Abstract:
A magnetic trip with a fixed magnetic circuit polarised by a permanent magnet. The magnetic circuit includes two preferably identical parallel wafers each defining a main branch and a deflection tab with the presence of a coil on each branch. At their ends opposite to the mobile pallet, the wafers have in cross-section an L shape. The insulation structure carrying the coils is formed of two half-shells tightly holding the wafers. The trip can be used in circuit breakers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic trip for an electrical switching device, comprising a fixed magnetic circuit which is in association with a permanent magnet, at least one coil able to be passed through by an electric current and in association with a circuit branch to determine a magnetic flow which is function of the current, and a moveable pallet acted upon by a spring and determining with the fixed magnetic circuit a main flow loop. 
     It is important to be able to manufacture such a magnetic trip so that its pallet activates the trip mechanism of the device as rapidly as possible, for example in a few tenths of a millisecond, in response to excess current in the coil. It is moreover desirable for the magnetic flow induced by the excess current not to lead to demagnetisation of the permanent magnet. 
     BRIEF SUMMARY OF THE INVENTION 
     The purpose of the invention is to make highly reactive a trip of the type described and to simplify its manufacture. 
     According to the invention, the magnetic circuit includes, near the magnet, at least one magnetic flow deflection tab defining a secondary flow loop equipped with at least one secondary air gap, and the tab is arranged relative to the fixed magnetic circuit and to the magnet so that an excess current in the coil deflects the flow of the magnet to the secondary loop. 
     Preferably, the magnetic circuit includes two identical parallel wafers each having on the one hand a main branch carrying a coil and on the other hand a deflection tab, the free ends of the tabs defining two secondary transverse air gaps, and the magnet is placed between the wafers near the tabs. 
     Each coil may be wound onto a U-shaped insulation half-shell enclosing by the wings of the U the small sides of the corresponding wafer, with the result that the coil is immediately adjacent to a lateral face of the wafer, the half-shells being assembled so as to form an insulation structure carrying the coils and containing the wafers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description will be given below of a non-restrictive embodiment of the invention, with reference to the appended drawings. 
     FIG. 1 is a cross-section elevation of a trip according to the invention. 
     FIG. 2 is a view of it from above in cross-section along the plane  2 — 2 . 
     FIG. 3 is a cross-section along the plane  3 — 3 . 
     FIG. 4 shows in perspective and in large scale the magnetic circuit of the trip. 
     FIG. 5 is an exploded perspective view of the trip. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The magnetic trip shown in FIG. 1 is intended to be mounted in a circuit-breaker, contactor-circuit-breaker or analogous switching device with a protection function and it includes a magnetic circuit M fitted with a fixed part  10 , called hereinafter a fixed magnetic circuit, and with a mobile part  11 , called hereinafter a mobile pallet; a permanent magnet A is in association with the fixed magnetic circuit  10  so as to impart to it a permanent magnetic flow. The fixed magnetic circuit  10  includes two wafers  10   a ,  10   b  parallel to each other, of a generally flat shape with median planes Pa, Pb extending along a direction X. The wafers are preferably identical. On the wafers  10   a ,  10   b  of the fixed magnetic circuit are placed two respective coils Ca, Cb. These coils are mounted electrically in series in a control circuit of the trip in order to provide, in the event of excess current in this circuit, the ampere turns necessary for the pallet  11  to be displaced. 
     The pallet  11  is moveable in translation in the direction X and it is coupled at one end  12   a  with an activation component such as a push-button  12 . The push-button is able to activate a trip mechanism of the circuit-breaker. The connection R between the end  12   a  of the push-button  12  and a central associated channel  11   a  of the pallet  11  is slightly swivelling, as shown in FIG. 1, so as to optimise the air gap between the pallet and the fixed circuit. The push-button is acted upon by a spring  13 , for example a compression spring, tending to separate the pallet from the polar ends  14   a ,  14   b  of the branches of the fixed magnetic circuit. The pallet is applied to the fixed magnetic circuit by the permanent magnet A against the effort of the spring. 
