Electrical Power- Active, Reactive and Apparent Power

Electrical Power

Electrical power is an important aspect of any electrical and electronic circuits. In this article, we will discuss all about Electrical power and its significance.

What is Electrical Power

In general science power is simply defined as the capacity to do work. In other words, it is defined as the rate of doing work. Whereas In electrical engineering, Electrical power is the rate per unit of time at which the amount of electrical energy is transformed into some other form of energy (such as heat, light, mechanical power, etc.). Electrical power is one of the key concepts associated with Electrical Engineering.

Mathematically, Electrical power is defined as the product of voltage drop across the electrical element in the circuit and current flowing through it. It is measured in terms of Electrical Energy per unit time.

Units of Electrical Power

When we talk about Electrical Power then it is considered as Active power consumed by the circuit element. So the unit of Electrical power (Active power) is Watt or joule per second.

Watt is the SI unit of the power which is defined as the rate of conversion of 1-joule electrical energy per unit second.

If we assume  V = 1 volt,  I = 1 Amp.
Then Electrical power (P) = V*I = 1*1 = 1 Watt

Hence the Power consumed in an electrical circuit is said to be 1 watt if one ampere current flows through the circuit when a potential difference of one volt is maintained across it.

Watt is a smaller unit of power. Whereas a larger unit of Electrical power is kW, MW, GW, etc.

1 kW = 1000 Watt

Types of Electrical Power

The classification of Electrical power depends on the nature of the current. So electrical power is mainly classified into two types.
  • DC Power: Power consumed in the DC circuit is known as DC power. It is produced by a fuel cell, batteries, DC generators, etc. Mathematically DC power is defined as the product of voltage and current through the circuit.

    So,     P = V * I
  • AC Power: The electrical power associated with an AC circuit is known as Complex Power. Whereas Complex Power is the combined form of Active, Reactive, and Apparent Power in AC circuits. So AC power or complex power is further divided into three parts.
  1. Active Power
  2. Reactive Power
  3. Apparent Power

Active Power (kW)

The power that is actually consumed or utilized in an AC circuit is known as Active Power. It is the True power transmitted to the load for energy conversion. That’s why it is also known as True power or Real power in AC circuits. It is represented by the English alphabet P’ and measured in Watt (W), kilowatt (kW), or Megawatts ( MW). In the case of a DC circuit or in a pure resistive AC circuit, active power is calculated as the product of voltage and current in
the circuit. Whereas in the case of an AC circuit, it is calculated as:
Active power

Reactive Power (kVAR)  

The power associated with reactive components (Inductors and Capacitors) of the circuit is known as Reactive Power. It flows in both ( back and forth) directions of the circuit. Reactive power is not a useful power for consumers so it is interpreted as wattless power. It represents an extra burden on the electricity supply system and on the consumer’s bill. This is required in the circuit to produce the electric and magnetic field for the working of capacitors and inductors in the circuit. It has a direct impact on the power factor of the circuit. It only exists in the electrical system when voltage and current in an AC circuit are not in phase.

A pure inductor and a pure capacitor do not consume any power in the circuit. Because in a half cycle whatever power is received from the source by these reactive components, the same power is returned to the source in the next half-cycle. Then the power that returns and flows in both directions in the circuit is known as Reactive power. This reactive power does not perform any useful work in the circuit. It is denoted by an English alphabet Q and measured in VAR,  kVAR, or MVAR.


In the case of the DC circuits, there are no concepts of Reactive Power. Whereas for the AC circuit, it is calculated as:

Reactive power

Apparent Power (kVA):

The combination of Active Power and Reactive Power is known as Apparent PowerIt is the total power of the circuit. Mathematically Apparent power is defined as the product of the root mean square (RMS) value of voltage and current irrespective of its phase angle. It is denoted by the English alphabet ‘S‘ and It is measured in kVA, MVA.

In the case of the DC circuit, it is the total power of the circuit. Whereas for the AC circuit, it is calculated as :Apparent power

Power Triangle

The relation between Active, Reactive, and Apparent power can be expressed by representing quantities as a vector in geometrical form is known as the Power Triangle. In other words, the Power triangle is the geometrical representation of Active power, Reactive power, and Apparent power. In this phasor diagram, voltage is considered as a reference phasor. It is a very useful triangle for finding the power factor of electrical circuits.
power triangle

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Hey, I'm Satish Gupta an Engineer by profession and blogger by passion. I am writer and founder of this blog, Here I publish contents related to Electrical and Electronics Engineering..

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