Laboratory studies of composite insulators by means of steep-front impulse voltage tests are presented. The tests were performed on four groups of insulators, i.e. on newly manufactured insulators, on insulators removed from service, on insulators earlier exposed to mechanical fatigue test and on insulators with intentionally introduced technological defects. Extensive results of these investigations indicate that application of steep-front impulses of 4 kV/ns provides a better diagnostic efficiency as compared with the standard testing by means of impulses with steepness of 1 kV/ns. It is shown that the application of 4 kV/ns impulses do not cause any damage to healthy insulators, while defected insulators are identified reliably. A new methodology allowing to assess the status of internal insulation in insulators removed from service is proposed based on the performed studies.

In this article, we presented the results of the tests performed on three sets of samples of glass-reinforced epoxy (GRE) core rods used in alternating current (AC) composite insulators with silicone rubber housing. The objective of this examination was to test the aging resistance of the rod material when exposed to direct current (DC) high voltage. We hypothesized that the long-term effects of the electrostatic field on the GRE core rod material would lead to a gradual degradation of its mechanical properties caused by ionic current flow. Further, we hypothesized that reducing the mechanical strength of the GRE core rod would lead to the breakage of the insulator. The first group of samples was used for reference. The samples from the second group were subjected to a temperature of about 50 °C for 6000 h. The third group of samples were aged by temperature and DC high voltage for the same time. The samples were examined using the 3-point bending test, micro-hardness measurement and microscopic analysis. No recordable degradation effects were found. Long-term temperature impact and, above all, the combined action of temperature and DC high voltage did not reduce the mechanical parameters or change the microstructure of the GRE material.

The paper presents a nondestructive ultrasonic method of investigating long-rod insulators used on overhead power lines and in substations. A correlation between the degree of degradation of porcelain C 120 and the ultrasonic wave propagation and attenuation parameters was established. The ultrasonic method was used to analyze the quality of groups of line and post insulators after many years of service. Also a new mechanoacoustic method of investigating the stages in the degradation of insulator porcelain was applied. As a result of the investigations carried out on samples of porcelain C 130 the successive stages in the degradation of ceramic insulators during their service life were determined.

Rainfall can be a dangerous hazard for outdoor composite insulators. In the paper, a laboratory method of testing of ageing resistance of aerial composite insulators exposed to high voltage and water, simulating heavy rainfall, is presented. The method is illustrated by the results which show the impact of shed profile of the composite insulator with the housing made from silicone rubber on their aging resistance.

Results of ageing tests of composite insulators exposed to AC (50 Hz) high voltage and cyclic water precipitation in a rain chamber were presented. The subject of the investigation were composite insulators destined for 20 kV rated voltage with their housings made of HTV silicon rubber. The insulators were tested in horizontal, vertical and inclined position. During the tests, the leakage currents were recorded and surface hydrophobicity was estimated. Photo and video registration of the behavior of water drops on the tested surfaces were made. The following phenomena were described: non-uniform loss of insulator surface properties, merging of water drops which caused creation of conduction current paths, development of surface electric discharges. Essential influence of insulator operating position on the way of its surface wetting during rainfall and development of ageing process was described.

The aim of this work was to investigate the effects of the currents flowing through surge arresters on the internal insulating textolite structure. The samples were removed from high-voltage arresters that were taken out of service due to malfunction or failure. Discharge (short-circuit) currents of diverse intensities and durations caused degradation effects of varying degrees of advancement in the material of the tested elements. The samples were examined using microscopic methods. The use of the microanalysis technique EDS (energy-dispersive X-ray spectroscopy) made it possible to register changes in the elemental composition of the surface layer of the textolite materials, along with the intensification of the degradation effects. It was found that the high discharge current flows were subject to melting, charring and even burning of the organic adhesive. These effects caused serious changes in the content of elements in the top layer of the textolite and were the cause of a reduction in the service life, durability and reliability of the surge arresters. It was shown that the textolite materials had insufficient resistance to the effects of the emergency operation of the arresters after moisture ingress, which was a consequence of unsealing of the housing. A solution to this problem proposed by the authors could be the use of silicone elastomer as a covering of the textolite internal structure of surge arresters.