     The appearance of excess current in the coils causes the separation of the pallet  11  relative to the fixed magnetic circuit  10  and the displacement of the push-button  12  thanks to the effort of the spring  13 . 
     Each wafer  10   a ,  10   b  has on its small sides, between its polar ends  14   a ,  14   b  and its ends  15   a ,  15   b  opposite to the ends  14   a ,  14   b , a recessed part  16   a ,  16   b  which receives the coils Ca, Cb so as to reduce the space requirement of the trip. The ends  15   a ,  15   b  of the wafers  10   a ,  10   b  are intended to hold the permanent magnet A tight and to determine a deflection path T 2  of the magnetic flow. The ends  15   a ,  15   b  of the wafers are configured in a specific way and include, so as to form two air gaps, on the one side a respective tab  17   a ,  17   b  and on the other side an edge  18   a ,  18   b  delimiting the contracted part  16   a ,  16   b . The free end of each tab  17   a ,  17   b  integral with a wafer defines with the opposite edge  18   b ,  18   a  of the other wafer a predetermined transverse air gap  20   a ,  20   b . “Transverse air gap” means that the air gap extends in a plane perpendicular to the direction X. 
     The tabs  17   a ,  17   b  constitute flow deflection branches of the magnetic circuit extending or continuing transversally (i.e. perpendicularly to the planes Pa, Pb and to the direction X) the main branches  19   a ,  19   b  formed by the wafers  10   a ,  10   b , so as to channel in excess current state the magnetic flow induced. The wafers thus present an L-shape—or with a small wing and a large wing—the large wing of which is constituted by the main branch and the small wing of which is constituted by the tab or secondary branch. The permanent magnet A is inserted between the wafers  10   a ,  10   b  at the level of the transverse tabs  17   a ,  17   b  and of the edges  18   a ,  18   b  so as to brace the wafers arranged rather head to tail (see FIG.  3 ); it may be seen in this figure that, in transverse cross-section, the wafers present at their ends  15   a ,  15   b  an L shape to embrace the magnet A by generating the two air gaps  20   a ,  20   b . It is advantageous to have identical wafers, which simplifies the manufacture of the trip. 
     The coils Ca, Cb are wound half over an insulation half-shell  21   a ,  21   b  and half over the respective wafer  10   a ,  10   b , so as thus to be in direct contact with the latter on its internal face (see FIG.  2 ). The half-shells are U-shaped enclosing the wafers  10   a , lob and present stops,  22   a ,  22   b  for shoulders  23   a ,  23   b  provided at any suitable place on the wafers. The assembled half-shells constitute an assembly shell or casing of the coils, this casing being housed in an insulation body D of the trip. The body D is fitted with an opening  24  for the push-button  12  and constitutes a support for the spring  13 . 
     The trip described operates in the following way. In the absence of excess current in the coils Ca, Cb, the pallet  11  is applied to the polar surfaces of the ends  14   a ,  14   b  of the magnetic wafers  10   a ,  10   b  by the permanent magnet A against the effort of the spring  13 . The flow developed by A circulates in a main loop T 1  formed by the main branches  19   a ,  19   b  of the wafers of the pallet  11 . In the event of excess current, the coils develop a magnetic flow which is opposed to the flow of the permanent magnet and which deflects it to the secondary branches constituted by the tabs  17   a ,  17   b ; the flow created by the permanent magnet then passes in a deflection loop T 2  including the tabs  17   a ,  17   b  of the wafers, the air gaps  20   a ,  20   b  and the edges  18   a ,  18   b  of the wafers. There is therefore no demagnetisation of the permanent magnet and the spring  13  provides an effort greater than that coming from the residual magnetisation at the ends  14   a ,  14   b  of the metal wafers  10   a  and  10   b , which very rapidly activates the push-button  12 . The particularly compact configuration of the fixed magnetic circuit with its polarisation magnet makes it possible to reduce the dimensions of the pallet and to make it lighter, which makes the trip more reactive. The symmetrical architecture of the trip makes it particularly straightforward to manufacture and to assemble.