Understanding transformer testing

Transformers are passive devices that are primarily used to convert or "transform" alternating current (AC) from one voltage level to another. One very common application of transformers is in AC to DC power supplies, in which mains voltage is stepped down before being rectified and filtered to produce DC. There are numerous other applications for transformers, such as providing electrical isolation or for impedance matching.

This educational note provides a brief technical introduction to measurements made on the types of transformers used in electronics. These transformers are typically physically small, work on relatively low voltages or powers, and are used for “indoor” applications. Although many of the testing concepts described below also apply to the larger, higher-power "outdoor" transformers used for electrical power distribution, the specific tests and test procedures for these types of transformers are often specified by standards bodies such as the IEEE and may differ substantially from the types of measurements described here.

Read this educational note and dive into the discussion about the six most important transformer measurements: turns ratio, mutual inductance, phase angle, primary and secondary inductance, leakage inductance, and interwinding capacitance.