Patent GB-430546-A (GB)
Title: Improvements in or relating to apparatus for indicating unbalance in three-phase networks
IPC: H02H3/34
Filed: 1934-06-12
Abstract: 430,546. Protective cut-out systems; induction relays. AKTIESELSKAPET ELEKTRISK BUREAU, 17, Middelthunsgate, Oslo, Norway. June 12, 1934, No. 17424. Convention date, June 16, 1933. [Class 38 (v)] A relay for indicating unbalance between loads which are connected in open V- connection in the phases of a threephase system, operates on the differential-impedance principle. The movable element is acted on by two adjustable, opposing moments, of which one is dependent on the load impedance between the first and second phase, as R-T, and the other on that between the second and third phase, as S-T, so that operation is caused by an impedancechange caused by, for example, extinguishing of a street lamp or earth-leakage on a conductor. The relay is preferably of the induction type and comprises discs 1, 2 on a spindle 49 attached to a torsion-wire 3, which is stretched between leaf springs 4 provided with screws 36 for adjusting the discs up and down and the tension of 3. The latter is also attached to sleeves 37 which are adjustable in the springs 4 by means of arms 38 whereby the position of the movable contact 39 with respect to the fixed contacts 40 can be adjusted. The disc 1 is acted upon by opposing current coils 9, 10 in conductors R, S, the coils being associated with further coils 11, 12 short-circuited through resistances 21, 22. The disc 2 is acted upon by opposing voltage coils 17, 18 which are connected across S-T and T-R, respectively, and have associated with them coils 19, 20 shorted through resistances 23, 24. The points J are earth connections. The arrangement is such that the moving system is normally at rest due to the current coils and voltage coils respectively balancing one another. Moreover, a voltage change in one phase that is independent of the load impedance in that phase is arranged to be compensated by a corresponding change in current in that phase, and the relay is unaffected thereby. The coils 17, 18 are always energized, being on the supply side of the interrupter B, and the current in coils 9, 10 depends entirely on the load current, so that both sets are unaffected by resistance-changes due to temperature. The resistance of coils 11, 12, 19, 20 can be made small compared with that of the resistances 21 .. 24 so that the coils are substantially unaffected by temperature, and the relay is further substantially unaffected by ambient temperature. In order to adjust the relay for balance with normallyunbalanced loads in the phases, induction resistances 27, 28 are provided in shunt to the coils 9, 10 and adjustable by means of iron members 29, 30. To ensure operation with an unbalance of 150 watts, the relay is adjusted to respond to between 80 and 100 watts, and such adjustment is effected and tested by artificially inserting resistances 41, 42 in parallel with the load by means of push buttons 45, 46. If 45 is depressed, 41 is inserted over lead 119 and increases the load in phase R-T by 100 watts, whereupon the relay should operate. If 46 is depressed, 41 and 42 in series are inserted but the relay should not operate. A similar arrangement is provided for phase S-T. All four coils may act on a single disc with pointed bearings and a control spring or springs.