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How to troubleshoot the medium-frequency electric furnace?

The medium frequency electric furnace is an induction heating device that uses the principle of electromagnetic induction to heat metal. It is a variable-frequency power supply device of the medium frequency electric furnace that passes alternating current to the induction coil to generate alternating current at the same frequency. The alternating current is generated in the medium frequency electric furnace induction coil. Variable magnetic field. The alternating magnetic field cuts the metal charge in the crucible, the charge in the induction coil of the medium frequency electric furnace generates an induced electromotive force, and an induction circuit is generated in the charge, so an induced current-” eddy current” is generated in the charge at the same time, and the charge is based on the “eddy current” Heating and melting cause the charge to generate heat. Heating according to this principle is called induction heating, which is the principle of a medium-frequency electric furnace.

Huaxin Electric Furnace is one of the professional induction furnace manufacturers in China. Through nearly 30 years of experience in the industry, the following experience has been obtained: From the principle of the medium frequency electric furnace, the failure phenomenon of the medium frequency electric furnace is divided into completely unable to start and unable to start after starting. There are two categories of normal work. As a general principle, when a fault occurs, the entire system should be inspected completely in the event of a power failure, which includes the following aspects:

(1) Medium frequency electric furnace power supply: Use a multimeter to check whether there is electricity behind the main circuit switch (contactor) and control fuse, which will rule out the possibility of disconnection of these components.

(2) Medium frequency electric furnace rectifier: The rectifier adopts a three-phase fully controlled bridge rectifier circuit, which includes six fast fuses, six thyristors, six pulse transformers, and a freewheeling diode. There is a red indicator on the quick-acting fuse. Normally, the indicator is retracted inside the shell. When the quick-acting blows, it will pop up. Some quick-acting indicators are tight. When the quick-acting blows, it will get stuck inside. , So for the sake of reliability, you can use a multimeter to test the fast-blow on/off gear to determine whether it is blown.

The simple way to measure the thyristor is to measure its cathode-anode and gate-cathode resistance with a multimeter electrical barrier (200Ω block), and the thyristor does not need to be removed during the measurement. Under normal circumstances, the anode-cathode resistance should be infinite, and the gate-cathode resistance should be between 10-50Ω. Too large or too small indicates that the gate of this thyristor fails, and it cannot be triggered to conduct.

The secondary side of the pulse transformer is connected to the thyristor, the primary side is connected to the main control board, and the primary resistance is about 50Ω measured with a multimeter. The freewheeling diode is generally not prone to failure. When checking, use a multimeter diode to measure its two ends. In the forward direction, the multimeter shows that the junction voltage drop is about 500mV, and the reverse direction is blocked.

(3) Medium frequency electric furnace inverter: the inverter includes four fast thyristors and four pulse transformers, which can be inspected according to the above methods.

(4) Medium frequency electric furnace transformer: Each winding of each transformer should be connected. Generally, the resistance value of the primary side is about tens of ohms, and the second pole is a few ohms. It should be noted that the primary side of the medium frequency voltage transformer is connected in parallel with the load, so its resistance value is zero.

(5) Medium frequency electric furnace capacitors: capacitors connected in parallel with the load may be broken down. The capacitors are generally installed in groups on the capacitor rack. The group of broken capacitors should be determined first during an inspection. Disconnect the connection point between the bus bar of each group of capacitors and the main bus bar, and measure the resistance between the two bus bars of each group of capacitors. Normally, it should be infinite. After confirming the bad group, disconnect the soft copper skin that each capacitor leads to the bus bar, and check each one to find the capacitor that has broken down. Each capacitor is composed of four cores. The shell is one pole, and the other pole is led to the end cover through four insulators. Generally, only one core will be broken down, and the lead on this insulator will jump off. The capacitor can continue to be used, and its capacity is 3/4 of the original. Another fault of the capacitor is oil leakage, which generally does not affect the use, but pays attention to fire prevention.

The angle steel where the capacitor is installed is insulated from the capacitor frame. If the insulation breakdown will ground the main circuit, measure the resistance between the capacitor shell lead and the capacitor frame to determine the insulation status of this part.

(6) Water-cooled cable for medium frequency electric furnace: The function of the water-cooled cable is to connect the medium frequency power supply and the induction coil. For a 500 kg electric furnace, the cable cross-sectional area is 480 square millimeters, and for a 250 kg electric furnace, the cable cross-sectional area is 300 to 400 square millimeters. The outer hose of the water-cooled cable adopts a pressure rubber hose with a pressure resistance of 5 kg, which is filled with cooling water. It is a part of the load circuit. It is subjected to tensile and torsion forces during operation. The connection is broken. The breaking process of the water-cooled cable generally involves cutting off most of the parts first, and then quickly breaking the unbroken part during high-power operation. At this time, the medium-frequency power supply will generate a very high overvoltage. If the overvoltage protection is unreliable, it Will burn out the thyristor. After the water-cooled cable is disconnected, the medium-frequency power supply cannot start to work. If you restart repeatedly without finding out the cause, the medium-frequency voltage transformer is likely to be burned out. When checking the fault, use an oscilloscope to clamp the oscilloscope probe at both ends of the load and observe whether there is an attenuation waveform when the start button is pressed. When confirming that the cable is broken, first disconnect the water-cooled cable from the capacitor output copper bar, and measure the resistance of the cable with a multimeter (200Ω block). The resistance value is zero when it is normal, and it is infinite when it is disconnected. When measuring with a multimeter, the furnace body should be turned to the dumping position to make the water-cooled cable fall off, so that the broken part can be completely separated, so that it can be correctly judged whether the core is broken.

The principle of the medium frequency electric furnace can be seen from the above description as an induction heating device based on electromagnetic induction, and the faults generated by it can also be analyzed and resolved from the principle of the medium frequency electric furnace.Induction melting furnace,induction furnace manufacturers