EP0855729B1 - High sensitive relay and method of coating contact surfaces of a highly sensitive relay - Google Patents

Abstract

The relay has a permanent magnet (7) which provides an attractive force used to hold the armature (6) in place while a fault current through the coil (10) on the U-core acts to oppose the permanent field and allows displacement of the armature under the pull of a spring (8). The arm (5a) of the core acts as a pivot on the contact surface (6a) of the armature or the contact surface and both poles of the core are covered with carbon in the form of diamond. The layer is 0.5-2 mu m thick and has a structure which is 2/3 diamond. The deposition is achieved by epitaxy chemical vapour deposition.

Description

The invention relates to a high sensitivity relay. and a method of coating contact surfaces a high sensitivity relay. In particular the invention applies to a high sensitivity relay constituting a mechanical actuator for a circuit breaker or a Differential Switch.

To ensure tripping of a circuit breaker or a differential switch on an electrical network, in the event of a malfunction of the network, high sensitivity relays can be used which activate the mechanical device of tripping of the circuit breaker.

Such high sensitivity relays are realized in the form of a magnetic circuit comprising a cylinder head and a pallet made of ferromagnetic material weak coercive field. The magnetic circuit which presents for example a rectangular shape has a cylinder head having the shape of a C with two branches parallel have end portions constituting polar surfaces to which apply two contact areas of the pallet made under the shape of a flat blade, in the closed position of the relay.

The cylinder head and the pallet are made up of magnetic parts made of a nickel alloy such as 50% alloy or 80% nickel alloy. These parts are processed at high temperature (at a temperature above 1000 ° C in a neutral or reducing atmosphere) so that the magnetic pieces have very weak coercive fields and for example coercive fields less than or equal to 150mA / cm).

A permanent magnet associated with the cylinder head and coupled to the magnetic circuit allows to exert a force of attraction on the pallet, so that it is held against the end parts of the cylinder head comprising the polar surfaces. A spring for example helical fixed at one of its ends on the pallet in the vicinity of a first contact area of the pallet with a first polar surface of the cylinder head and at its other end on a part secured to the cylinder head allows to exert on the pallet a restoring force in a direction tending to move the second contact zone away from the pallet of the second polar surface of the cylinder head by pivoting the pallet around an axis of rotation located at the first polar surface.

A coil is placed around part of the breech close to its second polar surface. The winding is supplied with electric current via a magnetic torus ensuring the detection of faults in the electrical circuit on which the circuit breaker. When the winding is excited by the toroid detector, the magnetic flux generated by the magnet decreases, which results in a decrease in the bonding effort exerted by the magnet on the pallet, so that the force exerted by the spring becomes predominant; the spring is then able to move the pallet, by pivot, to an open position. Move of the pallet from its closed circuit position magnetic to an open position allows actuation the mechanical circuit breaker control device. The movement of the pallet by pivoting between its position closing and its open position is accompanied a certain slip between the first bearing surface of the pallet and the first polar surface of the breech when rotating around the edge of the first polar surface. The resulting friction may cause some wear of the magnetic parts. Likewise, the second contact area of the pallet which comes to rest against the second polar surface of the cylinder head undergoes some wear during operation successive stages of the relay.

In order to obtain a high sensitivity of the relay, for example an electric triggering power less than 250µVA and preferably between 50 and 150µVA, the magnetic parts of the relay, i.e. the cylinder head and pallet must have a coercive field very weak and always less than 150mA / cm.

In addition, the relays must be able to carry out a very large number of operations without their performance are significantly degraded. In particular, the air gap between the magnetic pieces in their position closing must be kept low and constant. The polar surfaces of the cylinder head and the contact surfaces of the pallet must have a very good surface condition, so they must undergo a minimal degradation and wear during operation of the relay. In addition, the surfaces of the magnetic parts must withstand the climatic tests described in the French standard NFC.EN.61009. Document DE 28 36 572 A shows a relay according to the preamble of claim 1, with a coating of boride and graphite against wear.

Generally, magnetic alloys based on nickel used, especially when processed thermally to present a weak coercive field, have low hardness and low wear resistance. In addition, these nickel alloys are not stainless and their resistance to corrosion under conditions of use of the relay is insufficient. So we proposed improve the hardness and wear resistance of contact surfaces of the magnetic parts of the relays producing metallic coatings on these surfaces which also increase corrosion resistance contact surfaces.

