Main fault of the load circuit of the intermediate frequency induction furnace

Main fault of the load circuit of the intermediate frequency induction furnace
The load circuit includes an induction furnace (mainly an induction coil). IF compensation capacitors, intermediate frequency transformers, connecting busbars and water soft cables. Therefore, the load loop fault is mainly caused by the loss of the original index of the above components. When the load loop generates a fault, the following main phenomena will occur: 1 The intermediate frequency power supply cannot start the work; 2 can start the work, but the inverter fails when a certain voltage or current is reached, the protection action stops; 3 can start, but the irregular inverter occurs. Subversion; 4 power supply can work normally but often burns the inverter thyristor phenomenon.
1. The IF compensation capacitor is shorted. In the parallel inverter, the intermediate frequency compensation capacitor is connected in parallel with the inductor. When the intermediate frequency compensation capacitor is short-circuited, the load circuit is short-circuited, so that the load circuit cannot oscillate, and the intermediate frequency power supply cannot work. In order to find the short-circuited capacitor, the release test method can be used, that is, two or three intermediate frequency compensators are disconnected each time, the test is started, and the intermediate frequency can be normally started, indicating that the off-disconnection is short-circuited in the set of intermediate frequency capacitors. . At this time, the 10K file of the multimeter can be used to measure both ends of the capacitor. The short-circuit capacitor has zero resistance and cannot be charged; the normal capacitor is zero when the multimeter is connected, and then the pointer gradually moves to the high resistance end, and the general resistance exceeds 500KΩ. The capacitor is normal.
2. The intermediate frequency compensation capacitor has a reduced withstand voltage. At present, the main types of thyristor intermediate frequency power supply adopting intermediate frequency compensation capacitors are RWF0.75~180~1 or RWF0.75~360~1, and their withstand voltage is 750V. When the MF capacitor withstand voltage is reduced, the inverter will fail after the IF power supply operates at a fixed IF voltage. The fault detection method can be the same as the first point, and the capacitor with a resistance less than 500KΩ generally has a reduced withstand voltage.
3. The IF compensation capacitor is open. When the IF compensation capacitor is open, it has little effect on the normal operation of the IF power supply, except that the frequency of the power supply is higher than normal. At this time, only a few new IF compensation capacitors are on the slot to make the frequency reach the normal value.
4. The sensor is shorted between turns. When the sensor is severely short-circuited, the IF power supply cannot start working. If the sensor has two collisions, the intermediate frequency power supply may start, but the frequency is higher, the current is larger, and the power is slightly increased, which may cause the inverter to fail. Another phenomenon is that the sensor is loose. When the power is low, the power supply is not abnormal. However, when the power is increased, the current is increased, the electromagnetic force is increased, and the inductors are attracted to each other, or the vibration is increased during the feeding. In this case, the IF power supply sounds abnormally due to a sudden change in the operating parameters. The cause of the above-mentioned failure is generally caused by the water being broken during operation of the inductor and the severe insulation of the inductor between the turns. It is not difficult to find these faults as long as they are carefully checked before normal work. When the discriminating is difficult, they can be replaced by intact sensors to determine the presence or absence of the above faults.
5. The charge is shorted through the copper tube of the inductor, which is equivalent to the short circuit of the secondary side of the transformer, which is also equivalent to the short circuit of the inductor, so that the intermediate frequency power supply cannot start working.
6. The water cable is broken. When the molten steel is poured into the molten steel, the water-passing soft cable is tilted together with the furnace and often has a tortuous phenomenon. In particular, the connection to the melting furnace and the connection of the flexible cable are brazed and welded, so that it is easily broken at the weld. The breaking process of multi-stranded flexible cables is often broken off most of the time, and the unbreaked small part is quickly blown during high-power operation. At this time, the intermediate frequency power supply will generate a very high voltage. If the overvoltage protection is unreliable, The inverter thyristor will be damaged. After the water soft cable is disconnected, the intermediate frequency power supply cannot start working. Repeated start-up without checking the cause can damage other electrical components. Check whether the water-cooled cable is broken or not. First, disconnect the soft cable from the output bus of the IF compensation capacitor. When measuring, turn the furnace to the dumping position to lift the cable, so that the broken core wire and the joint are completely detached. Measured with the multimeter RX1 file, R is zero when continuous, and R is infinite when disconnected. In this way, the core breakage can be correctly judged.
7. The intermediate frequency compensation capacitor and the output busbar, the busbars of the busbar and the busbar, and the busbars and the flexible cables are loose. Since the current flowing through the busbar is large, the temperature of the busbar during operation is also high, so that the connecting bolt is easily loosened, the contact resistance is increased after loosening, and the temperature of the joint is increased. If the temperature is too high due to looseness, the surface of the busbar joint will be oxidized, causing poor contact and sparking. Inverter failure is often caused by fire disturbance. Therefore, all connecting bolts on the intermediate frequency power bus should be checked and tightened frequently to cause poor contact and open circuit failure.
8. The short circuit of the furnace inductor and the intermediate frequency compensation capacitor to the ground is the same as the short circuit of the main circuit to the ground, which often causes serious failure of burning the thyristor. Therefore, when there is a fault in the burnt-out thyristor, in addition to the inspection of the protection system, it is also necessary to check whether the induction coil is grounded or the intermediate frequency compensation capacitor casing is short-circuited or poorly insulated. Generally, the multimeter R×1K file is used to check that the resistance of the inductor and the compensation capacitor case should be about 10KΩ. The new snoring is low due to humidity, but it should not be less than 5KΩ. As for the insulation drop, it is difficult to judge because the voltage of the multimeter battery is low, and it can be inspected with 500~2500 volts megohmmeter.
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