What is the Difference Between Active and Reactive Power?

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Difference Between Active and Reactive Power

The difference between active and reactive power is that active power, measured in kilowatts (kW), performs useful work in electrical systems like lighting or heating. Whereas, reactive power, measured in kilovolt-amperes reactive (kVAR), sustains electromagnetic fields, important for voltage stability and transmission efficiency, but does not directly contribute to useful work output like active power.

What is Active Power?

Active power, also called real or true power, is the usable part of electrical energy in an AC circuit (measured in watts). It’s the power that gets consumed by devices like lights or motors. Unlike active power, some electrical energy flows back and forth without doing any work. This is called reactive power. To calculate active power, you multiply the voltage, current, and a factor called power factor (cosine of the phase angle between voltage and current). A perfect power factor of 1 means all energy is consumed (ideal scenario).In simpler terms, active power is the electricity you pay for, while reactive power contributes to inefficiencies.

What is Reactive Power?

Reactive power (VAR) isn’t directly used by your devices, but it’s like a hidden force in AC circuits. It flows back and forth due to inductors and capacitors, and while not useful itself, it’s needed to maintain voltage and current. The downside? It creates inefficiencies by inflating apparent power, requiring more current flow for the same work.

What is the Difference Between Active and Reactive Power

Active power represents the actual power consumed by electrical devices to perform useful work such as lighting or heating. Whereas, reactive power doesn’t perform any useful work but supports the transmission of active power by maintaining electromagnetic fields in electrical systems. While active power directly contributes to tasks, reactive power is important for voltage stability and efficient power transmission, ensuring that electrical systems function properly even though it doesn’t directly result in useful work output. Here we have mentioned the additional list of differences between Active and Reactive Power

Basis of Difference
Active PowerReactive Power
DefinitionThe fraction of total electric power that is used to do useful work and is consumed in the electric circuit is known as active power.The fraction of total power that flows back and forth from source to load in the electric circuit is called reactive power.
Alternate nameActive power is also known as real power or true power or useful power or watt-full power.Reactive power is also called imaginary power or useless power or watt-less power.
NotationActive power is usually denoted by the letter “P”.Reactive power is usually denoted by “Q”.
Unit of measurementActive power is measured in Watts (W). The larger units of active power are kilowatt (kW), megawatt (MW), gigawatt (GW), etc.Reactive power is measured in VAr (Volt-Ampere Reactive). The larger units of reactive power are kVAr, MVAr, etc.
Measuring instrumentA measuring device called a wattmeter is used to measure active power in the electric circuit.The reactive power in an electrical circuit is measured by using VAr meter.
Direction of flowThe active power always flows in one direction, i.e., from source to load.The reactive power flows in both directions between the source and load.
ExistenceThe active power exists in both AC and DC circuits.The reactive power exists only in AC circuits.
Existence in a pure resistive circuitIn a resistive circuit, the total power is equal to active power and is dissipated by the resistor in the form of heat.
There is no reactive power in case of a resistive circuit.
Existence of pure capacitive circuitThe active power is zero in a pure capacitive circuit. This means the pure capacitive circuit does not consume any active power. It is because the voltage and current are 90° out of phase in a pure capacitive circuit.
There is leading reactive power in a pure capacitive circuit. It is because the current leads the voltage by 90° in a pure capacitive circuit.
FunctionActive power is the amount of power that does useful work in the electric circuit. It is the power that is converted into other forms of energy such as mechanical energy, light, heat, etc.
Reactive power does no useful work in the circuit. However, its function in the circuit is to produce the required magnetic and electric flux.
Phase relation with voltageThe active power component is in phase with the voltage.
The reactive power component is 90° out of phase with respect to voltage.
ApplicationsActive power is useful to produce torque in motors, light in lamps, heat in heaters, etc.Reactive power is mainly used to measure the power factor of an electric circuit. It also plays a vital role in electrical appliances to produce the required magnetic and electric fields.

Application of  Active and Reactive Power in Real Life

Imagine electricity as water flowing through a pipe. Active power is the water you use, to power lights, devices, and appliances (watts). Reactive power is like pressure; it doesn’t do work but keeps things flowing (VAR). Too much pressure (reactive power) wastes energy and strains the system. We use capacitors and inductors to balance them, like adjusting a valve for smooth water flow. This saves energy and keeps the electricity grid healthy. Below we have stated some of the important real-life applications of these terms:

  • Active Power (Watts)- This is the power used by appliances (lights, motors) for their actual function (lighting, heating, etc.).
  • Reactive Power (VAR)- It helps motors and transformers work but isn’t used directly.
  • Apparent Power (VA) – Combines active and reactive power, showing total electrical demand.
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What is the difference between active power and reactive power?

Active power is the real power consumed by the load, while reactive power is the power oscillating between source and load.

Is active and reactive the same?

No, active and reactive power are not the same. Active power is the real power used for work, while reactive power is non-working power.

What is reactive power in simple terms?

Reactive power is the power needed to sustain the electric and magnetic fields in electrical systems, without performing useful work.

What is the difference between active and reactive power?

Active power is measured in kilowatts (kW), while reactive power is measured in kilovolt-amperes reactive (kVAR).

This was all about the “Difference Between Active and Reactive Power”.  For more such informative blogs, check out our Study Material Section, you can learn more about us by visiting our  Indian exams page.

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