Reliable delivery of electric power is, in great part, dependent on the reliable operation of power
transformers in the electric power system. Power transformer reliability is enhanced considerably by a
well-written test plan, which should include specifications for transformer tests. Developing a test plan
with effective test specifications is a joint effort between manufacturers and users of power transformers.
The written test plan and specifications should consider the anticipated operating environment of the
transformer, including factors such as atmospheric conditions, types of grounding, and exposure to
lightning and switching transients. In addition to nominal rating information, special ratings for
impedance, sound level, or other requirements should be considered in the test plan and included in
the specifications. Selection of appropriate tests and the specification of correct test levels, which ensure
transformer reliability in service, are important parts of this joint effort.