Effect of negative and positive reactive power on the generator
Effect of negative and positive reactive power on the generator
(OP)
Dear all,
can you please explain to me about the reactive power, especially on what it does to the generator when the value is positive or negative. And also about the capacitive and inductive load.
Thanks alot.
can you please explain to me about the reactive power, especially on what it does to the generator when the value is positive or negative. And also about the capacitive and inductive load.
Thanks alot.






RE: Effect of negative and positive reactive power on the generator
Initially, I found it a little confusing to understand. Now I am fine with this convention.
RE: Effect of negative and positive reactive power on the generator
the photo here says it all.
[img https://image.slidesharecdn.com/powerplanthorrorst...]
RE: Effect of negative and positive reactive power on the generator
A capacitive load supplies extra excitation and tends to drive the voltage up. The AVR will cut back its output to compensate for this.
An inductive load tends to draw the voltage down. The AVR will increase its output to compensate for this.
With a paralleled set, the load still determines the total VARs but you may adjust the VAR sharing between sets by adjusting the excitation.
Generally performance is best when all sets are run at the same PF.
There are important exceptions.
I have seen diesel sets run at the end of a long heavily loaded transmission line run with very little kW output to save fuel, but heavily overexcited to supply the VAR losses in the transmission line and raise the voltage at the terminal end of the line.
The capacity of many transmission lines is limited not by the ampacity of the line but by the ability of the On Load Tap Changers to compensate for the voltage drop in the transmission line.
By supplying VARs at the terminal end of the line to compensate or offset the reactive part of the line losses, the capacity of the line may be increased.
One of the limits on generator output is the heating of the stator by I2R losses. The more reactive current in the stator the less capacity for real power or kW, until the set reaches the rotor heating limit.
Bill
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"Why not the best?"
Jimmy Carter
RE: Effect of negative and positive reactive power on the generator
For stability, generators are locked my tightly to the system when they are supply vars, which means they are generating at a high voltage.
RE: Effect of negative and positive reactive power on the generator
Cheers,
Dave
RE: Effect of negative and positive reactive power on the generator
Wolf posted a couple of good links in thread238-255286: Operating Curves For generators which are still alive, and the one I mentioned above is available at http://files.engineering.com/getfile.aspx?folder=2...