Transmission And Distribution MCQ Questions & Answers | Electrical Engineering

Voltage regulation in transmission and distribution systems refers to the change in voltage from no-load to full-load conditions.
It's usually expressed as a percentage.
A lower percentage voltage regulation means there's less voltage drop from no load to full load.
This is desirable because it ensures that the voltage at the customer's end remains relatively constant, regardless of the load.
Consistent voltage is important for the proper functioning of electrical equipment.
Therefore, a lower voltage regulation is considered better.
Out of the given options, 2% represents the smallest change in voltage and is thus the best.

For a D.C. 2-wire feeder, the transmitted power is given by P = VI, where V is the supply voltage and I is the current.

Since the transmitted power remains constant, if the supply voltage is increased by 100%, the new voltage becomes 2V.

Therefore, the current becomes:

I' = P / (2V) = I / 2

The weight of copper required in a feeder is proportional to the conductor cross-sectional area, and for a given voltage drop, it is proportional to I².

Hence, when the current is reduced to half, the copper required becomes:

(I/2)² = I²/4

This means the new copper requirement is only 25% of the original amount.

Therefore, the saving in copper is:

100% − 25% = 75%

Thus, by doubling the supply voltage while transmitting the same power, the saving in copper is 75%.

Hence, Option C (75 percent) is the correct answer.

This question asks about the voltage drop at the middle of a uniformly loaded DC distributor
when it's fed from both ends compared to when it's fed from one end only.

Let's break it down:

Imagine a wire supplying power to multiple loads evenly spread along its length.

One-End Fed:
If the power comes from just one end, the farthest point (the other end) will have the lowest voltage.
The voltage drop increases as you move away from the feeding point.
The maximum voltage drop occurs at the far end, and the voltage drop at the midpoint will be significant.

Both-Ends Fed:
Now, imagine feeding the same wire from both ends with the same voltage.
Each end supplies power to half of the loads.
The point with the lowest voltage will now be the middle point, because it is the farthest point from each supply end.
However, the voltage drop to the middle point will be much smaller because it's only fed with half of the total current.

Here's the key idea for the mathematically inclined:
For a distributor fed at one end, the voltage drop is proportional to the square of the distance.
For a distributor fed at both ends, with uniform loading, the maximum voltage drop (at the midpoint) is one-fourth of what it would be if it were fed from only one end.

Therefore, the correct answer is Option A: One-fourth