Open Circuit(OC) and Short Circuit(SC) Test on Transformer
Open-circuit or No-load Test On Single Phase Transformers
- Switch on single phase AC supply,with the help of variac, increase the voltage until the voltmeter raeds the rated voltage of the LV side.
- At theinstant of rated LV voltage, Note down the readings of all three instruments.(Voltmeter, Ammeter and Wattmeter readings) are recorded.
Short Circuit Or Impedance Test On Transformer
- Apply voltage to HV side.
- Increase the voltage from the zero until the ammeter reading equals the rated current.
- At the instant of rated HV current, Note down the readings of all three instruments.(Voltmeter, Ammeter and wattmeter readings) are recorded.
Calculation of Efficiency of transformer from O.C. and S.C. Tests
Efficiency, η = Power output in KW/ Power input in KW
= Power output in KW/ (Power output in KW + Losses)
= Power output in KW/ (Power output in KW + Copper loss + Core loss)
Consider that the KVA rating of the transformer is S, a fraction of the load is x and the power factor of the load is Cos Φ. Then
Calculation of Regulation