These protective coatings can be produced by a process such as electrolysis, chemical deposition vapor phase (CVD) or chemical phase deposition plasma activated steam (PECVD).

The choice of metal deposited to constitute the coating layer must allow certain conditions with regard to the characteristics of the coating layer.

In particular, the layer must be thick limited so that we can get an air gap between the contact areas of the pallet and the polar surfaces of the cylinder head of a perfectly defined thickness and less than a low value of the order of 5 μm.

In addition, the hardness of the coating layer must be high to limit wear on the contact between the pallet and the cylinder head, during a use resulting in a very large number of relay operations.

Resistance to oxidation and more generally the corrosion resistance of the coating layer must also be very good.

The coefficient of friction of the surfaces of contact with each other must be weak, especially because the hinge axis of the pallet can be at one of the polar surfaces of the cylinder head.

We therefore proposed various metals or compounds metallic to constitute the coating and in particular chromium, in the form of hard chromium, nitride titanium, titanium carbonitride, a nickel-palladium alloy, gold or an alloy of gold and palladium, or still a nickel coating. None of the coatings metal offered so far has given entirely satisfaction in particular that it is necessary to deposit a relatively thick layer of coating on the contact surfaces and that the coefficient of friction of this deposited metal layer is relatively Student.

In addition, the hardness of the deposited layers is not generally not sufficient to provide long duration of the relay.

The circuit breaker control relays used so far therefore have a limited lifespan.

The object of the invention is to propose a relay high sensitivity with magnetic circuit comprising a cylinder head of magnetic material having a first and second polar surfaces and a palette consisting of a blade, made of a magnetic material, having on one of its faces or bearing face, a first and a second respective contact zone with the first and the second polar surface of the breech, in a closed position of the magnetic circuit, means of attraction of the pallet towards the closed position and means for recalling and moving the pallet by pivoting about an axis which can be located on the first polar surface of the cylinder head, towards a position opening in which the second contact area of the pallet is separated from the second polar surface of the cylinder head, this relay can have a very large air gap weak and perfectly defined between the surfaces of contact of the pallet and the cylinder head, a very large resistance to wear and oxidation and a coefficient very low friction between the contact surfaces.

For this purpose, at least one of the bearing surfaces constituted by the support surface of the pallet of a part and the polar surfaces of the cylinder head on the other hand, is covered by a coating containing carbon in the form of a diamond.

The invention also relates to a method for coating the contact surfaces of a high relay sensitivity.

In order to clearly understand the invention, we will now describe as an example, referring to attached figures, an embodiment of a high sensitivity relay according to the invention constituting an actuator of a circuit breaker of an electrical network and a method of coating the contact surfaces of this relay.

Figure 1 is a schematic view of a circuit breaker comprising a high sensitivity relay according to the invention.

Figure 2 is a perspective view of a high sensitivity relay according to the invention.

In Figure 1, we see a differential circuit breaker to interrupt the flow of current in an electrical network generally designated by the mark 1.

On a line of network 1 is placed a contactor 2 which can be moved by a mechanical device 3 actuated by a high sensitivity relay 4, to cut current flow in network 1, the whole comprising the contactor 2, the mechanical device 3, the relay 4 and a malfunction detector 11 of network 1 constituting the differential circuit breaker.

As can be seen in Figures 1 and 2, the relay 4 consists of a magnetic circuit which comprises a yoke 5 made of magnetic material having the shape of a C and a pallet 6 consisting of a blade plane which ensures the closing of the magnetic circuit in a closed position shown in Figure 2.

The cylinder head 5 has two branches substantially parallels 5a and 5b, the end parts of which constitute the polar surfaces of the cylinder head 5. The palette 6 has a bearing surface 6a (lower surface of the pallet in Figure 2) which comes into contact with the polar surfaces of the cylinder head 5, at the end of the branches 5a and 5b of the cylinder head, in the position of closing of the relay shown in figure 2.

A permanent magnet 7 is fixed on the branch central cylinder head 5 joining the two branches parallel 5a and 5b and ensures by magnetic coupling with cylinder head 5, the attraction and bonding of the pallet 6 on the polar surfaces of the cylinder head, in the closed position of the relay.

