Sumpner’s test is conducted on transformers to determine

• Temperature

• Stray losses

• All-day efficiency

• None of these

In a transformer, the resistance between the primary and secondary must be

• Zero

• 1 kΩ

• 100 kΩ

• Infinite

A 100 kVA single-phase transformer has a full-load primary current of 400 A and total resistance referred to primary is 0.006 Ω. If the iron loss amounts to 500 W, find the efficiency on full-load unity power factor.

• 98.19%

• 98.22%

• 98.58%

• 98.56%

An inductive load takes 4 MW. A 2 MVAR shunt capacitor is connected across the load to improve the load-end power factor of 0.97 lagging. If the capacitor is disconnected (or trips), the load-end power factor will be:

• 1

• 0.85 lead

• 0.80 lag

• 0.90 lag

The d.c. generator used for voltage boost is

• Shunt

• Series

• Separately excited

• Compound

What is the main drawback in NR method?

• Slow to converge

• A large memory allocation is required to store the Jacobian matrix

• The number of iterations is more

• All of these

If a permanent brake magnet is moved away from the spindle of the moving disc, energy meter

• Will run fast

• Will run slow

• No effect

• Will come to a stop

A 30-Cd standard light source is compared with a lamp of unknown intensity using a grease-spot photometer. The two light sources are placed 1 m apart, and the grease spot is moved toward the standard light. When the grease spot is 25 cm from the standard light source, the illumination is equal on both sides. Where should the grease spot be placed for the illumination by the unknown light source to be exactly twice the illumination of the standard source?

• 32 cm from standard

• 68 cm from standard

• 18 cm from standard

• 82 cm from standard

Buchholz relay in a transformer is placed in between

• The LV winding and the bushing

• The tank and the conservator

• The HV winding and the bushing

• The conservator and the breather

A 1000 µF capacitor initially uncharged is charged by a steady current at 50 µA. How long will it take the p.d. across the capacitor to reach 2.5 V?

• 20 s

• 50 s

• 100 s

• 400 s