DE755145C - Protection arrangement against inadmissible voltage increase in the excited state for medium and high frequency generators - Google Patents

Description

In the case of medium and high frequency generators for supplying ironless induction furnaces, a combined arrangement of capacitors connected in series and in parallel to the furnace is very often used for better current and voltage control on the furnace. Such a circuit is illustrated in the drawing. A capacitor ci is connected in series with the generator g, which feeds the coil s of an induction furnace, while capacitors c. and c. the furnace coil are connected in parallel. If the capacitive resistance of the series capacitor is approximately equal to the total inductive resistance of the generator, then in the event of a full or partial short circuit on the furnace coil or on the capacitors c., C .. the voltage at the terminals of the Generator with a very high generator current can reach very high values which endanger the winding of the generator. A fast de-energization of the generator provided for such a case would come much too late, since the voltage rises immediately, while the fast de-energization takes a considerable amount of time due to the required relay times and the existing magnetic inertia of the generator.

It is known that surge arresters are used to divert overvoltage waves to serve. According to the invention, the generator is thereby protected against an inadmissible increase in voltage in the excited state assured that he was by a cathode drop arrester of essential lower leakage resistance than required to divert surge waves is bridged, so that when a certain voltage is exceeded, an impermissible Self-excitation of the gentrator is prevented. For short-circuit-like bridging of the terminals of power generators, the surge arresters must therefore be dimensioned differently as for their actual purpose, and under otherwise equal conditions they have a much larger leakage resistance than for the purposes of the invention. To this In this way, an almost inertia-free bridging with a short-circuit-like effect is achieved achieved as a result of small resistance.

The machine and the very strong attenuation is known, in Central and "high-frequency machines Stoßkurzsehlußstroin and duration of short-circuit current, due to the high leakage reactance extremely small. The continuous short-circuit current is even smaller than the rated current. Therefore, if there is a risk of overvoltage, the generator can be bridged in the manner of a short circuit without disadvantage. However, a conventional switch cannot be used for this purpose, because the switch cannot be closed before the overvoltage occurs due to the required actuation time of such a switch. On the other hand, bridging in good time is possible with the aid of a cathode drop arrester, which becomes effective when a certain voltage is reached, without the voltage first assuming inadmissibly high values. At the same time, the subsequent rapid de-energization is advantageously initiated, which makes the machine de-energized.

Claims (2)

PATEIX CLAIMS: i. Protection arrangement against inadmissible voltage rise in the energized state for medium and high frequency generators, especially for those which work on an inductive resistance via capacitors connected in series and in parallel, characterized in that the generator (g) by a cathode drop arrester (k) of substantially smaller bleeder resistance than is necessary to dissipate overvoltage waves , so that if a certain voltage is exceeded, an inadmissible self-excitation of the generator is prevented. 2. Protection arrangement according to claim i, characterized in that the bridging of the generator (g) initiates a subsequent rapid de-excitation. To distinguish the subject matter of the invention from the state of the art, the following publications were taken into account in the granting procedure: German patent specifications No. 36o 974, 361 029, 324074, 364603; Special print DS 2392, "High Frequency Furnaces with Mercury Spark Stripes", published by Hirsch, Kupfer- und Messingwerke- AG, November 1, 1928; AEG list Tr. 4, 1935, p. Q and 21 -. VDE guidelines o675 / I, 38, p. 13, lines 1 to 3.