Types of Electrical Power

What is an Electrical Power?

Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field.

In physics, Electric power is the rate, at which electrical energy is transferred by an electric circuit per unit of time. The SI unit of power is the watt, i.e., one joule per second. 

Definition of Electrical Power

Electrical Power is defined as the rate at which work is done on an electrical system. As we have discussed recently that doing work generates energy, and therefore power can be given as the rate of consumption of electrical energy.

Definition of Electrical Energy

Electrical energy is the energy generated because of the potential difference in a circuit that causes current to flow through it. Electrical energy is measured in kWh (kilowatt-hour)
In simple words, Electrical energy is defined as the overall work done in an electrical circuit.
Energy specifies the amount of work done to move an object, and in an electrical circuit, electric charges show movement. The work done on the electric charges to make a movement is known as electrical energy.
Electrical energy and electrical power are the two major terms associated with electrical and electronics systems.

Electrical energy and electrical power are the two major terms associated with electrical and electronics systems.

Energy is denoted by E while electric power is denoted by P.

The fundamental difference between electrical energy and electrical power is that Electrical energy defines the energy generated due to the movement of charge carriers in a conductor. While electrical power specifies the rate of consumption of electrical energy by a device.

Unit of Electrical Power

Since the electrical power is the flow of energy per unit of time & the unit of energy is the joule.
Electrical power = Joules / Second = J/s
The SI unit of electrical power is a watt represented by W.
Watt, W = Joules / Second
One Watt is defined as the electrical power consumed when one volt of potential difference is applied to a circuit & it forces one ampere of current to flow through it.

Types of Electrical Power

Electrical power is mainly classified into two types based on the nature of the electrical current flow.
The two types of electrical current are Direct current (DC) & Alternating current (AC) and hence the electric power is mainly classified into –

  • DC Power
  • AC Power

What is DC Power?

The direct current (DC) flows only in one direction. The DC power is defined as the product of the voltage and current.

DC power was the most predominant form of power used in the 19th century when Thomas Alva Edison led the way to industrialize the usage of electricity.
Direct current may be converted into alternating current via an inverter.

What is AC Power?

An alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time in contrast to a direct current (DC) which flows only in one direction.

AC electricity alternates back-and-forth in direction 50 or 60 times per second, according to the electric system in the country.
This is called the frequency and is designated as either 50 Hertz (50Hz) or 60 Hertz (60Hz).

AC power has become the predominant source of power because AC power can be transmitted at high voltages and low currents for long distances. The characteristics alternating nature of AC minimizes the energy loss due to resistance in the conductors when transmitted over longer distances.

AC power sources are widely used power sources in the world. The foundations of AC power were laid by an American scientist Nikola Tesla in the late 19th century. After a long debate over the safety and reliability of AC and DC power, AC power has become the main source of power for both household and industrial machinery.

AC Power is classified into two types-

  • Single Phase
  • Three Phase

The AC Power is further categorized in three types of powers-

  • Active Power (Real or True Power)
  • Reactive Power (Phantom or Unreal Power)
  • Apparent Power (Total Power)

What is Active Power?

The Power which is really utilized and consumed for useful works in an AC circuit is known as Active Power.
It is also called True Power, Real Power, Useful Power, or Watt-full Power.
It is denoted by the capital English letter “P” and measured in Watts, kW, or MW.

What is Reactive Power?

The power which moves back and forth between source and load in the circuit is known as Reactive Power.
It is also called, Phantom Power, Useless Power, or Watt-less Power.
Reactive Power is denoted by the capital English letter “Q” and measured in VAR (Volt Ampere Reactive), kVAR or MVAR.

What is Apparent Power?

The combination of Reactive power and Active power is called Apparent power.
Apparent power is denoted by the capital English letter “S” and measured in Volt-Amps (VA), kVA, or MVA.
Since the apparent power is the combination of active & reactive power, they are related to each other. The relation can be explained using the following equation,
S = √P2 + Q2

  • S = Apparent Power
  • P = Real or Active Power
  • Q = Reactive Power

For more details on Active, Reactive, and Apparent Power please click on the following links or search with Google

What is Power Factor?

In an AC power system, the power factor is an important parameter that defines how efficiently electrical power is being utilized by the load.
It is a rational number between -1 and 1 but has no unit and is denoted as p.f.

In electrical engineering, the power factor of an AC electrical power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit and is a dimensionless number in the closed interval of −1 to 1. 
It is also defined as, the Cosine of angle between Current and Voltage.
P = VI Cosθ 


  • P = Power in Watts
  • V = Voltages in Volts
  • I = Current in Amperes
  • W = Real Power in Watts
  • VA = Apparent Power in Volt-Amperes or kVA
  • Cosθ = Power factor

The p.f of a system depends on the type of load present, whether capacitive, inductive, or resistive
Leading Power Factor
When the current leads the voltage, the power factor of the circuit is called ‘Leading‘.
When the AC circuit is capacitive, the power factor is “Leading” and ranges between -1 to 0.

Lagging Power Factor-
When the Current lags the voltage the power factor of the circuit is called the “Lagging” power factor.
When the AC circuit is Inductive, the power factor is “Lagging” and it ranges from 0 to 1.

Unity Power Factor-
When the current and voltage are in phase, the power factor of the circuit is called the “Unity” power factor.
When the load is purely resistive, the current flow to the load will be linear and hence the phase shift between the voltage and current will be zero and cos Φ will be unity.


In this post, I have walked you through the Types of Electrical Power. Now that you have understood what AC and DC Power, Active, Reactive, Apparent Power, and power factor is, and their relationship, you’re ready to handle any electrical query that comes your way.

In this post, I have tried to compile all freely available information on various internet sites, so ultimately you do not need to spend your time searching for it.

Now next in the series on Power Generation I will post about the safety and history of electricity.

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Suhas Ghatnekar
Suhas Ghatnekar

The author is an Electrical engineer from the National Institute of Technology Rourkela India, an enterprising techno-commercial professional in the
field of diesel engines and diesel generators.

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