STATIC PROTECTION IMPEDANCE RELAY

1299933 Protective arrangements ALLMANNA SVENSKA ELEKTRISKA AB 7 May 1970 [8 May 1969] 22048/70 Heading H2K A static impedance relay arrangement comprises a "current" circuit 1, 10 for producing, e.g. across a resistor 11, a first pulsating direct voltage proportional to the current of a protected circuit, a "voltage" circuit for-producing, e.g. across a resistor 14, a voltage which is the sum of a smoothed direct voltage and a second voltage which may be either a second pulsating direct voltage or an alternating voltage, both smoothed and second voltage being proportional to the voltage of the protected circuit, and a detector 15 responsive to a difference between the first voltage and the summed voltage to cause the operation of a relay 17. The smoothed direct voltage is produced from the secondary winding 22 of a transformer 20 having its primary winding 21 connected to a voltage transformer (not shown), the end terminals 26, 27 of the secondary winding being connected to a phase shifter comprising a resistor 50 and a capacitor 51, which together with a centre tapping 28 are connected to a bridge rectifier 35 with a smoothing capacitor 39. The second voltage is provided from a secondary winding 23 and a rectifier 43 with an unsmoothed output or directly from the winding 23, Fig. 3 (not shown). The first pulsating direct voltage is obtained from a transformer 1 having its primary winding connected to current transformers (not shown) and a full wave rectifier 10 or a half wave rectifier, Fig. 3 (not shown). Various characteristics are illustrated in impedance diagrams.