Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
  • H01H9/0005—Tap change devices
  • H01H9/0038—Tap change devices making use of vacuum switches

Definitions

• the present invention relates generally to tap changers for transformers, and in particular to a selector switch for switching over from one tap of the transformer to the next.
• on-load tap changers In power transformers, on-load tap changers (OLTC) are used to change tapping connections of transformer windings while the transformer is energised. To satisfy the needs of increased service life and reduced maintenance of on-load tap changers, they often use vacuum interrupters to control the switching and to quench the arc.
• OLTC on-load tap changers
• the vacuum interrupters in turn are controlled by rotating mechanisms.
• the rotating mechanism can be provided with one or several cam followers following a cam surface located on the inside of a cylinder.
• US 4,978,815 discloses an example of such tap changer.
• Fixed step contacts are disposed on a circle and are connected to taps of a step transformer.
• At least two switch contacts per phase are disposed in common on a pivotable contact carrier and are simultaneously pivotable on the circle.
• Two vacuum switches per phase are electrically built into the contact carrier and connected in series with the switch contacts.
• a cam race is disposed along the circle. Rollers run along the cam race for actuating the vacuum switches radially.
• Forks (22 in US 4,978,815) are arranged for controlling the vacuum switches (8).
• Each fork carries guide rollers (23) (see column 4, line 60-column 5 line 6) that slide in radial grooves (18') in the switch carrier (18) and allow the forks (22) to execute radial movement.
• the cam race and the rollers are current free.
• a slip ring is coaxial with the cam race and the circle.
• the cam race is disposed axially between and spaced apart from the fixed step contacts and the slip ring. Slip contacts slide on the slip ring.
• Each of the vacuum switches is electrically connected between a respective one of the switch contacts and a respective one of the slip contacts.
• the inventors of the present invention have noted some shortcomings with the known tap changer.
• the guidance of the vacuum interrupter seems not to be optimal. Horizontal movement of the vacuum interrupter may cause increased wear and tear caused by gravity and/or may put higher demands on the guidance of the vacuum interrupter.
• gas can be trapped outside the bellows of the vacuum interrupter, which may cause uneven mechanical strains and stresses and increased risk of fatigue of the material of the bellows .
• a selector switch for switching over from one tap of a transformer to the next, comprising a rotatable switching shaft insert, and fixed step contacts circumferentially arranged on a cylinder provided around the switching shaft insert and connected to taps of the transformer.
• the switching shaft insert includes, per phase, at least two switch contacts and a network terminal contact. A respective vacuum switch is connected between each of the switch contacts and the network terminal contact.
• a cam structure is circumferentially arranged on the inner surface of the cylinder, and, for each of the vacuum switches, a radially extending and radially movable lever provided in its outer end with a cam follower is arranged to follow the cam structure when the switching shaft insert is rotated.
• the switch contacts are arranged to be moved in and out of contact with the fixed step contacts and each of the levers is arranged to actuate a respective one of the vacuum switches upon rotation of the switching shaft insert.
• each pair of levers and vacuum switches comprises structural elements in mutual engagement with one another which force the vacuum switch to be actuated axially by means of the lever being moved radially.
• the structural elements force the vacuum switch to be actuated axially through the medium of a wedging effect as the lever is moved radially.
• the lever comprises an inclined plane and the vacuum switch comprises a roller or protrusion.
• the switch contacts may be moved in contact with the fixed step contacts to establish a radially or axially arranged electric connection.
• a radially arranged electric connection is meant a connection wherein the contact pressure between the contacts is obtained by a radially directed force
• an axially arranged electric connection is meant a connection wherein the contact pressure between the contacts is obtained by an axially directed force.
