Difference in kW ratings

FAQ: Difference in kW ratings

Posted in: Diesel Generators Engine & Drivetrain Performance

People buying diesel generators must be familiar with the kW ratings in relation to what amount of power they need their diesel generator to provide. Buying generators with less power than what is needed could be disastrous. On the other hand, you don’t want to waste money buying a commercial diesel power generator that outputs more power than you need.

There are key terms to understand when it comes to shopping diesel power generators for sale. Buyers often hear of kW or kilowatt and kVA or kilovolt-ampere.

Kilowatt (kW) refers to the unit of real power while kilovolt-ampere (kVA) refers to the unit of apparent power, also known as the real power added with re-active power. The difference between the kilowatt and the kilovolt-ampere is called the power factor of the generator. The power factor is an approximate value with the kilovolt-ampere having higher value than the kilowatt value. The power factor is typically measured as 0.8.

Kilowatt (kW) is used when buying industrial generators in the United States while the rest of the world uses kilovolt-ampere (kVA). The kilowatt (kW) rating refers to the power output of a generator based on the engine’s horsepower. The kilovolt-ampere (kVA) rating of a generator is determined by multiplying its engine’s horsepower by .746. Generators typically show both ratings.  The following formula will determine kilowatt and kilovolt-ampere ratio:

            .8(pf) x 625 (kVA) = 500 kW

The connected load of an industrial powered generator determines its power factor, which is the ratio between kilowatts (kW) and kilovolt-ampere (kVA) of the electrical load. A generator can transfer energy more efficiently to its connected load when it has high power factor. On the other hand, a generator with lower power factor cannot efficiently transfer energy to its connected load, hence making it uneconomical to operate.

Different Power Ratings

Diesel generator power ratings are classified as standby, continuous, and prime power ratings. A standby power generator, popular for power outages, is intended for emergency situations. It is used only for the duration of the emergency, such as an outage or power transmission breakdown. 

Generators with prime power ratings have unlimited run time. They are generators that are used as the primary source of power as differentiated from standby generators that are sparingly used.

Generators with continuous power ratings are almost the same with prime power generators but are characterized by a base load rating. They can provide a continuous supply of power but cannot have variable loads. They also do not have the ability to handle any overload.

Buy exactly what you need

When buying a generator, one has to clearly define the purpose for which it will be needed. After that, buy your industrial generator in accordance with what will be expected from the unit.

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