DC HiPot/Step Voltage
The HiPot test is performed at a test voltage higher than the Megohm test; that is, at voltages
typically encountered at start-up. Actual test voltages are based on the motor’s operating voltage
and appropriate standards and/or company guidelines.
Look for unusually high leakage currents or a leakage current that does not stay constant. High
leakage currents indicate weak ground wall insulation.
During a Step Voltage test, voltage is applied to all three phases of the winding and raised slowly
to programmed levels then held for a predetermined period. This process is executed in equal
increments (steps) until the target maximum voltage level is reached.
Because the test is most stable at the end of each step, data is logged at this point. If the leakage
current doubles from a given step to the next, an insulation weakness is indicated and testing
should be stopped. If leakage current increases consistently less than double, the motor insulation
is likely good.
Basic Testing Procedures
Surge
Effectively an electrical resonance test, the Surge test creates a nonlinear voltage drop across the
windings, stressing the turn-to-turn insulation. If weak insulation exists, the differential voltage will
short out a bit of the winding, causing the overall inductance to go down.
Surge testing measures pulse-to-pulse EAR (Error Area Ratio) by default, and can also measure line
to-line EAR. (Refer to the AWA-IV User Manual for details on Surge testing and EAR measurement
During testing, the voltage will be slowly increased on lead 1 to the voltage specified in the Test ID.
If no pulse-to-pulse EAR failures are detected, leads 2 and 3 will be tested.
A shift to the left in the waveform patterns is a common indicator of weak insulation.
Baker AWA -IV Static Motor Analyzer
www.megger.com
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