Electric Power | Definition | Formula | Units | Types

Electric Power

What is Electric Power

Electric power is defined as the rate of the transferred of energy in electric circuit per unit of time. It can also be defined as the rate at which work is done or energy is transformed into an electrical circuit. It is denoted by “P”. Its measured by SI Unit called watt, denoted by “W”.

Mathematically \\\;\;\;\;\;\; Electrical Power, P = V x I \\\;\;OR\\\;\;\;\;\;\;P = \frac{Work\;done (W)}{time (t)}\\\;\; OR \\\;\;\;\;\;\;P =I^{2} \times R\\Where \\ V = Voltage of Electric Circuit\\I = Current of Electric circuit\\R = Resistance of circuit

Unit of Electric Power

The unit of electric power is watt (W) or joule per second. \\If, V = 1 and I = 1\\Then, Power, P = VI = 1 x 1 = 1watt\\Thus, The power consumed in an electrical circuit is said to one watt if one ampere current flows through the circuit when a potential difference of 1 volt is applied across it.

Types of Electric Power

There are two types of electrical powers – DC Power and AC Power.

DC Power:- The DC power is defined as the product of the DC voltage and DC current. \\ Consider the electric circuit shown below. Let “V” is the DC Volatge across the circuit and “I” is the current in the circuit. Then \\ Electric Power, P = VI

AC Power:- The AC power are of three types – Apparent power , Active Power and Reactive Power.

  1. Apparent Power: It is the idle power. It is equal to the product of root mean square voltage (Vrms ) and root mean square current (Irms ). It is also called complex power. It is denoted by “S”. Its SI Unit is volt- ampere. \\\;\;\;\;S = Vrms x Irms\\It can also written as a combination of Active Power and Reactive Power.\\\;\;\;\;S = P + jQ\\where\\P = active power \\Q = Reactive Power
  2. Active Power: Active power is the power which is actually consumed or utilized in an AC Circuit. It is also called True power or real power. It is measured in Watt. It is the actual outcomes of the electrical system which runs the electric circuits or load.It is denoted by “P”\\\;\;\;\;P= VIcos\phi\\Where \phi is angle between Voltage (V) and current (I)\\cos\phi is called power factor of circuit or system
  3. Reactive Power: It is power developed by the reactive components (i.e. Inductors and Capacitors) of a AC circuit or system. It is unused power. It gets first stored and then released in the form of magnetic field or electrostatic field in case of inductor and capacitor respectively. It is measured by VARs (volt-amps reactive). It is denoted by “Q”. \\\;\;\;\;Q = VIsin\phi\\where \phi is angle between voltage (V) and Current (I).

Analogy of Apparent Power, Active Power and Reactive Power

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About AJAZ UL HAQ 137 Articles
AJAZ UL HAQ is an Assistant Electrical Engineer and has 10.5 Years of Experience in operation & maintenance, erection, Design of Transmission and Distribution Electrical System, Internal Electrification of Buildings, Electrical Substations. He has worked on Projects - Integrated Power development Scheme (IPDS), Prime Minister's Development Package (PMDP) and Re-structured Accelerated Power Development and Reforms Programme (RAPDRP).