AC CIRCUITS - Practice Mode

1) What is the purpose of phase sequence meter?

To control the speed of 3 phase motor To protect motor against short circuit fault To indicate the incorrect phase sequence of 3 phase To ensure the correct phase sequence of 3 phase system

Correct Answer: To ensure the correct phase sequence of 3 phase system

2) Calculate the apparent power of a star connected 3 phase load, if it is connected across 3 phase 415volt/50Hz supply at 0.8 p.f and the phase current is 10 Amps

12.45 KVA 57.50 KVA 3.320 KVA 7.188 KVA

Correct Answer: 7.188 KVA

3) What is the P.F if one of the wattmeters reading is zero and the other reads total power in 2 wattmeter method of 3 phase power measurement?

0.5 Zero Unity Below 0.5

Correct Answer: 0.5

4) Which electrical term is defined as the total opposition to current in AC parallel circuit?

Resistance Impedance Admittance Susceptance

Correct Answer: Impedance

Explanation:

Impedance (symbol Z) is a measure of the overall opposition of a circuit to current, in other words: how much the circuit impedes the flow of charge. It is like resistance, but it also takes into account the effects of capacitance and inductance. Impedance is measured in ohms.

5) In a 3 phase system, if the active power is 4 kw and the apparent power is 5 KVA, calculate the reactive power?

1 KVAR 2 KVAR 3 KVAR 4 KVAR

Correct Answer: 3 KVAR

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