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Reactive Power and Load or Line Impedance

06/25/2009 11:13 PM

" The reactive power in power system tends to be inductive during heavy load and capacitive during light load"

Can any one give commment to above statement?

I am wondering the change of reactive power type was due to the variation of load or the line impedance of transmission line. Can anyone tell me??

Thanks in advance.

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Guru

Join Date: Mar 2007
Location: India
Posts: 2593
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#1

Re: Reactive power in power system

06/26/2009 3:12 AM

Your second guess is correct.

The transmission lines are basically capacitive and the loads are in general inductive.

So as the load increases, the inductive portion increases, the capacitive portion remains constant.

http://www.allaboutcircuits.com/vol_2/chpt_14/3.html

http://en.wikipedia.org/wiki/Transmission_line

especially

http://www.siemens.co.in/en/about_us/index/our_business_segments/energy/power_transmission_and_distribution/introduction.htm

the portion under heading "Shunt Inductive Compensation"

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Guru
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Location: Nashville
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#2
In reply to #1

Re: Reactive power in power system

06/26/2009 6:18 PM

SB Quote " The transmission lines are basically capacitive and the loads are in general inductive."

I think I am going to disagree with your statement as it is posted. Transmission lines are mostly R + XL. There is shunt capacitive reactance between the conductors but its magnitude is much higher than that of the inductive reactance and many times it is neglected. If you look at the link below, the tables shows Xc with a value much greater that Xl. If you are including the capacitors that are install on the system for PF correction and reduction in line loss, then you statement is correct. The loading on a substation during heavy loads may be inductive and capacitive during light loads. This is because the correcting capacitors are still online and the inductive loads are not.

http://www.cable.alcan.com/NR/rdonlyres/BC388B10-A9C3-45B6-AA90-F5A9BA9D203D/0/ACSRweb.pdf

Guru

Join Date: Mar 2007
Location: India
Posts: 2593
Good Answers: 102
#3
In reply to #2

Re: Reactive power in power system

06/27/2009 12:29 PM

You are right, in general (as usual)

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