Power input to a 20 kVA, 200 V/400 V, single-phase two winding transformer during an open circuit test is measured to be 200 W. What is its core loss approximately when the transformer is fully loaded?

Core loss in the Transformer

The open-circuit test of a transformer is used to determine the core loss (iron loss), which consists of hysteresis and eddy current losses.

These losses are constant regardless of the load on the transformer because they depend only on the applied voltage, which remains the same in normal operation.

Explanation

• Transformer rating: 20 kVA
• Primary voltage (low-voltage side): 200 V
• Secondary voltage (high-voltage side): 400 V
• Power input during open-circuit test: 200 W

Since core loss is independent of load, it remains constant at all loading conditions, whether it is performed at no load or full load conditions.

Thus, the core loss when the transformer is fully loaded is still 200 W.