GB420282A - Improvements relating to protection devices for electrical discharge vessels, particularly rectifiers - Google Patents

Abstract

420,282. Rectifying alternating current. SIEMENS - SCHUCKERTWERKE AKT.- GES., Siemensstadt, Berlin. June 29, 1934, No. 19288. Convention date, Sept. 7, 1933. [Class 38 (ii)] In rectifier installations employing gridcontrolled discharge devices in which the grids are subjected to a negative biassing voltage on which are superimposed positive voltage impulses for effecting ignition, the circuits from which the two voltages are derived are made interdependent and provision is made whereby in the event of fault conditions arising the negative bias is increased and the ignition impulses are simultaneously reduced or suppressed. In one arrangement, Fig. 1, the ignition impulses are derived from a transformer 2 fed through a choke or series transformer 4 from a supply 3. The negative bias is derived from a secondary winding on the transformer 4 associated with rectifiers 5. The core of the transformer 4 is normally saturated by a winding 6 in the circuit of the exciter anode 7. In the event of fault conditions arising, a switch 8 in the latter circuit is caused to open thus allowing the core of the transformer 4 to desaturate and thereby causing an increase in the biassing voltage and, by reason of an increase in the choking effect of the series transformer, a decrease in the amplitude of the ignition impulses. In an alternative arrangement, Fig. 3, in which the ignition impulses are supplied by a transformer 10 and the biassing voltage by a series transformer 12 through a rectifier 13, an automatic switch 14 actuated under fault conditions by a current transformer 15 in the primary circuit of the main supply transformer suppresses the ignition impulses and increases the negative bias by interconnecting the leads between the transformers 10 and 12.