The use of steel-tank mercury-arc inverters for generating medium frequencies for induction heating

The paper presents in a non-mathematical way a general survey of the circuit operation and construction of 6-anode steel-tank mercury-arc inverters for the generation of medium-frequency power, in the output range up to 250kW at 1¿2kc/s. The basic operation of the inverter circuit is first described, together with some features of practical inverter circuits, including the problem of starting inversion without modifying or previously exciting the tuned output circuit. The characteristics and limitations of the inverter valve and other main-circuit components are discussed, together with the requirements of different types of melting and billet-heating furnaces. The problem of designing circuits to meet all the varied control requirements has been met by the development of an electronic grid-control unit, which ensures reliable starting and gives facilities for automatic frequency and voltage control. A general description is given of installations in service for forge heating and melting.