Patent GB-341985-A (GB)
Title: Improvements in or relating to electric protective systems
IPC: H02H1/00
Filed: 1929-10-29
Abstract: 341,985. Protective cut-out arrangements. REYROLLE & CO., Ltd., A., Hebburn-on-Tyne, and LEBEN, H., 8, Queen's Walk, Harrow, Middlesex. Oct. 29, 1929, No. 32821. [Class 38 (v).] In an impedance &c. protective system of the type in which time-discriminating relays for dealing with earth or interphase faults are brought into operation by means of initiating relays under the control of phase-selecting relays, in order to ensure connection of the time relays to the faulty phases, instead of employing voltage-responsive phaseselecting relays as described in Specification 320,969, [Class 38 (v), Electric switches &c.], in which relatively small operating forces may be available consequent on the reduction in voltage accompanying fault conditions, a single phase-selecting relay is provided which is operated by the degree of current unbalance between the phases of the line which is set up by the fault, this relay controlling, in conjunction with the initiating relays and other contactors, the connection of the time-relays to the faulty phases. As shown in Fig. 1 the phaseselecting relay 180 has opposing coils 182, 183 connected in the current-transformer secondary circuits 11, 13 corresponding to phases 1 and 3 of a supply line 1 .. 3 controlled by a circuit-breaker 4 and supplying a power transformer 6, 7 in a branch feeder. A potential transformer 20 is connected across the lines 1 .. 3, its secondary supplying a further step-down transformer 30 with tapped secondary windings. Initiating relays 90, 100, 110, which may be of the type described in Specification 320,968, [Class 38 (v), Electric switches &c.], are provided for interphase faults, their voltage windings 92, 102, 112 being connected across the secondary phases of the potential transformer and their current windings 91, 101, 111 in series with the current transformer windings 11-13. A similar initiating relay 80 is provided for earth faults its winding 82 being fed from a current transformer 9 in the earthed neutral lead of the power transformer primary 6 and its winding 81 in the neutral head 14 of the current transformer secondary 11 . . 13. The initiating relays control the operation of timediscriminating relays 50, 60 for dealing with interphase faults and 40 for earth faults. These timediscriminating relays are preferably of the kind described in Specification 319,637, [Class 38 (v), Electric switches &c.], and have current windings 41, 51 and 61 and voltage windings 42, 52 and 62, the latter being in series with variable resistances 43, 53 and 63, the contact arms 44, 54 and 64 of which are progressively operated during response by a timing mechanism 70 driven by a coil 71. The selective connection of the time-discriminating relays under the control of the initiating relays is governed by the combined action of the phaseselecting relay 180, D.C. electromagnetic contactors 150, 160, 170 for interphase faults and 120, 130, 140 for earth faults and of selective D.C. contactors 220, 210 for interphase faults and 190, 200 for earth faults. The main D.C. contactors 120 &c. and 150 &c. have multiple contacts corresponding to the circuits of the current voltage coils of the time relays, preferably circuits for the trip coil 5 and circuits for the timing mechanism 70. The combined action of the above relays assures the connection of a time-discriminating relay in the correct manner for any earth or interphase fault. Thus, for example, with a fault between phases 1 and 3 the initiating relay 90 first operates closing its contacts 93. This completes a circuit to the electromagnetic contactor 150 through contacts 211, 221 of the selective contactors 210, 220 which remain inoperative since the balanced currents coils 182, 183 of the phase-selecting relay 180 does not move the contact arm 181 from its neutral or non-contacting position. Thus the time-discriminating relay 50 is connected in a manner suitable for dealing with this fault. If, however, a fault between phases 1 and 3 or 2 and 3 had occurred the phase-selecting relay would have operated in one or other direction so operating one or other of the selective contactors and causing operation of one or other of contactors 160, 170 bringing in relay 50 with altered connections or relay 60 to deal with the fault. A three-phase fault operates through contactor 150 as balance in the phaseselecting relay is preserved in such a case. Similar selective operation of the earth-fault-responsive relays occurs after initiation by the operation of the relay 80, the time-discriminating relay connection being controlled as before by the phaseselecting relay 180 and its associated contactors. To prevent inadvertent operation of the interphase relays during response to earth faults or incorrect operation of the interphase relays in other circumstances, lock-out relays 230, 240 and 250 may be provided, operating in the manner described in Specification 341,986. In order to ensure correct operation of the phase-selecting relay under bearing fault conditions, this relay may be constructed so that it operates only after a certain degree of unbalance between its operating forces takes place. Thus, if a balanced beam type of relay is employed the beam may be provided with a double-pivot or an auxiliary electromagnet may be provided on each side of the beam to tend to hold it in its central position ; these electromagnets being energized in series with the operating coils. Similar restraining electromagnets may be employed in conjunction with an opposed torque induction type relay or discs may be shaped so that as a disc moves from the central position its torque decreases. A similar arrangement of the armatures may also be employed with balanced beam electromagnetically balanced relays.