Ageing behaviour of RIP material under several DC voltages and temperature

Abstract

The objective of the study was to characterize the ageing behaviour of Resin Impregnated Paper (RIP) material under several DC voltages and temperature. RIP is one of the main insulation system types, traditionally used for high voltage bushings in HVDC converter and substations.
Bushings are transformer’s crucial components since they are among the most frequent cause of transformer failure. It is therefore mandatory, for bushings’ manufacturers, to focus bushings’ design on improving reliability for long service life. The testing activities, performed in SuperGrid Institute contributed to assess the bushings RIP reliability.
Condenser type bushings are produced by wrapping paper on a central tube or conductor, with aluminium conductive layers as electrodes (thin metal foil) of certain length, being inserted at defined diameters, whose scope is to grade radial and axial voltage stresses to enhance the uniformity of the electrical field. This technology is well recognized on the market and mandatory for high voltage bushings manufacturing and test.
Two shapes of samples, smooth and sharp, have been tested to be representative of different parts of bushings, respectively homogeneous field at the middle of metallic foils and heterogeneous field at their edges. They were designed to avoid breakdown in insulating gas used for tests. They were metallized to improve contacts with electrodes, minimizing the risk of surface discharges.
The tests were performed using a negative HVDC source, connected to a Gas Insulated Substation (GIS) compartment and instrumented with 24 pistons (Figure 2). each allows to connect one sample, placed in a holder screwed on the HV conductive bar, and disconnect it after its breakdown allowing to resume the test. Each piston is insulated from the enclosure and connected to a current measurement card able to measure direct currents in the range between 50 pA and 20 µA with an uncertainty of 5%. The enclosure is filled with pressurized insulating gas and its temperature is regulated with heating resistors and temperature probes.

Matthieu DALSTEIN, Laura DE FINA (GE RPV), Frank JACQUIER, Cong Thanh VU, Armando PASTORE.

Presented at CIGRE 2024