Short circuit test is performed on a transformer with a certain impressed voltage at rated frequency. If the short circuit test is now performed with the same magnitude of impressed voltage, but at a frequency higher than the rated frequency then the magnitude of current:

Short circuit test:

• A short circuit test in the transformer is conducted on the high voltage side and the low voltage side is short-circuited.
• In this test, we need to increase the applied voltage gradually towards rated voltage up to rated load current passing in the secondary short-circuited winding by keeping the frequency constant.
• In HV winding, the rated current is less than LV winding. As rated current is less on the HV side, it is convenient to conduct this test on the HV side by short-circuiting the LV terminals.
• This ensures that the low range of meters can be used for conducting this test as the wattmeter is connected to the primary side (High voltage side).
• Therefore, the primary side is generally chosen as the primary side.
• A short circuit test can be performed on either side but generally performed on the HV side.

Power Factor (cos ϕ) = R / Z

Where,

R is the equivalent resistance

Z is the equivalent impedance

Z = R + j 2π f L

f is the supply frequency 

L is the equivalent inductance 

⇒ cos ϕ = R / (R + j 2π f L)

Power factor during the short circuit test is inversely proportional to supply frequency

Current (I) = V / Z 

Where,

V is the supply voltage

⇒ I = V / (R + j 2π f L)

The magnitude of current during the short circuit test is inversely proportional to supply frequency

Therefore as the frequency of a transformer increases both power factor and current decrease.