Patent GB-511136-A (GB)
Title: Improvements in or relating to electrical signalling systems for use in the protection of power lines
IPC: H02H1/00
Filed: 1938-02-09
Abstract: 511,136. Transmission over power circuits. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and TERRONI, T. B. D. Feb. 9, 1938, No. 4068. [Class 40 (iv)] [Also in Groups XXXVII and XL] In a signalling system for the protection of high voltage power lines in which both signal and speech currents are transmitted by high frequency currents, the occurrence of a fault initiates the transmission of a signal and interrupts the transmission of speech. Different frequencies are used for.speech and signal transmission and the signal serves to maintain a relay in operated condition to prevent a circuit breaker tripping on a non-faulty section. General operation. Fig. 1 (Prov.) shows the arrangements at stations A, B at the ends of a section of a power line RYB. Attendants at A, B may speak to each other through speech transmitters SPT1, SPT2 and receivers SPR1, SPR2, the speech being transmitted by carrier current over the power line through transformers TR1, TR2. The carrier currents for the two speech transmitters have different frequencies FAB, FBA, suitable filters FH1, FL2 being provided at the respective receivers. Should a fault occur, e.g. in the power line section B-C, phase-fault relays, operated at A and B, immediately break the speech circuits and cause a lock-in signal current of frequency Fs to be sent from each signal transmitter SIT1. SIT2 at A, B over the power line to signal receivers SIR2, SIR1, respectively, and serves at each station to maintain operated a relay which prevents energization of the tripping-coil of the A-B section circuit-breaker. In addition, local feed back circuits between the signal transmitters and receivers serve to lock-in those circuit-breakers. Directional relays at stations A, B now operate to indicate the direction of the fault current. Thus, the fault being in section B-C, the A-B section directional relay at station A is operated but not at B. This causes cessation of the lock-in signal from A to B, the circuits remaining in this condition until the circuitbreakers at B serving the B-C section trip to isolate this section. Should a fault occur on section A-B, the lock-in signal is transmitted in both directions as before. In this case, however, the directional relays at both A and B operate, the signal transmission in both directions, therefore, ceases and the circuit-breakers at both stations associated with the A-B section are tripped. Detailed operation. Fig. 1 (Comp.) shows the circuit arrangements at station B, the arrangement at A being identical except that the speech carrier-frequencies differ and the filters FL2, FH1 are arranged to pass only the desired speech carrier frequency. For speech transmission from B to A, lifting of the receiver R from its hook opens contacts SW3 to open the local bell circuit and closes contacts SW1, SW2. A relay BR now operates and at contact br applies potential to the cathodes of valves V6, V7. Valve V7 commences to oscillate at frequency FBA and the speech impulses from transmitter T are applied through a transformer TR7 and amplifier V6 to the valve V7 which operates as an oscillator-modulator. The output therefrom is applied through a transformer TR9, push-pull amplifier V4, V5, and transformers TR6, TR2 to the power line over which the speech is transmitted to station A where it is applied through transformer TR1 and filter FH1 corresponding to FL2 and apparatus corresponding to transformer TRIO and detector VS. The D.C. component of the detector output operates the relay CR at station A to close a circuit over contact cr for a bell similar to B. Upon reply of the attendant at A the bell circuit thereat is broken at contacts SW3 and contacts SW1, SW2 are closed with the same result as at station B. Conversation can now take place between the two stations. Should a fault occur, e.g. on the B-C section, one of the phase-fault relays 1PF, 2PF, 3PF (not shown) operates. Assuming that relay 1PF operates, then contact 1pf4 opens to disconnect potential from the cathodes of valves V6, V7 to stop speech transmission. Contact 1pf1 opens the local circuit (normally energized) of the windings LR2 of the lock-in relay LR. Contacts 1pf3 open to remove the shunt across the anode supply for the signal oscillator valve V3 which commences to oscillate at frequency Fs and transmits the signal over transformer TR5, push-pull amplifier V4, V5 and the same circuit TR6, TR2, and power line used for speech transmission to station A. The same operations occur at station A. Thus, at each station signal receiver SIR1 or SIR2, a lock-in signal is received from the other station over the power line and also from the local signal transmitter, the signal passing through a band-pass filter FB2 (which rejects both of the speech-carrier frequencies), amplifier VI and detector V2 to energize a relay SRI and the windings LR1 of the lock-in relay LR to maintain the armature contacts lr in the position shown. The supervisory relay SR1 is marginal in operation and serves to give a remote indication of the signal level, e.g. if signal current is initiated for test purposes by operating test contacts tc. As pointed out above the directional relay at station A only operates. Thus at station A the directional relay contact corresponding to dr1 is closed to prepare the circuit-breaker trip circuit, and contact dr2 is opened to stop signal transmission therefrom. The trip-coil TC at station. A is not operated, however, since the lock-in relay LR thereat is held operated by the signal from B. These circuit conditions remain until the section B-C is isolated as above described, when the relays go to normal and conversation may be resumed between A, B. If the fault were on section A-B, however, the directional-relays at both A and B would operate to stop both the signal transmitters so that the lock-in signal is immediately stopped. The lock-in relays LR at both stations A, B thus de-energize and circuits are closed over contacts lr thereof, 1pf2, dr1 to energize the trip-coils TC which open the circuit-breakers and isolate the section. Further contacts tr are provided for removing the short circuit on the anode of the oscillator V3 during, e.g. a routine test. The contact dr2 for stopping the oscillator could alternatively be in the anode circuit thereof. An earth return may be used for the carrier signalling system. Preferably two sets of phase-fault relays are used, one having a light setting and operating immediately a fault occurs as above described while the other has a heavy setting and operates only on release of relay LR. These heavy-set fault relays would carry the contacts 1pf2, 2pf2, 3pf2. Protective circuits PG1, PG2 located between the H.F. circuits and the power line preferably include resistances having a non-linear current-voltage characteristic to protect against surge voltages consisting of a mixture of silicon carbide with carbon and/or tungsten or molybdenum agglomerated under pressure and subsequently baked. Specification 493,375 is referred to.