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Voltage too high?
2

Voltage too high?

Voltage too high?

(OP)
Experiencing instaneous trip of an 8 ampere 3 ph. breaker
in AB MCC supplying a 230/460 vac. 2hp 1725 rpm 145TC motor.
 Removed motor load and breaker stays on
 This occurred during plant downtime and was the only
motor I tried to run.
 The voltage rises to 514 to 516 vac with no plant load.
 Have checked all ckts with megger and found load side
of disconnect wiring shorted to motor and repaired.
 Also replaced motor due to damaged winding in original.
 Remegged and all wiring and motor read clear.
 The motor with normal load ran for approximately
1 minute and breaker tripped.
 I suspect due to this motor being in a system with
many large and smaller motors with run time load drawing
voltage down under normal conditions the exceptional high
voltage may be the culprit when operating a small motor
at this voltage with no other load.
 Any thoughts???

RE: Voltage too high?

The motor is rated at 460 volts +10%. That's 506 volts. The motor may be at the knee of the saturation curve. You can expect the current to rise disproportionately as the motor approaches saturation.
respectfully

RE: Voltage too high?

Agree with waross - your voltage is too high.  If the breaker is tripping when the motor is started, reducing the voltage should help.  The breaker sounds like a mag-only breaker and should have adjustable instantaneous trip.  You should check to see if the inst. trip is set correctly.

RE: Voltage too high?

(OP)
Thanks, waross and dpc,
 I found a pin hole in the insulation of one of the wires
to motor in underground conduit ,compounded with high voltage and breaker set too low.
 The operator ,said he always had to reset the MCC
motor breaker and never the overload resets anytime he had an overload condition.
 Of course operators never speak of these problems until
they result in downtime.
 Thanks again.

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