How is Reactive Power produced?

Active?power?is the?power?that does useful work. It's quite easy to understand and visualize.

However, We find the concept of?Reactive?power?a little bit confusing because?reactive?power?does not contribute to doing useful work. From our childhood, we are taught that?Power?is a tendency to do work. If it does not contribute to doing useful work then how can it be?"Power"?

In the case of a purely resistive load like an incandescent lamp, electrical energy is directly converted into useful work (light and heat energy in this particular case), and no intermediate electric or magnetic field is required in between. And hence no power?is wasted in creating an electrical or magnetic field. Therefore the total?Power?is entirely Active?Power?that does useful work and there's no requirement for?Reactive?Power.

However, in the case of inductive loads like motors, electrical energy can't directly be converted into useful work (rotation of a motor in this particular case). This is because, to convert electrical energy into rotational energy, a magnetic field has to be created in between the gaps of the stator and the rotor of the motor. Hence, some amount of energy has to be used in creating a magnetic field. The portion of?power?that contributes to creating magnetic fields is known as?Reactive?Power. From the viewpoint of efficiency,?reactive?power?may be seen as?power?loss because its role is limited to creating magnetic fields and does not contribute to driving the load. Nevertheless,?reactive?power?isn't actually a loss because it creates the magnetic field without which electrical energy in the stator could not have been converted to rotational energy in the rotor.

Let us try to understand the concept of?Reactive?Power?by taking the simple example of an aircraft carrying?a crowd of passengers from place A to place B.?The main purpose of the flight is to carry the passengers from place A to place B. The fuel spent in carrying the total weight of all passengers combined is analogous to Active?Power. This fuel does the main work. However, some amount of fuel is also spent on lifting the weight of the aircraft itself. This can't be avoided. Without lifting its own weight, the aircraft can't transport passengers from place A to place B. Thisfuel (used in lifting its own weight) is analogous to?Reactive?Power.

Therefore, inductive loads like motors?demand some amount of?reactive?power?in order to create magnetic fields. The larger the inductive load is in?power?systems, the larger will be the demand for?reactive?power.

Now let us talk about how?reactive?power?is produced in?Power?System.?Reactive?power?is mainly produced by Synchronous Generators through rotor field current (Generator Excitation). The larger the demand for?reactive?power?in the system is, the larger should be the Generator field current to meet that demand. However, there is a limit to the magnitude of field current that can be given to the rotor windings of a generator in order to produce?reactive?power. Therefore it is not always possible to meet the entire?reactive?power?demand of a system only through the excitation of generator windings. This problem can be solved by installing Compensator devices (Capacitor banks) at the receiving end of a?power?transmission system. A capacitor bank at the load side locally generates?reactive?power?thereby reducing overall?reactive?power?demand as seen from the Generator side.

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