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Power Factor On Transmission Lines


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#1 knjelectric

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Posted 23 July 2010 - 01:19 PM

I would appreciate an explanation of power factor quality on end user transmission lines. In theory a strictly resistive circuit(overhead transmission line)would have a power factor of 1(unity). When inductance is introduced(motor,transformer) the power factor is lowered. Can the incoming line p.f. be measured without a load from the customer, in other words I get no reading from my 3 phase summing pf,kw ka meter from the incoming line and can only "see" anything when there is a load. I am interested in what the power company is actually delivering. The problem I have is I pf corrected a business 1 1/2 years ago and they recently started having problems again. The only thing I can see that is different is a machine shop(motors) 2 blocks away went out of business at the same time. There are 2 across the line cap. banks between these customers. Are the cap. banks pushing the current to lead because there are now overcompensating for the bad phase angle they had? I should mention that I corrected 3 individual large loads to take this company over 80% pf (consumers energy minimum benchmark).If I had any hair(i'm bald) I would be tearing it out by the roots! Please respond if you can enlighten me. Jim

#2 knjelectric

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Posted 02 August 2010 - 12:21 PM

QUOTE (knjelectric @ Jul 23 2010, 02:19 PM) <{POST_SNAPBACK}>
I would appreciate an explanation of power factor quality on end user transmission lines. In theory a strictly resistive circuit(overhead transmission line)would have a power factor of 1(unity). When inductance is introduced(motor,transformer) the power factor is lowered. Can the incoming line p.f. be measured without a load from the customer, in other words I get no reading from my 3 phase summing pf,kw ka meter from the incoming line and can only "see" anything when there is a load. I am interested in what the power company is actually delivering. The problem I have is I pf corrected a business 1 1/2 years ago and they recently started having problems again. The only thing I can see that is different is a machine shop(motors) 2 blocks away went out of business at the same time. There are 2 across the line cap. banks between these customers. Are the cap. banks pushing the current to lead because there are now overcompensating for the bad phase angle they had? I should mention that I corrected 3 individual large loads to take this company over 80% pf (consumers energy minimum benchmark).If I had any hair(i'm bald) I would be tearing it out by the roots! Please respond if you can enlighten me. Jim


#3 marke

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Posted 14 August 2010 - 11:08 PM

Hello knjelectric

The power factor at any point is determined by the supply voltage at that point and the current passing through that point.
The power factor of the lines and cables on the supply side do not affect the readings at that point.

The measured power factor only applies to the down stream connections from the point of measurement.

If the supply upstream of your connection is over corrected, it will not affect your metering at all, but it could cause the voltage to be higher than it should be. The other potential is that there ay be some resonance issues when the load is very low.

Best regards,
Mark.




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