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Power Factor Correction


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#1 rotomoulder

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Posted 08 July 2007 - 01:01 PM

Before I start let me tell you that I am not an expert in PFC so had to listen when when my factory was visited recently by a group of experts from UK who suggested many things that I could do to increase efficiency and one of their suggestions was to fit Power factor correction to the factory supply, so I started to read a little and understood even less than a little.
What I can say is that I use inverter drives on nearly all of my machines because I need to vary the speed of rotation as well as the direction of rotation of my equipment every few minutes. Actually every 3 minutes when we are cooking. So as I see it PFC is not possible on those machines. Am I correct?

I then looked at one of our machines that is Star/Delta start and runs at a stable speed and load which is another thing that most of my machines don't do.

This particular machine motor, an extruder, has the following specs.
Motor rating 380v 3 phase, 50 htz, 30 kw, 58.2 amps rpm 1454.

Measurements taken with the motor running with no drive belts connected
395v, 23amps rpm 1500

and with the motor running with my connected load

395v, 37.6 amps rpm 1480


The ambient temperature at this time of year ( I live in Qatar) is approximately 49 degrees centigrade in the middle of the day at which time the motor is to hot to touch for more than a few seconds. But runs for at least 12 hours a day and sometimes 24. Which is why I cannot load the motor or gearbox ( which is water cooled) any higher. I did run at about 45Amps for a few hours ( using different pulleys) but the gearbox started to overheat and that was during the winter.

I pay approximately 0.08 Qatar Ryals (0.022 USD) per KWHr. There are 3.65 QR per USD.

Do you think that PFC is going to be beneficial to me??

#2 marke

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Posted 08 July 2007 - 07:12 PM

Hello rotomoulder

Welcome to the forum.

The first and most important question is, do you pay any power factor penalty or maximum demand charge? If you pay only for KWHrs, then do not consider power factor correction.
Power factor correction will not reduce your KWHrs, but it could reduce your pf penalty and/or maximum demand charge.

Best regards,

#3 rotomoulder

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Posted 09 July 2007 - 09:15 AM

Thanks Marke We only pay for what we consume in KWH. However I would like to work out if there would be any energy saving if I fit PFC. But from what I understand, as I use Inverters I should not use PFC. At least that is what my instruction manual says.
Terry

#4 marke

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Posted 09 July 2007 - 09:36 AM

Hello Terry

Power factor correction does not save energy for the consumer, only for the supplier except under certain situations where there are long high loss cables between the machine and the meter.

As you are paying on KWHr only, I would forget about power factor correction.

You must not apply static correction to motors that are controlled by VSDs, but you can still apply bulk correction at the switchboard, but with a lot of VFDs, you will need to fit detuning reactors to the capacitors. This is an expensive exercise, and will not affect the KWHrs.

Best regards,

#5 rotomoulder

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Posted 10 July 2007 - 09:06 AM

Marke
Thanks for your feed back.
We live in a country(Qatar) in which everybody uses Air conditioners. In the main they are single phase capacitor start and run for both the compressor and the fan. Could it be that because of this the utility supplier does not worry about power factor Correction. At a guess, and it is a guess I would think that most of the power being supplied goes into single phase cooling units
Terry

#6 marke

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Posted 10 July 2007 - 09:21 AM

Hi Terry

I can not really tell. Sometimes, particularly if there is no shortage of supply, the authorities just don't bother to worry about pf. The major advantage of pf correction is that it increases the utilization of the power distribution system and reduces line losses.
If the consumer pays plenty for the KWHrs and there is no shortage, then why worry?

Best regards,

#7 kens

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Posted 10 July 2007 - 10:34 AM

QUOTE(rotomoulder @ Jul 9 2007, 01:01 AM) View Post


I pay approximately 0.08 Qatar Ryals (0.022 USD) per KWHr. There are 3.65 QR per USD.



