EP0519560A1

EP0519560A1 - Differential switch

Info

Publication number: EP0519560A1
Application number: EP92201715A
Authority: EP
Inventors: Daniel François Balthau
Original assignee: GE Power Controls Belguim BVBA
Current assignee: GE Power Controls Belguim BVBA
Priority date: 1991-06-20
Filing date: 1992-06-12
Publication date: 1992-12-23
Also published as: BE1004956A3

Abstract

The differential switch includes an externally operated, tiltable control knob (11), electric contacts (6,7) that try to a put a spring in the open position and the rotatable parts (7) of which are mechanically connected to one another, a toggle lever (14,15) which connects the control knob (11) with the rotatable contact parts (7), an arm (19), which is fixed and hinged to this toggle lever (14,15), a control lever (21) at which the arm (19) has a hinged connection, a hinged locking device (23) which includes a stop part (25) behind which, in the case of the lock (23) in the lock position, the control lever (21) is pulled, with the control knob (11) engaged and closed contacts (6,7), the lock (23) which, on rotation from the lock position, releases the lever (21), and a locking rocker (28) which includes a stop part (27), that, in one position, holds the lock (23) in the lock position but in the case of fault current detection is pushed out of this position, releasing the lock (23). When the control knob (11) is engaged, a locking spring (30) tries to get the lock (23) out of the lock position and in addition, exerts a force on the lock (23) that is considerably bigger than the force necessary to turn the lock (23) with respect to the control lever (21) when it is released.

Description

The present invention concerns a differential switch that includes a supporting structure, an electrical part fitted therein with a fault current detector and an activator, and a mechanical part mounted on the supporting structure with an externally operated, tiltable control knob which is tiltable between a rest position and an on position, at least two electric contacts, each with a fixed part and a rotatable part and with at least one spring which tries to drive these parts apart, and, as a result, put the contacts in the open position, in which the rotatable parts are mechanically connected to one another and turn about the same axis, a toggle lever which is on the one hand hinged at the control knob at a distance from its axis of tilt and on the other hand, hinged at the mutually-linked, rotatable parts of the contacts, fixed at a distance from their common hinge pin, an arm, which near the toggle joint of the toggle lever, is fixed and hinged to the latter, control lever mounted and hinged to the supporting structure and which, at a distance from its hinge pin, has a hinged connection with the arm, a locking device which is mounted and hinged to the supporting structure and includes a stop part behind which, in the case of the lock in the lock position and with the control knob engaged and closed contacts, the control lever is pulled by the action of the arm, the lock which, on rotation from the lock position, releases the lever, and a locking rocker which is also mounted and hinged to the supporting structure and includes a stop part, that, in one position, holds the lock in the lock position but in the case of fault current detection is pushed out of this position by the activator, releasing the lock.
A differential switch of this type is described in DE-U-8702467. In the on position and with closed contacts the locking rocker, in the case of fault current detection, is rotated by the activator until it releases the lock. This lock, once released, is rotated, first of all by the control lever itself, that is pulled aside by means of the arm of the toggle lever. This toggle lever is itself pulled aside by the springs of the contacts.
The unlocking force, i.e. the force that the activator requires to rotate the locking rocker is, because of the levers in this differential switch, actually reduced and is smaller than the force that has to be exerted by the control knob to put the lock in the lock position and the contacts in the closed position, but this unlocking force is highly dependent on the force with which the springs of these contacts try to put these in the open position. The control lever, in fact, pushes against the stop part of the lock that is aligned diagonally with respect to the longitudinal direction thereof with a force that depends on the force that the contact springs of the contacts exert when these contacts are closed. In addition, this control lever exerts a torque on the lock. A force is exerted on the locking rocker, by the lock, which prevents this rotation, a force which is dependent on the pressure that the control lever exerts and thus dependent on the force that the contact springs exert. In the case of a bigger force, the activator has to exert a bigger force in order to turn the locking rocker. In addition, because of wear and tear and possible corrosion, a new activator has to have a reserve force with respect to the force necessary in order to unlock. This known differential switch anyway requires a relatively powerful activator with a big reserve force with respect to the unlocking force in order to be used with two poles, or even with four or more poles.
