Principles and Functions of Inductors

The main components of an electrical circuit are resistors, capacitors, and inductors. Inductors play a role in suppressing current changes and can cause phase shifts in alternating current (AC). The wired static induction devices that have inductive effects are referred to as reactors. However, because inductors were developed first and are called reactors, the term "capacitor" is used to refer to capacitive reactors, while "reactor" specifically refers to inductors. Below, we will introduce their principles and the functions of different types of reactors:

Principle of Reactors

Reactors used in the power network are essentially hollow coils made of non-magnetic materials. They can be arranged in three assembly forms: vertical, horizontal, and triangular. During a short circuit in the power system, a large short-circuit current is generated. If not limited, it is very difficult to maintain the dynamic and thermal stability of electrical equipment. Therefore, to meet the short-circuit capacity requirements of certain circuit breakers, reactors are often connected in series at the outgoing circuit breaker to increase the short-circuit impedance and limit the short-circuit current.

With the use of reactors, a significant voltage drop occurs across the reactor during a short circuit, helping to maintain bus voltage levels and minimize voltage fluctuations on the bus, ensuring the electrical equipment of non-faulty circuits remains operational.

1. Functions of Shunt Reactors

Shunt reactors have numerous functions that can modify and enhance the reactive power-related operational status of the power system, often applied in reactive power compensation. In simple terms, reactors can improve voltage distribution along long transmission lines, absorb capacitive reactive power in cable lines, and effectively prevent self-excitation resonance phenomena when generators are connected to long lines.

2. Functions of Series Reactors

Series reactors are generally used to limit short-circuit currents. Additionally, they can be connected in series or parallel with filters and capacitors to limit the higher harmonics generated in the power network. Specifically, series reactors serve to limit current.

3. Functions of DC Reactors

DC reactors are typically installed between the rectification and inversion units in variable frequency systems. Their primary purpose is to limit the AC components superimposed on the DC current to a specified value, effectively ensuring the continuity of the rectified current and reducing the number of current pulses. Thus, DC reactors promote more reliable and stable operation of the inversion stage while improving the power factor of the variable frequency converter.

4. Functions of Input Reactors

Input reactors are mainly used to limit current surges caused by voltage spikes or operating overvoltages in the power grid. They can protect variable frequency converters and improve power factor by mitigating issues such as voltage defects arising from smooth power supply voltage, such as peak pulses or voltage defects caused by the commutation of smooth bridge rectifier circuits. Input reactors also help reduce harmonic current pollution from the rectification unit to the power grid.

5. Functions of Output Reactors

Output reactors can compensate for the capacitive effects over a distance of approximately 50 to 200 meters and suppress output harmonic currents, thereby enhancing output high-frequency resistance. They also reduce high-frequency leakage currents, protecting variable frequency converters and reducing equipment noise. When reactors are in a state of compensating power, they are typically subject to impacts from harmonic voltages and currents, which can lead to capacitor damage and reduced power factor, making it necessary to address harmonics during compensation.

Due to the variety of types and their different functions, reactors can be generally divided into two main categories based on circuit principles: series and parallel, with their primary functions being current limiting and filtering. The reactors commonly used in power systems are series and shunt reactors. Series reactors primarily limit short-circuit currents and can also be used in filters in conjunction with capacitors to ensure the stability of higher harmonics within the grid.