Baker D30R User Manual - page 61
Surge Test Applications
12/3/2009 | 71-022 V6
D30R
61
Keep in mind that different types and sizes of motors will give different traces, but the
principle of testing assembled motors is still the same. When interpreting the wave patterns
for good or bad windings, stability and symmetry are the most important factors.
Notes and tips for testing from the switchgear
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The test motor should be properly tagged during the test as a safety precaution.
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All of the limitations and guidelines covered for testing assembled motors apply .
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Any power factor capacitors in the circuit must be disconnected. If power factor
capacitors are present, no waveform will be observed when the voltage is raised. This
will also happen if the motor was not connected to the cable. Only a rise in the trace on
the far left will be noted.
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The surge test circuit will be loaded by the feeder cable capacitance as well as the motor.
Significantly higher output settings will be needed to reach the required test voltage. If
the surge tester is too small to handle both the cable and the motor load, a trace will be
observed but the proper test voltage will not be reached. A higher output surge tester
model will be required or the motor may have to be tested while disconnected from the
feeder cable.
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There is no precise science to determine what size motor, with what size and length
feeder cable a particular surge test model can adequately test. In general, the closer the
size of the motor is to the recommended maximum motor size for a given model surge
tester, the shorter the cables can be and still allow testing at the required voltage.
Conversely, the smaller the motor size, the longer the cable can be.
Transformers
Transformers contain similar insulation systems as motors: ground, turn-to-turn and phase
insulation. However, the spectrum of winding characteristics for transformers is much
broader than for motors.
The surge test is only one of many tests that should be performed to properly test a
transformer. If the transformer has thousands of turns, the surge tester may not be sensitive
enough to detect a single shorted winding. It may also sense the high inductance of a
transformer as an open.
The following procedures for single phase and three phase transformers provide the basics
necessary to surge test transformers. Please contact your representative for further
assistance or if difficulties are encountered when testing transformers.
WARNING!
The motor must be de-energized before testing!
Connect the test leads to only the load side of the open disconnect.
Fig 8-8: Single-phase transformer connection