When the system voltage, current or operating condition deviates from the normal value and reaches a certain critical value, corresponding protection should be implemented on the shunt capacitor compensation device. (1) When the current of the overcurrent protection capacitor bank exceeds the set value, it can send an opening signal to the circuit breaker for protection. (2) Over-current quick-break protection When the capacitor bank is short-circuited, it can send a quick-break signal to the circuit breaker for protection. (3) Overvoltage protection When the bus voltage exceeds the specified value, it can send an opening signal to the circuit breaker for protection. (4) Loss of voltage protection When the bus voltage drops to a specified value, it can send an opening signal to the circuit breaker. (5) Overload protection When the harmonic current reaches the set value, it can send an opening signal to the circuit breaker. (6) Single-phase grounding protection According to the author's understanding from the accident, there are at least three situations worth mentioning for the single-phase grounding in the capacitor bank. ①The short-term arc light grounding of the phase bus of the capacitor bank is generally very small, so my country's "Substation Operation Regulations" stipulates that the neutral point ungrounded system can run for no more than 2 hours at this time. However, a large number of facts have proved that this regulation does pose a great hidden danger to capacitor banks. If it is an intermittent arc grounding, sometimes a high overvoltage will be induced, which may cause fatal damage to the parallel capacitor compensation device, such as the main insulation breakdown of the capacitor. When it develops to two-phase or even three-phase, a high When overvoltage occurs, the capacitor case bursts or even catches fire, and the discharge coil or reactor is severely damaged, etc., all of which may occur. ②A dry-type iron-core reactor is used and connected to the power supply side. Its coil high-voltage end ignites and pulls the arc on the iron core until the coil catches fire. ③Integrated shunt capacitor compensation device, although there is an air-core reactor in front, because the voltage drop on the reactor is very small, at this time, the high-voltage end of the capacitor box discharges to the shell until it breaks down. These potential faults are very dangerous, so it can be said that the "single-phase grounding" protection here refers to the protection that can send an opening signal to the circuit breaker once they occur. The first four protections are generally configured for each set of devices, and any one of them should not be omitted; the latter two depend on the specific situation, and not necessarily every set of capacitors must be installed. For example, a capacitor bank with an appropriate reactance rate according to the background harmonics generally does not need to be equipped with overload protection; for a collective capacitor bank and a capacitor bank with a dry-type iron core reactor in front, it is advisable to add a single-phase grounding protection.