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Open circuit test on transformer gives
Copper loss
Core loss
Core and copper loss
Leakage reactance
Core loss
The Open Circuit (OC) test on a transformer is performed at rated voltage and frequency with the secondary winding kept open. Under these conditions, the transformer draws only the no-load current (I0тАЛ), which is very small, making the I2R copper losses negligible compared to the core (iron) losses.
The Open Circuit (OC) test on a transformer is performed at rated voltage and frequency with the secondary winding kept open. Under these conditions, the transformer draws only the no-load current (I0тАЛ), which is very small, making the I2R copper losses negligible compared to the core (iron) losses.
POCтАЛтЙИWiтАЛ
WiтАЛ=PhтАЛ+PeтАЛ=KhтАЛfBmaxxтАЛ+KeтАЛf2Bmax2тАЛ
The no-load current I0тАЛ creates a rotating magnetic flux in the core, causing hysteresis and eddy current losses, collectively known as core losses. Since the secondary is open-circuited (I2тАЛ=0), the primary current is limited to the excitation current, effectively isolating the measurement to constant core losses independent of the load.
OC test is performed on the low-voltage (LV) side for convenience.
The wattmeter connected in the circuit provides the value of core loss directly.
Copper losses are proportional to I2R, which is negligible at no-load.
The test determines the shunt branch parameters (R0тАЛ and X0тАЛ) of the transformer equivalent circuit.
Direct measurement of iron losses.
Requires low power input since no load is supplied.
Does not account for copper losses under loaded conditions.
Requires a variable voltage source to achieve rated flux density.
Efficiency calculations.
Determination of no-load parameters.
Core material performance verification.
The OC test is conducted at rated voltage and frequency to ensure the core is working at rated flux density.
Option A is incorrect because copper losses are measured via Short Circuit (SC) test.
Option D is incorrect as leakage reactance is determined through the Short Circuit test.
B is correct тАФ Open circuit test measures the no-load power input which corresponds primarily to the core losses of the transformer.
Always remember: OC test yields core loss (shunt parameters), while SC test yields copper loss (series parameters).