Maintenance of intermediate frequency melting furnace: failure to burn thyristor repair, do not start immediately after replacing the new thyristor, firstly check the system fault of the intermediate frequency melting furnace, and then confirm the failure of the intermediate frequency melting furnace, then turn it on again, otherwise there will be a boot It burns the thyristor. When pressing a new thyristor, it is necessary to pay attention to the pressure equalization. Otherwise, the chip inside the thyristor will be mechanically damaged, resulting in a significant drop in the withstand voltage of the thyristor, and the phenomenon of burning the thyristor when a power is turned on.

1. The thyristor intermediate frequency power supply operates normally, but burns more KP thyristors and fast melts during normal overcurrent protection. Analysis and processing:

In order to release the energy of the smoothing reactor to the grid during overcurrent protection, the rectifier bridge is switched from the rectified state to the inverting state. If α>120 degrees, it may cause active inverter subversion, burn more thyristors and fast. Melting, the switch trips, and accompanied by a huge current short-circuit explosion sound, causing a large current and electromagnetic force impact on the transformer, in severe cases, the transformer will be damaged.

2. The medium frequency melting furnace can start at no load, but the DC voltage does not reach the rated value. The DC smoothing reactor has shock sound and is accompanied by jitter analysis. Turn off the inverter control power supply and connect the dummy load to the output of the rectifier bridge. Observe the output waveform of the rectifier bridge with an oscilloscope. You can see the phase loss waveform of the rectifier bridge output. The reason for the lack of phase may be:

(1) The intermediate frequency melting furnace rectification trigger pulse is lost;

(2) The amplitude of the trigger pulse is not too narrow, which results in insufficient trigger power, which causes the thyristor to pass through;

(3) The pulse timing of the double pulse trigger circuit is incorrect or the pulse is lost;

(4) The control pole of the intermediate frequency melting furnace thyristor is open/short/poor.