Baker D30R, User'S Manual & Operating Instructions

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D30R Users Manual
83
Do Not Touch Test Leads while test is in Progress!
71-023 Rev C 5/8/2007
Note:
For additional reference for fault determination see Typical Winding
Faults.
Note:
If all three wave pattern comparisons in surge testing show considerable
separation when testing three phase windings, the motor has a Phase-to-Phase
short.
Maintenance Testing
Baker Instrument Company Surge Testers have become extremely popular for
industrial maintenance programs, troubleshooting, and to ensure that
replacement motors (spares, reconditioned motors, or rewinds) are thoroughly
tested. The following are guidelines for performing surge tests on assembled
motors in the field as part of maintenance testing.
Hard-shorted winding faults are rarely found in motors during maintenance
testing. Solid turn-to-turn winding faults happen when the insulation on
adjacent copper wires has failed to the point that adjacent wires are welded
together. It is a rare condition in maintenance testing because of a transformer
action, which occurs within the shorted windings which induces very high
current in a hard turn-to-turn short. The high current causes heating and
deterioration of the surrounding insulation systems. The single turn-to-turn
short rapidly compounds until the damage causes a failure in the ground wall
insulation. The high current will trip the circuit breaker and stop the motor. A
solid turn-to-turn, or hard-shorted winding fault is not the type of fault to expect
to see during maintenance testing. This condition is usually only found after the
motor has failed.
During surge testing, steady separation in the wave pattern comparisons is most
often the result of the rotor coupling with the stator. (See Rotor Loading
(Coupling) when testing Assembled Motors). In this case, a consistent double
wave pattern will be seen at all voltage levels. Separation due to rotor coupling
should
not
be interpreted as a fault.
The key to the surge test for maintenance is to detect a fault at a voltage level
above the peak operating voltage. For example, a 460V motor that shows a
good trace at 500V but shows an unstable, flickering patter, (regardless of rotor
coupling) at 1500V definitely contains a fault. When the fault is detected above
operating voltage, time is available to schedule service for the motor before a
hard short and rapid failure occurs.