The force that the contact springs exert usually depends on the number of poles of the differential switch. In addition, a sufficiently large contact pressure must be chosen, in the event of a fault, in order to resist the short-circuit current forces, which try to open the contact. There is a contact for each pole and a spring per contact or group of contacts. To increase the number of poles a proportional number of contacts are added in which the movable parts of these contacts are automatically and mechanically connected to one another. In the case of the aforesaid differential switch the reserve force of the activator decreases for an increasing number of poles and with higher contact pressure.
The present invention is aimed at rectifying this drawback and providing a differential switch in which the unlocking force is, comparatively speaking, little dependent, if any, on the combined force exerted by the contact springs and where the activator, as a result, only has to exhibit a small reserve force, regardless of the number of poles.
To this end the differential switch contains a locking spring which, if the control knob is engaged, tries to get the lock out of the lock position and in addition, exerts a force on the lock that is considerably bigger than the force necessary to turn the lock with respect to the control lever when the lock is released from the aforesaid lock position.
The turning of the lock when this is released by the locking rocker during fault current detection is, in the main, brought about by the locking spring. The force with which the lock pushes against the aforesaid part of the locking rocker and thus the force with which the activator can turn the locking rocker, held by the lock, depend basically on the locking spring.
In a particular embodiment of the invention the aforesaid stop part of the locking device that holds the control lever, in the lock position of the lock, extends according to a tangent plane to a circle with the rotational axis of the lock as its centre, so that the control lever exerts practically no torque on the lock.
Only the friction of the control lever against the stop part of the lock has to be overcome for the turning of the lock. The aforesaid force, for all intents and purposes, doesn't affect the force necessary to turn the locking rocker. And insofar as there is a certain effect, not only is this slight but such that when the pressure of the control lever on the lock is moreover increased, i.e. with an increasing number, therefore, of contact springs, the force necessary to turn the locking rocker, in fact, decreases.
In a notable embodiment of the invention the locking rocker is mounted on the lock and is put under pressure by the control knob, when this knob is engaged. An efficient locking spring is a torsion spring that is mounted around the rotational axis of the lock, with one end that acts together with a part of the lock and its other end that acts together with the control knob when this knob is engaged.
The differential switch can moreover include a spring which is installed between the lock and the locking rocker and which pushes the lock and the locking rocker into a relative position in which the locking rocker, with its stop part, can grip behind a part of this lock when engaging the control knob, the spring of which however is considerably weaker than the locking spring.
This additional spring makes sure that the lock and the locking rocker, in the rest position of the control knob, adopt a position relative to one another such that, on turning the control knob to the on position, the restraining part of the locking rocker can hold the lock.
In an advantageous embodiment of the invention the differential switch includes a testing device with a test circuit and a test button for activating the test circuit, the test button of which is formed by an elastic, deformable part of the supporting structure.
The differential switch preferably includes connection terminals with a fixed part, a movable part and a screw that is screwed into the movable part, as well as a spring-loaded lip, that is fastened to the fixed part, and that can clamp an end of the test circuit against the fixed part.
Other distinctive features and advantages of the invention will emerge from the description hereinafter of a differential switch according to the invention. This description is merely given as an example and doesn't limit the invention. The reference numbers relate to the drawings appended hereto, in which :

