CIRCUIT BREAKERS

Abstract: An RCCB generally comprises a current-monitoring system or device including electro-mechanical release means adapted to actuate a circuit-breaking operating mechanism upon current imbalance. The present RCCB is characterised in that the electro-mechanical release means has a rotational actuating action as opposed to the conventional axial actuating action. More specifically, the electro-mechanical release means has a construction similar to an electric motor, whereof an inter-polar gap within which a rotor of the motor rotates is sufficiently large to avoid any adverse effects of any microscopic dirt and/or moisture particles present thus avoiding failure or delay of operation of the electro-mechanical release means.

Description: CIRCUIT BREAKERS This invention relates to circuit breakers, particularly to residual current circuit breakers (hereinafter and in the claims for convenience called "RCCB") . An RCCB, as is well known to those skilled in the art, incorporates a current-monitoring system or device which monitors the currents passing through a plurality of conductors connecting a power supply to a load. Provided the currents passing through an RCCB, in closed circuit condition, are in balance then the current-monitoring system or device is inoperative. An imbalance of currents in an RCCB causes the cu ent-monitoring system or device to operate an electro-mechanical release means to render the RCCB into a circuit-breaking condition. The present invention is particularly concerned with such release means. The current differential in an RCCB necessary to attain the circuit-breaking condition is extremely small as is well known, say 20 to 30 milli-Amps for example, with a balanced current of the order of 100 Amps for example. The current monitoring system or device of an RCCB generally comprises a toroidal core with a primary winding formed by the main circuit conductors and a secondary winding providing a signal to the electro-mechanical release means. This electro-mechanical release means is generally a form of relay, the armature of which is normally held closed by the magnetic flux from a permanent magnet. When the signal from the current-monitoring system or device exceeds a predetermined level it causes the flux to be diverted other than through the armature which is then released and moves to an open position under the action of a spring. This movement is utilised to operate a latch to release a switch mechanism thereby opening the contacts of the RCCB. This known relay-type electro-mechanical release means is generally enclosed and magnetically shielded for protection purposes but the enclosure is not total since an actuating plunger projects out of the enclosure to act on the switch mechanism release latch. However there can be a tendency for the relay to fail, or to be slow, to function with consequent risk of damage to personnel or equipment being protected by the RCCB. This failure or tardiness of operation is generally caused by the presence of microscopic particles of dirt at the relay armature pole faces and/or a liquid cling effect due to moisture at the pole faces, the dirt and/or moisture possibly entering the relay enclosure via the plunger opening with the pumping action of the axially-moving plunger contributing to this ingress. It is an object of the present invention to obviate or mitigate the aforesaid drawback. According to the present invention there is provided an RCCB comprising a current-monitoring system or device including electro-mechanical release means adapted to actuate a circuit-breaking operating mechanism upon current imbalance, the RCCB being characterised in that the electro-mechanical release means has a rotational actuating action as opposed to the conventional axial actuating action. Also according to the present invention there is provided an RCCB comprising a current-monitoring system or device including ejectro-mechanical release means adapted to actuate a circuit-breaking operating mechanism upon current imbalance, the RCCB being characterised in that the eletro- echanical release means has a construction similar to an electric motor, whereof an inter-polar gap within which a rotor of the motor rotates is sufficiently large to avoid any adverse effects of any microscopic dirt and/or moisture particles present. As a result of this invention, the aforesaid customary axial pumping action of the plunger actuating the switch mechanism release latch is omitted thereby ensuring that failure or tardiness of relay operation is avoided. Preferably, the electro-mechanical release means has a rotary action with an output shaft projecting from its enclosure. The release means may be a stepper motor, the rotary output shaft of which minimises particle ingress by eliminating the pumping action of an axial actuating plunger as aforesaid. Preferably, the stepper motor is provided with a cam or ramp surface on the motor shaft engaging with a release flag which acts on a latch to release the switch mechanism of the RCCB. Preferably the release flag is pivotably mounted on one side of a support plate on the other side of which is mounted the stepper motor with the shaft of the latter extending through the support plate to engage the release flag. Preferably the release flag is of substantially quadrant configuration with a release detent formed in its curved peripheral surface for engagement with the stepper motor shaft and an actuating and reset surface adjacent its pivot for inter-action with a release lever or latch of the switch mechanism. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which:- Fig. 1 is an exploded perspective view of an RCCB incorporating an electro-mechanical release means according to the present invention; Fig.lA is a perspective detail view of the release flag and lever; Fig. IB is a fragmentary side elevation, to an enlarged scale, of the release flag and lever of Fig. 1A; Fig. 2 is a perspective view of the electro-mechanical release means to an enlarged scale; Fig. 3 is an elevation of the electro-mechanical release means from the other side of Fig. 2; Fig. 3A is a detail perspective view of the stepper motor shaft and; Fig. 4 is a fragmentary perspective view of the stepper motor rotor and stator. The construction and operation of the RCCB generally indicated at 10 is conventional and is well known to these skilled in the art. For this reason no detailed description of the RCCB is given although reference is made to the descriptive passages earlier in this specification, and only those parts of the RCCB pertinent to the present invention are illustrated. The RCCB comprises a body 11 within which are mounted, inter alia, and as is usual , a pair of conductors (not shown) each provided with cooperating contacts one pair of which are fixed while the other pair are carried by a common shaft movable in parallel elongate slots through the intermediary of an operating spring and lever mechanism (also not shown) actuable by a main operating dolly or switch 12. The spring and lever mechanism also includes a release lever 13 which is carried by a rotatable spindle 14 supported in parallel mounting plates 15 and baissed by a spring 16 to rotate in a direction to cause the release lever 13 to pivot towards an electro-mechanical release means generally indicated at 17. The release lever 13 is, again as is usual, operatively associated with the main operating dolly 12 of the RCCB 10, and, when the latter is in the "on" position, the pairs of contacts are closed and current is being fed through the conductors of the RCCB 10 from a power supply to a load (equipment). The RCCB 10 also, as is usual, comprises a test circuit (not shown) housed in a casing 18 from which extends a press actuator 19. A cover 20 is provided for the RCCB 10, which cover has apertures 21 and 22 respectively for projection thereout of the operating dolly 12 and press actuator 19. The RCCB 10, as aforesaid, comprises an electro-mechanical release means 17. According to the present invention this electro-mechanical release means 17 comprises a stepper motor 23 contained in a housing 24. The stepper motor 23 comprises, as is well known, a stepping coil 25 and spaced magnetic poles 26 defining an air gap 27 within which rotates a pemanent magnet rotor disc 28 connected to a shaft or spindle 29 rotatably supported in bearings (not shown). The rotatable shaft 29 is cut axially at its. free end (see Figs 3A and 4) to provide a flat ramp or cam face 30. The stepper motor 23 is mounted on one side of a support plate 31 secured to the body 11 of the RCCB 10 and the shaft 29 extends through support plate 31. A release flag 32 of generally quadrant shape is pivoted on a spindle 33 secured to the other side of the support plate 31. The release flag 32 at its curved peripheral side is formed with a release detent 34 with which the free end of the shaft 29 coacts . The release- flag "32 at its " pivot end has an actuating and release —s-urface 35 for coacting with the release lever 13. A spring 36 is supported by the spindle 33 and has an active arm 37 ' engaging the release flag 32 to urge the latter against the motor shaft 29. When the RCCB 10 is operational, i.e. "on", and the currents passing therethrough are balanced the stepper motor 23 is stationary and the release detent 34 of the release flag 32 is spring urged by the spring 36 into engagement with the cylindrical surface of the motor shaft 29. When a current imbalance occurs a signal current is fed to the stepper motor 23 causing it to "step" rotationally thus aligning the flat ramp or cam face 30 of the shaft 29 with the release detent 34. This allows the release flag 32 to pivot, under spring action, against the flat ramp or cam face 30 which causes the actuating and reset surface 35 to urge the release lever 13 from position A to position B which, as usual, causes the operating dolly 12 to be thrown to the "off" positions. The release flag 32 serves to amplify the output of the stepper motor 23, i.e. it amplifies the force applied to the release lever 13 to ensure satisfactory operational movement of the release lever 13. The gap 27 between the magnetic poles 26 is of such dimension that any dirt and/or moisture likely to be present will not impede rotation of the stepper motor 23 and consequently will not cause failure or tardiness in operation of the monitoring system or device. Electronic control means (not shown) is provided, to connect the output of the current monitoring system to a form suitable to ensure the necessary rotor movement for release when the residual current of the RCCB exceeds a predetermined level. The stepper motor 23 may re-set itself electromagnetically, or it may be spring assisted to the re-set position, or wholly re-set by spring action. The' customary re-set lever for the electro-mechanical release means 17 is provided, which lever (not shown) overlies the release lever 13 as usual.

