1) The circulating water system is the core concern in the normal operation of the complete set of equipment of the medium frequency boiler, which can be focused on from the following two points.

A. Cooling water temperature too high

In the medium frequency furnace system, when the outlet water temperature of the cooling water exceeds the specified allowable value, it is easy to cause scale, or even vaporize the water, resulting in accidents. Therefore, a water temperature gauge shall be set at the outlet of each branch water cooling pipe. When the water temperature at the outlet of any waterway exceeds the allowable value, an alarm signal will be sent back to the intermediate frequency power control system to stop the machine in time to prevent accidents.

B. Cooling water pressure decreases

When the water pressure of cooling water is lower than the required value, the cooling conditions will be destroyed. An electric contact water pressure gauge is installed on the main cooling water inlet pipe. When the water pressure drops below the allowable value, an alarm signal will be sent back to the intermediate frequency power control system to cut off the sensor power supply circuit in time.

2) Main circuit system protection measures

A. Overcurrent and short circuit protection

The differential protection overcurrent relay is installed. In case of overcurrent and short circuit accidents in the main circuit, the main circuit will be automatically cut off and an alarm signal will be sent.

B. Undervoltage protection

An undervoltage relay is connected in front of the main circuit closing contactor. When the main circuit is powered off, the closing contactor of the main circuit will automatically jump off with accident signal indication. Switch on again during the next call.

C. Overvoltage protection

An overvoltage absorber shall be installed at the secondary of the transformer to prevent operation overvoltage, transformer primary and secondary side puncture and overvoltage caused by lightning stroke.

D. Capacitor discharge protection

After the main circuit is powered off, the capacitor must be discharged for safety. The capacitor is automatically discharged through the load, and the variable capacitor is automatically put into the circuit of connecting resistance for discharge.

3) Transformer oil temperature indication and gas protection

The electric furnace transformer has oil temperature indication to monitor the oil temperature. Gas protection is also installed on the electric furnace transformer with large capacity (above 800kVA). When a fault occurs and the gas relay acts, the power supply circuit is cut off and there is an alarm signal.

4) Crucible leakage and main circuit grounding protection

Crucible alarm device is installed. When the crucible leaks or the main circuit is grounded, cut off the power supply and send out an alarm signal.