Reactive power means that in an AC circuit with reactance, an electric field or a magnetic field absorbs energy from a power source for a part of a period of time, and another part of time releases energy. The average power is zero over the entire period, but the energy is at the power source and reactance. Components (capacitors, inductors) are constantly exchanged. The maximum value of the exchange rate is "reactive power". In a single-phase AC circuit, the value is equal to the product of the voltage rms value, the current rms value, and the sine of the phase angle between the voltage and the current. The unit is watts and kilowatts.
Reactive power, many electrical equipment are based on the principle of electromagnetic induction, such as distribution transformers, electric motors, etc., they all rely on the establishment of alternating magnetic field to convert and transfer energy. The electric power required to establish the alternating magnetic field and the induced magnetic flux is called reactive power. Therefore, the so-called "reactive power" is not "useless" electric power, but its power is not converted into mechanical energy or thermal energy; therefore In addition to the need for a working power supply, a reactive power supply is required in the power supply system, and both are indispensable.
In the power grid, there are two types of electrical power supplied by the power supply: one is active power and the other is reactive power. 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). For example, a 5.5 kW electric motor converts 5.5 kW of electric power into mechanical energy, which drives centrifugal pump or thresher threshing; various lighting devices convert electrical energy into light energy for people to live and work with. Reactive power is relatively abstract, it is used in electric and magnetic fields in circuits, and is used to establish and maintain electrical power in electrical equipment. For electrical equipment with electromagnetic coils, reactive power must be consumed to establish a magnetic field. For example, a 40W fluorescent lamp requires 40W of active power (the ballast also consumes a part of the active power) to emit light. It also needs about 80var of reactive power for the ballast coil to establish an alternating magnetic field.
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.
Under normal circumstances, the powered device not only needs to obtain active power from the power supply, but also needs to obtain reactive power from the power supply. If the reactive power in the power grid is in short supply, and the power equipment does not have enough reactive power to establish a normal electromagnetic field, then the power equipment cannot be operated under the rated condition, and the terminal voltage of the power equipment is lowered. Affect the normal operation of electrical equipment.
