Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F7/00—Magnets
  • H01F7/06—Electromagnets; Actuators including electromagnets
  • H01F7/08—Electromagnets; Actuators including electromagnets with armatures
  • H01F7/16—Rectilinearly-movable armatures
  • H01F7/1607—Armatures entering the winding
  • H01F7/1615—Armatures or stationary parts of magnetic circuit having permanent magnet
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F7/00—Magnets
  • H01F7/06—Electromagnets; Actuators including electromagnets
  • H01F7/08—Electromagnets; Actuators including electromagnets with armatures
  • H01F7/121—Guiding or setting position of armatures, e.g. retaining armatures in their end position
  • H01F7/122—Guiding or setting position of armatures, e.g. retaining armatures in their end position by permanent magnets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
  • H01H33/02—Details
  • H01H33/59—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle
  • H01H33/596—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle for interrupting dc
• • 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
  • H01H71/10—Operating or release mechanisms
  • H01H71/12—Automatic release mechanisms with or without manual release
  • H01H71/24—Electromagnetic mechanisms
  • H01H71/32—Electromagnetic mechanisms having permanently magnetised part
  • H01H71/321—Electromagnetic mechanisms having permanently magnetised part characterised by the magnetic circuit or active magnetic elements
  • H01H71/322—Electromagnetic mechanisms having permanently magnetised part characterised by the magnetic circuit or active magnetic elements with plunger type armature

