Intermediate frequency furnace maintenance: overcurrent or overvoltage protection action when power is increased

Fault phenomenon

The IF power supply works normally at low power, and the overcurrent or overvoltage protection action occurs when the power is increased.

Fault analysis and processing

The following parts should be inspected for malfunctions.

(1) Check whether the thyristor components of the main circuit are aging, and whether the current and voltage withstand values are degraded.

(2) Check whether the main circuit thyristor RC absorption circuit is in poor contact, with or without damage.

(3) Check the insulation of the reactor and the insulation between the induction coils.

(4) Check if the cooling water circuit is blocked, if the water temperature is too high, and if the water pressure is too low.

(5) Check if the withstand voltage of the compensation capacitor drops.

(6) Check whether the anti-interference performance of the control system is degraded (especially the thyristor trigger circuit), because the interference will increase as the IF power increases, and the overcurrent or overvoltage protection may malfunction.

(7) Check if the inverter circuit triggers the lead angle too small. When the current rises, the commutation is unsuccessful and the overcurrent protection action is performed.

(8) Use the oscilloscope to check whether the thyristor waveform of the main circuit is normal (whether the rectifier circuit output is out of phase, and whether the inverter circuit output is out of phase).

(9) Check if the insulation of the main circuit is reduced.

(10) Check if the overcurrent and overvoltage setting values change.