Synchronous Motor Starting Transfer Scheme

[tinbau]

Does anyone have any experience with utilizing a VFD to start a large medium voltage synchronous motor and then transfering the motor off the VFD output and onto a direct line once the motor has reached synchronous speed? Essentially using the VFD as a soft start to reduce the impact on the utility system. The VFD would then be used to start and run another large medium voltage synchronous motor.

 

[Skogsgurra]

Yes.

I did that with 11 kV 6 MW refiner motors last year.

Four refiners that were started with a vactor drive, taken up to slight oversync speed and then coasting down to sync speed where an automatic syncronization device connected to the 11 kV bus.

You are in for a nerve-wrecking experience. It is not at all as easy as one would think. Especially if you do not have an encoder on the motor.

Sensorless vector control did not work very well. Drive lost synch about half way up. Finally, we switched to current source mode and had all motors start sucessfully. But do not try to start them under any load. At least not if your inverter is small compared to the motor.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jraef]

You used the descriptive term "large" which is totally subjective. It's better to use your entire keyboard to describe your application, you are not charged by the word here. To someone used to residential well pumps, "large" is 10HP, whereas to someone in the oil pipeline business, "large" is 10,000HP

Robicon (Siemens) has a very successful Synchronous (bumpless) Transfer scheme that is used all over the world on MV motors, but it may be a little spendy for a LV motor, even a large one. In involves frequency matching and placing an inductor in the circuit during transfer (or so I've been told) so that both the VFD and the Line power are feeding the motor for a brief moment. Other manufacturers have done it as well, but I'm not sure of the success rate or methodology.

 

[Skogsgurra]

Hi Jeff,

I think that "large" is in the beholder's eye. But, as soon as they need to be started using a pony motor or an extra inverter, the problem is the same.

I did this work for Siemens. And only because the Robicon solution couldn't fit in the space available. It was also rather "spacy" in economical terms. So, we used a standard 500 V 800 kW MasterDrive and fed an existing 0.5/11 kV transformer that was used for the starting.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[aolalde]

Althogh this was for an induction motor, it could give you some ideas. See thread237-187116