Nov 04, 2019 - 02:26 PM
Active power is the electrical power required to keep a consumer operating normally, that is, the electrical power that converts electrical energy into other forms of energy (mechanical, optical, thermal). Various lighting devices convert electrical energy into light energy for people to live and work with. The sign of active power is denoted by P and is expressed in watts (W), kilowatts (kW), megawatts (MW).
Reactive power is relatively abstract, it is used to exchange electric and magnetic fields in the circuit, and is used to establish and maintain the electrical power of the magnetic field in electrical equipment. It does not work externally, but instead transforms it into other forms of energy. For electrical equipment with electromagnetic coils, reactive power must be consumed to establish a magnetic field. Because it does not work outside, it is called "reactive." The sign of reactive power is represented by Q, and the unit is either Var or kVar.
Reactive power is by no means useless power, and it is very useful. The motor needs to establish and maintain a rotating magnetic field to rotate the rotor, thereby driving the mechanical motion. The rotor magnetic field of the motor is established by taking reactive power from the power source. The transformer also needs reactive power to generate a magnetic field in the primary coil of the transformer and induce a voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not be transformed, and the AC contactor will not pull.