Condenser bushing
The present disclosure relates to a condenser bushing including a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for conductor extending along an axis defining an axial direction, while an electric connection is provided to at least one of the field-grading layers, wherein pairs of neighbouring field-grading layers with the insulation material between them form sections of the condenser core of axial lengths L 1 through L n and with capacitances C 1 through C n , characterized in that a shape of at least one of the field-grading layers deviates from cylindricality in order to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming sections of the axial lengths L 1 through L n and with capacitances C 1 through C n .
1. A condenser bushing comprising:
a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for a conductor extending along an axis defining an axial direction, an electric connection being provided to at least one of the field-grading layers,
pairs of neighbouring field-grading layers with the insulation material between them forming sections of the condenser core of axial lengths L 1 through L n and with capacitances C 1 through C n ,
a shape of at least one of the field-grading layers deviating from cylindricality to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming corresponding sections of the axial lengths L 1 through L n and with capacitances C 1 through C n , and
at least one of the field-grading layers being shaped such that the diameter of said field-grading layer varies along the axial direction, the diameter of said field grading layer having at least one maximum between the edges of the field-grading layer, wherein the maximums of the field-grading layers increase in amplitude along a radial direction, but narrower in width along the axial direction, with increasing distance from the condenser core, wherein the terminating ends of each of the field-grading layers are straight in the axial direction.
2. The condenser bushing according to claim 1 , wherein the mean edge field stress level, defined as the ratio of the voltage U i of one of the sections and the radial width δ i of the section at its end in at least one section formed by a non-cylindrical field-grading layer is smaller than in the corresponding section of a condenser bushing with cylindrical field-grading layers forming sections of identical capacitances C 1 through C n and identical axial lengths L 1 through L n .
3. The condenser bushing according to claim 2 , wherein the absolute value of
(
U
i
δ
i
/
U
j
δ
j
-
1
)
is at least 20% smaller than the absolute value of
(
U
i
δ
i
′
/
U
j
δ
j
′
-
1
)
,
where
U
i
δ
i
and
are the mean edge field stress levels of two neighbouring sections, wherein at least one section is formed by a non-cylindrical field-grading layer and
U
i
δ
i
′
and
U
j
δ
j
′
are the mean edge field stress levels of two corresponding neighbouring sections the corresponding condenser bushing with the cylindrical field-grading layers.
4. The condenser bushing according to claim 1 , wherein the radial widths of the sections at their axial ends are substantially equal.
5. The condenser bushing according to claim 1 , wherein the innermost and/or the outermost field-grading layer is cylindrical.
6. The condenser bushing according to claim 1 , wherein the capacitances of all the sections formed by the field-grading layers are equal.
7. The condenser bushing according to claim 1 , wherein at least one of a ground connection, the electrical connection, and/or a voltage-tap connection is an integral part of a field-grading layer and has a substantially axially symmetric shape, with a conductive material volume reaching from the field-grading layer to the outer or inner surface of the condenser core.
8. The condenser bushing according to claim 1 , wherein the condenser core is shaped in such a way that the thickness of an insulating material between the each of the edges of adjacent field-grading layers and the outer surface of the condenser core is greater than the thickness of an insulating material between the middle point between the edges of the field-grading layers and the outer surface of the condenser core.
9. An additive manufacturing method to manufacture the condenser bushing according to claim 1 .
10. An electrical insulation system comprising:
an active part comprising a conductor;
a condenser bushing disposed around the conductor, the condenser bushing comprising:
a condenser core and electrically conductive field-grading layers, which are embedded in insulating material of the condenser core and arranged around a central channel for a conductor extending along an axis defining an axial direction, an electric connection being provided to at least one of the field-grading layers,
pairs of neighbouring field-grading layers with the insulation material between them forming sections of the condenser core of axial lengths L 1 through L n and with capacitances C 1 through C n ,
a shape of at least one of the field-grading layers deviating from cylindricality to reduce non-uniformity of electric field stress of the condenser bushing compared to a corresponding condenser bushing with the cylindrical field-grading layers forming corresponding sections of the axial lengths L 1 through L n and with capacitances C 1 through C n , and
at least one of the field-grading layers being shaped such that the diameter of said field-grading layer varies along the axial direction, the diameter of said field grading layer having at least one maximum between the edges of the field-grading layer, wherein the maximums of the field-grading layers increase in amplitude along a radial direction, but narrower in width along the axial direction, with increasing distance from the condenser core, wherein the terminating ends of each of the field-grading layers are straight in the axial direction.
11. The electrical insulation system according to claim 10 , wherein the active part is part of a high voltage component of one of a transformer, a generator, and a circuit breaker.
12. The electrical insulation system according to claim 10 , wherein the mean edge field stress level, defined as the ratio of the voltage U i of the section and the radial width δ i of the section at its end in at least one section formed by a non-cylindrical field-grading layer is smaller than in the corresponding section of a condenser bushing with cylindrical field-grading layers forming sections of identical capacitances C 1 through C n and identical axial lengths L 1 through L n .
13. The electrical insulation system according to claim 11 , wherein the absolute value of
(
U
i
δ
i
/
U
j
δ
j
-
1
)
is at least 20% smaller than the absolute value of wherein the absolute value of
(
U
i
δ
i
′
/
U
j
δ
j
′
-
1
)
,
where
U
i
δ
i
and
U
j
δ
j
are the mean edge field stress levels of two neighbouring sections, wherein at least one section is formed by a non-cylindrical field-grading layer and
U
i
δ
i
′
and
U
j
δ
j
′
are the mean edge field stress levels of two corresponding neighbouring sections the corresponding condenser bushing with the cylindrical field-grading layers.
14. The electrical insulation system according to claim 10 , wherein the radial widths of the sections at their axial ends are substantially equal.
15. The electrical insulation system according to claim 10 , wherein the innermost and/or the outermost field-grading layer is cylindrical.
16. The electrical insulation system according to claim 10 , wherein the capacitances of all the sections formed by the field-grading layers are equal.