Ceramic and hybrid support insulators for UHVDC systems

Abstract

The requirements for UHVDC installations in terms of length, mechanical strength, permissible deflection, creepage distance, shed profiles and pollution resistance are still a challenge for all existing technologies and solutions. Based on the positive long time experience with solid core porcelain post insulators and the pollution experience of insulators with silicone housings the fundamental concept of both were used to develop a new type post insulator with inside ceramic core and housing of silicone. The challenge was to provide a reliable and economical solution, which combines the advantages of both technologies. Realising the needs for high strength, low deflection under load for many applications PPC Insulators Austria began the development of hybrid post insulators. The ceramic solid core design provides superior advantages in terms of bending strength, also for torsion load and compression load. The silicone rubber housing allows thinner sheds and greater creepage distances, provides improved long term pollution flashover performance and protects the core from short circuit arc damage. As design for DC hybrid post insulators was chosen upright tapered, uniform and underhung tapered insulators columns stacked of single hybrid insulator sections. The single sections could be varied in core diameter, length, creepage distance, fittings and holepattern. The shed profile used for DC applications was defined according the recommendations given by CIGRE. Selected design tests, electrical and mechanical type tests were conducted according to the relevant parts of IEC standards for composite and ceramic insulators. Also a long term test installation was performed to establish a confidence in this product. The long term test installation has been energized at 725 kV DC and later the voltage was increased to 761 kV DC. The tests have served well in providing final qualification. Beside these voltage tests measurements of ESDD/NSDD, hydrophobicity and also visual inspections were carried out. The mechanical properties were driven from the seismic requirements and have been calculated by finite element modelling of the reactor and its support structure. For post insulators with silicone rubber sheds and with solid core porcelain may be the most stable solution and this type has been adopted in different 800 kV projects. One of the new insulator was chosen for smoothing reactor support for 800 kV DC system in India.