Figure 1 schematically shows the mechanical part of of a differential switch according to the invention, in the rest position;
figure 2 schematically shows the mechanical part from figure 1 in the on position with closed contacts;
figure 3 schematically shows the mechanical part from the above figures after opening the contacts due to a fault current detection;
figure 4 schematically shows a side view of the differential switch from figure 1 but with a side wall removed;
figure 5 shows a view, in perspective, of a part of the differential switch from figure 4;
figure 6 shows a section taken along the line VI-VI from figure 5;
figure 7 shows a view, in perspective, of a detail from figure 5.

The differential switch shown in the figures basically contains a supporting structure 1, made of an insulating plastic, an electrical part 2, fitted therein, for detecting a fault current and, mounted on the supporting structure 1, a mechanical part 3 which is operated by the electrical part.
The electrical part 2 contains, in the usual way, a fault current detector and an activator. These components are sufficiently familiar and are not described in detail here. In figures 1 to 3 only the movable part 4 of the activator is shown. This electrical part 2 also contains a test circuit 5 which will be described further on.
The supporting structure 1 consists of a plastic housing with a base 50 and a cover 51 mounted on it, a metal mounting plate 52 which is situated inside the housing and which is fixed to the base 50 and supporting elements 53, in plastic, which inside the housing 50, 51 are likewise mounted on the mounting plate 52 and where one of them, that supports the activator, is shown in figures 5 and 7.
The mechanical part 3 contains, per pole, which must be protected by the differential switch, a contact with a fixed part 6 that is secured to the base 50 of the supporting structure 1 and a rotatable part 7 that is mounted to turn about an axis 8 in the base 50 between the closed position which is shown in figure 2 and the open position shown in figures 1 and 3. A spring 9 pushes this rotatable part 7 into the open position, against a stop 10, if this part is able to turn freely.
The rotatable parts 7 of all the contacts 6,7 are mechanically connected with one another in a known way, not specified here, so that they can rotate together. One of the parts 7 is connected with a control knob 11 that is mounted on the supporting structure 1, rotatable about an axis 12, between the the rest position shown in figure 1 and the on position shown in figures 2 and 3 and which protrudes through an opening in the cover 51 so that it can be operated from outside. A spring 13 draws this control knob into the rest position.
The linkage between the control knob 11 and the rotatable parts 7 contains a toggle lever with two arms 14 and 15. The arm 14, at a distance from the axis 12, is fixed and hinged to the control knob 11 via the rotational axis 16. The arm 15, at a distance from the rotational axis 8 of the rotatable parts 7, is fixed to one of these parts 7 via a rotational axis 17. A third arm 19 is rotatable through the toggle joint 18 connected between the two arms 14 and 15 and is at the same time rotatable by means of a rotational axis 20 fixed to rotate at a cam-shaped control lever 21, at a distance from the rotational axis 22 with which this rotatable control lever is mounted on the mounting plate 52.
This control lever 21 can be held by a lock 23, free to rotate at one end about an axis 24 and mounted on the mounting plate 52. At a distance from the rotational axis 24 the lock 23 is fitted with a stop part 25, this is an outward projecting edge formed by a wider end that is situated around the rotational axis 24. This stop part 25 extends in a tangent plane to the theoretical circle, the centre of which coincides with the geometrical axis of the rotational axis 24. With the control knob 11 engaged and contacts 6,7 in the closed position this stop part 25 forms a stop for an end, situated near to the rotational axis 20, of the control lever 21 without the latter exerting a torque on the lock 23.
Near its free end the lock 23, which is shaped like a bent arm, has a projection 26 that is able to work in concert with a stop part 27 of a locking rocker 28, free to rotate about an axis 29, between its ends, and mounted on the mounting plate 52. At one end this locking rocker 28 includes a broad head, a projecting part of which, on the opposite side of the axis 24, forms the stop part 27 that extends according to a tangent plane to a theoretical circle, the centre of which is the geometrical axis of the axis 29, and such that the lock 23 doesn't exert any torque on the locking rocker 28. In the event of fault current detection, the movable part 4 of the activator acts on the other end of the locking rocker 28.
A torsion lock spring 30 is mounted about the rotational axis 24. One end of this locking spring 30 is held by a projection 31 at the far end of the lock 23. The other end, if the control knob 11 is in the rest position, is held by the aforesaid projection 31, but with the control knob 11 engaged, is held by this knob. Owing to the rotation of the control knob 11 from the first to the second position the torsion spring 30 is anyway put under great strain, so that, with the control knob 11 engaged, it tries, with an extremely big force, to turn the lock 23 out of the lock position shown in figure 2 to the unlocked position shown in figure 3.
The locking spring 30 is somewhat counteracted by a spring 32 that is fitted between the head of the locking rocker 28 and the lock 23. This spring 32 is also a torsion spring which surrounds a pin 33, mounted on the locking rocker 28. One end of the spring 32 is held against this head by a projection 34, with its other end held by a pin 35 positioned on the lock 23. With the control knob 11 in the rest position, this torsion spring 32 makes sure that the lock 23 and the locking rocker 28 take up a position relative to one another, from which the lock 23 can be turned with its projection 26 against the stop part 27 of the locking rocker 28.
The working of the differential switch is as follows :
The relative positions of the components in the rest position are shown in figure 1. The contacts 6,7 are open, the control lever 21 rests lightly against the stop part 25 and the stop part 27 lies at a short distance from the projection 26 of the lock 23, on the opposite side of the axis 29, the control lever 21 and the toggle lever 14,15.
