TESTS ON TRANSFORMER

1. Open Circuit Test or No Load Test

2. Short Circuit Test

3. Polarity Test

Open Circuit Test or No - load Test

The low voltage side is supplied with rated voltage while the high voltage side is left open. Electrical measurements are done on the low voltage side.

occoreloss PP

oc

ocm

P

ER

2

oc

ocm

Q

EX

2

ocococ IES

22

ocococ PSQ

where:

Poc = reading of the wattmeter during the test (watt)Eoc = reading of the voltmeter during the test (volt)I oc = reading of the ammeter during the test (ampere)

Example:

The no - load current of a transformer is 4A at 0.25 pf when supplied at 250 V, 60 Hz. Determine the

a. core lossb. resistance representing the core

lossc. magnetizing reactance

wattspfIEP

PP

A

ocococ

occoreloss

25025.04250

.

250250

250

.

22

oc

ocm

P

ER

B

55.6424.968

250

24.9682501000

10004250

.

22

2222

oc

ocm

ocococ

ocococ

Q

EX

VARPSQ

VAIES

C

Short Circuit Test

The low voltage side is short circuited while the high voltage side is supplied with voltage adjusted so that the high side will draw rated high side current. Electrical measurements are done on the high voltage side.