204,029. British Thomson-Houston Co., Ltd., (Assignees of Place, C. W.). Sept. 15, 1922, [Convention date]. Void [Published under Sect. 91 of the Act]. Switching-systems.-An electric supply system, comprising main sources of supply A and B and an auxiliary source of supply C, is provided with an automatic control system adapted to connect the source A to feeders D and E, upon an increase of load to disconnect the feeders D and E and to connect the source B to feeder E, to replace the source A or B by the source C when either of the sources A or B is out of action, and to connect the source C to assist the source A or B upon an increase of load. Circuit-breakers F, G, K, H and J, Fig. 1, are provided with closing coils 30 and with trip coils 31. The sources A, B and C are provided with voltage relays 32, 33 and 34, Fig. 2. The operation of the circuit-breakers is controlled by a six-position controller 42 driven by a motor 43 which is in turn controlled by relays 2, 5, 8, 10, 23, 25 and 28. The trip coils 31 of the circuit-breakers G, F, and K are also controlled by relays 12, 16 and 14. The source A is provided with an overload relay 39 and an under-load relay 35. A source B is provided with an overload relay 40 and the source C is provided with an underload relay 37. In the position VI of the controller 42 the sources A, Band C may be de-energized or the source C may be energized and the circuit-breakers K, H and J closed. If the sources A and B be energized when the controller 42 moves from position VI to position I, the circuits through the closing coils 30 of the circuit-breakers G and F are completed if these circuit-breakers are open and the circuit through the trip-coils 31 of the circuit-breakers H, J and K are completed if the circuit-breakers be closed, thereby connecting the sources A and B to the feeders D and E respectively, disconnecting the systems D and E, and disconnecting the source C. The controller 42 remains in position I only when the circuit-breakers F and G are closed, the sources A and B are energized and the current supplied by the source A exceeds a predetermined value. If the source A is energized and either the source B is de-energized or the source B is energized and either one of the circuit breakers F, G is open, the controller will move to position II. The circuits' through the closing coils 30 of the circuit-breakers F and H are completed if the circuit-breakers are open, the circuit through the closing coil 30 of the circuit-breaker K is completed if this circuit breaker is open and the source is energized, and the circuits through the trip coils 31 of the circuit-breakers G and J are completed if the circuit-breakers are closed. The circuit-breakers F, H and K are closed and the circuit-breakers G and J are opened so that the source A is connected to the feeder D, and the source C, if energized, is connected to the feeder E. The controller remains in this position only if the circuit-breakers F and K are closed, the source B is de-energized, the sources A and C are energized and the current supplied by the source A exceeds a predetermined value. If the source A is de-energized and either one or the other of the sources B and C are energized when the controller moves from position II to position III, the circuits through the closing coils 30 of the circuitbreakers G, K and J are completed if these circuitbreakers are open and the sources B and C are energized. The circuits through the trip-coils 31 of the circuit-breakers F and H are completed if these circuit-breakers are closed. Under these conditions the source B is connected to the feeder E and the source C to the feeder D. The controller remains in this position only if the source A is de-energized, the sources B and C are both energized, and the current supplied to the source C exceeds a predetermined value. When these conditions do not prevail the controller moves to position IV, completing the circuits of the closing coils 30 of the circuit breakers F, H and J and the circuits of the trip-coil 31 of the circuitbreakers G and K, thereby connecting the source A to the feeders D and E. The controller remains in this position as long as the source A is energized. and the contacts a of the overload relay 39 are closed. If the source A is de-energized and the circuit-breaker H is closed, or the circuitbreaker G is closed, and the contacts b<1> of the underload relav 37 are closed when the controller moves from position IV to V, the circuits through the closing-coils 30 of the circuit-breakers H and J are completed if these are open. The circuit through the closing coil 30 of the circuit-breaker G is completed if this be open and the source B be energized and the circuits through the trip-coils 31 of the circuit-breakers F and K are completed if these circuit breakers are closed. If, however, the contact 11 of the controller is not connected to the conductor 44, the operations enumerated above do not occur. The controller remains in position V if the source A is de-energized and the source B is energized and does not supply current above a predetermined value. If the source B is energized, the controller moves from position V to position VI and the circuitbreakers K, H and J are closed and the circuitbreakers G and F are opened if the source C is energized. The controller remains in position VI when all the sources are de-energized or if the source C is energized. The arrangement of the underload relays 35 and 37 which determine whether one source will supply the total load is satisfactory when the ratio of the loads connected to the two feeders D and E is substantially constant. When the ratio of the loads is subject to wide variation, the arrangement of the relays 35 and 37 is not satisfactory since the controller 42 would operate continuously to connect both feeders to one source and then to connect each feeder to a separate source. To prevent this continuous operation, the relays 35 and 37, Fig. 1, are placed by a single relay 80, Fig. 3, under the control of series transformers 81 in the supply circuits A, Band C.