What is reactive power and how to compensate the reactive power

What is reactive power

In an AC circuit the reactive power can be described as the unused power by the reactive components it is a consequence of the AC system it is used to build up magnetic fields. Reactive power compensation is to manage the reactive power in order to improve the performance of the alternating current power systems. Reactive power compensation in the transmission system will improve the stability of the AC system by increasing the active power.

This power cannot be converted into non-electrical quantity such as heat and torque. Active power is the power used to run electric devices, while reactive power is the power that is used to regulate the voltage. If the system voltage is not high enough then we can’t use active power, reactive power can be used to provide the voltage required for the active power to do the work. Reactive power is needed to move the active power to the transmission and distribution system to the customer. If there is not enough reactive power then, the voltage sags will be down and it is not possible to push the power demanded by loads through the lines. By maintaining a proper reactive power we could regulate the power factor of the system and also stability of the voltage could be done too, the reactive power is created by the inductive and capacitive loads.

Why do we need reactive power in a power system

  • To supply active power we need proper voltage reactive power will provide the voltage levels which is needed for transmission it is also used to move the active power through transmission and distribution system

  • Prevention of damage in power system could be done by reactive power by providing voltage control

  • Reactive power is directly proportional to voltage level so if reactive power is more voltage level would be high

  • It could avoid blackouts by giving proper voltage

  • Induction motor requires reactive power

  • Reactive power is needed to generate magnetic flux

  • Magnetization of the core is not possible without reactive power

  • Reactive power is absorbed by components like motor and inductor

  • Large and smaller loads require reactive power

  • It will improve the efficiency of power delivery

  • Reduces congestion

  • Grid reliability and stability

Reactive power is needed to maintain the voltage to deliver active power through the transmission. Motor and certain other loads need reactive power to convert the flow of electrons into useful work. The voltage sags will be down if there, not enough reactive power, so the demanded power can’t be transferred by the loads through the lines because of this. Heat energy is produced by the current in case of resistive loads while magnetic fields are produced by the current in case of inductive loads and it will further create the desired work. So the reactive power can be considered as the non-working power caused by the magnetic current to operate and sustain magnetism in the device. Reactive power is needed for the operation of the electric motor, reactive power can produce a magnetic field, it can also maintain the motor’s internal magnetic field in the motor. Reactive power is also required in the transformer to create magnetic flux in the core. Reactive power is also required for power transmission through the line.

What is the need for reactive power compensation

AC source would generate reactive power, and this could be stored in a capacitor or reactor during the cycle and in the next cycle, it would be sent to the source. Reactive power will oscillate between the source and the capacitor. So in order to avoid the circulation between the source and the load it should be compensated. The compensation of the reactive power would also help to regulate the power factor of the system and to maintain the voltage.

How to compensate reactive power

Shunt compensation

Shunt compensation of the reactive power could be done either at load, substation or transmission level the compensation must be provided close to the consumption to avoid the distribution in other parts. This device would be connected in parallel with the transmission line and it would be connected in the middle of the transmission line. It can be provided either by a current source, voltage source, or a capacitor. Overvoltages in reactors can be reduced by this type of compensation and the voltage level can be maintained in the capacitor by using this.


By using shunt capacitors

  • Reduction of the line current is done
  • Improves voltage level
  • Reduces system losses
  • Reduces the load of the alternator

These benefits are created by using the shunt capacitor to adjust the reactive power.

Series compensation

If a device is connected in series with the transmission line, then it is called a series compensator and they can be connected anywhere in the line. This type has two operating modes capacitive mode and inductive mode.

Synchronous condenser

This device is used to improve the PF of the electrical system and it is installed at the receiving end of the line. This will supply KVAR to the system and reduces the current. So the losses are reduced and better efficiency can be achieved. Thus more power can be delivered to the load and PF can be improved.

What are the limitations of reactive power

• It can’t travel very far

• They must be usually produced close to the location where it is needed

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Wow, this is very informative. I’ve learned a lot here!