OT_adding drive to pump motor

[allscott]

Can you post a hydraulic schematic of what you have? Is there a safety relief valve in the circuit? How long does it take the breaker to trip out after you have raised the pressure? Is there an overload on the motor circuit, is that is what is tripping or is the actual circuit breaker for the motor?

I am still pretty sure that your problem is hydraulic and not electrical. The problem is not that your breaker is tripping, the problem is that your motor is overloaded.

It almost sounds like you are stalling the motor. I've stalled hydraulic pump motors because of a defective relief valve. It's not pretty, if there is nowhere for the oil to go the pressure will jump DANGEROUSLY.

I'm Jack, as in Jack of all trades. I am not a motor or hydraulic expert. Having said that this shouldn't be a difficult problem to troubleshoot with the right information.

To answer your last question remember;
P = E*I

If E goes down I has to go up to supply the same pwoer.

 

[Sparkz]

Is it a fair statement to say that under the same load, the current used by the motor on a 400volt supply would be greater than the current draw on a 480 volt supply?

Yes it is, but...you should not use terms like same load for your application. Still thinking you're using a gear pump (could you please verify this?): Then there is no same load, because oil flow has dropped to 5/6th due to the change in net frequency. That's the only reason why motor power is allowed to drop at the same ratio, but still being able to deliver the original amount of pressure. May I suggest to read Tom's post once more.

There's just no electrical reason for the breaker to trip: The motor will not draw more current on a european net because the volt/Herz ratio stays exactly the same (480/60 = 400/50). Meaning it's the load (read: pressure) that is responsible for the overcurrent. For some reason you're allowing pressure to raise beyond the level the pump/motor assembly was intended for originally...

 

[DickDV]

Sparkz has got it just right if, by "same load", you mean torque or pressure. The volts per hertz ratio determines how much current is drawn for each ft-lb or N-m of torque.

If, however, you mean kw or hp by "same load", then the torque has to go up as the speed comes down. With increasing torque (and pressure) the motor draws more current as the speed decreases, as well.

Personally, I doubt that you have a constant kw or hp situation. Most likely, it is just as described by Sparkz and you have too much hydraulic pressure at the lower speed which requires to much torque, then too much current, then an unexpected release of the circuit breaker.

Since this is on a drive, just make sure that you have put the actual motor nameplate data in the drive software. It cannot process the volts per hertz ratio properly if you have somehow "lied" to it about the motor it is running.

 

[Sparkz]

...Since this is on a drive, just make sure that you have put the actual motor nameplate data in the drive software. It cannot process the volts per hertz ratio properly if you have somehow "lied" to it about the motor it is running.

I don't think Katratzi installed a drive yet, DickDV. In his original question, he asked if adding a drive would improve the situation.

 

[DickDV]

Yup, you're right, Sparkz. Got ahead of things a bit.