Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H69/00—Apparatus or processes for the manufacture of emergency protective devices
  • H01H69/01—Apparatus or processes for the manufacture of emergency protective devices for calibrating or setting of devices to function under predetermined conditions
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H71/00—Details of the protective switches or relays covered by groups H01H73/00 - H01H83/00
  • H01H71/74—Means for adjusting the conditions under which the device will function to provide protection
  • H01H71/7427—Adjusting only the electrothermal mechanism
  • H01H71/7436—Adjusting the position (or prestrain) of the bimetal

Definitions

• the present invention relates to an automatic magneto-thermic switch (or breaker) having thermal protection which can be calibrated mechanically, and an associated method of calibration.
• magneto-thermic switches are automatic switching devices in which two contacts are closed by a manual arming device (which can also be controlled manually to open them) and which must open automatically when the switch is overloaded whereby to ensure protection of electrical installations against overloads and short circuits.
• an electromagnetic actuator having a movable core excited by the load current which, in the event of a short circuit, acts on a release device causing immediate and rapid opening of the contacts.
• thermal protection requires precision and repeatability of operation and must ensure that for a predetermined overload condition, corresponding for example to a current of 20A, lasting for a predetermined time, for example 20 seconds, opening of the contacts will occur.
• Thermal protection of automatic switches therefore requires a calibration operation which must be performed on each individual switch and must ensure repeatability of action and prevent possible miscalibrations.
• the bimetallic element which constitutes the overload sensor, is generally in the form of a rigid beam mounted in a cantilever fashion on a relatively flexible support and the free end of which acts on the release device.
• a calibration screw accessible from outside the switch acts on the flexible support close to the bimetallic beam mount and allows the angle of the mount to be modified so as to rotate the beam at the mount and displace the end of the beam.
• Calibration involves mechanical and electrical operations.
• the adhesive is introduced into the switch through the same aperture used for acting on the calibration screw.
• a further disadvantage lies in the fact that calibration thus performed is capable of corruption: the glue on the calibration screw does not in fact prevent it from being screwed or unscrewed forcibly by the installer or by a careless user.
• magneto-thermic switch which is the subject of the present invention, which allows an exclusively mechanical repeatable calibration to be performed in a short time and, therefore, as well as being simple, fast and low cost, is capable of automation and integration into the production line.
• the probe is coupled to a transducer the signal from which is used to control the automated screwing or unscrewing of the calibration screw.
• a second aperture is also provided in the switch casing disposed in correspondence with the bimetallic beam mount to allow the introduction into the casing of cold polymerisable resin which sets the beam mount in the calibration position and thus prevents subsequent manipulation of the calibration screw from modifying the position) of the bimetallic element.
• an automatic switch comprises a casing 50 of generally rectangular form constituted by two coupled half-shells one of which is shown in section along the plane of coupling in order better to show the internally ribbed structure of the half-shells and to make more clearly visible the different apertures formed by these.
• the internal frames and ribs of the two half-shells suitably interpenetrate and hold the two half-shells and the different components housed within the casing together in a precise manner.
• the two half-shells are fixed together by means of screws or rivets passing through apertures 51, 52, 53, 54, 55 perpendicular to the plane of the drawing.
• the switch shown is of modular type for installation on rails next to adjacent modules positioned with the casing faces parallel to the coupling plane of the half-shells.
• the switch has on its rear wall a recess 56 intended to receive a rail of DIN regulation type to which the switch is engaged by means of toothed connector guides not shown.
• a plurality of mechanical and electrical components are housed and positioned with precision, and in particular these comprise:
• the terminal 57 is clamped by means of a clamping screw the head of which is accessible through an opening 63 in the casing co-axial with the screw (and open to the front of the casing).
• the external electrical terminations to be clamped by the terminal can be interposed between the jaws of the terminal through an aperture 64 of the casing (open on to the face of the casing which, in relation to normal installation conditions of the switch, corresponds to the lower face).