By engaging the control knob 11 the contacts 6,7, on the one hand, are closed by the action of the toggle lever 14,15, in which the springs 9 are put under great strain and, at the same time, the control lever 21 is pulled against the stop part 25 of the lock 23 and, on the other hand, this lock 23, put under pressure by the locking spring 30, itself put under strain by the knob 11, is pushed with great force against the stop part 27 of the locking rocker 28. The position is reached, as shown in figure 2.
When the fault current detector detects a fault current the movable part 4 of the activator pushes on the end, furthest from the head, of the locking rocker 28, which makes it tilt a little, releasing the lock 23. This lock 23 under the influence of the locking spring 30, then under strain, immediately turns so that the control lever 21 is released. Since the toggle lever 14,15 is now free to bend, the contacts 6,7 are no longer kept closed and they are pushed into the open position by the springs 9. The position is reached, as shown in figure 3. Because the lock 23 is rotated, the locking spring 30 is no longer under great strain and the control knob 11 is immediately returned to its rest position by the spring 13. The differential switch consequently reverts to its starting position, as shown in figure 1.
The force that the part 4 of the activator must exert on the locking rocker 28 in order that this locking rocker 28 might release the lock 23, depends on the force with which the lock 23, with its projection 26, pushes against the stop part 27. The last named force is basically determined by the force of the spring 30, less the much smaller force that the spring 32 exerts. The resultant force is not, or practically not, affected by the force with which the control lever 21, by the springs 9, through the action of the toggle lever 14,15, is pulled against the stop part 25. The control lever 21, after all, exerts no torque on the lock 23 but merely a force that runs according to the line through the point of tangency with the stop part 25 and the geometrical axis of the rotational axis 24 of the lock, so that only friction has to be overcome for the turning of the lock 23 with respect to the control lever 21. This is also true of the rotation of the locking rocker 28 with respect to the lock 23.
A fault current can be simulated by means of the test circuit 5. To this end a connection terminal 36, for one pole, is connected across a resistor 37, to the contact point of the movable part 7 of the contact 6,7 corresponding to another pole. The connection is achieved by pressing a test button 38 that forms part of a spring-loaded lip 39 which forms an elastic, deformable part of the supporting structure 1 and more specifically, of the plastic supporting element 53, as shown in detail in figure 6.
The test circuit 5 consists of the spring 9, which when the differential switch is engaged completes the circuit, at an end, with the aforesaid rotatable contact part 7, a torsion spring 40 that is installed on the supporting element 53, next to the lip 39, and a lead 41 in which the resistor is connected. On pressing the test button 38 an end of the torsion spring 40 is pushed against the spring 9 and the test circuit 5 is closed. The other end of the torsion spring 40 completes the circuit with an end of the lead 41. The other end of this lead 41 is clamped against the fixed contact part 42 of the aforesaid connection terminal 36 by means of a spring-loaded lip 43 which is secured to this fixed contact part. This fixed contact part 42, which is fastened inside a plastic supporting element, not shown on the figures, describes an angular S-shape. The lip 43 is part of a clamp support 44 which is permanently welded on to the lower part of the contact part 42, and extends, with a part within the upper half of this part 42, in order to prevent this part 42 from pushing to. At the top this clamp support is bent through 180 degrees inside a slot 45 in the top of the fixed part 42 so as to form the spring-loaded lip 43 on the outer side. The end of the lead 41 is fed through a slot 46 in the lip 43 between this lip and the rest of the clamp support 44 and clamped in place by the lip 43.
Placed separately through the slot 46 is a screw 47 which is screwed into the leg of the bracket 48. This leg is located inside the upper half of the fixed contact part 42. The other leg of the bracket 48 is located in the lower half of this part 42 and an electric wire can be connected to the connection terminal 36 by clamping its end between this other leg and the central part of the contact part 42, that which is brought about by screwing in the screw 47, which pulls the bracket 48 upwards.
The connection terminal 36 can also be used to connect a metallic strip that is then clamped between the head of the screw 47 and the upper part of the contact part 42. To this end the screw 47 has to be partly unscrewed and its head raised. In order, during this unscrewing, to prevent just the bracket 48 from being displaced downwards instead of the screw 47 upwards, a provision is made on that part of the contact support 44, lying in the upper half of the contact part 42, on the inner side of a projection 49, that restricts the downward displacement of the bracket 48.
The construction of the differential switch described above is relatively straightforward, among others in that no separate test button is required. The connecting of the wires and especially of the test circuit to a connection terminal is quite easy. This connection terminal is fairly compact and can be used for connecting the wires as well as for connecting the strips.
The reserve force that the activator has with respect to the force necessary for unlocking is practically independent of the force from the contact springs and therefore practically independent of the number of poles. An activator with a small reserve force in the case of two poles can, as a result, be used equally well with several poles.
The invention is in no way limited to the embodiment described above and many variations can be introduced to this embodiment within the scope of the patent application, among others with regard to the shape, the assembly, the configuration and the number of components that are used for the making thereof.

