GB962863A - Improvements in surge suppressors - Google Patents

Abstract

962,863. Protective arrangements. STANDARD TELEPHONE & CABLES Ltd. Aug. 10, 1962 [Aug. 15, 1961], No. 30797/62. Heading H2H. A surge suppressor for connection between the output terminals +, - of a supply source, such as a filter L, C1, and a load, e.g. a resistor R1, comprises the series combination of a resistor R2, a capacitor C2 and a siliconcontrolled rectifier W connected across the load, a Zener diode D for deriving a control potential, which is applied to the rectifier W, when the voltage at the output terminals of the source exceeds a predetermined value, and a discharge resistor R3 connected across the capacitor C2 in series with the contacts r1 of a relay RL bridging the resistor R2. Rectifier W is normally non-conducting, but is rendered conducting by the control potential from the Zener diode D which breaks down when the supply voltage rises to, say 10% above normal, as may happen when a transient voltage surge appears on removal of the load. When the rectifier W conducts, the current flowing through resistor R2 causes relay RL to operate, opening contacts r1 and allowing capacitor C2 to charge. The decrease in load current thus follows an exponential curve and the transient voltage surge at the output terminals +, - is limited to a predetermined value. When the current falls to a value below the hold-in current of the rectifier W, the relay RL falls out and the contacts r1 close; the capacitor C2 then discharges through the resistor R3 and the suppressor is prepared for a new transient. The circuit may include an auxiliary relay which gives the arrangement a longer release time (Fig. 3, not shown).