Trystan Casey
When it comes to electricity, kVA and kW are both units used to measure power. While both values express power, they are different. kW (kilowatts) is the unit used to measure actual power or the amount of power that is converted into useful working output. This tells you how much power is required to run electrical appliances, and this is why they are rated in kW. kVA (kilo Volts Amperes) on the other hand, is used to measure apparent power or the total amount of power in use in a system. In a 100% efficient system, kW will be equal to kVA. However, electrical systems are rarely 100% efficient, so only a portion of kVA will be used for useful work output.
| Characteristics | Values |
|---|---|
| Full Form | Kilo-Volt-Amperes (kVA) |
| Full Form | Kilowatt (kW) |
| Usage | Outside of the generator industry, the term Kilo-Volt-Amperes (kVA) is often met with confusion. |
| Usage | Kilowatt (kW) is what we learnt at school, it’s how our electrical items at home are rated and it’s the unit we see on our electricity bill. |
| Definition | kVA is known as the ‘apparent power’ of a particular circuit or electrical system. kVA tells you the total amount of power in use in a system. |
| Definition | kW (kilowatts), ‘actual power’, is the amount of power that is converted into useful working output. |
| Calculation | The relationship between kW and kVA is described as kVA=kW/power factor. |
| Calculation | The power factor, unless it is defined and known, is an approximate value which is typically 0.8. |
| Calculation | kW is the useful power that actually performs the work, and utility companies often charge customers based on the kW usage. |
| Calculation | A power factor of 1 (or 100%) means all the power is being used effectively as real power, and in this case, kW = kVA. |
| Calculation | If the power factor is less than 1, some of the power is wasted as reactive power, and kW will be less than kVA. |
| Example | If a generator is rated at 100 kVA and has a power factor of 0.8, the real power it can supply is: kW=100×0.8=80 kW. |
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What You'll Learn
Kilowatts (kW) represent real power
Kilowatts are used to measure the output of engines and power plants. For example, a car with a 100-horsepower engine uses around 74 kW of power. Kilowatts are also used to measure the capacity of electrical batteries and solar panels. A kilowatt-hour (kWh) is a unit of energy. It measures the amount of energy an appliance or device consumes in an hour.
The kilowatt was first used to measure the power output of steam engines. Today, it is used to measure the power output of all kinds of machines and devices. For instance, a standard 100-watt light bulb uses about 0.09 kilowatts (90 watts) of power. Kilowatts are also used to rate electrical appliances and devices, such as air conditioners, refrigerators, and electric stoves.
Kilowatts are most commonly used when referring to generators in the United States. This is why kW is the number you should be concerned about when choosing a diesel generator. The kW tells you how much power is required to run your appliances.
The relationship between kW and kVA can be described as: kVA=kW/power factor. The power factor is defined as the cosine of the angle between voltage and current.
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Kilo Volts Amperes (kVA) represent apparent power
Kilo Volts Amperes (kVA) is a term used to describe the 'apparent power' of an electrical system or circuit. Apparent power refers to the total amount of power in use within a system, including both real power and reactive power. Real power is the power that is converted into useful work output, while reactive power is the power that is wasted due to inefficiencies in the system.
KVA is calculated as the product of the root mean square (RMS) value of the current and voltage in a system. It is important when sizing electrical equipment, such as generators, transformers, and uninterruptible power supply (UPS) systems. These systems must be able to handle both the real and reactive power, so knowing the total load, or apparent power, is crucial for selecting the appropriately sized equipment.
The relationship between kVA and kW (kilowatts) is defined by the power factor, which measures the efficiency of power use in the system. The power factor is the cosine of the angle between the voltage and current waveforms and typically has a value between 0 and 1 or is expressed as a percentage. In a perfectly efficient system with a power factor of 1, the kVA would be equal to the kW. However, in reality, electrical systems are not 100% efficient, so only a portion of the kVA is converted into useful kW.
To illustrate this, consider a generator with a rating of 100 kVA and a power factor of 0.8. This means that the real power it can supply is 80 kW (100 x 0.8 = 80). So, while the generator can provide 100 kVA of apparent power, only 80 kW of that is doing useful work, and the remaining 20 kVA is lost as reactive power.
In summary, kVA represents the total power in an electrical system, while kW represents the useful power that is actually performing work. The power factor determines how efficiently kVA is converted into kW, and the closer the power factor is to 1, the more efficient the system is in utilising the apparent power.
