Electrical machines miscellaneous Easy Questions and Answers | Page - 6

Electrical machines miscellaneous

Power angle characteristic of a salient - pole synchronous machine working with a constant field excitation on an infinite bus system is shown in the given figure. If load on the machine is suddenly changed from P₁ to P₂ (P₂ > P₁), then machine will fail to maintain stability if

1. shaded area A₁ is greater than shade area A₂
1. shaded area A₁ is equal to shaded area A₂
1. shaded area A₁ is less than shaded area A₂
1. δ_m > δ₀

View Hint View Answer Discuss in Forum

The answer is based on 'equal area criterion' of stability. If area A₁ is greater than the area A₂, then machine will fail to maintain stability.

Correct Option: A

The answer is based on 'equal area criterion' of stability. If area A₁ is greater than the area A₂, then machine will fail to maintain stability.

A synchronous machine working in the motor made, is fed from an infinite bus and is delivering half full-load. If an increase in field current causes an increase in the armature current, then the motor will

1. deliver reactive power and active power to the bus
1. absorb reactive power and active power from the bus
1. absorb reactive power from the bus and deliver active power to the bus
1. deliver reactive power to the bus and absorb active power from the bus.

View Hint View Answer Discuss in Forum

The condition stated corresponds to overexcitation and it is known that an overexcited synchronous motor runs under leading p.f. condition. Therefore, motor (loaded) delivers reactive power and absorbs active power from the bus.

Correct Option: D

The condition stated corresponds to overexcitation and it is known that an overexcited synchronous motor runs under leading p.f. condition. Therefore, motor (loaded) delivers reactive power and absorbs active power from the bus.

If a 10 pole 25 Hz alternator is directly coupled to and is driven by a 60 Hz synchronous motor, then number of poles in a synchronous motor are
(a)

1. 48
1. 12
1. 24
1. none of these

View Hint View Answer Discuss in Forum

NA

Correct Option: C

NA

If power input to the d.c. field at a 15 kVA (input) synchronous motor is 6 per cent of the rates a.c. input, then direct current that excites the field at 120 volt, is

1. 7.5 amps
1. 125 amps
1. 15 amps
1. none of these

View Hint View Answer Discuss in Forum

NA

Correct Option: A

NA

If a synchronous condenser is installed to current the 2400 kVA, 0.65 power factor load in a plant to unity, then kilovolt ampere rating of condenser is

1. 27 kVA
1. 1560 kVA
1. 1825 kVA
1. 3690 kVA

View Hint View Answer Discuss in Forum

NA

Correct Option: C

NA