• Similar apertures 65, 66 are respectively provided for clamping and introduction of electrical terminations into the terminal 58.
• the terminal 57 is provided with a metal projection 9 the end of which is electrically connected to one end of the bimetallic strip 10 and to one end of a arc conveyor guide 67 for conveying the arc towards the arc quenching labyrinth.
• the walls of the casing 50 have suitable internal ribs ensure the positioning of the terminal 57 and the guide 67 within the casing, with limited play.
• the ends of the projection 9 and the guide 67 provide a cantilever support for the bimetallic element 10.
• the actuation of the screw 1 is effected through an opening 68 in the lower wall of the casing and causes rotation of the cantilever support of the bimetallic element 10 the free end of which turns proportionally.
• the projection 9, the bimetallic strip 10 and the flexible copper braid 6 ensure electrical continuity between the terminal 57 and the movable contact arm 5.
• the projection 69 and the winding of the electromagnet 59 one end 70 of which is connected to the terminal 58 ensure electrical continuity between fixed contact 3 and terminal 58.
• the current is interrupted by opening of the contacts 3 and 4.
• the contacts 3 and 4 are closed upon arming of the release device, effected manually by rotation of the lever 61 in the direction indicated by the arrow 71.
• the link 2 then presses the trip device into the armed position overcoming the thrust of the spring 11.
• Figure 2 is an enlarged and simplified partially sectioned view of the trip device and the elements interacting with it for a better understanding of the operation of the trip device and the thermal protection.
• the trip device is formed by a support lever 12 for the contact arm 5, articulated at one end on a pin 13 engaged in a predetermined fixed position in the casing.
• the contact arm 5 is pivoted at its end opposite from the contact 4 on a pin 14 rigidly connected to the free end of the support lever 12.
• the contact arm 5 is capable of relative rotation with respect to the support lever 12 on the pin 14, limited by a slot 15 in which the pin 13 is inserted.
• the lever 12 is provided with an arming tooth 16 on which the end of the link 2 presses.
• Rotation of the arming lever 61 into the position shown and defined by an abutment 72 of the casing acts through the link 2 on the support lever 12 and, by overcoming the action of the spring 11, causes a predetermined rotation of the pin 13 thereby making it assume a stable and defined armed position in relation to the casing.
• Rotation of the support lever 12 is accompanied by a rotation of the contact arm 5 which closes the contacts 3 and 4.
• a release lever or member 7 pivoted on the pin 13 is provided with a release tooth 17 which interacts with a tooth of the latch pawl 6 to cause its rotation and consequent release of the end of the link 2 from the tooth 16.
• the release member 7 is provided with an arm 18 (on which acts a striker 19 operated by the electromagnet) ending in a tooth 20 which interacts with the guide 8.
• the guide 8 is provided at its end with two teeth 22, 23 which interfere respectively with the end of the bimetallic strip 10 and with the tooth 20.
• the stroke which the guide 8 must perform and the position which it must assume to ensure release of the latch pawl 6 are uniquely defined in relation to the casing by the geometry of the release mechanism and known from the design, with the single uncertainty due to the working tolerances, which must be kept within predetermined limits.
• the position which the end of the bimetallic strip 10 must occupy in rest conditions at ambient temperature, when the bimetallic strip has no current flowing through it, is also defined in relation to the casing.
• the problem of calibration of the thermal protection device can be reduced therefore to positional adjustment of the free end of the bimetallic strip 10 in rest conditions.
• the adjustment is easily achieved by providing in the casing 1 a rectilinear opening 25, preferably of circular cross-section which extends from one wall (the lower wall) of the casing up to the end of the bimetallic strip 10 in a direction substantially perpendicular to the length of the bimetallic strip.
• a measurement rod 33 coupled to a transducer, for example a differential inductance transducer, which, when thrust with a minimum force into contact with the bimetallic element 10 allows measurement with high precision of the distance D of the end of the bimetallic strip from a reference plane of the casing perpendicular to the direction of heat-induced bending of the metal strip.
• a transducer for example a differential inductance transducer
• the reference plane can be the lower face of the casing into which the hole 25 opens, or more advantageously a parallel plane closer to the pin 13 of the trip mechanism in order to reduce to the minimum imprecisions due to the shrinkage of the casing 1 which is generally made of moulded plastics material, which shrinkage is subject to a certain variability.
