from the power system department...
power factor changes
 Posted by none on 6 September, 2012 - 10:50 pm
pls tell me how power factor changes according to various type of load and voltage. So that I will know about where power factor panel may be installed.

 Posted by CSA on 8 September, 2012 - 1:42 pm
I would suggest you consult some texts and/or electrical reference materials about the relationship between synchronous machine terminal voltage and power factor.

In the meantime, you likely already know that excitation is directly proportion to terminal voltage on a synchronous machine (motor or generator) operating at synchronous speed. (The voltage of a synchronous machine is proportional to speed and excitation, but since the speed is--or should be--constant, the only variable is excitation.)

Real power (watts, kw, MW) is directly proportional to the amount of torque being produced by the synchronous motor or the amount of torque being supplied to the synchronous generator.

The amount of VArs (be very careful when using the term "reactive power on control.com; you are likely to be chastised for doing so in a very brief and nebulous manner) flowing in a synchronous machine is directly proportional to the excitation level of the machine.

[Never mind that one definition of 'power' is V*A (Volts * Amps) and that VAr stands for 'Volt-Amperes reactive', we can't call VAr reactive "power" here on control.com, even though the rest of the industrialized world does so. You have been warned.]

For the purposes of this discussion, I'm NOT referring to so-called "island" installations of small real power loads with reactive components and one or two prime movers and generators. This discussion is with respect to larger grids of multiple (tens; hundreds; thousands) of generators and their prime movers, and synchronous motors.

If, on a synchronous machine at any load (watts, kw, MW), the excitation is such that the machine terminal voltage is equal to the voltage of the grid/source with which is connected the power factor will be 1.0. That is, the VAr meter will be at 0.0 VAr (or kVAr or MVAr) and the power factor meter will be at 1.0.

If, at any load the excitation is increased above the level required to maintain the machine terminal voltage equal to the grid/source voltage then the power factor meter will decrease from 1.0 in the Lagging direction, and the VAr meter will increase in the Lagging direction.

If, at any load the excitation is decreased below the level require to maintain the machine terminal voltage equal to the grid/source voltage then the power factor meter will decrease from 1.0 in the Leading direction, and VAr meter will increase in the Leading direction.

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