Test: Distribution System - Electrical Engineering (EE) MCQ

Let the power losses remain constant over the systems, then
2P²R/V² = 2P²R1/2*V²
or, R = R1/4;
As R = lρ/a;
a₁ = a/4;
So, V₁/V₁ = 1/4.

Let the power losses remain constant over the systems, then
2P²R/V² = 2P²R1/V²
or, R1 = R
As R = lρ/a;
a₁ = a
So, V₁/V₁ = a₁ * 2l/a₁ = 1/2.

Availability of two voltages in a 3-wire system is preferred over the 2-wire system for d.c. distribution. The principal advantage of this system is that it makes available two voltages at the consumer terminals.
V volts between any outer and neutral and 2V volts between the outers.

For the sub transmission level, there is no tapping at various level does not take place. For this a feeder is used.

A parallel distribution system has two end feeding and an alternative of parallel line, so in case there is a fault, the isolator can isolate the faulty part and let the healthy system operate.

For the discrete tapping of the power the consumer level it is the distributor which is employed at the sub stations and consumer levels.

The midpoint voltage will be V/√2.

I = P/V = 5000000/440000 = 11.36 A
Power loss = 2I2 * R = 2 * 11.362 * 20 = 5165 W.

A radial system is used for the medium requirement of loading and a medium dense population as it becomes easier to install and operate.

Radial Distribution System: 

This system is used only when the substation is located at the center of the consumers. In this system, different feeders radiate from a substation and feed the distributors at one end. Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction. It is the simplest system and has the lowest initial cost but it is not highly reliable.

Major drawbacks of a radial distribution system are,

• A fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors.
• Voltage is affected much at far away load from the substation.

Ring main system: 

In this system, each distribution transformer is fed with two feeders but in different paths. The feeders in this system form a loop which starts from the substation bus-bars run through the load area feeding distribution transformers and returns to the substation bus-bars.

Ring main distribution system is the most preferred due to its following advantages:

• There are fewer voltage fluctuations at the consumer's terminal.
• The system is very reliable as each distribution transformer is fed with two feeders. That means, in the event of a fault in any section of the feeder, the continuity of the supply is ensured from the alternative path.
• Voltage is affected less at far away load from the substation.

Interconnected distribution system: 

When a ring main feeder is energized by two or more substations, it is called as an interconnected distribution system. This system ensures reliability in an event of transmission failure. Also, any area fed from one generating station during peak load hours can be fed from the other generating station or substation for meeting power requirements from the increased load.