• the head of the switch in which the trip device is partially housed generally has a reference plane 26 particularly suitable for the performance of this measurement.
• Figure 3 schematically illustrates apparatus which allows the calibration operation to be performed automatically by putting into operation the method described.
• a switch 27 is disposed, in this case with automatic gripping devices, on a test bed 28 provided with a reference tooth 29 against which the switch 27 is pressed by a movable jaw 30 moved by an actuator 31.
• a position sensor 32 provided with a measuring rod 33 which is inserted into the aperture 25 of the switch until it comes into contact with the bimetallic strip.
• a sensor 32 provides a comparator 36 (which can be either of the analogue or digital type), with a signal indicating of the detected position of the bimetallic strip.
• This signal is compared with a reference value REF corresponding to the desired position of the bimetallic strip.
• the error signal ERR generated by the comparator is applied to the input of an amplifier 37 which supplies the motorised screw driver 34 with an electrical signal of suitable magnitude and sense to cause screwing or unscrewing of the calibration screw until the error signal becomes zero.
• the same apparatus can serve, by utilising the sensor 32, to measure the thermal deflection caused by a predetermined current in the bimetallic strip for a predetermined time, and to experimentally determine, on a certain number of samples, the position which the bimetallic strip assumes in order to cause the trip device to act, and the corresponding transducer signal.
• test operation which comprises applying to the switch a current of predetermined value and testing if the thermal protection intervenes with a delay lying between two predetermined values.
• the method is however capable of variations which allow integral compensation of the production tolerances on each individual calibrated switch.
• the magnitude of the thermal deflection of the bimetallic element is substantially independent of the production tolerances which to some extent influence only the position of the bimetallic strip relative to the reference plane of the casing, for which position intervention of the trip device occurs.
• the test bed includes a microprocessor 38 which controls the necessary operations in sequence.
• the switch to be calibrated is located on the test bed and armed.
• the calibration screw is actuated to cause rotation of the cantilever support of the bimetallic strip to simulate a thermal deflection thereof.
• the calibration screw is turned in an opposite sense to return the bimetallic strip to a rest condition in which the end of the strip is located at a predetermined distance from the now-identified trip position, equal to a predetermined thermal deflection.
• FIG. 3 shows a further advantageous characteristic of the switch formed in accordance with the present invention.
• an aperture 40 is provided in a side face of the casing in correspondence with the cantilever support of the bimetallic strip 10.
• injection of resin takes place with the switch disposed in a plane with the rear face orientated downwardly and this position is maintained for the time necessary for hardening of the resin.
• the trip device rather than having a latch pawl and an interacting trip member can have a simple hook pawl pivoted on the pin 13 or eccentrically thereof, acting directly on the end of the link and actuated by the guide 8.
• the aperture 25 orientated in the direction of the thermal deflection can be replaced by a pair of facing openings formed in both the half-shells of the casing at the free end of the bimetallic strip to detect its position using optical apparatus or mechanical sensors of different type from the feeler rod described.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Switches That Are Operated By Magnetic Or Electric Fields (AREA)
• Thermally Actuated Switches (AREA)
• Measuring Temperature Or Quantity Of Heat (AREA)
• Measuring Magnetic Variables (AREA)
• Magnetic Resonance Imaging Apparatus (AREA)
• Testing Or Calibration Of Command Recording Devices (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=11369730

Family Applications (1)

Country Status (7)

Cited By (6)

Families Citing this family (1)

Citations (5)

• 1994
  • 1994-10-18 IT IT94MI002127A patent/IT1275643B1/it active IP Right Grant
• 1995
  • 1995-10-16 DE DE69511819T patent/DE69511819T2/de not_active Expired - Lifetime
  • 1995-10-16 SI SI9530323T patent/SI0710973T1/xx not_active IP Right Cessation
  • 1995-10-16 ES ES95202791T patent/ES2136793T3/es not_active Expired - Lifetime
  • 1995-10-16 AT AT95202791T patent/ATE184132T1/de active
  • 1995-10-16 EP EP95202791A patent/EP0710973B1/fr not_active Expired - Lifetime
• 1999
  • 1999-10-07 GR GR990402529T patent/GR3031440T3/el unknown

Patent Citations (5)

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