Electrical machines miscellaneous Easy Questions and Answers | Page - 2

Electrical machines miscellaneous

An ac servomotor exhibits

1. two time constants which depend upon rotor inertia and mechanical friction
1. two time constants which depend upon rotor inertia, the slope of its torque speed characteristic and mechanical friction.
1. a dominant time constant which depends upon rotor inertia and mechanical friction
1. a dominant time constant which depends upon rotor inertia, the slope of its torque-speed characteristic and mechanical friction.

View Hint View Answer Discuss in Forum

NA

Correct Option: D

NA

If an a.c. servomotor has one of its winding excited by a.c., t hen voltage measured at the other winding with rotor running will be

1. zero
1. proportional to rotor speed
1. proportional to the square of the rotor speed
1. constant independent of speed.

View Hint View Answer Discuss in Forum

NA

Correct Option: B

NA

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.

Voltage across the open-circuited field terminals of a synchronous machine under slip test is

1. d.c.
1. d.c. of slip frequency
1. a modulated supply frequency ac voltage with slip frequency envelope
1. a.c. of supply frequency

View Hint View Answer Discuss in Forum

When then driving power from the prime mover driving the alternator is lost, but alternator remains connected to the supply network and the field supply also remains, the alternator will behave as a synchronous motor and will also continue to rotate the same direction.

Correct Option: B

When then driving power from the prime mover driving the alternator is lost, but alternator remains connected to the supply network and the field supply also remains, the alternator will behave as a synchronous motor and will also continue to rotate the same direction.

Damping winding in a synchronous motor is generally used to

1. prevent hunting and provide the starting torque
1. reduce eddy currents
1. minimise vibrations
1. reduce noise level

View Hint View Answer Discuss in Forum

NA

Correct Option: A

NA