Patent GB-197662-A (GB)
Title: Improvements in and relating to automatic reclosing circuit breaker systems
IPC: H02H3/06
Filed: 1923-04-17
Abstract: 197,662. British Thomson - Houston Co., Ltd., (Assignees of Walle, L. S.). May 12, 1922, [Convention date]. Protective arrangements. - In automaticallyreclosing circuit-breaker systems in which the reclosing of the circuit-breaker is controlled in accordance with the load resistance, a low-voltage alternating current is supplied to the load circuit when the circuit-breaker is open and the reclosing of the circuit-breaker is controlled by a wattmeter relay so connected to the load circuit that the torque on the rotatable relay element reverses when the load resistance exceeds a pre. determined minimum, so effecting the completion of the circuit-breaker reclcsing circuit. In Fig. 1, a generator 1 with one pole earthed supplies an earthed load through a circuit breaker 3 and line 2. In the closed position shown the circuitbreaker is maintained closed against an opening spring by a coil 4 the circuit of which is completed through the contacts 5 of an overload relay 6 whose energizing winding 8 is in series with the line 2. On overload, the opening of this maintaining circuit by operation of the, relay 6 allows the circuit-breaker to open, after which a circuit is completed through contacts controlled thereby from a low-voltage A.C. supply, e.g. the secondary 11, 12 of a transformer 10 through a resistance 14 in series with the load, ground, and the current coil 18 of a wattmeter relay 15. This relay has a rotating induction disc 26 with retarding magnet 22, and the shaft of the disc 26 carries a bridging contact 21 normally held by a spring 28 against a stop 29. The voltage coil 19 of the relay 15 is connected between a tapping 23 on the transformer secondary 11, 12 and a point between the resistance 14 and the load so that it receives an E.M.F. equivalent to the vector difference of the supply E.M.F. between the points 11, 23 and the volt drop across the resistance 14. This arrangement is such that if the load resistance is below a predetermined minimum the torque on the relay element 26 is such that it tends to assist the spring 28 to maintain it in the position shown, but as the load resistance increases up to and beyond this value the variation of the phase of the resultant E.M.F. impressed upon the voltage coil 19 relative to the current in the coil 18 causes the torque on the element 26 to reverse, so causing the member 21 to bridge the contacts 27, completing the circuit of the coil 4. The circuit-breaker 3 is now closed completing its maintaining circuit as described above and disconnecting the A.C. supply by contacts controlled by the circuit-breaker. Where this system is applied to electric traction systems, in order to compensate for the apparent increase of the load resistance due to skin effect in the conductor rails while carrying alternating current when the fault or overload is at some distance from the relay 15, a resistance 25 is inserted in series with the highly reactive voltage coil 19 to vary the angle of lag between its impressed E.M.F and magnetic flux, this having the effect of varying the relative value of the load resistance to the resistance 14 which will effect reversal of the torque on the disc 26 with different values of load reactance corresponding to varying distances between the circuit breaker and fault. The theoretical considerations underlying the above operations are set forth in the Specification. In order to ensure the reclosing of the circuit-breaker 3 if the load is completely disconnected after the circuit breaker is opened, a resistance 9 is connected in parallel with the load, which is of a sufficiently large value relative to the resistance 14 to effect re-closure of the circuit under these conditions in the manner above described. Other modifications are described as applied to systems in which several independent sources of D.C. power are provided. In these forms if all the D.C supplies are cut off simultaneously with the opening of circuit-breaker 3 the reclosing of the circuit proceeds in the manner desscribed with reference to Fig. 1, but if any source of D.C. remain connected to the load after the circuit-breaker 3 has opened, auxiliary relays responsive to direct but not to alternating current operate to preent damage to the low-voltage A.C. transformer. Voltage relays are also provided to operate under these conditions when the D.C. voltage across the load. increases to a given value corresponding to a sufficient increase in load resistance, and a resistance is then inserted in series with the resistance 14 in the A.C. circuit, this resistance being of such a value as to cause reversal of the torque on the relay 15, so completing the reclosing circuit of the circuit-breaker 3.