Ahmad Darus

Modeling leakage current and electric field behavior of wet contaminated insulators

The behavior of leakage current and electric field of insulators primarily depends on the environmental stresses. A mathematical analysis based on dimensional analysis technique is applied to develop the correlation of leakage current (LC) and electric field with the physical variables of the environmental stresses. The final model is established by relating the analytical results with the experimental results.

Leakage current and surface discharge phenomena: effect on tracking and morphological properties of LLDPE-natural rubber compounds

Polymeric insulators are widely used for high voltage outdoor insulating application due to their substantial advantages compared to the porcelain and glass insulators. Although polymer materials have been proven good, research on development of new polymer-based materials is still on going since the benefits of using polymeric materials are not yet utilised to their full potential. In this work, a new formulated thermoplastic elastomer materials that are composed of linear low-density polyethylene (LLDPE) and natural rubber (NR) filled with different loadings of alumina trihydrate (ATH) fillers is presented. A surface tracking and erosion test is conducted to investigate the characteristics of leakage current on the material surface under the influence of wet contaminated conditions. A computer-based leakage current monitoring system is developed to monitor the leakage current waveform pattern as well as its frequency spectrum. The scanning electron microscope is used to investigate the morphological properties of the materials before and after the tracking test.

Application of acoustic sensing and signal processing for PD detection in GIS

The presence of free moving metallic particles and discharges deteriorates the insulation strength of a compressed SF/sub 6/ (sulphur-hexafluoride) gas insulated switchgear (GIS) and causes serious limitation in its practical application. Free moving metallic particles and other defects inside the GIS cause partial discharge (PD) which can degrade the insulating properties of the insulant gas SF/sub 6/ to such an extent that breakdown may occur in the GIS system. So, it is necessary to detect partial discharge in the GIS at an early stage before system failure and extensive damage to the equipment and the rest of the power system. Partial discharge emits acoustic signals which can be detected by applying an acoustic emission sensor (AE sensor) outside the GIS chamber. This paper initially describes some fundamental aspects related to PD detection. Finally, the development of an acoustic PD detection system and some experimental investigations are presented.

Defect detection and identification of sources in GIS based on laboratory and on-site experience

The most common defects in GIS apparatus are due to the presence of metallic particles, protrusions, as well as floating shields which originate mainly from imperfect manufacturing process, operation of switches, or may become trapped during assemble. The presence of defects deteriorates the insulation strength of a compressed SF/sub 6/ GIS apparatus and causes serious limitation in its practical application. These defects can be detected by several techniques, one of which is that using acoustic sensors placed on the enclosure. This paper reports on the defect detection and identification of sources in GIS apparatus using acoustic technique, based on laboratory and on-site experience. The tests give satisfactory result.

Mathematical analysis of leakage current level in correlation with environmental stresses for solid insulating material under tracking test

Environmental pollution can cause the insulator material to become progressively coated with dirt and chemicals in the long run. In the presence of wet atmospheric conditions, the leakage current flows due to the development of conducting path across the insulator surface. The level of leakage current depends on the surface wetting and the degree of electrolyte contamination as well as the environmental factors. An analytical approach based on dimensional analysis technique is applied to develop a mathematical model of leakage current in correlation with the environmental stresses. In order to verify the developed model, an inclined-plane tracking test is conducted on the polymeric insulating materials. The experimental work is carried out by measuring the magnitude of surface leakage current at different levels of contamination. Simulation results of the model have shown good agreement to the experimental results and provide useful information on describing the test condition of the tracking test procedures.

Mathematical analysis for parameters variation in inclined-plane tracking test method

The inclined-plane tracking test (IEC 587) is an established standard test for evaluating tracking and erosion resistance of polymeric materials for outdoor insulation. The standard parameter values shall be strictly followed in order for the test result to be accepted. Each selected parameter value is related with the other parameter values. This paper presents the mathematical approach on development of parameters correlation in the IEC 587 standard test method using dimensional analysis technique. The result from mathematical model is then compared with empirical data from the standard.

Characterisation of acoustic signal and pattern recognition of free moving metallic particle motion modes in GIS

Free metallic particles, inside gas insulated switchgear (GIS) apparatus are considered hazardous to the insulation system, can be detected using acoustic sensors placed on the enclosure. From acoustic measurements, it is rather easy to determine the partial discharge pulses caused by loose or fixed particles. One can readily recognise the motion modes of the free particles by studying the acoustic signal. This paper presents the analysis of free metallic particle motion modes in GIS apparatus from acoustic measurements. The parameters such as maximum acoustic amplitude, number of acoustic pulses, mean value of maximum amplitude of 10 measurements, number of pulses which exceed the specified % of maximum amplitude characterising partial discharge activity of Al as well as Cu particles of different shapes are investigated.