A return spring 8 formed in the form a coil spring is attached to one of its ends on an end part of the pallet, in the vicinity a first contact area of the pallet made up on its bearing surface coming into contact with the first polar surface of the breech at the end of branch 5a. Spring 8 is fixed at its second end on a fixing piece 9 fixed to the body of the relay or on the cylinder head. Spring 8 exerts a force on the pallet 6 in the opposite direction to the force of attraction of the second contact area of the pallet coming to rest on the second pole surface at the end of branch 5b of the cylinder head.

A coil 10 surrounds the second branch 5b of the cylinder head 5. The winding 10 is supplied with current electric via fault detector 11 of operation of the electrical network 1 which can be constituted by a toroid detector capable of sending a current to the winding 10, in the case of the appearance a malfunction on the network 1.

In the event that a fault current flows in the winding 10, this generates a magnetic field and a flow in the branch 5b of the breech which thwarts the magnetic flux and magnet attracting force permanent 7.

Spring 8 with insufficient return force to take off pallet 6 from the second surface polar of the breech, against the force of attraction of the permanent magnet 7, takes off from the pallet 6 of the second polar surface of the cylinder head and the opening of the relay, when the winding 10 is supplied by a fault current.

Pallet 6 of the relay in the open position, as shown in figure 1, activates the mechanism 3, so as to unlock it. Mechanism 3 exercises then a large force on the contactor blade 2 to ensure its displacement and the interruption of the current flow in the electrical network 1.

Relay 4 must have a high sensitivity, the electrical triggering power of the relay in front be less than 250µVA and preferably between 50 and 100µVA. For this it is necessary to use to constitute the cylinder head 5 and the pallet 6 of the circuit relay 4, a high magnetic alloy performance whose coercive field is less than 150mA / cm. Generally a nickel alloy is used. 50 or 80% nickel. This alloy is further processed thermally at high temperature under neutral atmosphere or reductive.

In this metallurgical state, the alloys of used nickel have low wear resistance. In besides these alloys are not stainless.

When the relay opens, the spring 8 ensures the movement of the pallet 6 by pivoting around an axis 12 (see Figure 2) located on the first polar surface of the breech at the end of the branch 5a.

The movement of the pallet 6 between its position however, its open position is not not purely a pivoting movement, some slip occurring between the first area of contact of the bearing surface 6a of the pallet and the first polar surface of the cylinder head 5. It occurs therefore a friction between the contact surfaces of the relay and, during successive uses of the relay, a wear of these contact areas. Likewise, the maneuvers opening and closing of the relay cause a wear of the second contact area of the bearing surface 6a of the pallet against the second polar surface of the breech at the end of the branch 5b. In addition, the air gap high sensitivity relay, i.e. the sum of air gaps between the first contact area of pallet 6 and the first polar surface of the cylinder head 5 on the one hand and the second contact zone of the pallet 6 and the second polar surface of the cylinder head 5 else hand, must have a very low value and perfectly constant to ensure satisfactory performance of relay over time.

The relay air gap corresponding to the sum of air gaps at the contact zones of this relay must be as constant as possible and less than or equal at 5µm.

It is therefore necessary that the polar surfaces of the cylinder head and the surface contact areas support 6a of the pallet have a very low roughness. These areas can for example be subject to rectification and running-in.

In addition, the coefficient of friction of the palette on the cylinder head, especially at the first contact area of the pallet 6 resting on the first polar surface of the cylinder head must be very low.

The resistance to wear and therefore the hardness of contact surfaces must also be very high.

The high sensitivity relay according to the invention meets all of these conditions, because at least one of the bearing surfaces constituted by the bearing surface 6a of the pallet 6 on the one hand and by the polar surfaces at the end of branches 5a and 5b of the cylinder head on the other hand is covered with a layer of coating containing carbon in the form of a diamond.

Generally, the relay according to the invention has a coating layer on only one of the bearing surfaces, the best results being obtained by making a coating layer containing carbon in the form of diamond on the bearing surface 6a of the pallet only. The polar surfaces of the cylinder head 5 are then simply rectified or lapped. Of course, it is also possible to donate both the polar surfaces of the cylinder head and the surfaces pallet support.

