Tap changer

1. A tap changer for connection to a regulating winding of a rated regulation voltage, the tap changer having a tap selector; wherein the tap selector comprises:

a set of linearly arranged fixed contacts comprising at least two fixed contacts, each arranged to be connected to a tap of the regulating winding;

at least one current collector; and

at least one movable contact part having a moveable contact arranged to electrically bridge a contact gap between a current collector and a fixed contact, a moveable contact part being linearly moveable along a current collector;

the tap changer further comprising:

a shielding structure arranged to shield the tap selector from an external electrical field; wherein the shielding structure comprises:

a first shielding part for shielding the tap selector mainly from external electrical fields occurring behind the current collectors as seen from the fixed contacts, the first shielding part being arranged to be electrically connected to the connected tap of the regulating winding; and

a second shielding part formed at least partly by the fixed contacts;

wherein the first and second shielding parts are separated so that the distance between the first and second shielding parts reaches or exceeds the rated regulating voltage insulation distance of the tap changer.

2. The tap changer of claim 1 , wherein the first shielding part comprises a hollow structure having an open side towards the current collectors.

3. The tap changer of claim 1 , wherein the space formed between the current collector and the arrangement of fixed contacts contains no conducting parts, apart from conducing parts forming part of the moveable contact part.

4. The tap changer of claim 1 , wherein the moveable contact part comprises at least one shielding plate arranged between the moveable contact and the exterior of the tap changer, in order to shield the movable contact from the external electrical field.

5. The tap changer of claim 1 , wherein the second shielding part comprises a set of fixed-contact shields, each fixed-contact shield being arranged to shield a fixed contact, a fixed-contact shield having a curvature in the contact gap plane with a convex surface facing away from the fixed-contact towards the tap changer exterior, the fixed-contact shields being electrically separated from each other.

6. The tap changer of claim 1 , wherein the first shielding part comprises an edge shield having a curvature in the contact gap plane with a convex surface facing away from the current collector towards the tap selector exterior, the edge shield extending along a direction parallel to the current collector(s).

7. The tap changer of claim 1 , further comprising an electrically insulating structure arranged to prevent undesired matter from entering the tap selector.

8. The tap changer of claim 1 , wherein the first shielding part comprises a top and/or a bottom shielding part, where the top/bottom shielding part extends out of the current collector plane, towards the linear arrangement of fixed contacts, at a position along the extension direction which lies beyond the position of the end fixed contact, the top/bottom shielding part having a convex surface facing away from the fixed contacts and the current collector(s) towards the tap changer exterior.

9. The tap changer of claim 8 , wherein the top/bottom shielding part is formed from a bent rod.

10. The tap changer of claim 8 , further comprising an electrically insulating structure arranged to event undesired matter from entering the tap selector, wherein the insulating structure comprises a top and/or bottom insulating part which is located between the top/bottom shielding part and the arrangement of fixed contacts, and separated from the top/bottom shielding part by means of an air gap in order to reduce any creepage current.

11. The tap changer of claim 1 , wherein all conducting parts of the tap changer are arranged to be at an electrical potential within the potential range of the regulating winding when the tap changer is in use.

12. The tap changer of claim 1 , wherein no part of the tap changer is arranged to be at earth potential.

13. The tap changer of claim 12 , further comprising an electrically insulating attachment means for attaching the tap changer to an insulating structure.

14. The tap changer of claim 1 , wherein the distance between the first and second shielding parts is larger than, or equal to, the contact gap, so that the distance between the current collector and the fixed contacts at the two ends of the linear arrangement is the shortest distance over which the entire regulation voltage will occur during operation of the tap changer.

15. The tap changer of claim 1 , wherein

the tap changer comprises a first and a second current collector arranged in parallel;

the linear arrangement of fixed contacts comprises a first and a second line of fixed contacts, said first and second lines being arranged in parallel; and

the tap changer comprises a first and a second moveable connector, the first moveable connector is arranged to bridge the gap between the first current collector and the first line of fixed contacts, while the second moveable connector is arranged to bridge the gap between the second current collector and the second line of fixed contacts.

16. The tap changer of claim 1 , wherein the tap changer is a diverter switch tap changer having a diverter switch.

17. The tap changer of claim 16 , wherein the first shielding part is arranged to shield at least part of the diverter switch, the diverter switch being located in a space between the first shielding part and the current collector, behind the current collector as seen along a contact plane from the arrangement of fixed contacts.

18. The tap changer of claim 1 , wherein the tap changer is an on-load tap changer.

19. The tap changer of claim 1 , wherein the tap changer is arranged to be insulated by means of air or an air-like gas.