Patent GB-460571-A (GB)
Title: Improvements in and relating to electric circuit breakers
IPC: H01H33/70
Filed: 1935-06-26
Abstract: 460,571. Protective cut-out arrangements ; gas-blast switches. MILLIKEN, H. June 26, 1935, No. 18260. Convention date, Feb. 12. [A Specification was laid open to inspection under Sect. 91 of the Acts, Dec. 28, 1935.] [Class 38 (v)] In protective arrangements in which an automatically reclosing circuit-breaker K and a disconnecting switch 1 are connected in series and operated in succession by gas pressure in response to abnormal current in the circuit, the circuit-breaker contacts are shunted by a high resistance 15<1> which includes means, such as a solenoid 15b, to control the opening of the disconnecting switch, so that the latter opens if the shunt current exceeds a predetermined value but remains closed if the current is below that value. With transient faults, which are cleared by the opening of the circuit-breaker, the disconnecting switch does not open, and the circuit-breaker immediately recloses, but on more prolonged faults the opening of the circuit-breaker is followed by that of the disconnecting switch, which remains open when the circuit-breaker recloses. In the arrangement shown, the circuit-breaker is shunted by a byepass switch 3 which is the first to open when the gas-blast is initiated on the occurrence of a fault. For a three-phase system, three circuit-breakers K are provided, one for each phase, the circuit-breakers being supported on stacks of insulators arranged in truss formation on a steel frame embedded in concrete, as shown in Fig. 2. The compressed air storage tank 8 is connected through valves 9 and tubes 10, one for each phase, to the circuit-breakers. Each circuit-breaker comprises a number of units, Figs. 8 and 9, stacked one above the other, an air-blast distributer 60 extending vertically through all the units and distributing air to a plurality of horizontal arc shoots 13. In each of the latter is a spring-pressed contactor 12 bearing against a movable horn 16. The arriving air blast snaps open the contactor 12 and blows the arc to a contact 14, inserting resistances 15 in the circuit ; the horns 16 are then blown out of the arc shoots, the arcs being lengthened and finally extinguished by the air blast. When the air blast ceases, the horns are returned to the circuit-closing position bv springs 18<1>. On its way to the circuitbreakers, the air blast passes through a casing comprising two parts 122, 123, Fig. 11, containing the mechanism for opening the byepass switch 3. The passage through this casing is normally closed by a vane 110, which is opened, against the action of a spring, by the air blast. The vane is welded to a hollow shaft 111 carrying cranks 112 connected to insulating rods 114, which engage the lower end of the byepass switch 3 and disengage the contact 31 carried thereby from the fixed contacts 32, 33. At its upper end, the switch 3 is pivoted at 56 to a bracket 7, Fig. 13, attached to the top of the circuit-breaker K. The switch 3 is held open by air pressure taken from the top of the circuit-breaker by a small pipe connected through a valve 59 to a cylinder 50 carrying a piston 51 connected to the switch 3 ; the pressure in the cylinder maintains the switch 3 open against the action of a spring 57 until the air blast is cut off. The reclosing of the switch 3 by the spring 57 is delayed, in order to allow time for the opening of the disconnecting switch 1, by means of the valve 59, which only permits a slow leakage of the air from the cylinder 50 through a port 58. The disconnecting switch 1 is opened by air supplied through the pipe 21, Figs. 11 and 15, through a check valve 22 and valve 15c to the left-hand end of a cylinder 23. The valve 15c is normally closed, but is opened by the winding 15b in circuit with the resistance 151 shunting the circuit-breaker contacts when the current through the resistance exceeds a predetermined value. To reclose the switch, a coil 69, Figs. 14 and 18, is energized by closing a switch 103 ; this opens a valve 70 and allows compressed air to flow from a tank 83k through tubes 71, 72 and 73 to the right-hand end of the cylinder 23. When the coil 69 is de-energized, the valve 70 is closed by a spring, leaving compressed air in the right-hand end of the cylinder and tube 73. This is discharged to atmosphere by opening a valve 76 by means of a diaphragm 75 moved by air pressure in the tube 21a. In order to indicate at a distant switchboard the position of the switch 1, red or green lamps are adapted to be illuminated according as the switch is on or off by means of two-position switches 104 operated from a crank on the tube 72, the latter being rotatably mounted and connected to the switch 1 by links 1a. The valve 9 for initiating the air blast is shown in Fig. 16. It comprises a casing 82 containing a diaphragm 90, 90b normally closing an orifice 84 leading to the circuit-breakers and other blast-operated mechanism, the diaphragm separating a chamber 85 in constant communication with the source of air under pressure from a lower chamber of relatively small volume, but having a larger area exposed to the diaphragm. Air under pressure is supplied to the lower chamber through an adjustable valve 90g and normally presses the diaphragm against the orifice. The gas is released from the lower chamber to open the orifice by opening six valves 91, which are normally maintained closed by windings 91a adapted to be de-energized through relays 91m on the occurrence of an overload. When the valves open, the circuit of the relay 91m is interrupted at contacts 91s, and the valves reclose. An auxiliary valve 92 controlled by a winding 92j, Fig. 18, also responsive to abnormal current opens in advance of the valves 91 to admit a charge of compressed air to the air blast passages prior to the air blast proper, this charge serving to shorten the time of interruption but being insufficient, in itself, to operate the circuit-breakers. Compressed air is readmitted to the lower chamber, to shut off the air blast and allow the breakers to reclose, through a valve 83t connected by pipes 83i and 83u and a pressure operated valve 83f to the tank 83k. The relays 91m are operated from windings on the current transformers 5, Fig. 18, through relays 100. If switches 101 are closed, the operation of any of the relays 100 will open all phases of the circuit-breaker, but if these switches are open, each relay will affect only the valve 9 on its own phase. Non- automatic opening of the circuit-breaker is obtained by ciosing the switches 101 and a control switch 102, the valve 15c being byepassed by opening a valve 15d, Figs. 14 and 15. This is effected by a vertical movement of the shaft 72, obtained by upsetting a toggle 70b by energizing a winding 70d. The valve 15d is reclosed by energizing a winding 70c.