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Bulk Correction


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#1 Jim_N

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Posted 27 January 2003 - 02:12 PM

I'm new to the forum. I'm glad I found LMP's website and especially this message board - it's very informative. Thank you!

I am currently working on a project to repair / replace our existing capacitor bank. The unit was installed in 1987 and has never operated properly. The fuses were pulled for the automatic controls because they never worked and were causing problems (locking-up I was told). The engineering firm (no longer in business) could not fix the problem so we have been using a fixed amount of kVAR in lieu of automatic correction.

We are using bulk correction (12.47 kV) and currently have 1800 kVAR total capacitance (fixed) with a monthly PF averaging 0.77; there is more kVAR available but we don't have all of our capacitors on-line (we don't want to over-correct).

I don't know if I can retrofit our existing bank / controls or if replacement is our best option.

The existing installation consist of GE 200 kVAR, 7200 V, 1-Phase capactitors and Westinghouse switches. The automatic switching controls are custom and never operated properly.

Does anyone have any recommendations or know what manufactures / vendors offer the best solutions for bulk correction.

Thanks in advance.

#2 marke

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Posted 27 January 2003 - 06:08 PM

Hello Jim_N
Welcome to the forums.
Sounds like you hve had historical problems that are easily fixed.
Firstly however, you make a comment about not overcorrecting. This is generally not a problem with bulk correction, but is a bad problem with static correction. The problem ocurs when the motor is disconnected from the supply with overcorrection in parallel. As the motor runs down in speed, the frequency of the voltage generated drops below the line frequency ans passes through a resonance point between the motor and capacitors. This can not happen with bulk correction so the issue does not occur.

There are many suppliers of power factor correction equipment and I believe that the best solution for you is to deal with someone who is locally available. I would suggest that you talk to your local power supply authority and find out who is active in your area and use them as a starting point. With the amount of variable speed drives around today, and the resultant harmonics, you may also wish to consider the use of detuning reactors to improve the life of the equipment.

Best regards,

#3 Jim_N

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Posted 28 January 2003 - 06:58 PM

Thanks for the reply Marke. You stated that overcorrection is usually not a problem with Bulk Correction.

Wouldn't it be possible to overcorrect and have a leading PF with Bulk Correction if our plant load drops and Xc > XL?

If there is not a problem with this senario then why do we need automatic switching controls added to Bulk Correction Banks?

Our facility has recently switched to a 10 -4 production schedule that has certain departments down for 4 days at a time (once per month). This caused me some additional concern since our load fluctuates even more.

This is my first experience with Bulk Correction and I appreciate any information that you can provide.

Thanks again,
Jim

#4 marke

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Posted 29 January 2003 - 09:12 AM

Hello Jim_N

Essentially this is correct, however if you are applying power factor correction, you will be applying it to reduce a penalty of some form. If you over correct, the power factor drops , but is now a leading power factor. If you have a permanent connection, when you have high motor loading (lots of motors running) you will have an inductive or lagging power factor. If you have low motor loading (few motors) you will have a leading power factor and you will pay the same price for a leading power factor as a lagging power factor. Some supply authorities encourage a leading power factor, (not too much though) because it helps to compensate for the inductive nature of overhead lines.
Best regards,




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