Troubleshooting and Diagnosis of Common Electrical System Faults in Medium-Frequency Induction Melting Furnaces

Common electrical system faults in medium-frequency induction melting furnaces mainly involve the power supply, control, and induction circuit sections.

Fault Symptoms: Overcurrent/overvoltage protection, failure to start, or tripping during operation.

Possible Causes:

① Inverter thyristor/IGBT breakdown: Damage to power devices is one of the most serious causes, leading to direct short circuits or abnormal conduction of DC current.

② Load short circuit or grounding: Thinning or breakdown of the furnace lining causes molten steel to contact the coil, or insulation damage of the coil leads to a short circuit to ground.

③ Resonant capacitor breakdown: Internal short circuit of one or more capacitors leads to a sudden change in resonant frequency and a sharp increase in current.

④ Water-cooled cable disconnection or poor contact: Loose connections or broken strands inside the cable cause arcing and sudden changes in impedance.

⑤ Trigger circuit abnormality: Damaged pulse transformer or loose trigger wires lead to inconsistent thyristor/IGBT triggering.

Recommended Solutions:

① Immediately shut down the machine and disconnect the main power supply.

② Use a multimeter and megohmmeter to sequentially test the insulation resistance to ground of the inverter bridge power devices, capacitor bank, and induction coil (including the furnace lining).

③ Check the water-cooled cables and connecting bolts for burning or looseness.

④ Check if the trigger pulse signal is normal and synchronized.

⑤ Focus on checking for the risk of furnace leakage: Observe the condition of the furnace lining and verify using the furnace leakage alarm system.