Definitions

• This invention relates to an electrical actuator operating with magnetic latching and having holding forces and operating characteristics particularly suited for use in conjunction with electrical switchgear, particularly in relation to direct current circuit breakers such as vacuum circuit breakers, auto reclosers and contactors and for use on lower voltage air break equipment.
• US Patent Specification No. 3 886 507 describes an electrically operable, magnetically latchable, actuator having an electrical wire wound coil of rectangular cross-section with an axially outer end face and an axially inner end face, a plunger moveable co-axially of the electrical wire wound coil between an open position and a closed position, a sleeve of magnetisable material secured to the plunger, a permanent magnet array of substantially rectangular cross-section perpendicular to the plunger longitudinal axis positioned axially adjacent the axially inner end face of the electrical wire wound coil having a central aperture receiving the sleeve of magnetisable material secured to a mid-portion of the plunger and biassing means biassing the plunger to the open position.
• a main electrical current carrying bus bar having a portion extending in register with and adjoining at least one of the axial side faces of the permanent magnet array and corresponding side faces of the electrical wire wound coil is arranged such that flow of the main electrical current in the bus bar produces a magnetic flux effective to reduce the magnetic flux produced by the permanent magnet array.
• Figure 1 is a cross-sectional plan view of an electrical actuator operating with magnetic latching
• Figure 2 is an isometric perspective view of the actuator, and an associated circuit breaker mechanism.
• the actuator includes a parallelepiped housing 2 having bolted on end covers 4 and 6 through which extends a plunger rod 8 of non ⁇ magnetic material.
• One end of the plunger rod 8 is formed with a shoulder 10 providing a seating for a compression spring 12 bearing against an outer face of the end cover 6.
• the plunger rod 8 carries a soft iron plunger sleeve 14 formed with a stepped end face 16 of rectangular cross-section perpendicular to the longitudinal axis arranged to abut, in a closed position, a soft iron pole piece or armature 18 mounted on the end cover 4.
• An electrical coil 20 is positioned intermediate the housing 2 and the armature 18 and extends axially between an axially outer end face 19 adjacent the end cover 4 and an inner end face 21 beyond the armature 18.
• a permanent magnet array 22 in the form of rectangular cross-section blocks 24 is positioned intermediate the housing 2 and the plunger sleeve 14 adjacent the electrical coil 20 and spaced from the end cover 6. The magnet array 22 is secured in the housing 2 by means of a fixing plate and the magnetic flux is directed toward the plunger sleeve 14 through a soft iron core piece 26.
• the housing 2 is penetrated by a lateral slot 28 extending parallel to a side face of the housing and through which extends a twin strap copper conductor or bus bar 30 carrying a direct current supply subject to the action of an associated circuit breaker (shown in an isometric view in Figure 2) .
• twin strap copper conductor 30 is connected to a fixed jaw 32 of a circuit breaker mechanism associated with the actuator.
• a moveable jaw 34 is connected to the plunger 8 and carries a further portion 36 of twin strap copper conductor or bus bar.
• An air blast discharge head 38 is provided to discharge an arc extinguishing blast of air or other gas upon the moveable jaw 34 being moved from a closed position contacting the fixed jaw 32 to an open position as shown in Figure 2.
• a lever arm 40 and linkage 42 is mounted on the housing end cover 6 for effecting manual opening or closing of the actuator.
• the actuator is moved to a closed position by applying an electrical pulse to the coil 20 such that the magnetic flux produced by the coil causes the plunger sleeve 14 to move toward the armature 18, the magnetic flux produced by the coil 20 being in the same direction as, and augmenting, the flux arising from the permanent magnet array 22 to overcome the spring 12.
• the plunger sleeve 14 Soon after the plunger sleeve 14 reaches the closed position the coil electrical pulse is interrupted. However, the plunger sleeve 14 remains in the closed position since the attracting force between the plunger sleeve and the armature 18 is of sufficient magnitude as to hold the spring 12 compressed and overcome the magnetic flux arising from current flow through the bus bar 30.
• an electrical pulse is applied to the coil 20 such as to produce a magnetic flux opposing the flux arising from the permanent magnet array 22 thereby substantially reducing the net flux at the armature with a corresponding reduction in the holding force.
• the reduction is such that the spring force exerted by the compression spring 12 will exceed the force arising from magnetic flux and the plunger will be urged to an open position.
• the plunger sleeve 14 moves away from the armature 18 the magnetic flux flowing through the armature and the plunger sleeve spreads out or leaks. This, coupled with the increased air gap at the faces, causes a rapid reduction in the residual magnetic attraction force.
• the plunger 8 driven by the spring 12 thus accelerates toward the open position by virtue of the increasing net effect of the spring 12.
• This rapid movement induces a back electro-motive force in the coil 20, momentarily acting against any further increase in the current induced magnetic flux in the coil and acting to prevent the magnetic attraction force from re ⁇ establishing.
• the magnetic attraction force between the plunger sleeve 14 and the armature 18 is such as to prevent the electrical pulse (if still maintained) from urging the plunger sleeve 14 toward the closed position.
• the effect of the magnetic force between the plunger sleeve 14 and the armature 18 serves to increase the effectiveness of the actuator during the closing operation by restraining movement of the plunger sleeve 14 until the magnetic flux due to the coil has reached an appropriate magnitude. This magnitude is selected as to ensure that the full closing of the actuator is always achieved.
• the permanent magnet array 22 is composed of a stack of blocks of some seven millimetre thickness sheet, of a material such as isotropic neodymium ferro boron, bolted together. By varying the thickness of the stack of blocks, so the magnetic flux arising is varied.
• the spring rate of the compression spring 12 and the form and winding of the electrical coil 20 are selected to produce the required characteristics for the actuator.
• Isotropic neodymium ferro boron magnets exhibit a relatively high resistance to demagnetisation, that is, a high intrinsic coercivity, and are thus virtually unaffected by the opposing magnetic flux produced by the coil 20 during movement of the actuator to the open position.
• the plunger sleeve 14 is of parallelepiped form giving a cross-sectional external perimeter as large as possible for a required cross-sectional area and thereby achieving a high leakage flux even at small gaps.
• the stepped end face 16 of the plunger sleeve serves to maximize magnetic flux by minimizing gap reluctance during movement of the actuator to the closed position.
• the stepped end face 16 also gives rise to a rapid reduction in the magnetic attraction force during initial movement of the plunger sleeve to the open position since the magnetic flux is only concentrated whilst the faces actually make contact.
• Actuators of conventional design having two coils, one to effect movement to an open position, the other to effect movement to a closed position, or with a coil positioned externally of a permanent magnet array, require provision for the electrical pulse achieving opening movement to have an electrical current value of up to approximately half the value of the electrical current required to effect movement of the actuator to a closed position.
• initiation of movement to the open position is achieved with an electrical current of approximately only one tenth of the electrical current required to effect movement of the actuator to the closed position.
• the present invention by utilising but a single electrical coil axially adjacent a permanent magnet array rather than the two coils of conventional designs gives rise to an actuator exhibiting economy in cost and space as well as a reduction in complexity in design and operation.
• a conventional design of magnetic actuator having two coils it is found that, upon applying an electrical pulse to one of the coils, a current tends to be induced in the other of the coils tending to produce a magnetic flux in opposition to the flux produced in the first coil, leading to complex designs.
• actuators in which the electrical current pulses are controlled by electronic switches it is not practicable to place the coil not being energised in open circuit since dangerous over voltages can be produced.
• incorrect operation may occur upon attempting manual operation of a two coil actuator whilst a current path exists in either coil.
• the magnetic flux thereby generated is arranged to be of sufficient magnitude as to sufficiently oppose the hold-on force generated by the magnetic flux arising from the permanent magnet array 22 that the spring force exerted by the compression spring 12 will prevail and the plunger 8 will be moved to the open position by the effect of the spring 12.
• a direct acting instantaneous trip arrangement operative on the occurrence of an electrical current overload is provided effective in addition to, and electrically independently of, the arrangement whereby opening of the actuator is achieved by supplying a control current to the coil 20.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Electromagnets (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=10783981

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (2)

Family Cites Families (4)

• 1995
  • 1995-11-15 GB GBGB9523440.7A patent/GB9523440D0/en active Pending
• 1996
  • 1996-11-15 EP EP96938379A patent/EP0876669A1/de not_active Ceased
  • 1996-11-15 AU AU75827/96A patent/AU7582796A/en not_active Abandoned
  • 1996-11-15 WO PCT/GB1996/002825 patent/WO1997018569A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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