Method for troubleshooting thyristor burning loss of intermediate frequency electric furnace inverter bridge

GW MB10F 0.8A 1000V rectifier bridge

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Filter 18.432M

Before introducing the common faults of the Inverter Thyristor burning in the intermediate frequency electric furnace, let us briefly understand the basic working principle of the thyristor intermediate frequency power supply: the alternating current is rectified into a direct current through a three-phase Bridge Rectifier circuit to convert the 50 Hz power frequency alternating current into a direct current. It is filtered by a filter (DC reactor), and finally the DC is converted into single-phase IF (200 Hz to 8000 Hz) by the inverter to supply the load. Therefore, the working principle of this intermediate frequency power supply is actually: grid AC-rectifier DC--intermediate frequency communication.
Let us take the 3 ton intermediate frequency electric furnace as an example to illustrate the working principle of the intermediate frequency power supply: the power supply of the 3 ton intermediate frequency electric furnace is the company's power grid through the transformer, and the 570V power frequency 50 Hz alternating current is sent to the electric furnace control power supply, after three-phase bridge rectification, The 570V AC is rectified to about 750V DC. After being filtered by the reactor, it is connected to the inverter circuit and alternately turned on by the two bridge arms of the inverter thyristor to obtain a 1000V intermediate frequency power supply. After the compensation capacitor is doubled, it will be about 2000V. The intermediate frequency AC power is delivered to the induction coil, which is magnetized by the yoke, and the eddy current principle melts the molten iron.
Inverter thyristor burnout is the most common medium frequency electric furnace, but the most difficult to eliminate. Whether it is over-voltage or over-current caused by thyristor burnout, in general, it is necessary to use the elimination method to narrow the fault range and eliminate the fault.
The other main reason is that the current and large voltage are out of control, and the voltage of the high-voltage uncontrolled medium-frequency electric furnace principle rises to a certain value. The inverter is subverted and cannot operate under high impedance. The withstand voltage of the component is lowered or the cooling effect is not good. The insulation performance of the system is reduced. When the voltage of the intermediate frequency induction furnace rises, the machine is short-circuited to the ground, and the intermediate frequency capacitor and the furnace are checked. Interference may also cause the inverter trigger line to be higher than the main circuit. In addition, the large current is out of control, the back pressure angle of the intermediate frequency voltage is too small, the trigger circuit is in poor contact, and the continuity of the off time is also to be noted.
The following concludes that the maintenance technician can follow the steps below to check the inverter thyristor step by step, and narrow down the fault range.
The first step: whether the furnace body (1) insulation coil insulation layer is damaged (2) whether the insulation between the induction coil and the yoke is intact (3) whether the water-cooled cable has a drum package or whether the joint is loose (4) the furnace body cooling water pipe has No leakage and blockage (5) Whether the grounding protection is intact Note: After confirming that each checkpoint is in good condition, switch the furnace body to send the test furnace.
Step 2: Change the furnace switch (1) Change the furnace switch to be completely separated, no conductor overlap (2) Change the furnace switch contact to be smooth, effectively combine (3) Change the furnace switch Water-cooled pipeline unblocked Note: After power failure, Carefully check the components of each part of the furnace switch.
Step 3: Discharge copper (1) Separate the bakelite of the copper row with or without carbonization (2) Ensure that there is no overlap between the copper bars. (3) The water-cooled pipe at the copper-plated interface is well-connected. Note: Check each of the inspection points. Item, make sure it is normal.
The fourth step: compensation capacitor (1) check the compensation capacitor for leakage and drum kit (2) tap the capacitor housing, listen to the sound to determine whether the capacitor has internal space (3) capacitor water-cooled tube with or without leakage (4) Use a multimeter capable of measuring capacitance, measure the on/off of the capacitor (5) Discharge the reactor with good wiring Note: Check and repair according to the troubleshooting points.
The fifth step: filter reactance (1) filter reactor water-cooled tube must be intact (2) reactor core internal core no displacement Note: check and repair according to the inspection point.
Step 6: Inverter bridge (1) Check the thyristor installation concentricity and compression degree (2) Check whether the thyristor resistance capacity protection is intact (3) Check whether the voltage transformer is normal Note: You can prepare a set of inverter bridge on the ground Assemble and replace it on the power supply.
Step 7: Rectifier bridge (1) Check the thyristor installation concentricity and compression degree (2) Check whether the thyristor resistance and capacitance protection is intact (3) Check whether the current transformer is normal Note: Check and repair according to the inspection points one by one.
Step 8: Motherboard (1) When the electric furnace is in good condition, copy the main parameters of the thyristor to the main parameters of the thyristor. When the electric furnace fails, check whether the parameters are consistent, whether there is drift or not. (2) Check the motherboard carefully. Each plug, with or without wire breakage and looseness Note: Replace the motherboard for use.
However, the quality of electronic components manufactured today has passed, and if the process is good, the reliability is already very high. Inverter thyristors are relatively weak components. Frequent damage to the inverter thyristor can also be checked.
The resistance-capacitance absorption circuit of the inverter tube focuses on checking whether the absorption capacitor is open. At this time, a digital multimeter capable of measuring the capacitance should be used to detect the capacitor, and it is not enough to measure only its on and off. If the inverter absorption loop is broken, the inverter tube is easily damaged.
1) Check whether the electrical parameters of the pipe meet the requirements and eliminate the components flowing into the unqualified manufacturer.
2) Whether the water-cooled sleeve of the inverter circuit and other cooling water channels are blocked, although this situation is relatively rare, it does appear and is easy to ignore.
3) Pay attention to the phenomenon that the load is sparked to the ground. This situation will form a sudden high voltage, which will cause breakdown of the inverter tube.
4) If the running angle is too large or too small, it will cause frequent overcurrent of the inverter tube, which will damage the pipe and cause permanent damage.
5) Without affecting the start-up, appropriately increase the intermediate frequency loop wiring inductance of the intermediate frequency inverter power supply to the furnace body, which can alleviate the damage caused by the excessive di/dt of the inverter tube.