Surge testing applications
Maintenance testing
You will rarely find solid turn-to-turn (hard-shorted) winding faults in motors during
maintenance testing. This condition is usually only found after the motor has failed.
Solid turn-to-turn winding faults happen when the insulation on adjacent copper wires has
failed to the point that adjacent wires weld together. It is rare in maintenance testing because
of a transformer action that occurs within the windings, which induces very high current in
the shorted coils.
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 time to failure is seconds to minutes. When the ground wall
insulation is damaged to the point that line current flows to ground, the ground current circuit
breaker will trip and stop the motor.
During surge testing, steady separation in the wave pattern comparisons is most often the
result of the rotor coupling with the stator (refer to the “Rotor loading (coupling) when testing
assembled motors” section found later in this chapter). In this case, a consistent double wave
pattern displays at all voltage levels.
The key to maintenance testing is to detect a fault at a voltage level above the peak operating
voltage, but not above what the motor would withstand during start up. For example, a 460
V motor that shows a good trace at 500 V, but shows an unstable, flickering or shifting to the
left pattern (regardless of rotor coupling) at 1,500 V definitely contains a fault. When
detecting the fault above operating voltage, time is available to schedule service for the motor
before a hard short and rapid failure occurs.
Consider a 460VAC motor. The peak voltage with respect to ground is:
This 391 volts is the highest voltage any turn in the winding can see with respect to ground.
During normal operation, the motor will be in an environment where transients as high as 4 x
391V = 1564V exist. These transients are due to contacts opening and closing, other
components on the bus being energized/de-energized, lightning strikes, and so on. Now
suppose that the motor has an insulation fault at 500 V. This motor will probably fail while in
service well before it can be surge tested because the normal electrical environment the
motor experiences will continuously stress the fault.
SKF Static Motor Analyzer—Baker AWA-IV User Manual
129
Motor testing theory and reference
Summary of Contents for AWAIV-12
Page 1: ...SKF Static Motor Analyzer Baker AWA IV User manual ...
Page 2: ......
Page 14: ...xii SKF Static Motor Analyzer Baker AWA IV User Manual Table of Contents ...
Page 16: ...2 SKF Static Motor Analyzer Baker AWA IV User Manual About this manual ...
Page 28: ...14 SKF Static Motor Analyzer Baker AWA IV User Manual Baker AWA IV Instrument Overview ...
Page 88: ...74 SKF Static Motor Analyzer Baker AWA IV User Manual Database management and maintenance ...
Page 90: ...76 SKF Static Motor Analyzer Baker AWA IV User Manual Set up of the Baker AWA IV analyzer ...
Page 91: ...SKF Static Motor Analyzer Baker AWA IV User Manual 77 Set up of the Baker AWA IV analyzer ...
Page 92: ...78 SKF Static Motor Analyzer Baker AWA IV User Manual Set up of the Baker AWA IV analyzer ...
Page 124: ...110 SKF Static Motor Analyzer Baker AWA IV User Manual Special features of the Baker AWA IV ...
Page 166: ...152 SKF Static Motor Analyzer Baker AWA IV User Manual Typical winding faults ...
Page 180: ...166 SKF Static Motor Analyzer Baker AWA IV User Manual ...
Page 181: ...SKF Static Motor Analyzer Baker AWA IV User Manual 167 ...
Page 182: ...168 SKF Static Motor Analyzer Baker AWA IV User Manual ...
Page 210: ...196 SKF Static Motor Analyzer Baker AWA IV User Manual ...
Page 234: ...220 SKF Static Motor Analyzer Baker AWA IV User Manual ...
Page 240: ...226 SKF Static Motor Analyzer Baker AWA IV User Manual Glossary ...
Page 248: ...234 SKF Static Motor Analyzer Baker AWA IV User Manual Index ...
Page 249: ......