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
  • H01H9/0016—Contact arrangements for tap changers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/12—Contacts characterised by the manner in which co-operating contacts engage
  • H01H1/36—Contacts characterised by the manner in which co-operating contacts engage by sliding
  • H01H1/42—Knife-and-clip contacts
  • H01H2001/425—Knife-and-clip contacts with separate contact pressure spring confined between two contact knifes and urging the knifes onto a mating contact

Definitions

• the present disclosure relates to a contact system for an on-load tap changer (OLTC).
• the contact system may be part of a diverter switch.
• the contact system may be a main contact system or a resistor contact system of the diverter switch.
• the main contact system can be actuated by a back-and-forth rotating shaft of the OLTC. This can be accomplished, for example with a Geneva gear.
• the contact system may comprise one movable contact and two fixed contacts, wherein the movable contact engages with one of the fixed contacts at an end of a switching operation. During a switching operation, the movable contact moves freely from one fixed contact to the other fixed contact. The distance between the fixed contacts is determined by the respective minimum insulation distance requirements.
• the operations of the main contact system may be mirror-symmetric with respect to a middle of a stroke of the rotating main shaft.
• the fixed contacts may be in the form of jaws which are preloaded by a contact pressure.
• the movable contact When the movable contact comes into mechanical contact with the jaws, the movable contact spreads the jaws apart, overcoming the force of their contact pressure. Thereby, friction forces between the jaws and the movable contact occur.
• the movable contact continues to move between the contact jaws under sliding friction forces until the operating position is reached. Also on the return stroke, the movable contact is subjected to contact pressure and sliding friction, up to the point at which it disengages from the fixed contact. The friction forces during engagement and disengagement are undesirable and lead to significant wear on all contact surfaces.
• Embodiments of the disclosure relate to an improved contact system for an on-load tap changer and a method for operating a contact system for an on-load tap changer.
• a contact system for an on-load tap changer comprises a movable contact configured to switch between several fixed contacts in a switching operation.
• the movable contact comprises a contact portion for establishing an electrical contact with one of the fixed contacts in an operating position, wherein each of the fixed contacts comprises two jaws configured for clamping the movable contact, wherein each of the fixed contacts comprises two rollers, wherein the movable contact comprises a cam portion configured to move between the two rollers for opening the jaws in a switching operation.
• the contact system may be part of a diverter switch.
• the diverter switch may comprise vacuum interrupters for interrupting the electric current before the start of a switching operation.
• the diverter switch can be part of an on-load tap changer, which can be used for control of distribution transformers, reactors or phase shifters, for example.
• the contact system may be configured such that the cam portion opens the jaws when the movable contact enters a switched contact in a switching operation.
• the contact portion may not come into mechanical contact with the fixed contact before the movable contact is in or near to an operating position.
• the force required for opening the jaws is generated by an interaction with the cam portion and the rollers.
• wear of the contact portion can be reduced.
• rolling friction forces occur, which reduces a torque on the movable contact and also a shaft driving the movable contact.
• the cam portion may form a free end of the movable contact.
• the movable contact may comprise the shape of a rod.
• the cam portion may form the free end of the rod.
• the movable contact In each operating position, the movable contact is in engagement with one of the fixed contacts and an electric contact is established between the fixed contact and the respective movable contact when current is switched on.
• the movable contact may comprise a fixed end which is supported by a fixed bearing support.
• Each of the fixed contacts may have contact surfaces to be in mechanical and electrical contact with the contact portion of the movable contact when engaged with the movable contact in an operating position.
• the contact surfaces may be surfaces of the jaws.
• the contact portion of the movable contact may adjoin the cam portion.
• the contact portion may adjoin the cam portion in a direction towards a fixed end of the movable contact.
• the thickness of the contact portion may be larger than a thickness of the cam portion.
• the thickness direction is a direction vertical to a plane of movement of the movable contact. The larger thickness ensures that the cam portion is not in contact with the jaws when an electric contact is established between the contact portion of the movable contact and the jaws. Thereby electric insulation is ensured.
• the cam portion may have a curved surface. As an example, the cam portion may have a circular or elliptical cross section. Thereby a smooth interaction with the rollers is achieved.
• Each of the rollers and the cam portion may comprise a material with a higher hardness than the contact portion.
• the jaws, or at least the portions of the jaws providing contact surfaces for electrically contacting the contact portion of the movable contact may also have a higher hardness.
• the rollers and/or the cam portion may comprise steel as a material.
• the contact portion and/or the jaws may comprise brass or copper as a material. Due to the higher hardness, wear of the components which are subjected to most of the friction forces as being in mechanical contact when the movable contact slides into or out of the fixed contacts, is reduced.
