Patent GB-704893-A (GB)
Title: Automatic reclosing electric circuit breakers
Inventor: RYAN ANTHONY VAN
IPC: H01H75/04
Filed: 1951-07-02
Abstract: 704,893. Automatic reclosing circuit-breakers. McGRAW ELECTRIC CO. July 2, 1951, No. 15658/51. Class 38(5) When a desired number of reclosing operations have been performed in an automatic reclosing circuitbreaker by a movable magnetic member controlled by a winding opening a switch unit which is biased towards a closed position, a spring biased toggle mechanism is collapsed to move the magnetic member to the " open " position to lock open the switch. The circuit-breaker is oil immersed and has hydraulic timing mechanism arranged to ensure at least one rapid opening operation followed by a delayed reclosing operation and then at least one slower opening operation before the switch unit is locked open by the toggle mechanism. Electromagnetic switch opening mechanism.- The winding 26, Fig. 2, is connected in series with the switch contacts and is effective under overload fault conditions to pull down the movable magnetic member. or plunger 34 which through a non-magnetic rod 35 opens the snap-action switch unit secured below the winding. Oil trapped beneath a washer 42 serves as a cushion for the plunger at the end of its stroke. When the coil is de-energized by the opening of the contacts the switch unit recloses under the action of a spring 101 and restores the plunger 34 ready for a further opening operation if the fault persists. Hydraulic timing mechanism.-The plunger 34 is a close fit in an aperture in the upper plate 23 of the electromagnet and a loose fit within the tube 28 on which the winding is wound, so that when the plunger 34 moves down, the oil beneath it flows up around the plunger and through passageway 38, 39, Fig. 2, and 102, Fig. 13, into a cylinder 103 to force down a piston 104. The piston 104 uncovers a passageway 114, Fig. 14, and a passageway 115, Fig. 13, which has a check valve 116 with a bimetallic spring 117 to compensate for changes in the viscosity of the oil at different temperatures. The uncovering of these passages enables the free release of oil so that the plunger is able to make a quick opening stroke. The oil below the piston 104 flows through a passageway 108 and a non-return valve 110 into a cylinder 109 and raises a "counting" piston 112 a distance corresponding to one operation of the circuit-breaker (i.e. one step). The first part of the return motion of the plunger 34 is rapid, as it sucks oil from the cylinder 103 until the piston 104 is arrested by an adjusting screw 121. Thereafter the return motion is slow, as the plunger has to suck oil through a restricted orifice 118, Fig. 13, and a passageway 119 with a check valve 120, Fig. 2. This provides the delay between successive operations. When the desired number of rapid opening operations have been made, the " steps " made by the piston 112 will have moved it sufficiently for it to close the passage way 114. The subsequent switch opening operations are now slower since oil displaced by the plunger 34 can only escape through the passageway 115 past valve 116. The final tripping operation is made when the piston raises a lever 124 to trip the toggle linkage. Toggle linkage.-The toggle linkage comprises the lever 124 having a fixed pivot 140 and a link 139 pivoted at 138 on a bell crank lever 134 loosely mounted on a shaft 127. When the toggle is " broken " by the piston 112, it collapses under the bias of a spring 141 and an extension of the pivot pin 138 moves a bell crank lever 136, which is loosely mounted on the shaft and connected by a link 137 to the plunger 34. The circuit-breaker mechanism moves into the finally tripped position of Fig. 3. A lever 145 operates a counting mechanism (not shown). Hand resetting and operation.-A handle indicated at 128, which also serves as an indicator, is pushed up to turn the shaft 127 and with it a lever 130 secured to the shaft. The lever 130, in bearing against a shouldered part 135 of the bell crank lever 134, turns the lever 134 to reset the toggle, the plunger 34 being effective to re-open the switch in its normal sequence during the resetting or if the handle is held. The circuit-breaker may be tripped open at any time by pulling down the handle to turn the lever 130 against a spring 132 into engagement with the link 139 to break the toggle 124, 139. Automatic resetting.-If the fault condition is cleared before the sequence of operations is complete, the piston 113 is able to settle in the cylinder 109 as oil slowly escapes past it, so that in the event of a further fault, the operation starts from the beginning of the sequence again. Thermal tripping.-The circuit-breaker may also be tripped by a thermostatic element 126 heated by the oil in the container 1, the element engaging a pin 125 on the lever 124 to break the toggle 124, 139. Snap-action switch unit.-This unit comprises two switch arms 69, Fig. 9 (one shown), each carrying a contact 73 co-operating with a fixed contact 82. and moving between insulating partitions 54, 57. Arc extinction is facilitated by arc splitting barriers 60, 61 and the blow-out effect provided by the looped connections 44. The switch arms 69 are rigidly mounted on a sleeve 71 on a shaft 72, the sleeve having a cam 86, Fig. 2. When the rod 35 is moved down, it acts on a roller 98 and turns a lever 95. The latter moves a lever 91 causing a spring biased roller 90 to move along the cam 86. As the rod 35 nears the end of its movement, the roller 98 strikes a member 76 on the switch arms to initiate the switch opening movement and the roller passes over the point 89 of the cam 86 so that the pull of springs 94 on the roller 90 is effective to open the contacts rapidly. Figs. 18 to 20 (not shown) illustrate modifications of this snap-action arrangement.