How To Understand Active Power And Reactive Power? Circuit Knowledge

Active power is the electrical power required to maintain the normal operation of electrical equipment, that is, the electrical power to convert electrical energy into other forms of energy (mechanical energy, light energy, heat energy). For example, the 5.5 kilowatt motor is to convert 5.5 kilowatts of electrical energy into mechanical energy, driving the pump to pump or thresher to grain; All kinds of lighting equipment convert electrical energy into light energy for people to live and work. Reactive power is more abstract, it is used for the exchange of electric and magnetic fields in a circuit, and used to establish and maintain magnetic fields in electrical equipment. Instead of doing work, it transforms into some other form of energy. Any electrical equipment with electromagnetic coils, to establish a magnetic field, it is necessary to consume reactive power. For example, 40 watts of fluorescent lamps, in addition to the need for more than 40 watts of active power (ballast also needs to consume part of the active power) to light, but also need about 80 watts of reactive power for the ballast coil to establish an alternating magnetic field. Because it does not do external work, it is called "reactive work".

Reactive power is by no means useless power, it is very useful. The motor needs to establish and maintain a rotating magnetic field to make the rotor rotate, thereby driving the mechanical movement, and the rotor magnetic field of the motor is established by obtaining reactive power from the power supply. The transformer also requires reactive power to generate a magnetic field in the primary coil of the transformer and to induce a voltage in the secondary coil. Therefore, without reactive power, the motor will not turn, and the transformer cannot change voltage. Usually, the reactive power supplied from the generator and high-voltage transmission line is far from meeting the needs of the load, so some reactive power compensation devices should be set up in the grid to supplement the reactive power to ensure that the user needs the reactive power, so that the electrical equipment can work at the rated voltage. This is why the grid needs to install reactive power compensation devices.