Thats a nice price for electricity smile.gif




An expert is one who knows more and more about less and less until he knows absolutely everything about nothing

#8 rotomoulder

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Posted 14 July 2007 - 08:54 AM

QUOTE(kens @ Jul 10 2007, 01:34 PM) View Post

Thats a nice price for electricity smile.gif



Ken
Thats the best supply price. However in another factory 100metres away I pay on a sliding scale up to QR 1.2 which is about 50% more. Still very good.

We had experts from the UK visit us and thats the reason for my posting. They also said I should use natural lighting to save power. When I worked out the costings it would take more than 10 yrs to recoup our expenditure. Even that is doubtful as the sky lights would have to be replaced at some point due to UV degradation.

Its a case of applying laws that apply sensibly in one part of the world to another part where they dont work due to other reasons. Governments do it all the time.

In my first posting I spoke about one particular motor that we use. Would PFC make sense on that?

Regards
Terry

#9 marke

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Posted 14 July 2007 - 08:45 PM

Hello Terry

In the case of the motor quoted in your first posting, if you apply the correct amount of power factor correction, you will reduce the current in that circuit. NB the motor will still draw the same current, but the circuit will draw less as the capacitor supplies the vars to the motor.
Is this of value to you? No, you are paying for KWHrs only and the KWHrs will not be affected. It will only be of value if you have some other reason to reduce the current such as circuit capacity or voltage drop. - It will not reduce your power bill.

Installations where a transformer is fully loaded and the power factor is less than 0.95, can be power factor corrected to reduce the transformer loading. This can allow additional circuits to be connected.

Best regards,

#10 rotomoulder

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Posted 15 July 2007 - 12:10 PM

QUOTE(marke @ Jul 14 2007, 11:45 PM) View Post

Hello Terry

In the case of the motor quoted in your first posting, if you apply the correct amount of power factor correction, you will reduce the current in that circuit. NB the motor will still draw the same current, but the circuit will draw less as the capacitor supplies the vars to the motor.
Is this of value to you? No, you are paying for KWHrs only and the KWHrs will not be affected. It will only be of value if you have some other reason to reduce the current such as circuit capacity or voltage drop. - It will not reduce your power bill.

Installations where a transformer is fully loaded and the power factor is less than 0.95, can be power factor corrected to reduce the transformer loading. This can allow additional circuits to be connected.

Best regards,


Thanks Marke
Both for the patience and the expertise.

Terry

#11 jraef

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Posted 15 July 2007 - 09:28 PM

QUOTE(rotomoulder @ Jul 14 2007, 01:54 AM) View Post

...
We had experts from the UK visit us and thats the reason for my posting. They also said I should use natural lighting to save power. When I worked out the costings it would take more than 10 yrs to recoup our expenditure. Even that is doubtful as the sky lights would have to be replaced at some point due to UV degradation.


Not to mention the additional heat gain from letting the sun shine inside. That was a ridiculous suggestion for a place such as Qatar! You were right to question it.

QUOTE
Its a case of applying laws that apply sensibly in one part of the world to another part where they dont work due to other reasons. Governments do it all the time.


Very true.

By the way, did someone pay for these "experts" to come in from the UK? If so, whatever they paid was probably too much.

The definition of "Expert":
Ex... (as in has-been)
...Spurt (as in a drip under pressure)
"He's not dead, he's just pinin' for the fjords!"

#12 rotomoulder

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Posted 16 July 2007 - 07:13 AM

QUOTE(jraef @ Jul 16 2007, 12:28 AM) View Post

Not to mention the additional heat gain from letting the sun shine inside. That was a ridiculous suggestion for a place such as Qatar! You were right to question it.
Very true.

By the way, did someone pay for these "experts" to come in from the UK? If so, whatever they paid was probably too much.

The definition of "Expert":
Ex... (as in has-been)
...Spurt (as in a drip under pressure)



The Qatar government paid the bill as it was part of an efficiency exercise they were involved with which probably worked well with other companies but not ours.
Thanks for all of your help.
Terry




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