• a method of operating the selector switch of the first aspect of the invention comprises the steps of moving the switch contacts in and out of contact with the fixed step contacts and actuating a respective one of the vacuum switches by means of rotating the switching shaft insert, wherein for each pair of levers and vacuum switches, the vacuum switch is actuated axially by means of structural elements of the lever and the vacuum switch, which stand in mutual engagement with one another and which force the vacuum switch to be moved axially in response to the lever being moved radially.
• An advantage of the present invention is that guidance of the moving vacuum interrupter is easier. Gas will not be trapped next to the bellows of the vacuum interrupter.
• the design of the selector switch is very robust and efficient. The switching shaft insert is more easily mounted in the correct position in the cylinder. Simultaneously, a selector switch with radial cam operation is less sensitive to manufacturing tolerances .
• Figure 1 is a schematic top view of a selector switch illustrating the principles of the selector switch of the present invention.
• Figure 2 is a perspective view of major parts of a selector switch according to the invention.
• Figure 3 is an enlarged perspective view of a switch contact and a fixed step contact as comprised in the selector switch of Fig. 2.
• Figure 4 is an enlarged side elevation view of the interface between a switching shaft insert and a cylinder as comprised in the selector switch of Fig. 2.
• Figures 5A-C is a simplified cross section of a lever illustrating the lever and guiding means for the lever arranged on the switching shaft insert.
• a selector switch used to change the ratio of a transformer, by electrically or galvanically connecting a mains or network terminal 13 to fixed step contacts 14, which in turn are firmly connected to taps of a step winding of a transformer.
• a right hand switch contact 12 which is connected in series with a transition resistor 16 is first pivoted from a step contact n to the adjacent step contact n+1 by means of rotating a switch shaft insert 11, in the course of which a vacuum switch 14 connected in series with the right hand switch contact 12 and the resistor 16 opens prior to the lifting of the right hand switch contact 12 from the step contact n, and closes again only after the right hand switch contact 12 has been applied to the next step contact n+1.
• the opening of a vacuum switch 15 that is electrically connected in series with a left hand switch contact 12 takes place, so that the load current commutes to the right hand switch contact 12 and the vacuum switch 15 connected in series with the right hand switch contact 12. In this process, the voltage increases whereas the voltage decreases when the switching is performed in the opposite direction.
• the present invention relates to the vacuum switches 15 and their operation.
• the switch shaft insert 11 comprises two levers with cam followers which follow a cam structure upon rotation of the switch shaft insert 11.
• the selector switch comprises a rotatable switching shaft insert 11 which includes, per phase, two switch contacts 12 and a network terminal contact 13.
• Fixed step contacts 14 are circumferentially and fixedly arranged on an insulating cylinder 22 provided around the switching shaft insert 11, wherein the fixed step contacts 14 are connected to taps of a transformer. Upon rotation of the switching shaft insert 11, the switch contacts 12 are arranged to be moved in and out of contact with the fixed step contacts 14.
• the inventive selector switch is standing upright, i.e. its axial direction is parallel with a vertical axis and its radial direction is horizontal.
• An electrically conductive sleeve or ring 28 is fixedly arranged on the inner surface of the cylinder 22. Upon rotation of the switching shaft insert 11, the network terminal contact 13 operates as a sliding contact providing continuous electric contact with the sleeve 28.
• switch contacts 12 in the illustrated embodiment are arranged to be moved in contact with the fixed step contacts 14 to establish an essentially radially arranged electric connection (i.e. the force exerting the contact pressure is radially directed), the invention is not limited to such case.
• the switch contacts 12 may be arranged to be moved in contact with the fixed step contacts 14 to establish an essentially axially arranged connection (i.e. the force exerting the contact pressure is axially directed) .
• the network terminal contact 13 may be arranged to be moved in contact with the sleeve 28 while establishing a connection with an axially directed force exerting the contact pressure .
• a respective axially arranged vacuum switch 15 is connected between each of the switch contacts 12 and the network terminal contact 13.
• a typical current path is indicated at 41 in Figure 4 when the vacuum switch 15 is closed.
