True Reactive Power
True Reactive power, denoted as Q, is a measurement of the reactive power component in an electrical system. The power that fluctuates between the source and the load as a result of inductive or capacitive components in the circuit is referred to as reactive power. It does not perform any useful work but is necessary for the proper functioning of devices such as motors and transformers.
The equation for True Reactive Power is as follows:
In this equation:
Q represents true reactive power in Volt-Amps Reactive (VAR)
V refers to the voltage magnitude in Volts (V)
I denote the current magnitude in Amperes (A)
θ represents the phase angle between voltage and current waveforms
Apparent Power
The sum of real power (useful power) and reactive power in an electrical system is known as apparent power, or S. It represents the total power supplied or consumed by the system. Apparent power is determined as the product of voltage and current and is expressed in Volt-Amperes (VA). The following is the equation for apparent power:
In this equation:
S represents Apparent Power in Volt-Amperes (VA)
V refers to the voltage magnitude in Volts (V)
I denote the current magnitude in Amperes (A)
Power Triangle
To better visualize the relationship between true reactive power, apparent power, and real power, the power triangle is often used. The power triangle is a geometric representation that helps us understand the interdependencies between these power components.
In the power triangle:
S represents the hypotenuse, representing the magnitude of apparent power (S) in VA
P represents the adjacent side, representing the magnitude of real power (P) in Watts (W)
Q represents the opposite side, representing the magnitude of true reactive power (Q) in VAR
Example
An AC motor has a voltage magnitude of 120V and draws a current of 5A, and 30 degrees is the phase angle between the voltage and current waveforms. To calculate the True Reactive Power:
To calculate the apparent power:
Difference between True Reactive Power and Apparent Power
To further understand the concept of true reactive power and apparent power, the table below gives the difference between them:
| True Reactive Power | Apparent Power |
|---|---|
| True reactive power, also known as reactive power (Q), is the component of power in an AC circuit that oscillates between the source and load due to reactive elements such as inductors and capacitors. | Real power (P) and reactive power (Q) are both components of apparent power (S), which is the total amount of power in an AC circuit. |
| To measure the true reactive power, the volt-ampere reactive (VAR) unit is used. | To measure the apparent power, the volt-amperes (VA) unit is used. |
| True reactive power does not perform any useful work but is required to support the oscillating magnetic and electric fields in the circuit. | Apparent power represents the total power flow in the circuit, including both real and reactive components. |
| In an ideal system, the true reactive power is zero, indicating a perfect balance between the reactive power supplied and absorbed. | The sum of actual and reactive power determines apparent power, which is always larger than or equal to real power. |
| True reactive power is responsible for the reactive voltage drop across reactive elements in the circuit. | Apparent power determines the size of the components needed in a circuit, including conductors, transformers, and power supplies. |
| True reactive power can be positive (leading) or negative (lagging) depending on the phase relationship between voltage and current. | Apparent power is always positive, representing the magnitude of the total power in the circuit. |
Conclusion
Understanding true reactive power and apparent power is crucial for effective power management and system optimization. True reactive power represents the reactive component, while apparent power accounts for both real and reactive power. The power triangle provides a graphical representation of the relationship between these power components.
