Drive for Line Shaft

[sunrays]

I was commissioning a 90 kW 415 V Constant Torque Drive in Open Loop Vector Mode connected to a 75 kW 415 V Motor for Line Shaft Application in a Paper Machine.

The no load running of the motor in decoupled state was perfect up to its full speed.

The problem surfaced when the load was coupled. The motor speed was hunting and current (as viewed on the drive) was also oscillating. Suspecting a problem with the load a through check of the mechanicals was done but no solution was found.

After several hours of attempting to find a solution I changed the motor speed in the drive from 1440 rpm to 1500 rpm and the problem vanished in to thin air.

The manual states "Enter the rated full load speed of the motor (taken from the motor name plate)" for the motor speed parameter. In which case it should be 1440 RPM and not 1500, but 1440 RPM lead to the problem.

Could some one explain this?

Thanks!

 

[DickDV]

It's going to be difficult to offer anything specific because different brands approach sensorless vector and the related parameters differently.

I does sound like the full load motor speed is a sensitive part of the motor model and it may well be that the motor nameplate data does not match the actual slip conditions in the motor. This would be particularly true if the motor has been rewound. Ideally, it would be good to independently measure motor shaft torque and determine the actual slip of the motor. Then enter that for motor full load speed.

I assume that you tried retuning the speed loop to get rid of the hunting. If not, I would put the 1440 back into the drive parameter and try retuning under some load. No-load tuning often isn't good enough.

You've probably already done this but check to be sure your speed command isn't oscillating when the motor is loaded. I've seen stranger things.

Let us know how you are doing on this.

 

[sunrays]

The speed reference was stable. No doubt about that. Secondly the behavior was the same when run from the key pad of the drive also.

The drive has a rotating auto-tune that was done successfully with the motor decoupled. This is the advice in the manual.

I fine tuned the Current Loop as wells the Speed Loop gains with no effect.

The change in motor parameter was done out of expatriation and with no scientific reason. It worked like a magic wand waved over the problem!

The system is working since with no problem at all.

 

[Tumppi]

The reason for oscillation is slip compensation of open loop drive. Your motor slip is 60rpm and syncronous speed at 50Hz is 1500rpm. When you set motor nominal speed to 1500, then slip compensation is off.

Normally slip compensation for open loop drive works with the load/current. What higher load/current, that higher is slip compensation. Drive output frequency goes higher to compensate speed drop and back to set frequency when load goes low.

I quess your motor/load inertia ratio is high. This same happens with fans and all kind of over hauling loads.

Any way, you did right thig when taking off the slip compensation.
And, if it's working ok, who cares...

 

[DickDV]

Tumppi, you will note that the original poster stated Open Loop Vector. Or, commonly called sensorless vector.

Slip Compensation is not active in any Vector mode so I doubt that your explanation is applicable.