In electrical engineering, understanding the types of power in an AC circuit is essential. The three key types of power are Active Power, Reactive Power, and Apparent Power. These terms help explain how energy is consumed, stored, and transferred in electrical systems.
โก What is Active Power? (True or Real Power)
Definition:
Active Power (also known as Real Power or True Power) is the power that is actually consumed or utilized in an AC electrical circuit to perform useful workโsuch as lighting, heating, or rotating a motor.
- Measured in: kilowatts (kW) or megawatts (MW)
- Symbol: P
๐ธ Active Power Formula:
P=VรI ร cos \phi
What is Reactive Power?
Definition:
Reactive Power is the power that flows back and forth between the source and reactive components (inductors and capacitors) in an AC circuit. It does not perform any useful work but is necessary to maintain the electric and magnetic fields in the system.
- Measured in: kilovolt-amperes reactive (kVAR) or megavolt-amperes reactive (MVAR)
- Symbol: Q
Reactive power exists due to the phase difference between voltage and current. This type of power is needed to energize inductive and capacitive loads, such as motors and transformers.
๐ธ Reactive Power Formula:
Q=VรIรsin(ฯ)
What is Apparent Power?
Definition:
Apparent Power is the total power flowing in the circuit, which is a combination of both Active Power and Reactive Power.
- Measured in: kilovolt-amperes (kVA) or megavolt-amperes (MVA)
- Symbol: S
Apparent power represents the total capacity of an electrical system to deliver energy, regardless of whether the power is used for work or just circulating in the system.
It has been seen that power is consumed only in resistance. A pure inductor and a pure capacitor do not consume any power since in a half cycle whatever power is received from the source by these components, the same power is returned to the source. This power which returns and flows in both the direction in the circuit, is called Reactive power. This reactive power does not perform any useful work in the circuit.
In a purely resistive circuit, the current is in phase with the applied voltage, whereas in a purely inductive and capacitive circuit the current is 90 degrees out of phase, i.e., if the inductive load is connected in the circuit the current lags voltage by 90 degrees and if the capacitive load is connected the current leads the voltage by 90 degrees.
Hence, from all the above discussion, it is concluded that the current in phase with the voltage produces true or active power, whereas, the current 90 degrees out of phase with the voltage contributes to reactive power in the circuit.
Therefore,
- True power = voltage x current in phase with the voltage
- Reactive power = voltage x current out of phase with the voltage
The phasor diagram for an inductive circuit is shown below:
Taking voltage V as reference, the current I lags behind the voltage V by an angle ฯ. The current I is divided into two components:
- I Cos ฯ in phase with the voltage V
- I Sin ฯ which is 90 degrees out of phase with the voltage V
Therefore, the following expression shown below gives the active, reactive and apparent power respectively.
- Active power P = V x I cosฯ = V I cosฯ
- Reactive power Pr or Q = V x I sinฯ = V I sinฯ
- Apparent power Pa or S = V x I = VI
๐ Components of Current
Active component of the current
The current component, which is in phase with the circuit voltage and contributes to the active or true power of the circuit, is called an active component or watt-full component or in-phase component of the current.
Reactive component of the current
The current component, which is in quadrature or 90 degrees out of phase to the circuit voltage and contributes to the reactive power of the circuit, is called a reactive component of the current.
๐ง Final Thoughts
- Active Power is useful power that runs your appliances.
- Reactive Power is needed for maintaining the voltage levels.
- Apparent Power is the total power your system must handle.
Understanding the difference between active, reactive, and apparent power helps in designing efficient electrical systems, improving power factor, and optimizing load capacity.