Measurement of 3 Phase Reactive Power and Theory


Suppose, you are watching a cricket match. You have a packet of chips. And we know, the packet is not full of chips. there is some air. If the whole packet is apparent power, the part filled with chips is real power, and the part with air is reactive power. Today we will discuss the measurement of 3 phase reactive power theory.

What is Reactive Power?

If there is an inductive or capacitive component in the circuit, they store some energy. Because we know that, capacitor or inductor can store charge. A noticeable thing is, there is no waste of energy. It means no transformation is happening.

When the capacitor or inductor will discharge, we can get back the energy. That’s why it is called reactive power. Reactive power continuously rotates from source to load and load to source.

How We Can Measure Reactive Power?

We know current and voltage are out of phase in reactive power. 

Reactive power is measured by this equation:

Reactive power measurement is important because it helps to measure total system loss. More the reactive power, the less the load power factor. And this reactive power is measured by VARmeter. 


According to phase, VARmeter is of two types

1. Single-phase VARmeter

2. Polyphase VARmeter.

Single-Phase VARmeter

For measuring the reactive power of a single-phase power supply system, a single-phase VARmeter is used. It is mainly an electrodynamic wattmeter.

measurement of 3 phase reactive power theory.
Single-Phase VARmeter

Poly Phase VARmeter

When there is a phase difference between current and voltage, then there is reactive power in the circuit. The phase shift can be made by a phase shift transformer.

The phase shift transformer has two open circuit transformer, which is in an open delta configuration. The current coil is connected with a line in series and the pressure coil is connected with the autotransformer of the common terminal.

The pressure coil of the wattmeter is connected with 57% of tapping of the autotransformer. And the rest part is connected with 43%.

In pressure coil, occupied voltage is equal to line voltage but it has 90-degree shifting. In the same way, there is the 90-degree shifting of voltage in the second wattmeter. The reading of these two wattmeter gives reactive power.

pol yphase VARmeter
Poly Phase VARmeter

Amount of Reactive Power in a Three-Phase Balanced Circuit

For a three-phase balanced circuit, a single wattmeter measuring method is used for measuring reactive power. The pressure coil of the wattmeter is connected with a phase line and the current coil is connected with another phase. 

Suppose, the current flow in the current line is -12.

Occupied voltage in voltage coil is -V13.

So, the wattmeter reading is: V13*I2*Cos(90+θ) = √3*VI*Cos(90+θ) = √3*VI*Sinθ.

Three-Phase VARmeter
Three-Phase VARmeter

That’s all for today’s article measurement of 3 phase reactive power theory.

Hope it was helpful for you to understand the measurement of 3 phase reactive power theory.

You can also read: Combined-Cycle Power Plant Schematic Diagram and Explanation