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Example Transformer Measurements and Calculations

This page has some actual measurements and calculations on GE Type 5021G10 transformer, which was originally intended for an illumination power supply for a copier. It has a lot of leakage reactance to limit the current. The nominal specs are 120V input, 4500V output, 400mA short circuit output current. This transformer is interesting because it has a third winding, nominally 600V, for connecting a capacitor for power factor correction. At rated output, this transformer draws about 8.5Amps, i.e. about 1kVA

Open Circuit Tests

• Primary Voltage: 118V
• Primary Current: 5A
• Active Power to Primary: 69.6W
• Secondary Voltage: 4415

Short Circuit Tests

• Primary Voltage: 68V
• Primary Current: 5A
• Active Power: 40.7W

Calculated:

Reactive Power 585.9 Vars

Magnetizing Circuit R: 200 + j23.76 Ohms

Series equivalent: 1.628+j13.5 Ohms

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