• switch contacts 12 and the fixed step contacts 14 on one hand and the network terminal contact 13 and the sleeve 28 on the other hand are arranged at different axial positions.
• Each one of the switch contacts 12 and the network terminal contact 13 may be provided with spring biased contact pins in order to secure proper electric connection.
• other kind of means is provided for exerting an appropriate contact pressure.
• a cam based mechanism is provided.
• a cam structure 23 is circumferentially arranged on the inner surface of the cylinder 28, and the switching shaft insert 11 is provided, for each of the vacuum switches 15, a radially extending and radially movable lever 24 provided in its outer end with a roller 25 arranged to follow the cam structure 23 upon rotation of the switching shaft insert 11, and as a result the lever 24 moves radially.
• Each one of the levers 24 is arranged to actuate a respective one of the vacuum switches 15.
• each one of the levers 24 is provided in its inner upper end with an inclined plane or surface 26 and each one of the vacuum switches 15 is provided in its upper end with a roller 27 which is forced to rest against the inclined plane 26 during operation.
• a movement of a lever 24 radially inwards forces the vacuum switch 15 in engagement with the lever 24 to be moved axially upwards and as a result the vacuum switch 15 opens.
• the vacuum switch 15 in engagement with the lever 24 is forced to be moved axially downwards and as a result the vacuum switch 15 closes.
• the vacuums switches 15 are preferably spring biased with an axial force operating downwards. This force is also preferred to obtain appropriate electric contact pressure.
• Each of the levers 24 is arranged to actuate a respective one of the vacuum switches 15 forcing the vacuum switch 15 to be actuated axially by means of the lever 24 being moved radially upon rotation of the switching shaft insert 11.
• Each pair of levers 24 and vacuum switches 15 actuate the respective vacuum switch 15 axially through the medium of a wedging effect as the lever 24 is moved radially.
• the lever 24 comprises an inclined plane 26 and the vacuum switch comprises a roller 27, which plane 26 and roller 27 provides the wedging effect that transform the radial movement into axial movement, i.e. the horizontal movement into vertical movement in the illustrated preferred embodiment.
• Each lever 24 is steered into motion in a radial direction by guiding means 29, 30 that provides a radial track or radial path for the respective lever 24.
• the guiding means 29, 30 steer and force the lever 24 into radial movement when cam follower 25 meets a cam 23 on the cam structure during rotation of the selector switch insert 11.
• the guiding means 29, 30 can be similar to a system of guide rollers and radial grooves as used in Dl mentioned above.
• the guiding means 29, 30 is arranged to prevent movement of lever 24 in a circumferential direction. Thus, each lever 24 is prevented from rotating in the horizontal plane.
• the guiding means is also arranged to prevent movement of each lever 24 in the vertical direction; the axial direction of the illustrated tap changer.
• the guiding means are exemplified in the figure as knobs 29 extending vertically from a horizontal surface, which knobs 29 surround the lever 24.
• the knobs 29 are arranged to cooperate with a groove 30, extending longitudinally on the sides of the lever 24.
• the combination of longitudinal grooves 30 on the sides of the radially extending lever 24 with the guiding knobs 29 acts to steer the lever 24 into radial motion during manoeuvring of the switching shaft insert 11.
• the guiding means 29, 30 can be provided in different ways, cooperating with parts or sections of the corresponding lever 24 into guiding the lever 24 in a radial movement and prevents circumferential motion, rotation and also vertical motion.
• a tunnel shaped element such as a cylindrical bore or bores can be used together with a cooperating correspondingly designed sliding element, like a cylindrical piston section or element, which complementary elements can be arranged in either part.
• Other possible and suitable types of guiding means and corresponding embodiment of lever 24 include rails and rollers arranged for providing radial movement and preventing movement in other directions.
• the guiding means can alternatively or additionally be a part or section of actuating rod of the vacuum switches 15, for example using a wheel or roller 27 designed to cooperate and steer the lever straight radially and prevent the lever from turning from its radially extending direction, restricting lateral movement, perpendicular to the radial motion, in the horizontal plane.
