Electric motor voltage

[Tblessing]

I received a call from a friend that his V'S is acting up and would like me to look at it. The VSD controls one 20 hp motor. The VSD is in fault mode showing over voltage. When I check the voltage it is correct with what is supposed to be present. "480/240 3 phase.
This system has 12 motors that are being fed from a plant generator.
I have isolated all 12 motors to check each one individually. When I energize on of the motors the phases go unbalanced, phase to ground readings L1/2.4 volts-L2/498 volts, L3/498 volt. I
I assume this high voltage feed back is what is causing the VSD to fault but is is the generator under load causing the problem or the one motor leaking due to bad windings or stater. Also the motor seems to be work fine with no visual problems.

 

[waross]

Find the ground fault and either repair or replace the faulty component. It may be a fault in the motor or it may be a ground fault in a conductor feeding the motor.
After you have done that call us back.

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

 

[mikekilroy]

You do not specify if the 2.4v phase is on the input or the output: if output, then yep fix the offending motor as Waross says.

If on the input, who cars?

Are you SURE it is THIS issue? Overvolts fault is not the one you would get if phase to ground fault on output, and phase to ground on input is a "I dont care."

Overvolts is from stopping too fast; ie., sending too much energy back to the drive stopping the motor. Solution to it is either slow down your decel or add more DB braking.

Something is not quite jiving yet....

http://www.KilroyWasHere<dot>com

 

[ScottyUK]

Is this a delta connected source or an ungrounded star? Either way, floating supply systems are usually bad news for VFDs. If it's supposed to be grounded then you need to fix that.

Mike - "...phase to ground on input is a 'I dont care.' " is often not true because of filter components connected to the frame.

 

[jraef]

When I check the voltage it is correct with what is supposed to be present. "480/240 3 phase.

No such voltage configuration. 480/277 wye, yes. 480 delta, yes. 240 delta, yes. So what is it really? No guessing.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[mikekilroy]

Thanks ScottyUK for your correction; I should have included phase to ground on input is a 'I dont care' when diagnosing an output overvolts fault. I have blown my share of input MOVs on grounded corner delta systems!

http://www.KilroyWasHere<dot>com