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

Fault analysis and treatment are as follows:

a. One thyristor of the inverter circuit is damaged. When one thyristor in the inverter circuit is damaged, the equipment can be started sometimes, but the above fault phenomenon will occur after startup. Replace the damaged thyristor and check the cause of damage.

b. One of the inverter thyristors does not turn on, that is, the "three legs" work. It is possible that the thyristor gate is open, or the wire connected to it is loose and has poor contact.

c. If signal sampling circuit has open circuit or wrong polarity. This reason is mostly due to the open circuit of the if voltage signal in the line using the intersection angle method or the reversal of the polarity of the if voltage signal when repairing other faults.

d. The inverter leading forward angle phase shift circuit is faulty. The load of if power supply is capacitive, that is, the current is ahead of the voltage. In the sampling control circuit, phase-shifting circuit is designed. If the phase-shifting circuit fails, this fault phenomenon will also be caused.