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OPEN TRANSITION CONTROL


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#1 Guest__*

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Posted 18 July 2005 - 05:53 PM

GUYS, WHY IS IT THAT A CAPACITOR BANK INSTALLATION , IS NOT RECOMMENDED TO THE FOLLOWING:

1.] OPEN TRANSITON MOTOR CONTROL MODES,

2.] DUAL SPEED MOTOR CONFIGURATION,

3.] ELEVATOR MOTOR APPLICATIONS.


THANKS IN ADVANCE!!

#2 marke

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Posted 18 July 2005 - 07:54 PM

Hi

Open transition switching does create all sort of potential problems on the supply. The addition of pwer factor correction can exagerate those problems.

I have not seen a recommendation as you describe, perhpaps you can give us more detail and we can comment in context.

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#3 jraef

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Posted 22 July 2005 - 08:09 PM

Marke,
In the Eng-Tips forum, I have been involved in a similar thread (thread237-129693) that deals with the same issue. One of our fellow posters has asked a pertinent question as to whether having open transition starters anywhere on the same circuit as the PFC caps would pose a problem.

Your thoughts?
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#4 marke

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Posted 23 July 2005 - 07:38 AM

I have seen power factor controlled by the starter, i.e. static correction, in many open transition star delta starters without any obvious problems, however after thinking about it, I would suggest that the connection of the power factor correction connected close to the starter during the switching transition, would provide a very low transient supply impedance and could effectively increase the magnitude of the current and torque transients.
If static correction was applied to an open tranistion starter, it would be very easy to effectively over correct the motor in star connection or in low speed connection and this could result in resonance during the open transition stage. This would happen if the correction was permanently connected to the output of the delta contactor.
I would suggest that the best way to control the capacitors is with a separate contactor that closes after the transient occurs.

The ideal application of static correction will use a separate contactor and detuning reactors. This is not commonly done, but gives much higher protection against the effects of over correction and harmonic currents.

Best regards,




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