What does kVA
When looking at generators you will undoubtedly hear various power ratings expressed in different forms , such as Watts, Kilowatts, Amps, Volts , Kilowatt Mechanical , Kilo-volt-amperes… Most of these ratings are well known and often you will see Amps or Watts on many electrical appliances in your home however the term that isn’t as well known outside the power generation industry is kVA . kVA stands for Kilo-volt-amperes – a term used for the rating of an electrical circuit. kVA is the product of the circuits maximum current and voltage rating. It is also known as Apparent Power.
There are three factors that we need to look at: Apparent Power, Actual Power and the Power Factor.
Apparent Power (kVA)
kVA (Kilo-volt-amperes)is a measure of apparent power. It describes the total amount of power being used by a system, for example in a 100% efficient system the kW would equal kVA precisely. However in reality electrical systems are not 100% efficient and so not all of the systems apparent power is being output.
Let’s start with the basics: 1 kVA is equal to 1,000 Volt Amps. A Volt is a measurement of electrical pressure and an Amp is a measurement of electrical current. The term apparent power is equal to the product of the Volts and Amps.
Example: A 30 kVA 3 phase generator is capable of producing 10 kVA per phase or approximately 43 Amps per phase in a 415/240V system.
Actual Power (kW)
kW ( Kilowatt) is actual power or real power, it is the amount of power that is converted into an output
Power Factor (PF)
Power Factor is only relevant in AC circuits and in its simplest form is the ratio of kW to kVA. Thus the ratio is always a number between 0 and 1. Diesel Generators have a power factor of 0.8. This makes it nice and easy to convert kVA to kW because you know the efficiency level of the electrical system in question.
Power Factor can be represented by a clock face, where Power Factor 1 (1.00) is the 12 o’clock position. 0 can be either side of the 12 o’clock position, either at 9 o’clock or 3 o’clock depending on which way the kVArs are flowing in reference to the kW. The number isn’t signed and is usually accompanied by leading or lagging i.e the current is leading or lagging the voltage.
Power Factor is caused by kVArs which are signed. When a generator is producing ( positive) kVArs the load is inductive, such as a motor, and thus the current is lagging the voltage. Terms used to explain this are inductive, lagging and over excitation.
When a generator is absorbing (Negative) kVArs the load is capacitive such as fluorescent lighting and long cable runs, and thus the current is leading the voltage. Terms used to explain this are capacitive, leading and under excitation.
If the generator is feeding a purely resistive load, such as a heating element, there are no kVArs and the Power Factor is 1, also known as unity. This is when kW=kVA.
kVArs are always at 90 Deg to the kW and can be represented by the below diagram:
The cosine of the angle between the kVA and kW (cos ф) is the Power Factor.
The kW to kVA Formula:
- Apparent power (kVA) x power factor (pf) = actual power (kW)
e.g. 100 kVA x 0.8 = 80 kW
- The formula for converting kW into kVA is:
Actual power (kW) / power factor (pf) = apparent power (kVA)