Analysis Of The Cause Of the Burning Of The Thyristor

During the use of medium frequency furnace, thyristor burning often occurs, which often annoy the maintenance workers of intermediate frequency furnace, and sometimes can not solve them. 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.The water cooling jacket of the inverter thyristor is cut off or the cooling effect is reduced, so the water cooling sleeve needs to be replaced. Sometimes it is enough to observe the water quantity and pressure of the water cooling jacket, but often due to the water quality problem, a layer of scale is attached to the wall of the water cooling jacket. Because the scale is a kind of thermal conductivity differential although there is enough flow of water flow, the heat dissipation effect is greatly reduced because of the isolation of the scale. The method of judging is that the power is running at a power of about ten minutes lower than that of the overflow value. Then power stopped quickly, and the core of the silicon controlled element touched quickly with the hand after stopping. If it feels hot, the fault is caused by this reason.

2.The connection between the groove and the conductor is poor and broken. Check the slot and connect the wires, and handle them according to the actual situation. When the channel connection wire has tie condition of bad contact or broken line, the power rise to a certain value will produce the phenomenon of fire, which affects the normal work of the equipment, which leads to the protection of the equipment. Sometimes a transient overvoltage is generated at both ends ot the thyristor due to tire. It the overvoltage protection is too late, it will bum the thynstor element. Overvoltage and overcurrent often occur at the same time.

3.The instantaneous burr voltage of the thyristor is too high when the thyristor is reversed. In the main circuit of the medium frequency power supply, the instantaneous reverse phase burr voltage is absorbed by the resistance and absorption. If the resistor and capacitor circuit are open in the absorption circuit will cause the instantaneous reverse burr voltage too high and burn out the thyristor. In the case of power failure, we use the WAN Xiu table to measure the absorpti on resistance and the capacitance of the absorption capacitor, so as to determine whether there is a fault in the resistance capacitance absorption circuit.

4.The load reduces the in sulation of the grou nd: the insulation of the load loop decreases, causing the load to fire between the ground, interfering with the triggering time of the pulse or forming a high voltage at both ends of the thyristor and burning the thyristor element.

5.Pulse trigger circuit fault: If the trigger pulse is suddenly lost when the device is running, it will cause an open circuit of inverter and produce a high voltage at the output end of the intermediate frequency power supply and burn the thyristor element. This kind of fault is usually the formation of the inverter pulse and the fault of the output circuit. It can be checked by the oscilloscope, and it may also be the bad contact of the inverter lead wire, and can shake the wire joint with the hand and find the fault position.

6.The equipment opens when the load is running: When the device is running at high power, if the sudden load is in open circuit, the silicon controlled element will be burned out at the output end.

7.The load is short circuited when the equipment is running: When the equipment is running in high power, if the load is suddenly short circuited, it will have a large short circuit current impact on the SCR: and if the over current protection action can not be protected, the SCR elements will be burned out.

8.Protection of the system failure (failure of protection): The safety of SCR mainly depends on the protection system. If there is a failure in the protect)on system, the equipment is slightly abnormal in its work, which will bring the crisis to SCR safety. Therefore, it is essential to check the protection system when the SCR burns out.

9.SCR cooling system failure: Thyristor is very heat at work and needs cooling to ensure its normal operation. Generally, there are two ways to cool the silicon controlled rectifier: one is water cooling and the other is air cooling. Water cooling is widely used, and air cooling is only used for power supply less than 100KW. Usually, the medium frequency equipment with water cooling is equipped with water pressure protection circuit, but it is basically the protection of the total influent. If some water is blocked, it can not be protected.

10.The reactor is in trouble: The internal ignition of the reactor causes the curre nt side of the in verier side to be interrupted.

Post time: Jan-04-2023