Off-line motor circuit analysis (all testing is non-destructive)

Tests include:

a)      Resistance to Ground (RTG) temperature corrected to 40 degrees C at 5,000 volts DC on 4160 volt motors, 2,500 volts DC on 2400 volt motors, and 500 volts DC on 480 volt motors.  RTG looks at the insulation system integrity.

b)      Polarization Index which is a graphed 10 minute RTG test of the motors cable and winding insulation resistance to ground leakage potential.  The graph will show if there are momentary RTG value decreases over the 10 minutes which could indicate the problems not evident using non-graphical analog or digital testers.

c)      Capacitance to Ground (CTG) which looks at the cleanliness of the stator windings-conductive material buildup.  CTG is correlated with RTG to determine when a motor should be sent out for a clean dip and bake.

d)      Resistance Phase to Phase (RP-P) which looks for high resistance connections which can cause overheating and voltage imbalances.

e)      Inductance Phase to Phase (IP-P) which looks at the stator and the rotor for turn to turn or phase to phase shorting, broken rotor bars or end rings, eccentricity and casting voids.

f)       Average Inductance which is used to compare like motors for possible problems such as a motor not being re-wound correctly.

g)      All-Test III impedance and phase angle tests are performed to detect inter-turn winding faults such as shorted turns, shorted coils, reverse connected coils, open windings and shorted phases.

All off-line tests are performed from the de-energized load side of the contactor so test lead connection points need to be made safely available.  MTI requires the plant to provide a qualified electrician to assist with identifying where to connect as well as physically connecting the test leads.