Power transformers are important and expensive components in the electric power system. The knowledge of the actual status of the transformer insulation behavior, load tap changer performance, temperature, and load condition is necessary in order to evaluate the service performance concerning reliability, availability and safety. Systems abnormalities, loading, switching and ambient condition n...

Irregularity in charge distribution of an insulator may lead to accelerated aging and electrical breakdown. However, knowledge of charge distribution on the insulation surface is still insufficient albeit has gained worldwide attention. The insufficiency is particularly on the charge profile along the string insulator under AC excitation. Therefore, charges distributions on the surfaces of glas...

Partial discharge inside a transformer is mainly responsible for the insulation aging and damage of the transformer. However, partial discharge is usually accompanied by external signals like sound, light and electrical signals and detectable physical phenomena such as characteristical gas and dielectric loss. Therefore, it is of great significance to monitor online the external signals and phe...

This paper describes an accelerated ageing experiment of transformer oil/paper insulation with preset moisture levels. These samples were tested with return voltage and polarisation/depolarisation measurements. Molecular weight has also been measured with Gel Permeation Chromatography (GPC). Results suggested the impact of moisture on the ageing of oil/paper insulation. An attempt has been made...

Polarization-depolarization current (PDC) measurements are now being used as a diagnosis tool to predict the ageing condition of transformer oil-paper insulation. Unfortunately, it is somewhat difficult to obtain the ageing condition of transformer cellulose insulation using the PDC technique due to the variation in transformer insulation geometry. In this literature, to quantify the ageing con...

Oil/paper insulation degradation in transformers involves chemical and physical changes in the materials. Some of the chemical reactions involve very reactive intermediates called free radicals. Free radicals play a major role in a wide variety of ageing processes. The detection of these reactive species in oil may, in principle, provide useful information for monitoring oil degradation. This m...

Degradation of polymeric insulation systems of electrical equipments increases the space charge density and the concentration of electrical dipoles. By consequence, the maximum values and the slopes of absorption/resorption (A/R) currents can change with insulation systems ageing. In this paper, an analysis of the nature of the A/R currents and the importance of their components, especially the...

Moisture inside the footwear can considerably affect the thermal insulation. In this study with a thermal foot model there was simulated three sweat rates (3, 5 and 10 g/h). Five types of footwear with various insulation levels (dry insulation from 0.19 to 0.50 m2. K/W) were tested. The footwear insulation reduction was calculated for 1.5 hour period. The reduction in insulation was related to ...

One of the cardinal properties of the insulation system of the electrical equipment is its electrical strength. Usually it is expressed as value of breakdown voltage. There is not electrical destruction of material under this one. The determination of breakdown voltage exactly is possible only by doing electrical strength test. It is a destructive test on insulation system made by solid materia...

In this paper, the thermal performance of four common insulators in two internal and external insulation systems is investigated for the ASHRAE setpoint range by applying detailed numerical simulation and Anti-Insulation phenomenon. Anti-Insulation phenomenon and consequent extra load on the HVAC system can occur following the thermal insulation of a building if proper temperature setpoint is n...