The crawling in an induction motor is caused by

(A) Improper design of the machine
(B) Low voltage supply.
(C) High loads.
(D) Harmonics developed in the motor.

The magnetizing current in a transformer is rich in

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

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

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

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 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

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

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

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

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

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 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

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

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

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

A 2/1 ratio, two winding transformer is connected as an auto transformer. Its KVA rating as an auto transformer compared to a two-winding transformer is

A)     Same

B)      1.5 times

C)      2 times

D)     3 times

On the two sides of a star/delta transformer

A)     Voltages and currents are both in phase

B)      Voltages and currents both differ in phase by 30⁰

C)      Voltages differ in phase by 30⁰ but currents are in phase

D)     Currents differ in phase by 30⁰ but voltages are in phase

The efficiency of transformer at full-load 0.85 pf lag is 95%. Its efficiency at full-load 0.85 pf lead will be

A)     Less than 95%

B)      More than 95%

C)      95%

D)     100%

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

Transformer excited from a sinusoidal voltage source will draw a no-load current which

A)     Is sinusoidal and of the same frequency as the voltage source

B)      Comprises the fundamental frequency (same as that of the voltage source) and the peaking third harmonic

C)      Comprises the fundamental frequency and the depressing third harmonic

D)     Is sinusoidal of frequency three times that of the voltage source