Deep bar rotors are used in induction motors to increase

A)Full load torque
B)Full load current
C)Starting current
D)Starting torque

Two transformers A and B each rated for 40kVA have core losses of 500W and 250W respectively and full load copper losses of 500W and 750W respectively. Which transformer will be preferred to supply lighting loads with the following output pattern? Four hours: Full load, Eight hours: Half load, Remaining twelve hours: No load

A)Cannot be predicted
B)Either Transformer A or Transformer B
C)Transformer B only
D)Transformer A only

If a 3-phase induction motor is running at super synchronous speed for self excitation then the machine

A)Feeds reactive power to the mains
B)Draws reactive power from the mains
C)Feeds real power to the mains
D)Draws real power from the mains

The power loss due to hysteresis in the transformer core of 0.05 m3 volume at 50 Hz frequency having an area of the loop is 800 J/m3 will be

A)2000 W
B)4000 W
C)1000 W
D)500 W

In a shaded pole induction motor, shading coils are used to

A)Produce rotating magnetic field  ,
B)Reduce windage losses
C)Protect against sparking
D)Reduce winding losses

While performing the open-circuit and short-circuit tests on a transformer to determine its parameters the status of the low voltage (L.V) and high voltage (H.V) will be such that

1. In Open circuit L.V is open and in short circuit H.V is shorted
2. In Open circuit H.V is open and in short circuit L.V is shorted
3. In Open circuit L.V is open and in short circuit L.V is shorted
4. In Open circuit H.V is open and in short circuit H.V is shorted

An auto-transformer having a transformation ratio of 0.8 supplies a load of 3kW. The power transferred conductively from primary to secondary is

1. 0.6 kW
2. 2.4 kW
3. 1.5 kW
4. 0.27 kW

The magnetizing current in a transformer is rich in

1. Third harmonics
2. Fifth harmonics
3. Seventh harmonics
4. Thirteen harmonics

A 2-phase, 4 pole permanent magnet stepper motor has a step of

1. 90 degrees
2. 45 degrees
3. 30 degrees
4. 22.5 degrees

A 200/100V, 50 Hz transformer is to be excited at 40 Hz from the 100V side. For the exciting current to remain the same, the applied voltage should be

1. 150 V
2. 125 V
3. 100 V
4. 80 V

The utility of delta-connected tertiary windings in star-star connected power transformer is that it

1. Makes supply available for small loads
2. Provides low reactance paths for zero sequence currents
3. Is used to suppress harmonic voltages
4. All of these

If a sinusoidal voltage source is connected to a power transformer, its no-load current would be

1. Sinusoidal and lagging the voltage by ninety degrees
2. Sinusoidal and lagging the voltage by less than ninety degrees
3. Rich in third harmonic and its fundamental would lag the voltage by ninety degrees
4. Rich in third harmonic and its fundamental would lag the voltage less than ninety degrees

The voltage regulation of a large transformer is mainly influenced by

1. No-load current and load power factor
2. Winding resistances and load power factor
3. Leakage fluxes and load power factor
4. Winding resistances and core losses

A 220/440 V, 50Hz, 5kVA single phase transformer operates on 220V, 40 Hz supply with secondary winding. Then

1. The eddy current loss and hysteresis loss of the transformer decrease
2. The eddy current loss and hysteresis loss of the transformer increase
3. The hysteresis loss of the transformer increases while eddy current loss remains the same
4. The hysteresis loss remains the same whereas eddy current loss decreases

Supply to one terminal of delta-star three-phase core type transformer which is on no-load fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be

1. 230, 230,115
2. 230,115, 115
3. 345, 115, 115
4. 345, 0, 345

Keeping in view the requirement of parallel operation, which of the 3-phase connections given below are possible?

A)     Delta-delta and delta-star

B)      Delta-delta and star-delta

C)      Star-star to delta-delta

D)     Delta-star to star-delta

Auto transformer is used in transmission and distribution

A)     When operator is not available

B)      When iron losses are to be reduced

C)      When efficiency considerations can be ignored

D)     When the transformer ratio is small

A single phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at

A)     Maximum supply voltage

B)      Zero supply voltage

C)      1/1.414 maximum supply voltage

D)     0.5  times maximum supply voltage

A 2500/250V, 25kVA transformer is connected as an auto transformer to give 2500/2750 V. Its rating would be

A)     250 kVA; 225 kVA is transformed conductively

B)      250 kVA; 225 kVA is transformed inductively

C)      275 kVA; 250 kVA is transformed inductively

D)     275 kVA; 250 kVA is transformed conductively

In a transformer the phase angle between primary and secondary terminal voltage is

A)     90⁰; primary voltage leading the secondary voltage

B)      90⁰; primary voltage lagging the secondary voltage

C)      A few degrees, primary voltage leading the secondary voltage

D)     A few degrees, primary voltage lagging the secondary voltage