October 15, 2020

Diesel Generator Specifications: kW, kVA, and Power Factor


A consistent power supply is very crucial for the smooth running of activities in any building. Connecting the building to the power grid is the primary solution. However, grid coverage experiences occasional blackouts or emergencies hence cutting electric supply. Besides, some places have no grid coverage, such as distant mining facilities and remote oil fields.

Diesel generators are used to deliver backup power and serve as permanent power solutions in the said areas. Therefore, it's necessary to understand the various specifications of a diesel generator and how they affect a generator's choice in different settings.

A genset operating within the conditions it was designed for will last longer and have higher efficiency. First things first, let see the relationship between kW(kilowatts), (kVA) Kilovolt-amperes, and (PF) power factor in generators.

Relationship between kW, kVA and Power Factor

  • Kilowatt (kW): This is the measure of the real power produced by the generator. This is the power utilized by electric appliances or equipment in the building.
  • Kilovolt-amperes(kVA) is the measure of apparent power, which includes the real power and reactive power(kVAR) drawn by appliances.
  • The proportion between real and apparent power gives us the power factor (PF) of a generator. For example, a commercial structure consuming 950kW and 1000kVA results in a power factor of 0.95 or 95%.

Both new generators and used generators have a nameplate indicating the values of each of the specs. Nevertheless, the operating conditions are dependent on the connected load size and not the generator itself. Having a proficient electrical engineer determining your building's power needs is recommended to ensure you acquire the correct unit.

Factors that Limit the Output of a New or Used Generator

The diesel engine driving the generator is the limiting factor of its maximum kW yield. Let’s consider a generator with an efficiency of say 95% driven by a 2000-hp diesel engine:

  • 2000 horsepower will provide energy equal to 1492 kW. Equating with the 95% efficiency rate, we get the maximum output as ~1417 kW.

Likewise, as the name suggests, kilovolt-amperes (kVA) hang on the voltage(V) and current(A) ranking of the generator. Drawing more power than the maximum kW overloads the engine while exceeding the kVA overwhelms the generator windings even if the kilowatt output is maintained below the maximum. So, disregarding either of them can damage the genset.

Given the kW and kVA stays below their respective rating, a generator can operate at an exceeded power factor without aftermath. The generator performs less efficiently if it works below the rated power factor.

Leading and Lagging Power Factor: How they Affect Generators

Leading and lagging are effects caused by unmatching voltage and current in a device. For instance, connecting a generator to a resistor results in a corresponding waveform on a digital meter, meaning that it has a 100% PF. On the other hand, most appliances will have unmatching waveforms signifying a PF of less than 100%.

  • Lagging: when a load has a higher voltage than current, we say it's lagging. Such loads are referred to as inductive (e.g., motors, transformers)
  • Leading: A device with a leading power factor means its current is ahead of the voltage value. These devices are called capacitive (e.g., capacitor banks, batteries)

The net effect of most buildings is a lagging power factor because devices are mostly inductive. Diesel generators, including large commercial generators, are specifically designed to handle this effect effectively. On the opposite effect (where a building has more capacitive equipment), the leading power factor causes an unstable voltage supply. And in such a case, the generator will automatically cut electricity supply to the building. Having the right unit for your installation is, therefore, imperative.

Which Generator is Fit for My Building?

After we've learned all this, you might be wondering which and where to get the right diesel generator. Worry no more! Power Systems Services has established a relationship with different leading generator dealers and vendors. Our team of experienced professionals is committed to delivering the best solution tailored specifically for your project. We deal with both new and used generators. Contact us today, and let's get started.