AC MACHINE (Motors)

C. Starting compensator

An auto-transformer used for starting induction and synchronous motor to reduce the current drawn from the supply lines a. Motor starter b. Reducer transformer c. Starting compensator d. Four point starter

B. Lagging current

An under - excited synchronous motor takes a. Leading current b. Lagging current c. Both A and B d. None of the above

D. Only at synchronous speed

A synchronous motor can develop synchronous torque a. When under loaded b. Below or above synchronous speed c. While over excited d. Only at synchronous speed

B. Synchronous condenser

A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as a. Static condenser b. Synchronous condenser c. Condenser d. None of the above

C. 25%

A squirrel cage motor is started at 50% it's rated voltage. What is the starting torque relative to its rated voltage starting torque. a. 50% b. 100% c. 25% d. 75%

D. Over - excited

A synchronous motor can be used as synchronous capacitor when it is a. Under - loaded b. Under - excited c. Over - loaded d. Over - excited

C. Either A or B

Direction of rotation of split phase motor can be reversed by reversing the connection of a. Running winding only b. Starting winding only c. Either A or B d. Both A & B

A. Universal motor

If a particular application needs high speed and high starting torque, then which of the following motor will be preferred a. Universal motor b. Capacitor start motor c. Shaded pole motor d. Capacitor start and run motor

A. Blown fuses

If a single phase motor runs hot the probable cause cannot be a. Blown fuses b. Low voltage c. High voltage d. Shorted stator coils

B. Draw excessive current & overheat

If starting winding of a single phase induction motor is left in the circuit, it will a. Run faster b. Draw excessive current & overheat c. Run slower d. Spark at light load

A. The motor will not start

If the capacitor of single phase motor is short circuited a. The motor will not start b. The motor will burn c. The motor will run in reverse direction d. The motor will run in the same direction at reduced rpm

A. Lagging

If the field of synchronous motor is under-excited the power factor will be a. Lagging b. Leading c. Unity d. More than unity

D. Not start

In a capacitor start motor, the capacitor is replaced by an inductor having the same reactance as in capacitor. Then the motor will ____ a. Be damaged b. Start and run at its rated speed c. Start but run at low speed d. No start

B. Low resistance and high inductance

In a split phase motor, the running winding should have a. High resistance and low inductance b. Low resistance and high inductance c. High resistance and high inductance d. Low resistance and low inductance

B. Motor takes 5 to 7 times it's full load current

It is advisable to avoid line starting of induction motor and uses starter because a. Starting torque is very high b. Motor takes 5 and 7 times it's full load current c. It will pick up very high speed and may go out of step d. It will run in reverse direction

B. Ns = 120f/P

Magnetic flux produced due to the stator winding with three phase current frequency f and which is of constant value, rotates at synchronous speed. If P is the number of poles of the motor then the synchronous speed is given by a. Ns = 120P/f b. Ns = 120f/P c. Ns = 120 fP d. Ns = 60f/P

A. Slip rings

Squirrel cage induction motor differs from the slip ring type in that it has no a. Slip rings b. Rotor winding c. Windings on the stator d. Rotating part

A. The power factor may be varied

The advantage of a synchronous motor over a wound rotor motor is that a. The power factor may be varied b. It's speed does not depend on the frequency of the supply c. It has no brushes to contend with d. It's speed may be more readily controlled

C. Torque angle

The angle between the rotor poles and stator poles, in a synchronous motor is known as a. Power factor angle b. Synchronizing angle c. Torque angle d. Angle of retardation

A. %slip S=(Ns-N)/Ns x 100

The difference between the synchronous speed Ns and the actual speed N of the rotor is known as slip. It can be expressed as a percentage and is given by a. %slip S=(Ns-N)/Ns x 100 b. %slip S=(N-Ns)/N x 100 c. %slip S=(N-Ns)/Ns x 100 d. %slip S=(Ns-S) ​

B. f' = Sf

The frequency of the rotor current in an induction motor is given by (if F is the supply frequency and f' is the rotor frequency & S is the slip) a. f = Sf b. f' = Sf' c. f' = Sf d. S = ff'

C. Current is induced in its rotor

The induction motor differs from the synchronous motor is that it a. Requires a dc source for its rotor b. Does not required a rotating magnetic field c. Current is induced in its rotor d. Current is conducted in rotor

B. Pull - in torque

The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as a. Pull - in torque b. Pull - in torque c. Pull - out torque d. None of the above

C. Shaded pole motor

The motor used for the compressor is a. DC series motor b. Capacitor start capacitor run motor c. Shaded pole motor d. Reluctance motor

D. Carbon steel

The shaft of induction motor is made of a. High speed steel b. Cast iron c. Stainless steel d. Carbon steel

A. Electrolytic capacitor

The starting capacitor of a single phase motor is generally a. Electrolytic capacitor b. Paper capacitor c. Ceramic capacitor d. None of these

A. Periodic variation of load

Under which of the following conditions hunting of synchronous motor is likely to occur? a. Periodic variation of load b. Over - loading for long period c. Over - excitation d. Small and constant load

D. 0

What is the average slip of percent of a synchronous motor at running speed a. 2.5% b. 3% c. 2% d. 0

D. Dial indicator

What is the instrument often used to check the degree of motor shaft alignment a. Micrometer b. Voltmeter c. Clamp-on ammeter d. Dial indicator

C. The motor stops

When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected a. It runs as a reluctance motor at lower speed b. It runs as reluctance motor at the speed c. The motor stops d. None of the above

A. Two winding displaced from each other

Which of the following is NOT a reason why single-phase induction motor run a. Two winding displaced from each other b. Hysteresis c. One of the current is made out of phase between lines d. Shaded poles

C. Synchronous motor

Which of the following is non - selt starting a. D.C series motor b. Squirrel cage induction motor c. Synchronous motor d. Wound round induction motor

C. Capacitor run motor

Which of the following motor will give relatively high power factor a. Capacitor start motor b. Split phase motor c. Capacitor run motor d. Shaded pole motor

A. Capacitor start motor

Which of the following motor will give relatively high starting torque a. Capacitor start motor b. Split phase motor c. Capacitor run motor d. Shaded pole motor

B. Shaded pole motor

Which of the following type of motor is used in electric toys a. Split phase motor b. Shaded pole motor c. Capacitor start motor d. Permanent split