Claims: CLAIMS 1. An RCCB comprising a current-monitoring system or device including electro-mechanical release means adapted to actuate a circuit-breaking operating mechanism upon current imbalance, the RCCB being characterised in that the electro-mechanical release means has a rotational actuating action as opposed to the conventional axial actuating action. 2. An ' RCCB comprising a current-monitoring system or device including electro-mechanical release means adapted to actuate a circuit-breaking operating mechanism upon current imbalance, the RCCB being characterised in that the eletro-mechanical release means has a construction similar to an electric motor, whereof an inter-polar gap within which a rotor of the motor rotates is sufficiently large to avoid any adverse effects of any microscopic dirt and/or moisture particles present. 3. An RCCB as claimed in claim 1 or 2, in which the electro-mechanical release means has a rotary action with an output shaft projecting from its enclosure. 4. An RCCB as claimed in claim 3, in which the electro-mechanical release means is a stepper motor, the rotary output shaft of which minimises particle ingress by eliminating the pumping action of an axial actuating plunger. 5. An RCCB as claimed in claim 4, in which the stepper motor is provided with a cam or ramp surface on the motor shaft engaging with a release flag which acts on a latch to release the switch mechanism of the RCCB. 6. An RCCB as claimed in claim 5, in which the release flag is pivotably mounted on one side of a support plate on the other side of which is mounted the stepper motor with the shaft of the latter extending through the support plate to engage the release flag. 7. An RCCB as claimed in claim 5 or 6, in which the release flag is of substantially quadrant configuration with a release detent for-med in its curved peripheral surface for engagement with the stepper motor shaft and an actuating and reset surface adjacent its pivot for inter-action with a release lever or latch of switch mechanism. 8. An RCCB as claimed in claim 7, in which the release flag in spring-urged against the free end of the stepper motor shaft.

Inventors: KIDD ALAN LISTER, KIDD, ALAN, LISTER
Applicants: SCHOLES GEORGE H PLC
Application year: 1988
Main classification: H01H71
IPC codes: H01H71