In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

A synchronous motor installed at the receiving end substation operates with such an excitation that it takes power at lagging power factor. Now if the applied voltage of the synchronous motor goes down, the power factor of the synchronous motor will

A

remain same

B

go down

C

improve

D

none of the above

An over excited synchronous motor on noload is known as

A

synchronous condenser

B

generator

C

induction motor

D

alternator

As the load is applied to a synchronous motor, the motor takes more armature current because

A

The increased load has to take more current

B

The rotor by shifting its phase backward causes motor to take more current

C

The back e.m.f. decreases causing an increase in motor current

D

The rotor strengthens the rotating field causing more motor current

In an actual transformer the iron loss remains practically constant from noload to fullload because

A

value of transformation ratio remains constant

B

permeability of transformer core remains constant

C

core flux remains practically constant

D

primary voltage remains constant

The net armature voltage of a synchronous motor is equal to the

A

vector sum of Eb and V

B

arithmetic sum of Eb and V

C

arithmetic difference of Eb and V

D

vector difference of Eh and V

When load on an over-excited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is

A

more

B

less

C

equal

D

twice

The armature current of the synchronous motor has higher values for

A

high excitation only

B

low excitation only

C

both (A) and (B)

D

none of the above

If excitation of a synchronous motor running with a constant load is decreased from its normal value, ignoring effects of armature reaction, it leads to

A

increase in both armature current and power factor angle

B

increase in back e.m.f. but decrease in armature current

C

increase in both armature current and power factor which is lagging

D

increase in torque angle but decrease in back e.m.f.

In a synchronous motor, the armature current has large values for

A

high excitation only

B

low excitation only

C

both high and low excitation

D

none of the above

The armature current of the synchronous motor

A

has large values for low excitation i niy

B

has large values for high excitation only

C

has large values for low and high excitation

D

any of the above

In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then

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