All transformers undergo two kinds of industry-standard tests, routine and design, to ensure the transformer will perform as designed. Further optional tests explore the quality of the transformer's construction, assurance, and adherence to standards.

Manufacturers in the United States perform tests in accordance with applicable IEEE and NEMA standards (as approved by ANSI procedures). Overseas customers may require their transformers comply with IEC (International Electrotechnical Commission) specifications. Generally, the manufacturer repeats tests for witnessing for only those you specify. If you have no specific requests, the manufacturer will conduct routine ANSI tests. These include:

  • Ratio and phase relation;

  • Resistance;

  • Excitation loss and current;

  • Load loss and impedance;

  • Applied voltage; and

  • Induced voltage

Design tests, also called type tests, are required only on one of a series of similar or duplicate units. However, you may request the manufacturer perform any of the design tests (usually impulse tests) on any unit. These include:

  • Impulse;

  • Short circuit;

  • Temperature (heat run);

  • Insulation power factor;

  • Insulation resistance;

  • Sound; and

  • Partial discharge