost exclusively generated, transmitted and distributed as ac. 

However, for certain applications, d.c. supply is absolutely necessary. 

For instance, d.c. supply is required for the operation of variable speed machinery ( dc. moto for electro-chemical work and for congested areas. 

Where storage battery reserves are necessary. 

For this purpose, a.c. power is converted into d.c. power at the substation by using converting machinery e.g., mercury are rectifiers, rotary converters and motor-generator sets. 

The d.c. supply from the substation May be 

✓ 2-wire 

✓ 3-wire 

2-wire d.c. system

As the name implies, this system of distribution consists of two wires One is the outgoing or positive wire and the other is the retum or negative wire. 

The loads such as lamps, motors etc. are connected in parallel between the two wires. 

This system is never used for transmission purposes due to low efficiency but may be employed for distribution of d.c. power. 

3-wire d.c. system

It consists of two outers and a middle or neutral wire which is earthed at the substation. 

The voltage between the outers is twice the voltage between either outer and neutral wire. 

The principal advantage of this system is that it makes available two voltages at the consumer terminals viz. 

V between any outer and the neutral and 2V between the outers. 

Loads requiring high voltage (eg. motors) are connected across the outers, whereas lamps and heating circuits requiring less voltage are connected between either outer and the neutral.