How to limit the current of reactor

In power system, short circuit fault is a common but extremely harmful abnormal state. Short-circuit current often exceeds the rated working current of equipment, which may lead to serious consequences such as equipment damage, system collapse and even fire. In order to limit short-circuit current, protect power equipment and maintain system stability, reactors are widely used as an important current limiting device. This paper will introduce the basic principle of reactor and its function and application in current limiting.

First, the basic principle of reactor

The reactor is essentially an inductance element, and its main function is to hinder the current change through its inductance characteristics. According to the principle of electromagnetic induction, the inductance element has inductance to AC current, and the inductance is proportional to the frequency and inductance. When a short circuit occurs in the system, the current rises rapidly. At this time, the reactor generates an electromotive force in the opposite direction of the current change through its inductance characteristics, thus restraining the sharp rise of the current and limiting the current.

Second, the working mechanism of reactor current limiting

After the reactor is connected to the power system, it is equivalent to adding an impedance element to the circuit. During normal operation, due to the small current, the reactor has limited influence on the voltage drop of the system and will not cause obvious energy loss; In the case of short circuit or overcurrent, the current increases rapidly, and the inductance produced by the reactor also increases, thus significantly limiting the peak value and duration of short circuit current.

For example, after installing a series reactor in the distribution system, when a short-circuit fault occurs, the reactor will limit the magnitude of the fault current, so that protection devices (such as circuit breakers and fuses) have enough time to act and cut off the fault circuit, thus protecting the safety of equipment and lines.

Third, the application form of reactor current limiting

1. Series reactor
Series reactor is the most common current limiting method, usually installed between power supply and load. It effectively reduces the short-circuit current level by directly limiting the current flowing through the circuit. It is often used in substations, industrial distribution systems and new energy grid-connected systems such as wind power generation and photovoltaic power generation.

2. Split reactor
Split reactor consists of two or more coils and is usually used in double-loop or multi-loop systems. They show little mutual inductance in normal operation, but when a circuit is short-circuited, it can significantly improve the reactance of the circuit, thus limiting the short-circuit current.

3. Variable reactors and controllable reactors
With the development of power electronics technology, controllable reactors (such as thyristor controlled reactor TCR) are also applied to dynamic current limiting occasions. By adjusting the control element, the reactance value can be adjusted in real time, and the dynamic response and accurate control of current can be realized, which is suitable for occasions with high requirements for system stability.

Fourth, the advantages of using reactor to limit current

-Improve system stability: limiting short-circuit current can reduce the impact on system voltage and prevent voltage collapse.
-Protect electrical equipment: reduce the impact of short-circuit current on transformers, cables, switchgear, etc., and prolong the service life of equipment.
-Simplifying protection configuration: reducing the requirements for breaking capacity of protection equipment such as circuit breakers and saving investment costs.
-Improve the reliability of power supply: reduce power failure accidents caused by short circuit and ensure the continuous and stable operation of power system.

V. Conclusion

To sum up, as a current limiting device with simple structure and high reliability, reactor plays an irreplaceable role in modern power system. With the continuous expansion of power system scale and the wide application of new energy, it will be more important to rationally configure and use reactors to improve the safety, economy and stability of the system. In the future, with the development of smart grid and flexible transmission technology, the performance and application mode of reactors will be continuously optimized and innovated.