Claims

A differential switch which includes a supporting structure (1), an electrical part (2) fitted therein with a fault current detector and an activator (4), and a mechanical part (3) mounted on the supporting structure (1) with an externally operated, tiltable control knob (11) which is tiltable between a rest position and an on position, at least two electric contacts (6,7), each with a fixed part (6) and a rotatable part (7) and with at least one spring which tries to drive these parts (6 and 7) apart and, as a result, put the contacts (6,7) in the open position, in which the rotatable parts (7) are mechanically connected to one another and turn about the same axis, a toggle lever (14,15) which, on the one hand, is hinged at the control knob (11) at a distance from its axis of tilt (16) and on the other hand hinged at the mutually-linked, rotatable parts (7) of the contacts (6,7), fixed at a distance from their common hinge pin (8), an arm (19), which near the toggle joint (18) of the toggle lever (14,15), is fixed and hinged to the latter, a control lever (21), mounted and hinged to the supporting structure (1) and at a distance from its hinge pin (22) has a hinged connection with the arm (19), a locking device (23) which is mounted and hinged to the supporting structure (1) and includes a stop part (25) behind which, in the case of the lock (23) in the lock position and with the control knob (11) engaged and closed contacts (6,7), the control lever (21) is pulled by the action of the arm (19), the lock (23) which, on rotation from the lock position, releases the lever (21), and a locking rocker (28) which is also mounted and hinged to the supporting structure (1) and includes a stop part (27), that, in one position, holds the lock (23) in the lock position but in the case of fault current detection is pushed out of this position by the activator (4) and releases the lock (23), characterized in that it contains a locking spring (30) which, if the control knob (11) is engaged, tries to get the lock (23) out of the lock position and in addition, exerts a force on the lock (23) which is considerably bigger than the force necessary to turn the lock (23) with respect to the control lever (21) when the lock (23) is released from the aforesaid lock position.
A differential switch according to the above claim, with the characteristic that the aforesaid stop part (25) of the locking device (23) that in the lock position of the lock (23) holds the control lever (21), extends according to a tangent plane to a circle with the rotational axis of the lock (23) as its centre, so that the control lever (21) exerts practically no torque on the lock (23).
A differential switch according to one of the above claims, with the characteristic that the aforesaid stop part (27) of the locking rocker (28), that in one position of the locking rocker (28) holds the lock (23) in the lock position, extends according to a tangent plane to a circle, the centre of which is the geometrical axis of rotation of the locking rocker (28), such that the lock (23) exerts practically no torque on the locking rocker (28).
A differential switch according to one of the above claims, with the characteristic that the locking spring (30) is mounted on the lock (23) and, on engaging the control knob (11), is put under strain by this knob.
A differential switch according to the above claim, with the characteristic that the locking rocker (30) is a torsion spring that is mounted around the rotational axis (24) of the lock (23), with one end that acts together with a part (31) of the lock (23) and its other end that acts together with the control knob (11) when this control knob (11) is engaged.
A differential switch according to one of the claims 4 and 5, with the characteristic that the mechanical part (3) includes a spring (32) which is installed between the lock (23) and the locking rocker (28) and which pushes the lock (23) and the locking rocker (28) into a relative position in which the locking rocker (28), with its stop part (27), can grip behind a part (26) of this lock (23) when engaging the control knob (11), the spring (32) of which however is considerably weaker than the locking spring (30).
A differential switch according to one of the above claims, with the characteristic that the stop part (25) of the lock (23) is formed by an outward projection on the side along which the toggle lever (14,15) lies and, with the lock (23) in the lock position, the stop part (27) of the locking rocker (28) is situated on the opposite side of the lock (23).
A differential switch according to one of the above claims, with the characteristic that it includes a testing device with a test circuit (5) and a test button (38) for activating the test circuit (5), the test button (38) of which is formed by an elastic, deformable part (39) of the supporting structure (1).
A differential switch according to one of the above claims, with the characteristic that it includes connection terminals (36) with a fixed part (42), a movable part (48) and a screw (47) that is screwed into the movable part (48), as well as a spring-loaded lip (43), that is fastened to the fixed part (42), and that can clamp an end of the test circuit (5) against the fixed part (42).
A differential switch according to the above claim, with the characteristic that the spring-loaded lip (43) is a part of a clamp support (44) which is permanently welded on to the fixed part (42), this clamp support (44) containing a projection (49) that restricts the displacement of the movable part (48) with respect to the fixed part (42), when unscrewing the screw (47).