The faults of induction furnace can be divided into two categories according to the fault phenomenon: completely unable to start and unable to work normally after starting. Therefore, these two factors are mainly considered in the maintenance of induction furnace. As a general principle, when the fault occurs, the whole system should be comprehensively checked under the condition of power failure, mainly from the following aspects:
1. Power supply: use a multimeter to check whether there is power behind the main circuit switch (contactor) and control fuse, which will eliminate the possibility of these components open circuit.
2. Rectifier: the rectifier adopts three-phase full control bridge rectifier circuit, which includes six fast fuses, six thyristors, six pulse transformers and one freewheeling diode. There is a red indicator on the fast fuse. Normally, the indicator is retracted in the shell. When the fast fuse is burnt out, it will pop up. Some fast fuse indicators are tight. When the fast fuse is burnt out, it will be stuck in it. Therefore, for the sake of reliability, you can use the multimeter to measure the fast fuse to determine whether it is burnt out.
3. Inverter: the inverter includes four fast thyristors and four pulse transformers, which can be checked according to the above methods.
4. Transformer: each winding of each transformer should be connected. Generally, the primary side resistance value is about tens of ohm, and the secondary pole resistance value is several ohm. It should be noted that the primary side of the medium frequency voltage transformer is in parallel with the load, so its resistance value is zero.
5. Capacitor: the electric heating capacitor in parallel with the load may be broken down. The capacitors are generally installed on the capacitor rack in groups. The group of the broken down capacitor should be determined first during the inspection. Disconnect the connection point between the bus bar and the main bus bar of each group of capacitors, 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 sheet from each electric heating capacitor to the bus bar, and check one by one to find the broken capacitor.
6. Water cooled cable: the function of water cooled cable is to connect intermediate frequency power supply and induction coil. It is made of 0.6 - 0.8 copper wire with each diameter. For a 500kg furnace, the cable cross-sectional area is 480 sq. mm. For a 250kg furnace, the cable cross-sectional area is 300 to 400 sq. mm. The outer rubber tube of the water-cooled cable is a 5kg pressure rubber tube with cooling water inside. It is a part of the load circuit. When it works, it is pulled and twisted and tilts with the furnace body, so it is easy to break at the flexible connection after a long time.
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