Generator, reactive power
Generator, reactive power
(OP)
If a generator is at 0.95 power factor, and importing reactive power are they producing reduced active power?
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Generator, reactive power
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RE: Generator, reactive power
RE: Generator, reactive power
RE: Generator, reactive power
The KVA rating is generally based on a power factor of 0.80.
As long as the generator is operating above 0.80 PF full reactive power should be available.
PS. In most instances a generator operating at 0.95 power factor will be exporting reactive power.
Bill
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"Why not the best?"
Jimmy Carter
RE: Generator, reactive power
The kW output is the same in either case. As long as the turbine or engine kW output does not change, the generator kW output will not change for various power factors, neglecting the minor increase in losses at lower power factors due to higher KVA.
Example, MVA at 0.95 power factor = 105.2% of the MVA at 1.0 pf for the same MW. The I^2R losses will be 10.8% higher at 0.95 power factor but still small in comparision to the output. From a chart for a 157 MVA gas turbine generator, at 150 MW 1.0 pf losses are about 1880 kW and 2020 kW at 0.95 power factor. The increase of 140 kW is less than 0.1% of MW output.
RE: Generator, reactive power
David Castor
www.cvoes.com
RE: Generator, reactive power
You need to reduce the active power output if you want to push the unit to its mvar leading limit and remain within the reactive capability curve. If you don't reduce the active power output you can reach the under-excited or stator winding heating limit.
May you grow up to be righteous, may you grow up to be true...
RE: Generator, reactive power
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If we learn from our mistakes I'm getting a great education!
RE: Generator, reactive power
Also the power capability limits of a generator are mostly thermal related limits. If the system voltage is raised, the current is lowered and the power capability can be
extended.
ScottyUK,
A bit off topic:) but, could you please let me know why the power stations in the UK would tap GSU tx in order to modify reactive output, insted of instructing the AVR directly?
I understand the reactive output might be limited by the voltage on the 24 kV busbar where the generator is connected and by tapping you extend the margin of reactive power output, but I believe the tap changer is one of the weakest points of a tx.
May you grow up to be righteous, may you grow up to be true...
RE: Generator, reactive power
That is certainly not always the case. It will depend on the unit size. I suspect the majority of hydro generators are not water-cooled.
David Castor
www.cvoes.com
RE: Generator, reactive power
Our generating plants use the OLTC to provide coarse control of the reactive load and the AVR to provide fine control. I've never really considered why this is the case! My opinion is that the UK's Grid Code is quite demanding in requiring the machine capability to be available over a reasonably wide variation in terminal voltage, so the OLTC is a means of providing this while allowing the machine to maintain reasonably constant terminal voltage to keep away from the V/Hz limiter and the under-excitation limiter. Also the UK's grid is quite stiff because of the small geographic area and relatively large number of generating sites in that area, so the GSU transformer has a relatively high impedance to control system fault levels. A high GSU transformer impedance makes an OLTC almost mandatory to achieve a wide reactive capability.
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If we learn from our mistakes I'm getting a great education!
RE: Generator, reactive power
rasevskii