• Each of the rollers may be supported by one of the jaws.
• the jaws may comprise recesses in which the rollers are arranged.
• the jaws may be pressed towards each other by a spring.
• the spring provides the contact pressure between the fixed contact and the movable contact in the operating position.
• the fixed contacts may have a first side where the movable contact enters the fixed contact and a second side where an electric connection between the movable contact and the fixed contact is established in an operating position, i.e. where the contact surfaces are located.
• the rollers may be positioned between the first side and the second side.
• Each of jaws may have a shape such that a mechanical contact between the first contact portion and the jaws is prevented when the fixed contact enters one of the movable contacts in a switching operation.
• each of the jaws have recesses at a position where the movable contact enters the fixed contact.
• One of the fixed contacts may have a mirror symmetric shape of the other one of the fixed contacts.
• the fixed contacts may not have the
• a diverter switch comprises a contact system.
• the contact system may be as described in the foregoing.
• the diverter switch may further comprise a vacuum interrupter to interrupt a current through the movable contact before a switching operation is initiated.
• an on-lead tap changer comprises a contact system.
• the contact system may be part of a diverter switch.
• the contact system may be as described in the foregoing.
• a method for operating a contact system for an on-load tap changer comprises moving the movable contact to one of the fixed contacts in a switching operation, wherein the cam portion moves between the rollers and opens the jaws.
• the method may further comprise moving the movable contact further in the same direction such that the cam portion slides between the rollers and moves out from between the rollers.
• a mechanical contact between the contact portion and the fixed contact may occur first when the cam portion moves out from between the rollers. Thereby, wear of the contact portion can be reduced. Furthermore, due to the rolling interaction of the rollers with the cam portion, rolling friction forces occur, which reduces a torque on the movable contact and also a shaft driving the movable contact.
• the present disclosure comprises several aspects and embodiments. Every feature described with respect to one of the aspects and embodiments is also disclosed herein with respect to the other aspects and embodiments, even if the respective feature is not explicitly mentioned in this context.
• Figure 1 shows a contact system 1 for an on-load tap changer.
• the contact system 1 may be part of a diverter switch.
• a new tap position is pre-selected by a tap selector, while the diverter switch accomplishes the transfer of the electrical load from one tap to another.
• the diverter switch may comprise vacuum interrupters for extinguishing electric arcs occurring during the load transfer.
• the contact system 1 may be a main contact system carrying the full load current.
• the on-load tap changer may comprise such a contact system 1 for each phase. It is also possible that the contact system is a resistor contact system. It is also possible that the contact system 1 is used in another switch than the diverter switch.
• the switch may be a power switch carrying the full load current.
• the contact system 1 comprises a movable contact 2 and two fixed contacts 3, 4. It is also possible that more than two fixed contacts 3, 4 are present.
• the movable contact 2 is configured to make an electrical connection with one of the fixed contacts 3, 4 and change to the other one of the fixed contacts 3, 4 during a tap change.
• Each of the fixed contacts 3, 4 comprises a set of jaws 5a, 5b.
• the jaws 5a, 5b act as a clamp in which the movable contact 2 is clamped in an operating position when an electrical contact is established.
• Each of the jaws 5a, 5b comprises a contact surface for establishing an electric contact with a contact portion 9 of the movable contact 2.
• Each of the jaws 5a, 5b can be rotated about an axis 7a, 7b for opening and closing the clamp.
• Each of the jaws 5a, 5b is L-shaped, wherein the contact surface is provided on one part of the L-shape.
• the second part is formed by a support portion 8a, 8b, which rests on a support structure 9 in a relaxed state of the jaws 5a, 5b i.e. when the movable contact 2 is not engaged with the respective fixed contact 3, 4.
• the support structure 9 functions as a limiter for the movement of the jaws 5a, 5b.
• the contact pressure is provided by a spring 10, in particular a tensile spring.
• the contact pressure may be lower than in case of a main contact system.
• Each of the fixed contacts 3, 4 comprises a set of rollers 11a, 11b for interaction with a cam portion 12 of the movable contact 2 for enabling a smooth opening and closing of the jaws 5a, 5b.
• Each of the rollers 11a, 11b is mounted rotatable about an axis 13a, 13b.
• the rollers 11a, 11b are located in recesses 14a, 14b of the jaws 5a, 5b.
• the thickness of the contact portion 6 of the movable contact 2 is larger than the thickness of the cam portion 12.
• the thickness is the extension in a vertical direction.
• the vertical direction is perpendicular to a plane in which the movable contact moves.
• the larger thickness ensures that the cam portion 12 is not in contact with the jaws 5a, 5b and also not in contact with the rollers 11a, 11b in the operating position when an electric contact is established between the contact portion 6 of the movable contact and the jaws 5a, 5b.
• a preset distance from both the rollers 11a, 11b and the jaws 5a, 5b is established.
• the rollers 11a, 11b are formed from a material with high surface hardness.
• the cam portion 12 is formed from a material with high surface hardness.
• the surface hardness is higher than for the material of the jaws 5a, 5b and the material of the contact portion 6 of the movable contact 2.
