Example 3 of induction furnace trouble shooting

Fault phenomenon: it is difficult to start. After starting, the medium frequency voltage is more than twice of the high DC voltage, and the DC current is too large.

Fault analysis and treatment are as follows:

A. one thyristor in the inverter circuit is damaged. When one of the thyristors in the inverter circuit is damaged, the equipment can be started sometimes, but the above fault phenomenon will appear after starting. Replace the damaged thyristor and check the cause of damage.

B. one of the thyristors in the inverter is not conducting, that is, three legs work. It is possible that the gate of the thyristor is open at this time, or the wire connected with it is loose or in poor contact.

C IF signal sampling circuit has open circuit or in the maintenance of other faults, the polarity of if voltage signal is reversed will cause secondary fault.

D. the front angle phase-shifting circuit of the inverter is faulty. The load of medium frequency voltage is capacitive, that is, the current is ahead of the voltage. In the sampling control circuit, there is a phase-shifting circuit, if the phase-shifting circuit failure will also cause this fault phenomenon.

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