EE SHORT NOTES TRANSFORMERS PART 1

1

In a transformer minimum voltage regulation occurs when the power factor of the load is
leading

2

Current transformers for meters and relays usually have
5-A secondaries

3

Increase in secondary current of a transformer brings about increase in primary current. This is possible because
primary and secondary windings are inductively coupled

4

The output current corresponding to the maximum efficiency for a transformer having core loss of 200 W and equivalent resistance referred to secondary of 0.5 ohm is
20 A

5

Burden of a current transformer is usually expressed in
volt amperes

6

The yoke sections of transformers using hot-rolled laminations is made 15 per cent greater than that of the core so as to
to reduce the iron loss in yoke and magnetizing current

7

The humming sound in a transformer is mainly due to
magnetostriction

8

Spiral core transformer which has core made up of steel strip has the following advantage.
Less weight, lighter construction, minimum losses

9

Which value of flux is involved in the e.m.f. equation of the transformer ?
Maximum value

10

Which of the following insulating materials is used in power transformers ?
Tapes of glass, press board, synthetic resin bonded paper.

11

In some transformers, the tapping are provided on
H.V. side

12

Minimum voltage regulation occurs when the power factor of the load is
leading

13

The hum in a transformer is mainly attributed to
magnetostriction

EE SHORT NOTES TRANSFORMERS PART 1

14

Which of the following protection is normally not provided on small distribution transformers ?
Buchholz relay

15

In a power or distribution transformer about 10 per cent end turns are heavily insulated
to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

16

Natural air cooling is generally restricted for transformers up to
1.5 MVA

17

Which type of winding is used in 3- phase shell-type transformer ?
Sandwich type

18

An ideal transformer is one which has
no losses and magnetic leakage

19

The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be
400 W

20

Which of the following properties is not necessarily desirable for the material for transformer core ?
High thermal conductivity