• the cam portion 12 and/or the rollers 5a, 5b may be made from steel.
• the contact portion 6 and/or the jaws 5a, 5b are made of a softer material.
• the contact portions 6 and/or the jaws can be made from brass or copper, for example.
• the cam portion 12 may have a curved surface for enabling a smooth interaction with the rollers 11a, 11b.
• the cam portion 12 may have a circular or elliptical cross section.
• the movable contact 2 is mounted on a fixed bearing support 15 and performs a rotary movement about a preset angle for switching from one of the contacts 3, 4 to the other one of the contacts 3, 4.
• the movable contact 2 can be driven by a Geneva gear.
• a driven part 16 is provided at the rear end of the movable contact 2.
• the driven part 16 may be a Geneva sector.
• the driven part 16 has a slot 17, in which a pin 18 of a control disc 19 enters for driving the driven part 16.
• the pin 18 can be in the form of a roller.
• the control disc 19 is mounted on a control shaft 20.
• the control shaft 20 may be the main control shaft of a diverter switch.
• the main control shaft may also control vacuum interrupters and other contact systems.
• control shaft 20 with the control disc 19 is at a preset angle and the pin 18 is disengaged from the driven part 16.
• the movement of the movable contact 2 is restricted on one side by a blocking portion 21 on the control disc 19.
• the contact system 1 is positioned on an insulating plate 23.
• the insulating plate 30 can be also regarded as part of the contact system 1.
• a stop 22 on the insulating plate 23 restricts the movement of the movable contact 2 on another side.
• FIGs 2 to 4 show the contact system 1 of Figure 1 during a switching operation.
• the movable contact 2 is in electrical contact with the first fixed contact 3, as can be seen in Figure 1 .
• the contact portion 6 is clamped between the jaws 5a, 5b.
• the movable contact 2 in a switching operation, is rotatably driven by the control shaft 20 via the coupling of the control disc 19 with the driven part 16. Due to the geared engagement, the direction of rotation 25 of the movable contact 2 is opposite to the direction of rotation 26 of the control shaft 20.
• the cam 12 moves towards the rollers 11a, 11b and comes into contact with the rollers 11a, 11b. During further movement, the cam 12 slides between the rollers 11a, 11b and pushes the rollers 11a, 11b and, thereby, also the jaws 5a, 5b apart. The jaws 5a, 5b are opened such that the contact portion 6 of the movable contact 2 is freed and gets out of mechanical contact with the jaws 5a, 5b. During further movement, the cam portion 12 slides out of engagement with the rollers 11a, 11b and the jaws 5a, 5b move towards each other. The movement is stopped by the contact of the support portions 8a, 8b with the support structure 9.
• the contact portion 6 does not come again into mechanical contact with the jaws 5a, 5b when the cam portion 12 slides out of the engagement with the rollers 11a, 11b and the jaws 5a, 5b starts to close and come into their relaxed state.
• the jaws 5a, 5b have recesses 27a, 27b at the position where the contact portion 6 and the cam portion 12 enters or leaves the fixed contacts 3, 4. Therefore, during the entire movement from the operating position towards the second fixed contact 4, only a mechanical contact of the cam portion 12 with the rollers 11a, 11b is present, once the jaws 5a, 5b have been opened sufficiently at the beginning of the movement.
• Figure 3 shows the further advanced switching operation, when the movable contact 2 reaches the second fixed contact 4. Due to the shape of the jaws 5a, 5b the contact portion 6 does not come into mechanical contact with the jaws 5a, 5b when the movable contact 2 slides between the jaws 5a, 5b.
• the cam portion 12 comes into contact with the rollers 11a, 11b and presses the jaws 5a, 5b apart. Due to the hard material of these elements, the impact of the movable contact 2 is taken up at great speed. A rolling friction occurs during the opening of the jaws 5a, 5b. Thereby, a fast motion of the contact system 1 is enabled and friction is reduced.
• Figure 4 shows the movable contact 2 in the second operating position, where an electrical contact of the contact portion 6 with the second fixed contact 4 is established.
• the cam portion 12 is not in mechanical contact with the jaws 5a, 5b and the rollers 11a, 11b.
• the movable contact 2 moves in the opposite direction again. Accordingly, the movable contact 2 moves back and forth between the two fixed contacts 3, 4 and the two operating positions.
• Figure 5 shows schematically an on-load tap changer 30 comprising a diverter switch 31.
• the diverter switch 31 comprises a contact system 1 as described in the foregoing embodiments.
• the contact system 1 may be a main contact system of the diverter switch 31. It is also possible that the contact system 1 is a resistor contact system 1 of the diverter switch 1.
• the diverter switch 31 further comprises vacuum interrupters 32 to interrupt a current through the movable contact 2 of the diverter switch 31. The vacuum interrupters 32 and the contact system 1 may be driven by the same control shaft 20.
• the on-load tap changer 30 further comprises a tap selector 33 for selecting the tap to which the load current is transferred by the diverter switch 31.
• the on-load tap changer 30 can be used for control of power or distribution transformers, for example.
• the on-load tap changer 30 can be also used for control of other types of electrical devices, such as reactors or phase shifters, for example.

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• Contacts (AREA)
• Rotary Switch, Piano Key Switch, And Lever Switch (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

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ID=91331116

Family Applications (1)

Country Status (2)

Citations (3)

• 2024
  • 2024-05-29 EP EP24178852.0A patent/EP4657477A1/de active Pending
• 2025
  • 2025-05-28 WO PCT/EP2025/064849 patent/WO2025248005A1/en active Pending

Patent Citations (3)

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