APPLE
Which type of alternator is used in hydroelectric power stations?
Salient pole alternator
The field system of an alternator is usually excited at
250Volts dc supply
The number of poles on turbo alternator is usually
2 (minimum)
The ratio of starting torque to running torque in a synchronous motor is
1
Voltage regulation formula for alternator
E0-V/V
Regulation of an alternator supplying resistive or inductive load is
Always +ve
V curve of synchronous generators shows the variation of
Armature current Vs field current
Under short-circuit conditions, the power factor of an alternator is
Almost zero lagging
Which of the following methods would give higher than actual value of regulation of an alternator?
EMF Method
The maximum power developed in cylindrical synchronous machine is occurs at a load angle of
90 degree
Distributed winding is preferred over concentrated winding as it
Improves the generated emf waveform from harmonics and adds mechanical strength to the winding
The short pitch winding is preferred over full pitch winding for an alternator because it
harmonics can be reduced or totally eliminated
To obtain sinusoidal flux distribution, chamfering of poles is done in
Salient pole alternators only
The phase sequence of a three-phase alternator will reverse if
The field current remains the same but the direction of rotation is reversed
Power factor of an alternator driven by constant prime mover input can be changed by changing the
Excitation of the field winding
Armature reaction mmf and leakage reactance of a synchronous machine are determined by ( test )
Open circuit and Zero Power factor Test
The synchronous reactance in an alternator is the Combined reactance due to
leakage flux and armature reaction
The reactive power delivered by a synchronous generator can be controlled by
Changing the excitation
slip of synchronous motor is
o
A synchronous generator is feeding a zero-power factor (lagging) load at rated current. The armature reaction is
Demagnetizing
Damper bar used in synchronous motor
starting and eliminate hunting
During hunting when the speed becomes super synchronous speed the damper bar develop
induction generator torque
An alternator with higher value of SCR has
Better voltage regulation and higher stability limit
emf equation of alternator
E= 4.44 f phi N
if alpha is short pitch angle of the winding the coil pitch factor is
cos (alpha/2)