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Do I need PFC capacitors


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#1 shah

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Posted 11 August 2006 - 10:57 AM

I need to know whether I really need PFC capacitors for my industrial installation described below. Right now, I do not pay any PF charge or penalty, but the Power Company has plans to levy it in the future.

1. Tubelights ~ 10, ventilation fans etc
2. 2-ton 3-phase Air conditioner
3. Few machines like a small bench grinder, a drilling machine, all used occasionally.
4. Machine no.1, rated 10kVA, consisting of 2 Induction motors ~ 6.6kW total; plus a cooling tower & pump ~ 1kw
5. Machine no. 2, transformer coupled resistance heating machine, single-phase transformer connected across 2-phases of a 3-phase 440v supply, rated 30kVA

Usage pattern -

1. items 1 & 2 used daily (PF ~ 0.76 with only tubes on, shown on PowerCompany Energy Meter)
2. machine no. 1 , fairly frequently
3. machine no. 2 to be re-commissioned soon and then shall work in tandem with machine no.1

Q1 - Do I need or will I need PFC capacitors ?
Q2 - Do PFC capacitors 'consume' electricity? is it negligible? What does the Current Rating on the PFCC indicate?


#2 jraef

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Posted 11 August 2006 - 06:00 PM

QUOTE(shah @ Aug 11 2006, 03:57 AM) View Post

I need to know whether I really need PFC capacitors for my industrial installation described below. Right now, I do not pay any PF charge or penalty, but the Power Company has plans to levy it in the future.

1. Tubelights ~ 10, ventilation fans etc
2. 2-ton 3-phase Air conditioner
3. Few machines like a small bench grinder, a drilling machine, all used occasionally.
4. Machine no.1, rated 10kVA, consisting of 2 Induction motors ~ 6.6kW total; plus a cooling tower & pump ~ 1kw
5. Machine no. 2, transformer coupled resistance heating machine, single-phase transformer connected across 2-phases of a 3-phase 440v supply, rated 30kVA

Usage pattern -

1. items 1 & 2 used daily (PF ~ 0.76 with only tubes on, shown on PowerCompany Energy Meter)
2. machine no. 1 , fairly frequently
3. machine no. 2 to be re-commissioned soon and then shall work in tandem with machine no.1

Q1 - Do I need or will I need PFC capacitors ?
Q2 - Do PFC capacitors 'consume' electricity? is it negligible? What does the Current Rating on the PFCC indicate?


Hello shah,
Usage patterns 1 (items 1 and 2) and 2 (item 4) will see some benefit once your PoCo starts assessing penalties, until then don't bother. Usage pattern 3 (machine 2) will not. Resistive loads do not affect PF. Machines used occasionally as listed in item 3 are probably not worth the cost of correcting.

PFCCs do not consume energy. The current rating is a maximum reactive current that they can safely supply. Most PFCCs are internally fused (or should be) anyway, that rating is to give you an idea of how to size the conductors feeding the PFCCs. Capacitors should be sized per the motor's rating to correct the PF to .95 lagging.

Cautionary notes:
Connect PFCCs for each individual induction motor on the load side of the controlling device so that the capacitors are only on line at the same time as the motor. Do not "float" capacitors on your system as it will lead to over correction (leading PF) which has other negative consequences.

If any of the induction motors are controlled by soft starters, be sure to read all the instructions regarding how and where to connect the PFCCs.

If any of the induction motors are controlled by VFDs, you will not need PFCCs for those loads.
"He's not dead, he's just pinin' for the fjords!"

#3 shah

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Posted 13 August 2006 - 11:00 AM

Thanks jraef, things are pretty clear now.

Regarding machine no.2, I am not sure whether to term it as a resistive load. It is like this -

A Voltage Stabiliser *beep* step down transformer drops the 3-ph voltage from 440V to 380V (The supply from PoCo is good)
In the machine, 380V primary is converted to ~5V secondary by transformer. The work-load consisting of Graphite elements is directly connected across the secondary.

Will such a machine require correction?


#4 Rzn

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Posted 12 October 2006 - 10:51 AM

Dear Shah,

(1) If you can afford the installation cost of a PFC panel with PF controller, I would suggest you to do it. This will decrease your line losses.
(2) Yes, PFCC consume electricity. For example, a 100kvar Nokian capacitor consume 144A at 400V application. ( I = QC/Vx1.73). Over-correction will cause to consume electricity from system.


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#5 kens

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Posted 12 October 2006 - 09:35 PM

QUOTE(Rizwan ullah @ Oct 12 2006, 11:51 PM) View Post


(2) Yes, PFCC consume electricity. For example, a 100kvar Nokian capacitor consume 144A at 400V application. ( I = QC/Vx1.73). Over-correction will cause to consume electricity from system.
Rizwan tongue.gif


This is reactive current (kVAr) not kW (Energy)
Ken
An expert is one who knows more and more about less and less until he knows absolutely everything about nothing




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