Diagnosis and analysis of causes of burnout and damage to medium frequency induction heating power supply

1. The water in the inverter thyristor water-cooling jacket of the intermediate frequency furnace is cut off or the heat dissipation effect is reduced - replace the water-cooling jacket. Sometimes it is sufficient to observe the water output and pressure of the water-cooling jacket, but often due to water quality problems, a layer of scale adheres to the wall of the water-cooling jacket. Since scale is an object with poor thermal conductivity, although there is sufficient water flow, However, due to the isolation of scale, its heat dissipation effect is greatly reduced. The judgment method is: run the power at a power lower than the overcurrent value for about ten minutes, stop it quickly, and quickly touch the core of the thyristor component with your hand after stopping. If it feels hot, the fault is caused by caused by this reason.

2. The tank connection wire has poor contact or disconnection - check the tank connection wire and deal with it as appropriate according to the actual situation. When the tank connection wire has poor contact or disconnection, sparking will occur after the power rises to a certain value, affecting the normal operation of the equipment and causing equipment protection actions. Sometimes an instantaneous overvoltage will be generated at both ends of the thyristor during ignition. If the overvoltage protection is not activated in time, the thyristor element will be burned out. This phenomenon often occurs when overvoltage and overcurrent operate simultaneously.

3. The insulation between the load and the ground is reduced - the insulation of the load circuit is reduced, causing sparks between the load and the ground, interfering with the triggering time of the pulse or forming high voltage at both ends of the thyristor, burning out the thyristor components.

4. When the thyristor of the intermediate frequency furnace is turned off in reverse phase, the instantaneous glitch voltage that withstands the reverse voltage is too high - in the main circuit of the intermediate frequency power supply, the instantaneous reverse glitch voltage is absorbed by resistance and capacitance absorption. If the resistor and capacitor in the absorption circuit are open-circuited, the instantaneous reverse phase glitch voltage will be too high and the thyristor will be burned out. When the power is off, use a Wanxiu meter to measure the resistance of the absorption resistor and the capacity of the absorption capacitor to determine whether the resistance-capacitance absorption circuit is faulty.

5. Pulse trigger circuit failure - if the trigger pulse is suddenly lost when the equipment is running, it will cause the inverter to open circuit, generate high voltage at the output end of the intermediate frequency power supply, and burn out the thyristor components. This kind of fault is generally caused by the inverter pulse formation and output circuit fault, 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 joint by hand to find out the fault location.

6. The load is open-circuited when the equipment is running - When the equipment is running at high power, if the load suddenly becomes open-circuit, high voltage will be formed at the output end and the thyristor element will be burned out.

7. The load is short-circuited when the equipment 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 over-current protection action is not enough, it will burn. Bad thyristor element.

8. Protection system failure (protection failure) - Whether the thyristor is safe or not is mainly guaranteed by the protection system. If the protection system fails and the equipment is not working properly, the safety of the thyristor will be jeopardized. Therefore, it is essential to check the protection system when the thyristor burns out.

9. Failure of the thyristor cooling system - the thyristor generates a lot of heat when working and needs to be cooled to ensure normal operation. Generally, there are two ways to cool the thyristor: one is water cooling and the other is Wind chill. Water cooling is widely used, and air cooling is generally only used for power equipment below 100KW. Usually, water-cooled IF equipment is equipped with a water pressure protection circuit, but it is basically protected against total water inflow. If there is a water blockage in a certain channel, it cannot be protected.

10. Reactor failure - internal ignition of the reactor causes intermittent current on the inverter side, and also generates high voltage on the inverter input side and burns out the thyristor. In addition, if the reactor is replaced during maintenance, and the inductance and core area of the reactor are less than the required values, the reactor will lose its current limiting function due to saturation and burn out the thyristor when operating at high current.