Difference between Apparent Power and Real Power

Differences Electric Power System Electronics & Electrical

In an electric circuit, the rate at which the work is being done (or the energy is being expended) is known as electric power. Mathematically, electric power can be defined as the work done (or energy expended) per unit time, i.e.,

$$\mathrm{Power,\mathit{P}\:=\:\frac{Work\:done\:(\mathit{W})}{Time(\mathit{t})}}$$

The unit of electric power is Joules per second.

Based on the type of current, the electric power can be of two types viz.: DC power and AC power. The AC power is further classified into three main types as −

Apparent power (S)
Active power (P)
Reactive power (Q)

In this article, we will discuss about what the apparent power and the active power are and the key differences between the apparent power and the active power.

What is Apparent Power?

In an AC electric circuit, the total amount of electric power flowing from source to load is termed as apparent power. The apparent power is measured as the product of the RMS value of voltage and RMS value of current. It is denoted by the letter 'S'.

$$\mathrm{Apparent\:power,\mathit{S}\:=\:\mathit{V}\cdot(\mathit{I})}$$

The apparent power is measured in volt-ampere (VA).

What is Active Power or Real Power?

In an AC electric circuit, the portion of total power (or apparent power) which does the useful work in the circuit is known as active power. The active power is also known as real power. The active power is denoted by the letter 'P' and is measured in Watts.

The active power is the AC power which is absorbed and utilized by the load in the circuit. The real power or active power is always less than or equal to the apparent power. Mathematically, the active power is given by the following expression,

$$\mathrm{Active\:power,\mathit{P}\:=\:\mathit{VI}\cos(\phi)}$$

Where, cos$\phi$ is the power factor of the circuit.

Difference between Apparent Power and Real Power

The major differences between active power (or real power) and apparent power are given in the following table −

Basis of Difference	Real Power (or Active Power)	Apparent Power
Definition	The part of total power in an AC circuit which is consumed by the equipment to do useful work is called real power or active power.	The total amount of power flowing from source to load in an AC circuit is known as apparent power.
Denotation	Real power is denoted by letter 'P'.	Apparent power is denoted by the letter 'S'.
Expression	Real power is given by the product of RMS values of voltage and current in the circuit and power factor of the circuit, i.e. $$\mathit{P}\:=\:{VI}\cos(\phi)$$	Apparent power is given by the product of RMS values of the voltage and current in the circuit, i.e.$$\mathit{S}\:=\:\mathit{VI}$$
Unit of measurement	The measuring unit of real power is Watt (W).	The unit of apparent power is Volt-Ampere (VA).
Function	The function of real power is to do useful work in an electric circuit. Thus, real power is the one which converts the electrical energy into other forms of energy.	Apparent power provides the total power i.e. active power as well as reactive power in the circuit.
Dependency on circuit power factor	Real power is affected by the power factor of the circuit or load.	Apparent power is independent of the circuit power factor.
Measuring instrument	Real power is measured by using a measuring device known as 'wattmeter'.	A measuring device known as 'kVA meter' is used to measure the apparent power in a circuit.
Uses	Real power is used to define the ratings of various electrical appliance that are used as the load such as fan, lamp, heater, motor, etc.	The apparent power is useful in defining the ratings of devices which are used as the source and transmitter of power such as alternator, transformer, inverter, etc.

Conclusion

In this article, we have highlighted several noticeable differences between real power and apparent power in the tabular form. However, the most significant difference between active power and apparent power is that the active power (or real power) is the portion of total power that does the useful work in an electric circuit, while the apparent power is the total power that flows from source to load in the circuit and provides both active power and reactive power component in the circuit.