Motor current

[flexoprinting]

Good morning!

I have 220V to a motor wired Delta, it's rated current is 13.2A. The draw is 16A and tripping overload.
Megger readings are good, resistance shows slight difference between windings, however inductance reading
on two windings is 9.3mh the third is 9mh.

Would .3mh indicate a shorted winding and would such small a value cause that much more current? What is the
formula for calculating this difference?

Thank's

 

[DHambley]

This 9.3mH vs 9.0mH may be simply due to the difference between Lq and Ld. If you turned the rotor a few degrees, do these values change?

Darrell Hambley P.E.
SENTEK Engineering, LLC

 

[flexoprinting]

I don't know, but will try that when I get to the shop.

Thanks for your reply!

 

[waross]

That motor should draw about 4 or 5 amps when it is running, possibly less. It may draw 80 amps at locked rotor. That is a ratio of about 20:1.
That is also the ratio between the inductive reactance when the motor is stopped and when it is running.
A couple of basic questions;
Is the current high on one phase, two phases or on all three phases?
What does the motor drive?
Was the motor driving its normal load when the 16 amps was measured?
What is the voltage on all three phases?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[flexoprinting]

Hello Waross

Think I found the fly in the ointment, turns out overload was set for 50Hz from when it came across the pond. At 60Hz it is rated for 16.6A. Not sure why this showed up now, it has been running for two years and no complaints. There is a quick disconnect between motor and supply, I neglected to check voltage drops here and suspect a bad connection. Another Tech has replaced the pump and sorry to say I can't test it now.

The motor drive's a Rietschle Vacuum pump, bearings and pump in good shape, rotor spins freely. I rechecked the inductance today per DHambley's reply with ~10 degree
rotation from lowest to highest.

9.59mH - 9.82
9.60mH - 9.91
9.68mH - 9.93
We could have done a better job of trouble shooting this and could have saved some
$$, going to chalk it up for experience I guess.

Thanks for your help Gentleman.