Deck 1: Transformer Fundamentals and Operation

Question 1

Which of the following does not change in a transformer ?

A)Current
B)Voltage
C)Frequency
D)All of the above

Answer 1

Frequency

Question 2

In a transformer the energy is conveyed from primary to secondary

A)through cooling coil
B)through air
C)by the flux
D)none of the above

Answer 2

by the flux

Question 3

A transformer core is laminated to

A)reduce hysteresis loss
B)reduce eddy current losses
C)reduce copper losses
D)reduce all above losses

Answer 3

reduce eddy current losses

Question 4

The degree of mechanical vibrations produced by the laminations of a transformer depends on

A)tightness of clamping
B)gauge of laminations
C)size of laminations
D)all of the above

Question 5

The no-load current drawn by transformer is usually what per cent of the full-load current ?

A)0.2 to 0.5 per cent
B)2 to 5 per cent
C)12 to 15 per cent
D)20 to 30 per cent

Question 6

The path of a magnetic flux in a transformer should have

A)high resistance
B)high reluctance
C)low resistance
D)low reluctance

Question 7

No-load on a transformer is carried out to determine

A)copper loss
B)magnetising current
C)magnetising current and loss
D)efficiency of the tr

Question 8

The dielectric strength of transformer oil is expected to be

A)lkV
B)33 kV
C)100 kV
D)330 kV

Question 9

Sumpner's test is conducted on trans-formers to determine

A)temperature
B)stray losses
C)all-day efficiency
D)none of the above

Question 10

The permissible flux density in case of cold rolled grain oriented steel is around

A)1.7 Wb/m²
B)2.7 Wb/m²
C)3.7 Wb/m²
D)4.7 Wb/m²

Question 11

The efficiency of a transformer will be maximum when

A)copper losses = hysteresis losses
B)hysteresis losses = eddy current losses
C)eddy current losses = copper losses
D)copper losses = iron losses

Question 12

No-load current in a transformer

A)lags behind the voltage by about 75°
B)leads the voltage by about 75°
C)lags behind the voltage by about 15°
D)leads the voltage by about 15°

Question 13

The purpose of providing an iron core in a transformer is to

A)provide support to windings
B)reduce hysteresis loss
C)decrease the reluctance of the magnetic path
D)reduce eddy current losses

Question 14

Which of the following is not a part of transformer installation ?

A)Conservator
B)Breather
C)Buchholz relay
D)Exciter

Question 15

While conducting short-circuit test on a transformer the following side is short circuited

A)High voltage side
B)Low voltage side
C)Primary side
D)Secondary side

Question 16

In the transformer following winding has got more cross-sectional area

A)Low voltage winding
B)High voltage winding
C)Primary winding
D)Secondary winding

Question 17

A transformer transforms

A)voltage
B)current
C)power
D)frequency

Question 18

A transformer cannot raise or lower the voltage of a D.C. supply because

A)there is no need to change the D.C. voltage
B)a D.C. circuit has more losses
C)Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
D)none of the above

Question 19

Primary winding of a transformer

A)is always a low voltage winding
B)is always a high voltage winding
C)could either be a low voltage or high voltage winding
D)none of the above

Question 20

Which winding in a transformer has more number of turns ?

A)Low voltage winding
B)High voltage winding
C)Primary winding
D)Secondary winding

Question 21

Efficiency of a power transformer is of the order of

A)100 per cent
B)98 per cent
C)50 per cent
D)25 per cent

Question 22

In a given transformer for given applied voltage, losses which remainconstant irrespective of load changes are

A)friction and windage losses
B)copper losses
C)hysteresis and eddy current losses
D)none of the above

Question 23

A common method of cooling a power transformer is

A)natural air cooling
B)air blast cooling
C)oil cooling
D)All of the above

Question 24

The no load current in a transformer lags behind the appliedvoltage by an angle of about

A)180°
B)120"
C)90°
D)75°

Question 25

In a transformer routine efficiency depends upon

A)supply frequency
B)load current
C)power factor of load
D)both (b) and (c)