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kW is used in the US, kVA is used elsewhere
While both kW and kVA express electric power, they are quite different. kW, or kilowatts, is the amount of power that is converted into useful working output. In other words, it is the power that does valid work. This is why all electrical appliances are rated in kW. kVA, or kilovolt-amperes, on the other hand, is the apparent power of a particular circuit or electrical system. It tells you the total amount of power in use in a system.
In a 100% efficient system, kW would be equal to kVA. However, electrical systems are never 100% efficient. Only a portion of kVA is used for useful work output. The relationship between kW and kVA can be described as: kVA x power factor (pf) = kW. The power factor, unless it is defined and known, is an approximate value which is typically 0.8. The closer the power factor is to 1, the more efficient a particular device’s electrical usage will be.
When it comes to generators, you will find that any good generator manufacturer will use both kW and kVA. kW is most commonly used when referring to generators in the United States, while the majority of the rest of the world typically uses kVA as the primary value when referencing diesel generator sets. Companies will predominantly advertise their generators in kVA, but they will be able to provide a generator in kW if requested.
The difference in usage between kW and kVA can also be seen in electrical circuits due to the difference between AC and DC circuits. In a DC circuit, the kW and kVA are equal because the current does not get out of phase. However, in an AC circuit, there are several differences. For solving real power, we need a nebulous value which varies depending on electrical appliances.
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kVA = kW/power factor
KVA and kW are both units of electric power. kW, or kilowatts, is the unit of 'actual power' or 'real power' and measures the amount of power that is converted into useful working output. This tells you how much power is required to run electrical appliances, and so all electrical appliances are rated in kW. kVA, or kilovolt-amperes, is the unit of 'apparent power' and tells you the total amount of power in use in a system. In other words, it is the amount of power being demanded by the utility.
In a 100% efficient system, kW would be equal to kVA. However, electrical systems are never 100% efficient. This means that only a portion of kVA will be used for useful work output. The relationship between kW and kVA can be expressed as kVA = kW/power factor. Power factor is the ratio of working power (kW) to apparent power (kVA). It is a measure of how effectively the incoming power is being used in the electrical system.
The power factor is typically 0.8, though this is an approximate value unless it is defined and known. The closer the power factor is to 1, the more efficient the electrical system. In other words, the closer the power factor is to 1, the more efficiently kVA is being converted into useful kW. In a DC circuit, the power factor is 1, and so kW and kVA are equal.
To give a tangible example of this relationship, consider a glass of beer. The beer is kW, or active power—it is the liquid beer that is useful and does work. The foam is kVAR, or reactive power—it is wasted power that does not do any work. The glass is kVA, or apparent power—it is the demand power, or the power being delivered by the utility.
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kW is the power used to perform work
Kilowatts (kW) and kilo-volt amperes (kVA) are two different units of measurement used to describe electrical power. While both values express power, they are quite different. kW is the unit used to measure actual power or real power—that is, the amount of power that is converted into useful working output. This tells you the amount of actual power that does valid work. This is why all electrical appliances are rated in kW, so you know exactly how much power is required to run them.
KW is the number you should be concerned about when choosing a generator. It is a measure of how much power an electric appliance consumes and is equal to one thousand watts of electrical power. For example, if you use a 100-watt device, such as a plasma TV, you would have to watch TV for 10 hours to reach 1 kilowatt-hour (kWh).
The relationship between kW and kVA is described as: kVA=kW/power factor. The power factor is an approximate value that is typically 0.8. The closer the power factor is to 1, the more efficient a particular device’s electrical usage will be. To put it simply, the total contents of your pint glass (liquid and foam) are the kVA, but only the liquid part of your beer is actually useful for quenching your thirst—this is the kW. The better the bartender (the more efficient the electrical system and the power factor), then the more beer (kW) you get.
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Frequently asked questions
kVA stands for kilovolt-ampere and is a unit of apparent power. It measures the total power consumed by a device or system, including both real power (kW) and reactive power.
kW stands for kilowatt and is a unit of real power. It measures the amount of power that is converted into a useful output, such as running a motor, lighting, or heating.
The main difference between kVA and kW is that kVA measures the total power in a system, while kW measures the amount of power that is actually used or converted into useful work.
kVA is important when sizing electrical equipment, such as generators, as they need to supply the total apparent power (both real and reactive power).
To convert between kVA and kW, you need to know the efficiency or power factor of the electrical system. The formula for converting kVA to kW is kVA = kW / power factor.
