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Synchronous Transfer With Powerflex 7000


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#1 VladM

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Posted 26 August 2008 - 07:15 AM

Dear All,


Please let those who witnessed the synchronous transfer with Rockwell Automation MV VFD comment the following.

There is an option in MV VFD area called "synchronous transfer". I myself saw how this works with 6kV Robicon Perfect Harmony drive. This transfer with Robicon looks very good since in no case the motor is just "flying free and uncontrolled" - Robicon controls the motor all time during both up and down transfers - of course until the motor is suppied directly from the mains.

There is also MV VFD called PowerFlex 7000 from Rockwell Automation (Allen Bradley). Their electric circuit topology doesn't allow this drive to do the transfer in the way Robicon does. For very short periods of time Rockwell MV drive looses control of the motor - both during up and down transfer operations. As far as I see there might be sizeable speed sags and severe current strikes when using transfer with PowerFlex 7000. This transfer does not such look smooth to me as in case with Robicon. However I have never seen how Rockwell is doing it with my own eyes - all above mentioned is just what I think based on general knowledge and technical description of the process. Therefore I am wondering how it looks in practise.

Have anybody seen this with PowerFlex 7000? What are Your feelings about it?

Thanks in advance for Your comments.


Yours faithfully, VladM.

#2 marke

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Posted 26 August 2008 - 09:48 AM

Hello VladM

Welcome to the forum.

The Robicon essentially uses closed transition switching and the AB uses open transition switching.

Open transition switching is used in open transition star delta starters. There is quite a lot of information on open transition starters, but essentially, during the transition, the motor continues spinning. The rotor has a magnetic field as a result of the voltage applied while ramping up. The rotor field decays away over a period of time dependent on the time constant of the rotor. The rotating rotor field causes a voltage to be generated in the open circuit stator. The motor is acting as a generator.
At the instant of reconnection, there will be a phase difference between the generated voltage and the line voltage and this causes a very high current transient (inrush current) to resynchronise the stator field to the supply. This open transition switching causes a very high current transient and torque transient.

Best regards,
Mark.

#3 VladM

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Posted 26 August 2008 - 12:06 PM

Hello Marke

Thanks for welcoming.
BTW - have You seen the synchronous transfer with PowerFlex 7000? If Yes, then what is Your impression?

Kind regards,
Vladimir.

#4 rotormtr

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Posted 03 November 2008 - 09:41 PM

QUOTE (marke @ Aug 26 2008, 09:48 AM) <{POST_SNAPBACK}>
Hello VladM

Welcome to the forum.

The Robicon essentially uses closed transition switching and the AB uses open transition switching.

Open transition switching is used in open transition star delta starters. There is quite a lot of information on open transition starters, but essentially, during the transition, the motor continues spinning. The rotor has a magnetic field as a result of the voltage applied while ramping up. The rotor field decays away over a period of time dependent on the time constant of the rotor. The rotating rotor field causes a voltage to be generated in the open circuit stator. The motor is acting as a generator.
At the instant of reconnection, there will be a phase difference between the generated voltage and the line voltage and this causes a very high current transient (inrush current) to resynchronise the stator field to the supply. This open transition switching causes a very high current transient and torque transient.

Best regards,
Mark.


Hi Mark

I know that ABB make a separate synchro module specifically for use on any variable speed drive so that bypass can be acheived without any problems. Have you seen this module at all or know of anyone that has used it?

Regards
Rotomtr




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