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Negative Power Factor

01/29/2018 4:23 AM

In a capacitor bank (APFC display)initially it was showing power factor without any sign. Recently it is showing Negative power factor. No new load added. Same time capacitors are not switched on. What are the causes? is there any adverse effect?

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Guru
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#1

Re: Negative power factor

01/29/2018 4:27 AM

<...What are the causes?...>

  1. A failure to read an apply the contents of the equipment user manual.
  2. A failure to raise the equipment manufacturer on the telephone, and talk it through.
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#2

Re: Negative power factor

01/29/2018 5:03 AM

Presume the APFC is monitoring the PF at the incomer level of the switchboard. When you say, negative power factor, do you mean leading? If true, It could happen if there are any synchronous motors connected to the switchboard busbars or if there are long but less loaded cable feeders.

Capacitors are switched on based on the pf settings and that too in various stages. It is not necessary for the capacitors to be ON once the power factor is low unless it is below the set threshold.

Hope the above will help in your investigations. Please share your findings.

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#3
In reply to #2

Re: Negative power factor

01/29/2018 5:24 AM

Thank you sir. But the feeder is charged 4 months back. Now only we are facung this problem No additional load added. Please advise.

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Guru
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#4

Re: Negative power factor

01/29/2018 6:48 AM
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#5

Re: Negative Power Factor

01/29/2018 10:25 AM

Similar to what I said in that previous thread, this may be nothing more than how you are interpreting the readings on the display. RTFM (Read The FACTORY Manual) and report back what it says a minus sign in the display means: Leading or Lagging? Looking for answers and implementing changes before knowing for sure what you are really looking at may lead to more mistakes.

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Guru
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#6

Re: Negative Power Factor

01/29/2018 10:40 PM

The normal practice is a portion of capacitors are permanently connected and other portion of capacitors are added with an APFC . When the transformer is on "no load condition" there is only inductive load of transformer but as there is no load the current transformer (CT) controlling the APFC cannot give any signal to the APFC so the PF cannot be corrected. But when the load is switched on the CT will give correct signal to switch on capacitors to correct the PF to the required level. So you may consult the supplier of the APFC for proper advice.

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Guru

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#7

Re: Negative Power Factor

01/29/2018 11:53 PM

Check The PF meter and it’s connection. The analog pf meters will show the last reading and its marker will remain static till new changes takes place in the load and it’s pf.

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Guru

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#8

Re: Negative Power Factor

01/30/2018 5:21 AM

Personally I don't think lead or lag power factors matter. If it was not for the meter, you would not know. Reasons for leading PF have been given.

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#12
In reply to #8

Re: Negative Power Factor

02/01/2018 11:00 PM

Yes if the power factor is below a pre contracted value the Electrical service provider will charge low power Factor penalty. The power factor has to be corrected at the consumers end to avoid low power factor penalty.

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Guru

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#13
In reply to #12

Re: Negative Power Factor

02/02/2018 6:09 AM

That's at point. Yes, it might matter for a large user - there could be a penalty for larger users (usually for a lagging pf that only affects their electric bill)- but they are likely to know about it and perhaps not ask the question here.

For this OP I was thinking of the pf in terms of equipment and engineering when I said it doesn't matter. The OP can decide if it does now there are a few replies.

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Guru

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#9

Re: Negative Power Factor

01/30/2018 10:33 AM

Most likely you are reading changes in your incoming power service. Someone up the line from you did something. Your equipment is just monitoring incoming line conditions.

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Guru

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#10

Re: Negative Power Factor

01/30/2018 11:49 AM

Personally I don't think lead or lag power factors matter. If it was not for the meter, you would not know. Reasons for leading PF have been given.

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Associate

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#11

Re: Negative Power Factor

01/31/2018 1:20 AM

Thanks for giving good information.

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#14

Re: Negative Power Factor

02/02/2018 12:05 PM

Have you recently carried out some maintenance of the APFC panel? Please check whether CT secondary connection to PF meter has been altered (polarity reversed ) due to some mistake.

Manindra

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