The coating of the contact surface (s) of the relay is achieved by a chemical deposition process in vapor phase assisted by a plasma (PECVD process).

The part to be coated, for example the heat treated magnetic alloy constituting the pallet 6 is introduced into a chamber in which we can create a vacuum. The room is evacuated and we introduces into the chamber a gas containing carbon, for example a hydrocarbon. We add to the filling gas the chamber a doping agent such as a borane. We produce an electrical discharge between the blade to be coated and a part of the chamber, so as to raise the temperature from the slide to a moderate reaction temperature, for example between 100 and 200 ° C and to be transformed part of the gas filling the plasma chamber from in contact with the part to be coated. It is formed on the part to be coated with a layer composed of carbon which contain other elements such as hydrogen, in which a high proportion of the bonds between atoms of carbon is of the type of bonds of carbon atoms in the diamond. Typically, we get a compound whose structure for 2/3 is similar to that of the diamond.

Such a compound is known by the name D.L.C. or under the trade name Diamolith Carbon.

The duration of the coating treatment is set so as to obtain a coating with a thickness desirable.

We were able to show that, in the case of the coating of a pallet of a high sensitivity relay of a electric circuit breaker, minimum layer thickness coating to obtain the required properties contact surfaces of the relay is only 0.5µm. The layer obtained is also extremely smooth. The low thickness of the coating layer and a very good condition of the surface of this layer allow to obtain a weak and perfectly defined air gap between the relay contact surfaces.

Usually, we will perform on relay contact surfaces preferably on the pallet support surface, a coating layer containing a high proportion of carbon in the form of diamond having a thickness close to 1 μm. So more general, we will aim for a coating thickness between 0.5 and 2µm.

We carried out different tests on a slide of nickel alloy relay coated with a compound of carbon containing a high proportion of carbon under diamond shape. We measured the hardness, the load critical of chipping, tear resistance, friction coefficient and corrosion resistance of the coating layer.

Comparable tests have been carried out on other layers of coatings consisting of hard chromium, titanium nitride, carbonitride titanium or a nickel-palladium alloy.

The test results have been reported in the table given below. material Hard cr TiN TiCN Ni-Pd DLC Hardness (Kg / mm2) 800 2300 3000 1000 4000/6000 critical flaking load Pc (Newton) 60 (20 µm) 10.3 17.3 33 tear resistance (Mpa) 2064 354 595 1135 coefficient. friction (at 5N) 0.35 0.45 0.4 0.5 0.09 minimum deposit thickness (µm) 2 2 2 1 0.5 corrosion resistance good good good excellent

The last column of the table relates to a coating of a contact surface of a next relay the invention.

Corrosion resistance tests have been carried out according to French standard NFC.EN.61009. The relay is placed in the closed position and exposed, during 24 hour exposure cycles to an atmosphere containing 100% humidity, at a temperature of 70 ° C, for twenty-eight days. We test the relay and checks its trigger characteristics. If the trigger characteristics are not changed measurably after the test, the resistance to corrosion is considered excellent. If the relay continues to operate at the end of the test but with modified characteristics (up to 30%), resistance to corrosion is considered good. Corrosion resistance is considered bad if the relay does not no longer works after the test.

The results presented in the table above show that the coating layer according to the invention has a hardness significantly higher than the hardness other coatings including coatings titanium nitride and carbonitride.

The contact surfaces of the following relays the invention therefore exhibit resistance to wear significantly higher than the wear resistance relays with metallic coatings of the type known. This resistance to wear and the operation of the relays are also improved by the fact that the coefficient friction between the coated contact surfaces of a diamond-like carbon compound is much lower than the coefficient of friction of coatings metallic.

Coating of relay contact surfaces according to the invention also has a critical charge chipping and tear resistance satisfactory, these characteristics not being superior, for coatings according to the prior art, only in the hard chrome. Additionally, as noted above, the minimum coating thickness of the coating to be produced on the contact surfaces of a relay is substantially lower in the case of a relay according to the invention (0.5 µm) if compared to surface coatings of relay contact according to the prior art (thickness 1 or 2 µm).

Relays according to the invention comprising on their contact surface a thin deposit perfectly smooth carbon compound in the form of diamond, therefore have very characteristic superior to known high-sensitivity relays the contact surfaces of which are coated with a layer metallic.

