Zhengzhou Gou's shared an example of troubleshooting for medium frequency induction furnaces (middle)

(3)Troubleshooting examples

①Fault phenomenon: The equipment cannot be started. The DC ammeter on the right side of the startup port has an indication, but the DC voltage and intermediate frequency voltmeters have no indication.

Fault analysis and handling are as follows.

a. There is a lack of pulse in the inverter trigger pulse. Use an oscilloscope to check the inverter pulses (it is better to check on the G-K of the thyristor). If there is a lack of pulses, check whether there is poor contact or open circuit in the connection, and whether there is a pulse output in the front stage.a. There is a lack of pulse in the inverter trigger pulse. Use an oscilloscope to check the inverter pulses (it is better to check on the G-K of the thyristor). If there is a lack of pulses, check whether there is poor contact or open circuit in the connection, and whether there is a pulse output in the front stage.

b. Inverter thyristor breakdown. Use a multimeter to measure the resistance between A and K. In the absence of cooling water, the value between A and K should be greater than 10K ohms. If the resistance is 0, it is broken. If two are damaged during measurement, you can remove the connecting copper bar of one and then determine whether one or both are damaged. Replace the thyristor and check the cause of damage to the thyristor.

c. Capacitor breakdown. Use the ×1K scale of the pointer multimeter to measure whether each column of the capacitor is charging or discharging to the common terminal. If there is no phenomenon, it means that the column is damaged. Remove the damaged capacitor pole.

d. The load is short-circuited or grounded. A 1000V megger (wogger) can be used to measure the resistance of the coil to ground (when there is no cooling water). It should be greater than 1M ohm. Otherwise, short circuit points and ground points should be eliminated.

e. There is an open circuit or short circuit in the intermediate frequency signal sampling loop. Use an oscilloscope to observe the waveform of each signal sampling point, or use a multimeter to measure the resistance value of each signal sampling loop without power supply to find open or short circuit points. Focus on checking whether the primary side of the intermediate frequency feedback transformer is open circuit (caused by a virtual connection of the discharge inductor).

②Fault phenomenon: It is difficult to start. After starting, the intermediate frequency voltage is more than twice the DC voltage, and the DC current is too large.

Fault analysis and handling are as follows.

a. One thyristor in the inverter circuit is damaged. When a thyristor in the inverter circuit is damaged, the equipment can sometimes be started, but the above fault phenomenon will occur after starting. Replace the damaged thyristor and check the cause of the damage.

b. One of the inverter thyristors is not conducting, that is, it works with "three legs". It is possible that the thyristor gate is open at this time, or the wire connected to it is loose or has poor contact.

c. There is an open circuit or polarity error in the intermediate frequency signal sampling circuit. This reason is mostly found in lines using the intersection method. This fault phenomenon will occur if the intermediate frequency voltage signal is opened or if the polarity of the intermediate frequency voltage signal is reversed when repairing other faults.

d. The inverter front angle phase shift circuit is faulty. The load of the intermediate frequency power supply is capacitive, that is, the current leads the voltage. In the sampling control circuit, a phase shift circuit is designed. If the phase shift circuit fails, this fault will also occur.

③Fault phenomenon: It is difficult to start. After starting, the DC voltage can only rise to a maximum of 400V, and the reactor vibrates loudly and the sound is dull.

Fault analysis and treatment: This fault is a three-phase fully controlled rectifier bridge fault, and its main features are as follows.

a. If the rectifier thyristor has open circuit, breakdown, soft breakdown or electrical parameter performance decline, use an oscilloscope to observe the tube voltage drop waveform of each rectifier thyristor, find the damaged thyristor and replace it. When a damaged thyristor breaks down, its tube voltage drop waveform is a straight line; when the voltage rises to a certain value during soft breakdown, it becomes a straight line; when the electrical parameters decrease, the voltage rises to a certain value, and the waveform changes when the voltage reaches a certain value. If the above phenomenon occurs, the DC current will cut off, causing the reactor to vibrate.

b. Missing a set of rectification trigger pulses. Use an oscilloscope to check each trigger pulse separately (it is better to check on the thyristor). When a circuit without pulse is detected, use the backward method to determine the fault location and replace the damaged components. When this phenomenon occurs, the output wave head of the DC voltage will lack a wave head, causing the current to cut off and causing this fault phenomenon.

c.整流可控硅门极开路或短路。造成不能触发可控硅。一般G-K间阻值在10～30.Q.

