Why the generating station rating is in KW though the rating of generators in KVA?

Answer 1

The volt ampere is a measurement of apparent power, while the watt is a measurement of true power. Apparent power is simply the product of voltage and current; the output of a transformer, therefore, is the product of its rated secondary voltage and its rated secondary current -i.e. the apparent power of the transformer. The power supplied, in watts, is determined by the power factor of the load, so there is little point in rating a transformer in watts, as the designer has no means of knowing the power factor of the load it is to supply.

Answer 2

The major losses in a generator are copper loss and core loss. In order to express the rating of a machine, we've to include the losses too. Copper loss (I2R) depends on the current flowing through the machine and core loss or insulation loss depends on the voltage rating of the machine. So the most convenient way of expressing the rating of a generator (also transformer) is to express in volt amperes. Hence the rating of a generator is expressed in KVA and for a transformer it is also KVA. Very large Transformers will also be expressed in MVA.

Answer 3

A small AC generator rating may be specified in kW, because that is the maximum useful (real) power that can be produced by that generator. If the purpose of the generator is to run small power tools, some lights, maybe a TV or grill, this is a more useful value for the Average Joe to know.

On bigger generators, KVA is usually specified with a specific power factor; Usually a power curve is provided (or can be requested) with these showing their operating capabilities at different power factors. At utility sizes, this is much more useful information (than just a kW or MW rating), as the real and reactive power must be controlled on the power system to keep everything in a stable state.

Answer 4

KVA is the equivalent of Kw. KVA=Kw. Kw=KVA. Volts multiplied by Amps equals power which is measured in Watts.

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There are two losses in electrical generation. One is copper loss which depends on current and the other is iron loss which depends on voltage. These two factors are not affected by the power factor. This is why the equipment is rated in KVA and not KW. Single phase KVA = Amps x Volts/1000. Single phase KW = Amps x Volts x pf/1000. 3 phase KVA = Amps x Volts x 1.73/1000. 3 phase KW = Amps x Volts x 1.73 x pf/1000.

Answer 5

generators are limited by the amount of power available

1a at 1200v, 10a at 120V, 100A 12v all the same true power for resistive load

generators usually fixed voltage so give 120v constantly

almost no current with inductive load lots of current with capacitive load

but will usually stall the motor when power limit is reached

Answer 6

Generators can be rated in kW or kVA at a certain power factor. Synchronous generators have several limitations depending on how much power is being exported. At unity power factor, they can only generate real kW equivalent to the power provided by the prime mover. If generating VARs with a lagging power factor (pushing reactive power out of the generator), the generator runs into a limit of heating of the field winding (due to excessive field current). If generating VARs in a leading power factor (pulling reactive power into the generator), the generator runs into several other limits - end rotor heating, or stability. This is why the power factor should be specified regardless of whether the generator is rated in kW or kVA. From an economic perspective, generators typically make money off the real power (kW) generated, not the reactive power, so this may be more important in some instances.