Thyristor Controlled Motor

Hi HIT;

You've got a few things to check: with the power down, measure drive-to-motor wiring insulation respect to ground, if its OK proceed to disconect your motor and measure the resistance from Driver terminals A+ and A- to AC input lines, compare to another motor driver that is known good, if you find a too low resistance, you most likely have a bad thyristor and/or diode.

Yahlasit

First thing: Cheque for field amps and volts.

If they are not within spec then you may have a shorted or open field.

Without field flux you do not develop torque.

T=k*Φ*Ia

Vt= Ra*Ia + k'*Φ*ω

Ra*Ia is usually less than 10% of Vt.

Φ varies with If, and is approximately linear at low strength, tends to saturate at rated If.

Essence of above is that if Φ is low T drops and so does the terminal volts for a given rpm.

Since the drive is probably speed regulated it applies more current up to current limit. But without field it does not develop torque to overcome the losses.

Thanks for your trouble shooting technique.The real problem was with a covered pulley. The metallic rope jumped out and mechanical load increased.

Why do operations always call the E/I department first?

In this plant after electrical checking,mechanical department solve the problem,but maximum are electrical faults.your method will be useful for further faults.thank you very much.