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Why does the thyristor burn out in intermediate frequency induction furnace?

Author:admin      Time:2018-10-24 10:25
In the process of using intermediate frequency furnace, thyristor burnout and other phenomena often occur, which often upset the maintenance personnel of intermediate frequency furnace, and sometimes can not be solved. According to the maintenance records of the medium frequency furnace for many years, the data can be seen below for reference by maintenance personnel.

1, reverse cooling thyristor water cooling or cooling effect drop - replace water cooling sleeve. Sometimes the observation of water cooled jacket water quantity and pressure is sufficient, but often due to quality problems, a layer of scale attached to the water jacket on the wall, because the scale is a kind of low thermal conductivity of the object, although there is enough water flow through, but because the scale isolation makes the heat dissipation effect is greatly reduced. The judgment method is: the power operation in the lower power of the current value of about ten minutes, quickly stop, stop quickly with the core of hand touch SCR, if feel hot, this is the cause of the fault.

2. There are bad contacts and broken wires in the groove connection wires-check the groove connection wires and deal with them according to the actual situation. When the groove connection conductor has bad contact or broken wire, when the power rises to a certain value, it will produce a fire phenomenon, affecting the normal operation of the equipment, resulting in equipment protection action. Sometimes a transient overvoltage will occur at both ends of the thyristor due to ignition. If the overvoltage protection action is too late, the thyristor component will be burned out. Overvoltage and overcurrent often occur at the same time.

3. The instantaneous burr voltage withstanding the reverse voltage is too high when the SCR is reversed interrupting. In the main circuit of the intermediate frequency power supply, the instantaneous reverse phase burr voltage is absorbed by the resistance-capacitance absorption. If the resistor and capacitor open circuit in the absorption circuit will cause the instantaneous reverse burr voltage to burn out the thyristor too high. In the case of power failure, the absorptive resistance value and the absorptive capacitance capacity are measured with a Wanxiu meter to determine whether the resistance-capacitance absorption circuit is faulty.

4. Load-to-ground insulation reduction--Load circuit insulation reduction, causing load-to-ground firing, interfering with the triggering time of the pulse or forming high voltage at both ends of the thyristor, burning out the thyristor components.
5. Fault of pulse trigger circuit-If the trigger pulse is suddenly lost when the equipment is running, the inverter will be opened, high voltage will be produced at the output of intermediate frequency power supply, and SCR components will be burned out. This kind of fault is usually caused by the formation of inverter pulse and the fault of output circuit. It can be checked by oscilloscope or the bad contact of inverter pulse lead. The fault position can be found by shaking the wire connector by hand.
6. Load open circuit when the equipment is running at high power, if the sudden load is in open circuit state, high voltage will be formed at the output end, burning out the SCR components.
7. Load open circuit when the equipment is running - when the equipment is running at high power, if the load is suddenly short-circuit state, there will be a large short-circuit current impact on SCR, if the overcurrent protection action is not timely protection, will burn the SCR components.

8. Protection system failure (protection failure) - whether SCR is safe or not depends mainly on the protection system to ensure that, if the protection system fails, equipment slightly abnormal operation, will endanger the safety of SCR. Therefore, it is essential to check the protection system when the SCR burns out.
9. Trouble of SCR cooling system--SCR has a lot of heat when it is working, so it needs to be cooled to ensure normal operation. Generally, SCR cooling has two ways: one is water cooling, the other is air cooling. Water cooling is widely used, and air cooling is only used for power supply less than 100KW. Usually the water-cooled medium frequency equipments are equipped with Who-ah protection circuit, but the basic is the total water intake protection, if there is water blockage in a certain way can not be protected.
10, reactor failure - the internal ignition of the reactor causes the current side of the inverter side to be interrupted.