Baker D30R, User'S Manual & Operating Instructions

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D30R Users Manual
100
Do Not Touch Test Leads while test is in Progress!
71-023 Rev C 5/8/2007
Rotor Loading (Coupling) when Testing Assembled
Motors
When testing assembled motors, the rotor can influence the shape of the surge
wave pattern. These influences are as follows.
1. Loss of wave pattern amplitude: The inductive loading of the rotor
causes rapid dampening (little to no cycles of the ringing pattern) of the
wave pattern.
2.
Separated wave pattern comparisons for good windings: Imbalance in
the inductive coupling between the rotor and stator winding causes the
wave patterns of two good phases to appear separated when they are
compared. By turning the rotor, this coupling effect can be balanced
out so the wave patterns superimpose.
Rotor loading can be understood when the rotor is considered as a secondary of
a transformer. When one phase being surges has a different number of rotor
bars under its stator windings than the other phase being surged and compared,
there is a different transformer action existing for each phase. The wave
patterns on the display indicate this difference by displaying separated wave
patterns when they are compared.
Not all motors exhibit this characteristic. It is most prevalent in smaller, high
efficiency motors with small tolerance air gaps. Separation of wave patterns
that are due to rotor coupling can be determined when the wave patterns
separate from the first positive peak downward, cross one another at the bottom
(first most negative point) and separate again as they go upward (positive).
Fig 8-7: Wave pattern comparisons for motor with rotor in place.
The recommended procedure for testing assembled motors where rotor coupling
may occur is as follows. Refer to Three Phase Motor Surge Test and Setup for