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Power Factor Correction


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#1 kana

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Posted 21 June 2009 - 02:00 AM

Hi,

How can we add capacitor bank to a new installation which has inductive loads such as motor and fluorescent lights without knowing the total power factor?

Kana

#2 yuri

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Posted 21 June 2009 - 06:43 AM

Inductive load is not constant - it is changing all the time as motors (major "culprits" of disbalance) switch on and off, as their loads change, as other - "active" - consumers of energy switch on and off (and proportion of working active and inductive loads thus changing). So if you chose a steady capacitance there may be moments when it would not be correcting the power factor, but instead, itself introduce reactive currents.
Probably you would not do without a special automatic appliance which monitors the disbalance and regulates capacitance needed.

#3 yuri

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Posted 21 June 2009 - 07:06 AM

However, if you are tight on budget, find some minimal load at that place which indeed remains constant throughout the working day. Then, I see it so : measuring the apparent currant add - safely, through switches - capacitors, so, that the curr was dropping. Add so much cap-s untill curr stops decreasing. The resultant capacitance will be equal to the reactive inductance at that particular, constant, load.
All the best, I hope having not said an utter nonsense.

I meant doing it on the major feeder at that place - applying appropriate cap-s and with all the safety measures.

#4 kana

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Posted 21 June 2009 - 12:57 PM

Hi,

Yes, I understand that but what I meant was how do we estimate the size of capacitor bank(bulk correction) during the designing stage of a new electrical system, say for a high rise building or an industrial plant? Are we supposed to take in account the power factor of each load which will be connected to the system? Is there any other method?



Kana





#5 yuri

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Posted 21 June 2009 - 05:27 PM

El motors have power factor on their name plates. I believe other equipment must have that too in their specifiactions. It seems fluorescent fixtures already contain a cap for the PF correction. I am not an expert on that issue, but probably, one calculates all the reactive loads and choses capacitance.

#6 kana

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Posted 02 July 2009 - 03:28 AM

Yes, that's right motors have their power factor stated at their name plate. As for lights, we assume that all lights have pf correction capacitor installed. From what I heard, during the designing stage of an electrical installation we assume the overall power factor to be 0.8 and we do a power factor correction so the overall power factor would be 0.95. Iím not sure about this but I really appreciate if anyone could clarify this.

Regards,
Kana



#7 marke

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Posted 04 July 2009 - 05:32 AM

Hello kana

You do need to have some idea of what the reactive current is before you can neutralise it.

If you have motors on the supply, it is normal for the name plate to indicate the full load power factor.
From this information, you can calculate the reactive current for each motor. You can then add all the reactive curents and apply correction for this current.
The best method is to measure the reactive current or the power factor.

Best regards,
Mark.

#8 kana

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Posted 04 July 2009 - 11:58 AM

Thanks Mark & Yuri.

Regards,
Kana




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