Online PD analysis provides an initial value for an end
user’s later PD measurements on an installed machine. It is
necessarily performed after assembly, because it requires
installed PD couplers on the main terminal box, and the
motor must be running. The online test reflects actual
operating conditions faced by the stator winding in terms
of voltage, temperature, load, and vibration but may show
higher-than-expected values because the new winding insulation
will not yet be seasoned. The test will “see” PD only
in the line-end coils; thus, end winding activity cannot be
determined because the phases cannot be tested together at
the same potential, and an overvoltage is not applied.