For carrying Short Circuit Test on Power Transformer Do the following:
1] Isolate the Power Transformer from service.
2] Remove HV/LV Jumps and Disconnect Neutral from Earth/Ground.
3] Short LV Phases by Cu/Al plate which could withstand short circuit current and connect these short circuited terminals to Neutral
4] Energise HV side by LV supply (440 3ph Supply) with OLTC tap position on Normal.
5] Measure Current in Neutral, LV line voltages, HV Volatage and HV Line Currents on various OLTC Tap position.
Analysis:
If Neutral current is near to zero transformer windings are OK
If Neutral current is higher or equal to Line current between LV Phase one of the winding is Open.
A: Usually smoke and smell
These two tests are performed on a transformer to determine (i) equivalent circuit of transformer(ii)voltage regulation of transformer(iii) efficiency of transformer. The power required for theseOpen Circuit test and Short Circuit test on transformeris equal to the power loss occurring in the transformer.
The transformer can be tested on open and short circuit to find the iron losses and copper losses separately, which uses a fraction of the power than having to run the transformer on full-load.
A fuse or a circuit breaker can be added directly after the power source (and possibly a transformer) to do this.
A short-circuit test is done to determine the power lost in the resistance of the primary and secondary windings of the transformer. It is done at full load current but with only enough voltage to give the required current with the secondary short circuited. An open-circuit test is done at full load voltage but no current is taken from the secondary, and this enables the power lost in the magnetic core of the transformer to be measured. As well a power, the tests also allow the inductances to be measured as well as the resistances, in order ot characterise the transformer fully.
The short-circuit test runs the rated current through the windings of the transformer to measure the copper-loss, or power lost in the winding resistances. Because the transformer is run at low voltage for this test, there is very little additional power loss in the iron core of the transformer.
Short circuit current will increase a lot.
why does have to short-circuit secondary wire of current transformer ?
Short circuit test and open circuit test are widely used to test the efficiency of the transformer.
If you take a power source like a dc battery or AC transformer secondary winding and connect an ammeter directly across these power sources you can read the short circuit current available from that source. This gives a measure of internal resistance of the battery or the available wattage of the transformer.
For carrying Short Circuit Test on Power Transformer Do the following: 1] Isolate the Power Transformer from service. 2] Remove HV/LV Jumps and Disconnect Neutral from Earth/Ground. 3] Short LV Phases by Cu/Al plate which could withstand short circuit current and connect these short circuited terminals to Neutral 4] Energise HV side by LV supply (440 3ph Supply) with OLTC tap position on Normal. 5] Measure Current in Neutral, LV line voltages, HV Volatage and HV Line Currents on various OLTC Tap position. Analysis: If Neutral current is near to zero transformer windings are OK If Neutral current is higher or equal to Line current between LV Phase one of the winding is Open.
When 2 turns of an inductor or transformer short together.