④Fault phenomenon: It can be started, but it stops immediately after starting, and the equipment is in a state of repeated starts.

Fault analysis and treatment: This fault is an equipment fault that belongs to the frequency sweep startup method. The reasons are as follows.

a. The lead angle is too small and repeated starts are caused by commutation failure after startup. Use an oscilloscope to observe the intermediate frequency voltage waveform and increase the inverter lead angle appropriately.

b. When the load oscillation frequency signal is at the edge of its scanning frequency signal range, readjust the scanning range of its scanning frequency.

⑤Fault phenomenon: After the equipment is started, when the power rises to a certain value, the equipment is prone to over-current protection. Sometimes the thyristor components will be burned out. After restarting, the phenomenon remains the same.

Fault analysis and handling are as follows:

a. If overcurrent is likely to occur under low voltage just after starting, it is caused by the inverter lead angle being too small, which prevents the inverter thyristor from being able to shut off reliably.

b. The water in the inverter thyristor water-cooling jacket 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 is attached to the wall of the water-cooling jacket. Since scale is a substance with extremely poor thermal conductivity, although there is sufficient water flow, However, the heat dissipation effect is greatly reduced due to the isolation of scale. The judgment method is: run the power at a power lower than the overcurrent value for about 10 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 this caused.

c. If 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. o When the tank connection wire has poor contact or disconnection, an interruption will occur when the power rises to a certain value. The phenomenon of fire affects the normal operation of the equipment. Ka,. After the value is set, sparking will occur, affecting the normal operation of the equipment, resulting in equipment protection action. Sometimes due to sparking, there will be a spark at both ends of the thyristor. An instantaneous overvoltage occurs, and if the overvoltage protection action is too late, the thyristor components will be burned out. This phenomenon often causes overvoltage and overcurrent to operate at the same time.

⑥Fault phenomenon: There is no response when the equipment is started. After observation, the phase loss indicator light on the control circuit board lights up.

Cause of failure: The quick fuse is blown. Generally, quick fuses have a blowing indication. You can judge whether the fuse is burned out by observing the indication. However, sometimes the quick fuse does not indicate or the indication is unclear due to long use time or quality reasons. You need to use a multimeter to measure it after the power is turned off. 

The solution is: replace the quick fuse and analyze the cause of the blowout. Generally, there are four reasons for blowing the fast fuse: a. The equipment operates under high power and high current conditions for a long time, causing the fast fuse to heat up, causing the fuse core to melt; b. The rectifier load or intermediate frequency load is short-circuited, causing an instantaneous fuse. A large current impact will burn out the fast fuse, so check the load circuit; c. A fault in the rectifier control circuit causes an instantaneous high current impact, and the rectifier circuit should be checked; d. The contacts of the main switch are burned out or the front-end power supply system is defective. If there is a phase fault, use the AC voltage range of the multimeter to measure the line voltage at each level to determine the fault location.

⑦Fault phenomenon: The DC current has reached the rated value when the equipment is running, but the DC current and intermediate frequency voltage are low. Use an oscilloscope to observe the intermediate frequency voltage waveform. The waveform is normal and the inverter lead angle is also normal.

Fault analysis and treatment: This fault phenomenon is not an intermediate frequency power supply fault, but is caused by the load impedance being too low, and the load impedance must be readjusted.

a. In the boost load circuit, if the series compensation capacitor is removed due to damage and is not replaced, or if the compensation capacitor is blindly required for high power and the compensation capacitor is increased without restraint, causing the load compensation amount to overcompensate, this fault phenomenon will occur. . The solution is to readjust the compensation amount of the compensation capacitor so that the device can operate at rated power.

b. The sensor has an inter-turn short circuit. If the inductor has a turn-to-turn short circuit, the impedance of its load will also decrease. There are two possibilities for short circuit between turns: the same tube of the sensor is directly short-circuited; the fixed bakelite pillar of the sensor is severely carbonized. Since carbon has conductive properties, the turns of the sensor are directly connected due to the carbonized bakelite, resulting in a short circuit between turns. Yes. The solution is to eliminate the inter-turn short circuit. We will introduce you to more technical issues regarding troubleshooting of medium frequency induction furnaces. Zhengzhou Gou's induction heating equipment manufacturer welcomes you to ask questions about induction heating at any time. Gou's has 15 years of technical experience and is willing to be your capable partner in induction heating.