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Inverter System Grounding Alarm

At Medium-frequency furnace During operation, the furnace coil and capacitor form a high-voltage resonant circuit. Once high-voltage discharge to ground occurs in a situation where the ground insulation resistance is low, it can easily lead to a serious safety accident. To ensure the proper functioning of the equipment, it is necessary to install a leakage protection device.

Common ground fault protection systems perform two functions:

First, check whether there are any abnormally low-resistance paths inside the capacitor, furnace coil, and busbar for current convergence.

 

Second, check whether there is an abnormally low-resistance path between the furnace coil and the metallic charge. This could be caused by “iron penetration” in the furnace lining that has infiltrated the metallic charge, or by excessive moisture content within the furnace lining. Additionally, conductive debris falling into the furnace lining during tamping can also lead to a decrease in resistance.

 

The principle of a common alarm system is as follows: in Resonant circuit A low-current DC power supply is connected between the coils of a conventional medium-frequency furnace. Since there is only slight insulation between the coils, the applied DC voltage will induce a tiny leakage current between the coils and the molten pool, which can be detected using a milliammeter. When an ultra-high-frequency signal indicative of leakage current appears, it indicates that the ground resistance of the resonant circuit has dropped abnormally. The melting furnace is equipped with leakage protection: typically, stainless steel wires are led out from the furnace lining at the bottom of the furnace body and grounded. This not only ensures that the molten pool remains at zero potential but also prevents safety accidents during slag removal. Furthermore, this setup enables the system to accurately detect the "iron leakage" condition.

 

To check whether the ground fault alarm system is functioning properly at all times, you can: Resonant circuit By using a small amount of wire in the grounding inductor and contactor, and manually creating a ground short circuit through control of the contactor, you can test the sensitivity of the alarm system.