Abstract: The functional condition of an induction crucible furnace is checked by first establishing a set-point parameter corresponding to an optimum functional condition of the induction crucible furnace and characterizing the vibratory behavior of same. Then, during normal operation of the furnace, an actual-value parameter of the vibratory behavior is determined. These two parameters are then compared and, if a magnitude of a difference therebetween exceeds a threshold, an alarm is generated.

Abstract: The invention relates to an induction crucible furnace and to a magnetic return element for an induction crucible furnace. The induction crucible furnace has a corresponding coil and a plurality of magnetic return elements, which are designed in the form of individual units arranged on the outer lateral surface of the coil with peripheral spacing. In order to guide the magnetic flux produced by the coil, the magnetic return elements each have an assembly consisting of a plurality of elongate individual elements of magnetically permeable material that are electrically insulated from each other and extend parallel to the furnace axis. Said individual elements consist at least partially of bars, which are electrically insulated from each other and the longitudinal axes of which extend parallel to the furnace axis. In this way, both eddy currents that hit the assembly from the radial direction and eddy currents that hit the assembly with a transverse component are minimized.

Abstract: A method and an apparatus for automatically detecting the intactness of ground electrodes in the bath of an induction furnace are described. According to the method a low DC or AC current is applied to an additional insulated electrode extending through the furnace bottom and being in connection with the melt. After melting of the charge this current is measured and compared with a reference value. If the magnitude of the current drops below the reference value an alarm signal is generated. Furthermore, methods and devices for localizing a ground fault are described. By this, the security of the operation of an induction furnace is improved.

Abstract: An apparatus for detecting ground faults in a multifurnace installation with at least two induction furnaces and a multifurnace installation are described. A ground-fault sensor is associated with each induction furnace and is connected to the electrical supply line to the induction furnace coil. Furthermore, the apparatus has a ground-leak sensor. Moreover, the apparatus includes an additional ground-fault sensor that measures at the same location as the ground-leak sensor. In this manner an improvement of security during the operation of the system is obtained.

Abstract: A method and an apparatus for detecting a ground fault in an induction furnace as well as an induction furnace are described. When a ground fault is detected by means of the ground-fault detector the ground fault is localized. By doing this it is determined if the ground fault is caused by a failure of the refractory lining or by other reasons. If the ground fault is caused by other reasons it is ascertained if it is caused by a defective magnetic yoke insulation. Furthermore, it can be ascertained which magnetic yoke of the induction furnace causes a ground fault. In this manner the induction furnace can be operated with improved security and smaller expense.