What are the reasons why the thyristor is burned out
The thyristor was burned mainly due to the following reasons：
1. When the thyristor is anti-correlation breaking, the instantaneous glitch voltage of the reverse voltage is too high. In the main circuit of the intermediate frequency power supply, the instantaneous inverted glitch voltage is absorbed by the resistance-capacitance absorption circuit. If the resistance and capacitance in the absorption circuit are open, the thyristor will be burned out if the inverted glitch voltage is too high. In the case of power failure, use a multimeter to measure the resistance value of the absorption resistance and the capacity of the absorption capacitance to determine whether the resistance-capacitance absorption circuit is faulty. Loose connection wires can also generate high voltage.
2. The insulation of the load to ground is reduced. The insulation of the load circuit is reduced, causing the load to ignite to the ground, which interferes with the triggering time of the pulse, or high voltage is formed at both ends of the thyristor, which burns out the thyristor components.
3. The pulse trigger circuit is faulty. If the trigger pulse is suddenly lost when the equipment is running, the inverter thyristor will open, and high voltage will be generated at the output of the intermediate frequency power supply, which will burn out the thyristor components. This kind of fault is generally a circuit fault formed by the inverter pulse, which can be checked with an oscilloscope. It may also be caused by poor contact of the inverter pulse lead. You can shake the wire connector by hand to find the fault location.
4. The load is open when the device is running. When the equipment is running at high power, if the load is suddenly open, high-voltage burnout components will be formed at the output.
5. The load is short-circuited when the device is running. When the equipment is running at high power, if the load is suddenly in a short-circuit state. There will be a large short-circuit current impact on the thyristor. If the overcurrent protection action is too late to protect, the thyristor element will be burnt out.
6. Protection system failure (protection failure). The safety of the thyristor is mainly guaranteed by the protection system. If the protection system fails, the equipment does not work properly, and the safety of the thyristor will be at risk. Therefore, it is essential to check the protection system when the thyristor burns out.
7. Thyristor cooling system failure. The thyristor generates a large amount of heat when it is working, and it needs to be cooled to ensure normal operation. Generally, there are two ways to cool the thyristor: one is water cooling, the other is air cooling. Water cooling is widely used, and air cooling is generally only used for power equipment below 100kW. Usually the intermediate frequency equipment that adopts the water cooling method is equipped with a water pressure protection circuit, but it is basically the protection of the total water inlet. If a water block occurs in a certain road, it cannot be protected.
8. The reactor is faulty. The internal fire of the reactor will cause the current on the inverter side to be intermittent, and it will also produce high voltage on the inverter input side to burn out the thyristor. In addition, if the reactor is replaced during maintenance, and the inductance of the reactor and the core area are less than the required value, the reactor will lose the current limiting effect due to magnetic saturation and burn out the thyristor when the reactor is working at a large current.
9. The commutation inductance has water seepage, and the inter-turn insulation is reduced, which causes the current to be unstable.