Single VFD running two motors - One motor temperature much hotter.

[edison123]

Single VFD running two 400 HP AC motors driving on-shore oil drill via gears.
One motor is original winding and one was rewound with 10% more copper area and hence 10% lower DC resistance.
Both the motors had the same inductance since the turns are the same.

Upon recommissioning, the rewound motor with lower resistance was running much hotter (60 deg C hotter) than the original one.
Then client VFD team did “ID run that made the motors compatible” whatever that means.
And the 60 deg C temp difference between the motors just vanished.

Can the drive gurus here explain this? Thanks.

 

[LionelHutz]

Probably changed the V/Hz ratio.

 

[mparenteau]

An ID run is a procedure whereby the VFD "learns" the motor(s) characteristics via an algorithm. I'll defer to jraef on the rest...

Mike

 

[jraef]

An ID run is a procedure whereby the VFD "learns" the motor(s) characteristics via an algorithm. I'll defer to jraef on the rest...

Mike

Correct, ID Run is what ABB calls their “autotune” procedure and is necessary when running motors in any form of vector control (SVC, FVC, FOC, DTC). But you can’t do any of those control methods when you have more than one motor, you are only able to do V/Hz control, because no two motors have the same electrical characteristics even if they appear to be the same.

So if the user is trying to do SVC or something higher with two motors, that’s the problem from the outset and may have contributed to one of them failing. They need to either switch to V/Hz control, or get separate drives and run the motors in torque sharing mode as a master/follower pair. If some salesperson told them they could run two motors from one drive and use something like DTC, they led them astray.

Some newer SMALL drives will requires an ID run procedure even if using V/Hz control, because the newest transistor packs are now switching 10x faster than before, which means slight variations in motor circuits can sometimes have bigger effects. But I doubt that would be the case on an 800HP drive.

 

[edison123]

Thanks all. But why would tuning / not tuning the drive or whatever mode affect the motor winding temperature so drastically?

 

[iop95]

What is VFD model?
Both motors drive same load?