This document describes a recommended procedure for measuring
insulation resistance of armature and field windings in rotating
machines rated 750 W or greater. It applies to synchronous
machines, induction machines, dc machines, and synchronous
condensers. It does not apply to fractional-horsepower
The document also describes typical insulation resistance
characteristics of rotating machine windings and how these
characteristics indicate winding condition. It recommends minimum
acceptable values of insulation resistance for ac and dc rotating
Other IEEE standards that include information on insulation
resistance measurement are listed in Clause 2.
The purpose of this recommended practice is to address the
a) Define insulation resistance and polarization index testing
of the winding of a rotating machine.
b) Review the factors that affect or change insulation
c) Recommend uniform test conditions.
d) Recommend information methods for measuring insulation
resistance with precautions to avoid erroneous results.
e) Provide a basis for interpreting insulation resistance test
results to estimate winding suitability for service or for an
overvoltage test. In particular, this standard describes typical
insulation problems detected by the insulation resistance test.
f) Present recommended minimum acceptable insulation resistance
values and polarization indices for various types of rotating
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