| Purpose |
To measure core (iron) loss |
To measure copper (I²R) loss |
| Transformer Side Energized |
Low Voltage (LV) side |
Low Voltage (LV) side |
| Other Side Condition |
High Voltage (HV) side open |
High Voltage (HV) side shorted |
| Input Voltage |
Rated voltage (full voltage) |
Very low voltage (5–10% of rated) |
| Current Drawn |
Small (no-load current) |
Rated current |
| Wattmeter Reading Represents |
Iron loss only |
Copper loss only |
| Loss Considered |
Core (hysteresis + eddy current losses) |
Copper loss (primary + secondary winding resistance) |
| Copper Loss Significance |
Negligible (due to low current) |
Major (due to rated current flow) |
| Core Loss Significance |
Major (due to rated voltage applied) |
Negligible (due to low voltage) |
| Instruments Used |
Voltmeter, Ammeter, Wattmeter |
Voltmeter, Ammeter, Wattmeter |
| Power Factor |
Low (magnetizing current lags voltage) |
High (resistive circuit) |
| Parameters Determined |
No-load current, iron loss, magnetizing impedance |
Equivalent impedance, copper loss, resistance, reactance |
| Side for Measurement |
Usually done on LV side for safety and ease |
Usually done on LV side, shorting HV side |