• Lever 24 is steered into moving straight and extends radially during the whole movement.
• the guide means can comprise four wheels 29 arranged by means of ball bearings on respective axles, which wheels run in tracks provided in the lever 24.
• the guiding groove or grooves 30, can be C-shaped preventing circumferential as well as vertical movement when cooperating with rolling wheels, rollers or sliding knobs 29.
• the guiding means can be provided with mutually engaging slide surfaces, provided similar to the drawer in a chest of drawers .
• FIG. 5A A further example is illustrated in figure 5A, wherein a perspective view of a lever 24 with a lateral protruding and longitudinally extending edge section 29A sliding in a guide rail 3OA having a C-shaped sliding recess.
• FIG. 5B A further example is illustrated in figure 5B, wherein a lever 24 having profiled sides 29B with inclined surfaces extending into a recess of a guide provided with roll bearings 3OB.
• FIG. 5C A further example is illustrated in figure 5C, wherein a lever 24 having C-shaped grooves 29C in its lateral sides, cooperates with ball bearings 3OC on axles 31C in steering the lever 24 radially in relation to the insert 11.
• the levers 24 are preferably spring biased with a radial force operating outwards.
• the rollers 25 of the levers 24 are arranged to follow axially separated portions of the cam structure 23, which portions have different shapes. However, this is not a prerequisite.
• the levers are arranged in the same axial position and their rollers follow the very same cam profile.
• rollers 27 can be provided by arranging wheels or ball bearings on a horizontal axle, perpendicular to the vertical direction of the vacuum switches and perpendicular to the radial direction of the lever 24. These rollers 27 with ball bearings are arranged to roll on the inclined plane or surface 26 of the lever 24, during the radial movement of the lever 24.
• the inclined plane or surface 26 is illustrated as a straight slope, but it can be provided as a curved slope, such as concave or convex surface. A curved slope makes it possible to vary the opening rate of the vacuum switch when the shaft insert 11 is rotated at a constant angular velocity.
• a curved slope can be designed together with designing the curvature provided by the cam follower 25 and cam structure 23, so that a maximum speed of the activating rod of the vacuum switch 15 is provided at the most critical switching moment.
• each pair of levers and vacuum switches comprises structural elements in mutual engagement with one another which force the vacuum switch to be actuated axially by means of the lever being moved radially.
• the structural elements force the vacuum switch to be actuated axially through the medium of a wedging effect as the lever is moved radially.
• the structural elements may comprise an inclined plane as disclosed above, a groove, or a slot in mutual engagement with a roller as disclosed above, or protrusion.
• the lever comprises the inclined plane, groove, or slot
• the vacuum switch comprises the roller or protrusion.
• the rotatable switching shaft insert may comprise one or several further switch contacts and a respective further vacuum switch connected between each one of the further switch contact (s) and the network terminal contact (not illustrated) .
• a radially extending and radially movable lever is provided, the lever being provided in its outer end with a cam follower arranged to follow the cam structure, wherein, upon rotation of the switching shaft insert 11, each one of the further switch contact (s) is arranged to be moved in and out of contact with the fixed step contacts 14, and each pair of the further lever (s) and the further vacuum switch (es) comprises structural elements in mutual engagement with one another which force the vacuum switch to be actuated axially by means of the lever being moved radially.

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• Driving Mechanisms And Operating Circuits Of Arc-Extinguishing High-Tension Switches (AREA)

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Applications Claiming Priority (2)

Publications (1)

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Cited By (5)

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Citations (5)

• 2009
  • 2009-06-10 EP EP09162444A patent/EP2261935A1/en not_active Withdrawn
• 2010
  • 2010-06-08 BR BRPI1012952A patent/BRPI1012952A2/pt not_active IP Right Cessation
  • 2010-06-08 WO PCT/EP2010/058011 patent/WO2010142680A1/en active Application Filing
  • 2010-06-08 EP EP10724819.7A patent/EP2441079B1/en not_active Not-in-force
  • 2010-06-08 CN CN201080026199.5A patent/CN102460623B/zh not_active Expired - Fee Related

Patent Citations (5)

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