Generator Power Factor

Power Factor - facts vs fiction

generators (the electrical portion) are rated for VA - so with the powerfactor and the relevant watts, convert into the VA and then load it.

Not putting the prefix since I don't know it is VA or KVA or MVA...

all information on the name plate tells you its rated parameters. In the same way, the pf helps you to know the rated reactive power of your generator for a name plate that has the active or apparent values.

Gud question.. because we can control the power factor of generator by controlling the field excitation so why this parameter is mentioned on name plate of generator?

and plz answer one more thing that if we can control the power factor of generator so why don't we keep it unity?

The power factor of the generator is the power factor of the load itself. When the generator is running in parallel with the system, variation in the excitation will result in the variation of the reactive load supplied by the generator. In other words, this means a change in the power factor. But once again, this reflects the power factor of the load. However, when a single generator is running, any variation in the field excitation will vary the voltage and the pf remains the same as that of the connected running load. It is for this reason the generator rating is given in kVA.

In most of the cases generators are seldom run at UPF. A generator is usually overexcited in order to deliver reactive power to the system. The extent of running of the generator in UPF and leading power factor region will be available in generator capability curves. UPF and leading operation leads to cross magnetization and magnetization respectively, of the main field.

But my question is what does the name plate pf indicate? Does it refer to the thermal characteristics of the generator stator winding?

As I mentioned, the KVA ratings are the ones that limit the generator (in terms of copper)

http://www.frontierpower.ca/library/generatorratings.htm

You do rise a very good point here and definately you almost got the answer to your question. the gen set excitation is set to achieve as unity pf as possible. but because in the practical world, we NEVER have linear/purely resistive loads, this's hard to achieve even when they are testing the gen set in the factory at its nominal values i.e rated load. Reason: we have MAINLY the thermal characteristics of the generator bring in the extra elements of capacitance and inductance which change the pf from unity, so this PF and not the UPF will be placed on the name plate. moreso, this helps the design engineer to give allowance for this extra current (the one which goes reactive) so that he determines the right cable sizes for the generator.

This has been covered innumerable times

You do not control generator power factor.

The pf is decided by load and not generator. You feed the load demanded reactive power through generator excitation control. In the return, the generator coils carry excess current.

Additionally, prime mover is rated for a certain KW, and just by improving the pf, a 500 MVA Turbo-generator will not become a 500MW TG Set. The Turbine will not be able to cater to this need.

The significance of the power factor on the name plate of the generator enables you to know the portion of the apparent power (kva) of the generator that is converted to active power (kw) of the generator, or it tells you the ratio of the active power(kw) of the generator to the apparent power(kva).

PF=KW/KVA

Patrick Whowha

There is limitation on regulating the excitation of field. That is why the pf is mentioned on the generator name plate.

In a clearer language,the the importance of the power factor metioned on the name plate of a generator enable someone to know the ratio of active power to the apparent power of the generator, or it indicates the extent to which apparent power of the generator is converted into active power.

Patrick Whowha

The significance is only in knowing the kW or HP loading on the prime mover. I have an interseting paper on this topic. If you can mail me your ID, I will share the same with you.

pl mail it to colin_mng@yahoo.co.in

I think the pf on the gen nameplate,apart from telling us how much of useful power is required,it goes a long way to tell us that the gen can perform better when the rated pf is maintained under load conditions and as such should be maintained on that pf rating.

For example,if the gen is rated at 0.8pf and under load condition,it drops to 0.6 or 0.7 because of much inductive loads,if not corrected and maitained at 0.8pf,the generator will not be performing at its best and would also consume more fuel/diesel than its rated average consumption.

All this has to do with the performance of the gen and the need to maintain the generator rated power factor for best performance and long life span.

Patrick Whowha

Reactive power demand on a generator or a drop in the active loading of the gen-set will lead the pf to drop. This will not lead to more consumption of fuel by the prime mover.

If power factor correction techniques are applied it will relieve the generator from supplying certain portion of the reactive load and thereby better utilizing the generator capacity to supply more active power loadings within its full load current rating.