Due to the poor overload capability of the thyristor module, short-term overvoltage or overcurrent may cause its damage. Although it is necessary to select component parameters reasonably and leave a safety margin when selecting the thyristor module, it is still necessary to take appropriate protective measures against the working conditions of the thyristor module to ensure the normal operation of the thyristor device.

1. Overvoltage protection of the thyristor module The main causes of the overvoltage of the thyristor module are operating overvoltage and surge overvoltage. According to the position of overvoltage protection, it can be divided into AC side protection, DC side protection and component protection. Overvoltage protection measures that can be used by thyristor devices.

2. Overcurrent protection of thyristor module When the current flowing through the thyristor module exceeds its normal working current, it is called overcurrent. When an overcurrent occurs, if there is no protective measure, the thyristor module will be damaged due to overheating. Therefore, before the thyristor module is damaged, overcurrent protection measures must be taken to quickly eliminate the overcurrent. One or more of them can be selected as the overcurrent protection of the thyristor device according to the actual situation.

The functions of each overcurrent protection measure are as follows:

① The thyristor module connects the reactor in the AC input line in series (when there is no rectifier transformer), or uses a transformer with large leakage reactance to limit the short-circuit current and protect the thyristor, but the load voltage drops.

②The thyristor module is equipped with a current detection device on the AC side, and the overcurrent signal is used to control the trigger, so that the trigger pulse quickly moves backward (that is, the α angle increases) or instantaneously stops turning off the thyristor to manipulate the overcurrent. However, in a reversible system, the inverter will fail after the pulse stops, so the method of moving the pulse backward is usually used.

③ The AC side of the thyristor module is connected to the overcurrent relay through a current transformer, or the DC side is connected to the overcurrent relay. It can work in the event of overcurrent and disconnect the automatic switch at the input. The setting value must be connected in series with the fast fuse of the thyristor module. Compatible with overload characteristics.