Browse Prior Art Database

High voltage direct current (HVDC) bushing with resistive field grading

IP.com Disclosure Number: IPCOM000237364D
Publication Date: 2014-Jun-16
Document File: 3 page(s) / 179K

Publishing Venue

The IP.com Prior Art Database

Related Documents

US2013/0120956A1: PATAPP

Abstract

The HVDC bushing comprises at least one of a linear or nonlinear resistive field grading material element which connects a grounded wall with a HV end of the bushing along an external surface of the bushing. The selection of the field grading material and its appropriate arrangement on the bushing lead to equidistant equipotential curves and to a decoupling of the DC field distribution inside and outside the bushing. Thus the size of the bushing can be minimized.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

Page 01 of 3

High voltage direct current (HVDC) bushing with resistive field grading

Abstract

The HVDC bushing comprises at least one of a linear or nonlinear resistive field grading material element which connects a grounded wall with a HV end of the bushing along an external surface of the bushing. The selection of the field grading material and its appropriate arrangement on the bushing lead to equidistant equipotential curves and to a decoupling of the DC field distribution inside and outside the bushing. Thus the size of the bushing can be minimized.

Technical Background

A high voltage (HV) direct current (DC) bushing leads a HV energized conductor through a wall (see Fig. 1 left) that is a grounded "plane" that stands perpendicular to the conductor, and thus leads to high fields. The bushing must be designed such that no flashover along the bushing surface, which separates the bushing insulation (often solid with capacitive foils) from the outside insulation (liquid or gas), occurs. The two insulations can have completely different resistivity, and surface charges can accumulate, which may lead to a lack of robustness of the field distribution and to field enhancements. The difference between AC and DC field distributions are shown on the right side of Fig. 1. In DC, the voltage drop along the interface can be very inhomogeneous; for instance field enhancement in the outer region near the HV conductor may appear.

Figure 1


Left: Sketch of a bushing.

Right: Difference in AC and DC field distributions according to A. Küchler, HV Engineering. Legend: Durchführung = bushing, geerdeter = grounded, Wechselspannung = AC voltage, gut leitfähiges Öl = well conductive oil, hochohmiger Durchführungskörper = highly resistive bushing body, Gleichspannung = DC voltage.

Prior art

There already exist embodiments of the HVDC bushing which avoid the inhomogeneous voltage drop. These bushings are mainly based on local field grading. A HVDC bushing of pressboard/oil insulation with local resistive grading is known from the afore-mentioned book of A. Küchler and is shown in Fig. 2 on the left. A further HVDC bushing is described in the published US patent application 2013/0120956 (ABB) which is shown on the right of fig.2 and which comprises specific shield electrodes.

1


Page 02 of 3

Figure 2


Left: DC Bushing with pressboard barriers (Pressspan = press board, Ölspalt = oil gap). Right: ABB HVDC bushing with shielding elements (8=bushing body, 1=oil)

It is to mention that resistive electric field grading is state of the art in HVDC cable joints and terminations. The main problems that are solved...