Questions

Question 1

In a transformer, sections of both primary and secondary windings are usually wound on each limb to.

Answer 1

Reduce magnetic leakage

Question 2

Silicon steel is used for the laminations in a transformer core because it?

Answer 2

Has high permeability

Question 3

In a transformer the component of no load current which lags the primary voltage by 90* is the

Answer 3

Magnetising Current

Question 4

The secondary voltage of a transformer is produced by

Answer 4

Mutual Induction

Question 5

The primary and secondary currents of a single phase transformer are approximately

Answer 5

180 degrees out of phase

Question 6

With increasing non-inductive load the secondary terminal voltage of a single phase transformer would

Answer 6

Fall Slightly

Question 7

The secondary power factor of a three phase transformer is dependant on

Answer 7

Power factor of the load

Question 8

The hysteresis loss in a transformer

Answer 8

Is proportional to the frequency

Question 9

If the load on a transformer is doubled, the iron losses are

Answer 9

Constant

Question 10

The efficiency of a transformer

Answer 10

Varies with the load

Question 11

If the acidity of transformer oil has reached an unsatisfactory level the oil should be

Answer 11

Run through filters for reconditioning

Question 12

A positive crackle test of transformer oil would reveal the presence of

Answer 12

Water

Question 13

In order to obtain maximum cooling effect a transformer tank should be

Answer 13

Tubed

Question 14

High grade silicon steel is used for transformer cores because it

Answer 14

Reduces hysteresis loss

Question 15

The no-load current of a transformer is

Answer 15

The phasor sum of the magnetising and iron loss currents

Question 16

Tap changing devices on transformers are used to maintain

Answer 16

The secondary voltage constant

Question 17

The effective operation of a Buchholz relay depends on

Answer 17

Gas bubbles

Question 18

A breather on a transformer is used to

Answer 18

Allow expansion and contraction of oil

Question 19

The secondary current of a standard current transformer is

Answer 19

5 amps

Question 20

The standard secondary voltage of an instrument type potential transformer is

Answer 20

110 volts

Question 21

The iron loss of a transformer can be determined by measuring the power taken by the transformer when

Answer 21

The secondary is open circuited and normal voltage is applied to the primary winding

Question 22

Transformers operated in parallel must have the same

Answer 22

Regulation

Question 23

In order to determine the percentage impedance of a transformer a certain test is carried out being the

Answer 23

Short circuit test

Question 24

The purpose of adding fan cooling to zone transformers is to

Answer 24

Increase rated load

Question 25

A transformer that has more turns on the secondary winding than the primary winding is called a ..... transformer

Answer 25

Step up

Question 26

In practice the ..... load current of a transformer is constant

Answer 26

No-load

Question 27

The no-load current of a transformer lags the applied voltage by an angle of ......

Answer 27

90 degrees

Question 28

Joints in the laminations of a transformer core are staggered so as to minimise .....

Answer 28

Reluctance

Question 29

In the phasor diagram for a transformer Im stands for the .... current

Answer 29

Magnetising

Question 30

Maximum efficiency of a transformer occurs at the load which makes the ..... losses equal to the ..... losses

Answer 30

Iron and Copper

Question 31

Short circuit test on a transformer is used to determine the .... losses

Answer 31

Copper

Question 32

The laminations of a transformer are usually insulated from each other by means of an .....

Answer 32

Oxide layer

Question 33

Transformers are connected in parallel to provide more ..... at the same .....

Answer 33

Power output and Voltage

Question 34

..... steel is used for the laminations in a transformer core.

Answer 34

Silicon

Question 35

The secondary voltage of a transformer is produced by .....

Answer 35

Mutual induction

Question 36

The core losses of a transformer are made up of .... and ....

Answer 36

Eddy current and Hysteresis

Question 37

Maximum efficiency of a transformer occurs when the constant losses equals the .....

Answer 37

Variable