Aim:- To perform short circuits test on a single phase transformer to calculate:
1.
The
equivalent circuit parameters of the transformer.
2.
The
short circuit loos/copper variable use of the transformer.
Apparatus Required:-
S.
No. |
Name
of Equipment |
Type |
Range |
Quantity |
1. |
Single Phase Transformer |
- |
5kVA, 230V 21.74 A, 50Hz |
1 |
2. |
Voltmeter |
PMMI |
|
1 |
3. |
Ammeter |
PMMI |
|
1 |
4. |
Wattmeter |
Dynamometer |
128ohm, 2.5Amp |
1 |
5. |
Single Phase Varic |
- |
230V, 28A, 50Hz |
1 |
Theory:- In this test high
voltage winding (secondary) is connected to a supply of normal voltage and
frequency through variac and the low voltage winding (primary) is short
circuited as shown in Figure. The high voltage winding is supplied to a very
low voltage such that the rated current would flow in short circuit branch. This
test is performed at rated current flowing in both the windings. Since the
applied voltage is very less therefore iron loss occurring in the transformer
under short circuit condition is very less and can be neglected. Therefore the
total losses occurring under short circuit condition are mainly the copper loss
of both the windings which are indicated by the wattmeter connected in the
circuit.
Hence,
Wattmeter reading
in short circuit condition = Wsc
Voltmeter reading in short circuit condition =
Vsc
Ammeter reading in
short circuit condition = Isc
From the observation of short
circuit test of single phase transformer, the short parameters Ryand Of the
transformers equivalent circuit referred to particular winding can be
calculated as follows;
Total
copper loss = Wsc
Equivalent resistance
referred to HV winding Req = Wi/(Isc)2
Equivalent resistance
referred to HV winding Zeq =
Vsc/Isc
Equivalent resistance
referred to HIV winding Xeq =√
Circuit
diagram.
Procedure:-
1. Make
the connections as per the circuit diagram.
2. Make
sure that the secondary side of transformer is sorted.
3. Keep
the variac at 0 position before switch on the supply.
4. Switch
on AC supply.
5. By
varying the variac apply full load current to the transformer and note the
reading of voltmeter, wattmeter, and ammeter.
6. Keep
the various at zero position and switch off the supply.
Observation
Table:-
S. No. |
Voltmeter Reading (Vsc)
|
Ammeter
Reading (Isc) |
Wattmeter Reading (W) |
1. |
11 |
21.5 |
70 |
Calculation:-
Least count of voltmeter = 0.5V
Least count of ammeter = 0.5V
M.F. (multiplying factor) of wattmeter = 2
Copper
loose = wattmeter reading
=
70 x 2
= 140
Short circuit current = 21.5 amps
Precautions:-
1.
All
the connection should be tight and clean.
2.
Special
care should be taken while selecting the range of the metres for conducting
short circuit test.
3.
While
conducting the short circuit test the voltage applied should be initially set
at zero and then increase slowly. if a little higher voltage than the required
voltage be applied (by mistake) there is a danger of transformer being damaged.
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