Reactor, also known as inductor, is a kind of solenoid with wires of different materials, which is the so-called air core reactor. Sometimes, in order to make the solenoid have greater inductance, an iron core is inserted into the solenoid, which is called iron core reactor. Reactance is divided into inductive reactance and capacitive reactance. The more scientific classification is inductor (inductor) and capacitive reactance (capacitor), which are collectively referred to as reactor. However, in the past, there was inductor first, and it was called reactor, so now people say that capacitor is capacitive reactance, and reactance specifically refers to inductor.

The reactor used in power system is essentially an air core coil without magnetic material. It can be arranged in three assembly forms: vertical, horizontal and zigzag. When a short circuit occurs in the power system, a large value of short circuit current will be generated. It is very difficult to keep the dynamic stability and thermal stability of electrical equipment without restriction. Therefore, in order to meet the requirements of breaking capacity of some circuit breakers, reactors are often connected in series at the outlet circuit breakers to increase the short-circuit impedance and limit the short-circuit current.

Due to the use of reactor, the voltage drop on the reactor is large in case of short circuit, so it also plays a role in maintaining the voltage level of the bus, so that the voltage fluctuation on the bus is small, and the stability of the operation of the user's electrical equipment on the non fault line is ensured.

High voltage core starting reactor in motor is a kind of current limiting reactor. Because the current of large asynchronous motor is very large during starting, it also causes serious voltage reduction, so the current limiting reactor is connected in series in the line to limit the starting current of motor and cut it off automatically after starting. The motor starts to work normally.