329,425. General Electric Co., Ltd., and Angold, A. E. March 9, 1929. Systems depending on static transformers.- Apparatus for operating a switch (particularly for a transformer tap-changer) comprises an energystoring device, and a device the position of which is dependent on the energy stored and which allows the stored energy to operate the switch only if it has reached a given value sufficient to operate the switch, the latter then being operated by the stored energy. The lines 1 - - 4 of a three-phase, 4-wire, system energize the similar control systems of two transformer tap-changers, the actual tap-changing operation being effected by a maltese cross 18 as described in Specification 324,460, [Class 38 (ii), Electric currents, Converting &c.]. The cross is driven by a motor 5 through gearing which also drives a drum controller 13 (Fig. 2) for effecting the necessary control circuit changes during an operation. The motor shaft has at one end a flywheel 6 controlled by a solenoid-retracted brake 7, and at the other end a centrifugal switch 9 which closes contacts 10 at low, and contacts 11, 169 at high, speeds of the motor 5. The latter is controlled by forward and reverse contactors 21, 22, with closing coils 32, 44 respectively energized by push-button switches 33, 34, for individual operation. Limit switches 7 are adapted to be opened by gearing driven from the motor 5 after the final tap-changing operations are over, these switches opening the motor, brake, and contactor circuits to prevent further operation in the forward and reverse direction. The transformer is connected to the bus-bars by an oil switch 53 closed by a motor 58 controlled through contactors 59, 60 by a push-button 61, 62 being a pushbutton for tripping the switch. The drum 13 is adapted to make one revolution for every tapchange and carries contact segments 76 - - 87 co-operating with contacts in leads 67 - - 75 and additional segments 171, 172 for use on a transformer disconnected from the busbars. A changeover switch 84 on each unit controls the connections for individual and parallel control. For individual control of, say, No. 1 unit, switch 84 of that unit is moved to the dotted position and, a trip coil 56 and no-volt coil 55 being permanently connected across the lines 1, 4, the push-button 61 of the unit is pressed to energize the coil 99. The coil 99 makes a maintaining circuit for itself and closes the contactor 60, which energizes the coil 107 to close contactor 59 and start up the motor 58. When the latter has closed the switch 53 and connected up the transformer, the contacts 103, 108 are opened to de-energize the contactors 59, 60 and stop the motor. To raise the transformer voltage, button 33 is pressed thereby energizing the coil 43 and closing contactor 21 and also removing the brake 19. The motor 5 starts up and after a time the " accelerating segment 77 on the drum 13 breaks its connection with the leads 68, 71 and the contactor 21 opens. The energy of the flywheel 6, however, causes the completion of the tap-change, but only if the speed is enough to close contacts 11, 169 and hold the brake 7 off. If the speed is not high enough the contacts 10 will be closed instead, so as to energize the contactor 22 and reverse the motor to return the parts to their original position. If, while the actual tap-change is being performed, the speed falls sufficiently, the contacts 10 will close and establish a circuit between 63, segment 87, and 74, to short-circuit the no-volt coil 55 and open the main switch 53. At the end of a successful tap-change, the segment 85 makes contact and contacts 10 close, thus energizing the contactor 21 and causing the drum to creep home. To lower the voltage, the reverse push-button 34 is closed and a similar operation takes place in the reverse direction. For parallel operation, the switches 84 are moved over and the transformer connected to the bus-bars by the buttons 61. The forward button 37 is pressed to energize the closing coil 45 of the forward contactor 35, which in turn closes the contactor coils 43 of both units. If either motor fails to speed up, both units are returned to the original position on closure of the contacts 10 of the faulty unit. The reverse operation is similar, using the button 38 and contactor 36. The switches 53 are adapted to be tripped open on fault by closure of contacts 120, 121 to energize a lock-out relay 57. The latter, which is locked out after operation, closes the circuit of the trip coil 54, indicators 152 indicating the nature of the fault according to which of the contacts 120 or 121 are closed. Specification 325,319, [Class 38 (v), Electric switches &c.], is referred to in this respect. Means for indicating which tap is in circuit may be provided, as described in Specification 329,736. In the case of parallel operation, even if one transformer is tripped out, its controller will run in synchronism with the other, so as to be ready for switching in again. The flywheels may be provided with handles for speeding up and tap-changing manually. The Provisional Specification also states that, after, say, two unsuccessful attempts to effect a change, means may be provided for preventing further attempts and that means may be provided for ensuring that an incoming transformer is connected to the right tap.