In particular, a low deposit thickness and perfectly controlled provides a perfectly air gap constant and limited to a low value.

The relay has a very strong resistance to oxidation, even in the case of using a deposit of thin. The high hardness of the coating makes on the other hand the relay according to the invention practically insensitive to wear, following a very large number of maneuvers.

The low coefficient of friction between the contact surfaces helps limit deterioration of these contact surfaces, at the pivot axis of the pallet of the first polar zone of the breech.

In addition, the coating which is carried out at a very moderate temperature does not deteriorate properties parts of the relay. The next relay the invention therefore has a triggering power which can be set to a low value and in particular less than 250µVA.

The invention is not limited to the embodiment that has been described.

This is how the magnetic circuit constituting the relay can be realized in a form different from that which has been described, that the means of recall and actuation of the relay pallet can be different from those that have been described.

In addition, the invention applies to relays with high sensitivity different from relays constituting actuators for a circuit breaker or a differential switch of an electrical network.

Claims (8)

1. High-sensitivity relay comprising a magnetic circuit including a yoke (5) of magnetic material having a first and a second polar surface and a plate (6) which is constituted by a sheet of magnetic material and which has, on one of its faces (6a), or bearing face, a respective first and second region of contact with the first and the second polar surface of the yoke (5), in the position closing the magnetic circuit, means for attracting the plate (6) towards the closing position and means for returning and displacing the plate (6), by pivoting about an axis which may be located on the first polar surface of the yoke, towards an opening position in which the second contact region of the plate (6) is separated from the second polar surface of the yoke, characterised in that at least one of the bearing surfaces constituted by the bearing face (6a) of the plate (6), on the one hand, and the polar surfaces of the yoke (5), on the other hand, is covered with a coating containing carbon in the form of diamond.
2. Relay according to claim 1, characterised in that only the bearing face (6a) of the plate (6) is covered with a coating containing carbon in the form of diamond.
3. Relay according to claim 1, characterised in that the polar surfaces of the yoke (5) and the bearing face (6a) of the plate (6) are both covered with a coating containing carbon in the form of diamond.
4. Relay according to any one of claims 1 to 3, characterised in that the coating containing carbon in the form of diamond has a thickness of from 0.5 to 2 µm.
5. Relay according to any one of claims 1 to 4, characterised in that the coating has a structure of which 2/3 is the structure of the diamond.
6. Relay according to any one of claims 1 to 5, characterised in that the plate (6) of the relay is associated with a mechanism (3) for triggering a circuit breaker, the relay constituting a mechanical activator of the circuit breaker.
7. Relay according to claim 6, characterised in that it comprises a permanent magnet (7) associated and coupled with the yoke (5) in order to bring about the attraction and the adhesion of the plate (6) to the polar surfaces of the yoke (5), a spring (8) for returning the plate (6) into an opening position and a winding (10) for compensating for the force of attraction and adhesion of the plate (6) exerted by the permanent magnet (7), which winding is supplied with electric current by a device (11) for detecting faults in the electrical network (1).
8. Process for coating a contact surface of a high-sensitivity relay comprising a magnetic circuit including a yoke (5) having a first and a second polar surface and a plate (6) which is constituted by a sheet of magnetic material and which has, on one of its faces (6a), or bearing face, a respective first and second region of contact with the first and the second polar surface of the yoke (5), in the position closing the magnetic circuit, means (7) for attracting the plate (6) towards the closing position and means (8, 10) for returning and displacing the plate, by pivoting about an axis which may be located on the first polar surf-ace of the yoke, towards an opening position in which the second contact region of the plate (6) is separated from the second polar surface of the yoke (5), characterised in that at least one of the magnetic members constituted by the yoke (5) and the plate (6) is arranged in a coating chamber, in that a vacuum is formed, in that a gas containing carbon, such as a hydrocarbon, is introduced into the chamber, in that a discharge is produced between the magnetic member (5, 6) and a portion of the chamber in order to heat the magnetic member (5, 6) to a temperature of from 100 to 200°C and to convert the gas containing carbon into plasma, and in that a layer of coating containing carbon in the form of diamond, which coating is obtained by plasma-activated vapour phase chemical deposition, is deposited on the magnetic member (5, 6).

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