At present line and apparatus composite insulators are widely accepted for use on AC overhead lines and in high voltage substations. The present paper concentrates on measurements of different pollution parameters of naturally exposed apparatus composite insulators tested at five different sites covering coastal, tropical and semi-desert environments. In general all tested silicone rubber apparatus insulators (for the period from 1 to 8 years) performed well. However, the difference in pollution layer is evident even for the sites formally belonging to the same class, e.g. coastal sites. The standard parameters, ESDD/NSDD are not enough to understand and proper evaluate the pollution performance of composite insulators. It is suggested to use the Wettability Class (WC) and Hydrophobicity Transfer (HT) tests in addition to the standard parameters.

Modern power thyristor valves have a high power rating and are difficult to test in a back-to-back test circuit in the test laboratory. Verification of thyristor valve design with synthetic test circuits is an alternative. The core to design a synthetic test circuit is to correctly reproduce the stresses applied on the thyristor valves. Voltage and current stresses on the thyristors under four operational states are highlighted in this paper. A new synthetic test circuit has been developed by ABB Power Systems. This new circuit reproduces the correct stresses applied on the high voltage direct current (HVDC) thyristor valves in service. Verifying tests reveal that the circuit design was a success

The breakdown development of a covered rod/plane air-gap arrangement was investigated under lightning impulse stress. At positive polarity of the rod a flashover along the cover surface is followed by a breakdown of the air-gap. At negative polarity a breakdown of the air-gap is followed by a flashover along the cover surface

In laboratory set-ups, polymer covering of the electrodes has resulted in the reduction of the insulating distances by a factor two. One of the problems with covered conductors is however that of creeping discharges on the surface of the covering. The aim of this work was to investigate how creeping discharges develop under lightning impulse (1.2/50 /spl mu/s) on two covered conductors at a 90-degree angle to each other. Furthermore, the aim was to investigate how to stop the propagation of a creeping discharge. This was achieved by inserting at least one cable termination, e.g. the type of termination used for high voltage cables, into the discharge path. The experiments showed that a set-up with two crossing cables can withstand very high voltages without any shed or termination of the creeping discharges. Further tests show a considerable increase of the breakdown voltage in other arrangements comprising covered electrodes. This was accomplished by using two cable terminations at each cable end to stop the propagation of creeping discharges.

The application of high DC voltage to a polymer/air insulation system can result in space charges on the interface. The space charges can cause significant distortions of the electric field distribution, which may trigger a surface flashover or breakdown in the insulation system. In the present investigation, an attempt has been made to measure the space charge on a polyester/air and PTFE/air interface by using a pressure wave propagation technique (PWP) under DC voltage

Dispositif concu pour proteger, dans une centrale electrique des objets (1, 7, 27) contre des surintensites provenant de defectuosites, lesdits objets etant relies a un reseau electrique (3) ou a un autre equipement de la centrale electrique. Un ensemble (5) servant a limiter les surintensites est relie a une ligne (2) reliant le reseau ou l'equipement (3) et l'objet (1, 7, 27) et est mis en service afin de limiter les surintensites avec l'aide d'un ensemble servant a detecter une condition de surintensite.

A 1000 h salt-fog test using low salinity with resting periods between the salt-fog cycles was employed for the comparison and ranking of a series of silicone rubber and EPDM rubber materials. In addition, these materials have been analysed by Attenuated Total Reflection-Infrared (ATR-IR) spectroscopy, in order to determine the degree of surface oxidation. The electrical analyses involved the measurements of high-frequency and low-frequency leakage current components during the actual salt-fog tests. The leakage current measurement enabled a rough ranking of the materials essentially into two groups whereas ATR-IR spectroscopy provided data which more sensitively ranked the different materials. It was shown that samples with a higher degree of surface oxidation also during the salt-fog test exhibited higher leakage currents. In another test series involving only silicone rubber materials modified with different silicone oils, differences in the salt-fog test results were small. However, the samples with the highest leakage current exhibited a diminished alumina trihydrate content at the surface which apparently protected the rubber from oxidation.