page 6 | Electrical Machines MCQ for Engineering Students

Q61. A Cylindrical rotor Synchronous motor , connected to infinite bus , is working with load angel of \(30^\circ\) if the load on motor is doubled , Keping excitation constant ,then the load angel will be

60 degree

30 degree

90 degree

45 degree

Q62. If the excitation (field current) of a synchronous motor is increased to a large value its power factor will be

lagging

leading

zero

none of these

Q63. Identify the equation of synchronous motor when operating in leading power factor.

\(E_f^2 = (V_t - I_aR_a)^2 +(I_aX_s)^2\)

\(E_f^2 = (V_t \cos \phi - I_aR_a)^2 +(V_t \sin \phi + I_aX_s)^2\)

\(E_f^2 = (V_t \cos \phi - I_aR_a)^2 +(V_t \sin \phi - I_aX_s)^2\)

\(E_f^2 = (V_t \cos \phi + I_aR_a)^2 +(V_t \sin \phi + I_aX_s)^2\)

Q64. Power factor of a synchronous motor can be varied by varying

supply frequency

load

applied voltage

excitation

Q65. Synchronizing power comes into play, when rotor speed is

Equal to Synchronous speed

Less than Synchronous speed

Greater than Synchronous speed

Either more or less than Synchronous speed

Q66. Slip test is performed to determine

Slip

direct axis and quadrature axis reactances

positive and negative sequence reactances

sub transient reactance

Q67. An alternator is supplying a load of 500 kW at a p.f of 0.5 lagging. If the power factor is raised to unity, how many more kW can alternator supply for the same kVA loading?

500 kW

1000 kW

250 kW

750 kW

Q68. Two synchronous generators G1and G2 are equally sharing the KVAR of the load while operating in parallel. Keeping the terminal voltage fixed in order to shift part of the KVAR load from G2 to G1

The field current of G1 is lowered

The field current of G2 is raised

The field current of G1 is raised and of G2 lowered

The field current of G1 is lowered and of G2 is raised

Q69. The phenomenon of hunting is observed in

Induction motor

DC shunt motor

DC series motor

Synchronous motors

Q70. A winding of 4 pole alternator having 36 slots & a coil span of 1 to 8 is short pitched by

20 Degree

80 Degree

140 Degree

40 Degree

MCQ

ELECTRICAL MACHINES