Electrical Power- Active, Reactive and Apparent Power

In this article we are going to discuss what is Electrical power and its significance.

Electrical Power Definition:

In general science power is simply defined as the capacity to do work. In other word, it is defined as the rate of doing work.

Whereas In Electrical Engineering, An Electrical power is the rate per unit time at which the amount of electrical energy that 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 it 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.

Unit of Electrical Power:

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

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 maintains across it.

Watt is a smaller unit of power. Whereas a bigger 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 divided into two types.

They are DC power and AC power.

1. 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

2. AC Power

Electrical power associated in AC circuit is known as Complex Power. Complex Power is the combined form of Active, Reactive and Apparent Power in AC circuit. So AC power is further classified into three types.

These are Active Power, Reactive Power, and Apparent Power.

Active Power (P): 

The power which is actually consumed or utilized in AC circuit is known as Active Power. It is also known as True Power or Real Power in AC circuit. It is denoted by an English alphabet 'P'. It is measured in Watt (W), kilowatt(kW), or Megawatt ( MW). In the case of DC circuit or in Pure Resistive AC circuit, It is calculated as the product of voltage and current in the circuit. Whereas in the case of AC circuit it is calculated as:

Reactive Power (Q):  

The power associated with reactive components (Inductors and Capacitors) of the circuit is known as Reactive Power. It flows in both (i,e back and forth) direction of circuit. It is not a useful power so it is interpreted as wattless power. It represents an extra burden on the electricity supply system and on the consumer's bill. Whereas it is required in the circuit to produce the electric and magnetic field for working of capacitors and inductors in the circuit.

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 which returns and flows in both the direction 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. It is measured in VAR,  kVAR, or MVAR.

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

Apparent Power (S):

The combination of Active Power and Reactive Power is known as Apparent Power.
It is total power of the circuit. Mathematically it is defined as the product of root mean square (RMS) value of voltage and current. It is denoted by an English alphabet 'S' and It is measured in kVA, MVA. In the case of DC circuit, it is total Power. Whereas for the AC circuit it is calculated as :

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 Power Triangle. In this phasor diagram, voltage is considered as reference phasor. 

Also Read: What is power factor and why is it important?