GB801505A - Improvements in measuring electromagnetic relay devices - Google Patents

Abstract

801,505. Electromagnetic relays. ALLMANNA SVENSKA ELEKTRISKA A.B. Jan. 28, 1957 [Jan. 31, 1956], No. 2926/57. Class 38 (5). An arrangement including a D.C. relay which operates when a current or voltage changes suddenly by an amount exceeding a predetermined value or changes by an amount per unit of time which exceeds a predetermined value, comprises, Fig. 1, a normally balanced bridge circuit having resistors 1 ... 4, the resistor 1 being shunted by a condenser 5, so that when there is no change in the supply connected to 6, 7 there is no voltage across the relay winding 10. However, should the supply increase or decrease the condenser 5 will charge or discharge and a voltage arises across the winding to operate the relay. The arrangement may be made to respond to an increase only, or a decrease only by using a polarized relay or by connecting a rectifier in series or in parallel with the relay winding. In a modification (not shown) the relay has two oppositely-acting windings connected in the bridge arms 1, 2. According to the Fig. 2 arrangement which responds only to an increase in the supply the oppositively-acting relay windings 11, 12 are series connected and shunted, respectively, by a resistor 17 and by a resistor 16 and condenser 14 through a rectifier 15. When the condenser is charged upon an increase in the supply a higher voltage arises over the winding 11 than over the winding 12 and the relay operates. In a modification of Fig. 2 (Fig. 3, not shown) a changeover switch is provided permitting the condenser to be replaced by a resistor whereby the arrangement then functions as an overcurrent relay. In the several arrangements the relay may automatically reset but, alternatively, it may be held operated by a self-holding winding.