Question

An energy meter rated as 5A, 230 V makes 600 revolutions per kWh. If in a test at full load upf, it makes 6 revolutions in 30 seconds. Which of these given statement(s) is/are not correct?

• A. Meter runs faster than its nominal speed.
• B. The error associated with particular meter is 4.16%
• C. Meter akes 720 revolutions in one hour during test.
• D. Meter can be corrected by placing a braking magnet closer to the center of the disc to slow down its speed.

Answer 1

Answer: (B), (D)

Meter can be corrected by placing a braking magnet closer to the center of the disc to slow down its speed.

Total no. of revolutions made by meter = meter constant (revolution/kWh) $\times$ Power $\times$ time (kWh)

Total no. of revlutions made by meter at rated load during tested in one hour $\left(N_2\right)$

$=\frac{6}{30}\times 3600=720revolution/hr$

$\because$ meter constant is 600 rev/ kWh,

So number of revolution it should make is $\left(N_1\right)$

$=600\times \frac{5\times 230}{1000}=690revolution/hr$

$N_2>N_1$ so meter is running faster

$\%error=\frac{N_2-N_1}{N_1}\times 100=\frac{720-690}{690}\times 100=4.3478$

$\Rightarrow$ By placing a breaking magnet closer to center of disc, meter can be made faster.