Patent GB-609869-A (GB)
Title: Improvements in or relating to carrier-current or other pilot-channel protective relay systems
IPC: H02H3/30
Filed: 1946-03-20
Abstract: 609,869. Protective cut-out systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 20, 1946, No. 8624. Convention date, March 29, 1945. [Class 38 (v)] In a system for protecting a section of a three-phase transmission line, filter circuits 5, 6, at each end of the section separate out the negative phase sequence components and the positive plus zero phase sequence components respectively. The output of circuit 5 is applied to the coil FD of a fault detector and to a resistor 14 over a saturating transformer 9 and rectifiers 11. Similarly, the output of circuit 6 is applied to the coil FD over a saturating transformer 19 and a rectifier 21 and also to the grids of two gas-filled triodes VI, V2. The coil FD is energized to close contacts 32 by the greater of the negative or positive plus zero phase components. An intermediate voltage of the network-terminals 23, 24 is obtained at a point 25 joining two resistors R1, R2, the point 25 being also connected to the negative pole of a battery Ec, in series with the resistor 14. During positive half-cycles of the voltage output from transformer 19, the grid of V1 becomes sufficiently positive to fire V1, and produce a series of restraining impulses, and during negative half-cycles V2 fires to produce a series of operating impulses. The voltage drop in a resistor R3 in the cathode circuit of V1 is used for operating an oscillator OSC of a carrier-current transmitter which is coupled to transmission line C for transmitting the restraining impulses to the far end. The voltage drop in a resistor R4 is used to apply an operating voltage component from cathode circuit 27 of V2 to the grid of a valve V4. A carrier current receiver 40 for the restraining impulses from the remote end has its anode connected through a capacitor C5 and resistor CCR to the cathode circuit 27, the condenser C5 being also connected through a condenser C6 to the left-hand diode of a valve V3, the lefthand anode of which is connected to the grid of V4 and to a resistor R7 connected to the cathode circuit 27. When no carrier-current is being received, the anode-terminal 42 of the receiver valve REC is practically at the potential of the positive battery terminal (+) and condenser C5 is charged by the potential difference between circuit 27 and the anode terminal 42, the anode potential being pulled down to nearly that of the negative terminal when carrier-current is being received, thereby shortcircuiting C5, which discharges through the resistor R7 and the left-hand diode of V3, a smaller current passing through CCR to recharge condenser C5. When nothing is being received again, the right-hand diode of V3 conducts, and condenser C6 is charged, both C5 and C6 being discharged through resistor R7 when receiving again, thus producing a voltage drop therein, making the grid of V4 more negative to block the valve. The receiver REC preferably has a constant-current characteristic so that, whenever, it is firing, the plate current is approximately constant. The grid-voltago of V4 has three components: (1) the negative grid bias voltage between a potentiometer 52 and the negative battery terminal (-), (2) the operating volts from resistor R4, and (3) the restraining voltage from resistor R7. V4 fires only during positive half-cycles of the grid volts, i.e. on an internal fault when the operating volts are not opposed, thereby energizing a relay R through a rectifier 56 to close contacts R in the trip circuit of the circuit-breaker 3, V4 preferably having a constant-current characteristic also. On an external fault, the grid voltage of V4 is negative and the valve does not fire. The saturating transformer 19 and a neon tube 20 ensure that the operating voltage varies only slightly for relatively large line- Current increases. The current-responsive setting of V2 must be considerably higher than that of VI, so that the first valve at the distant terminal will fire before the second valve at the relaying end fires. The fault detector may have two coils, Fig. 2 (not shown), energized by the sum of the phase sequence components and it may be of the voltage responsive, impedance, reactance or mixed impedance or reactance types. Fig. 2 also illustrates an arrangement for use where no adequate zero-component is available at one terminal, wherein the terminals 23, 24 receive the negative plus zero component and resistor 14 receives the positive component.