Zainuddin Nawawi

Effect of Humidity on Time Lag of Partial Discharge in Insulation-Gap-Insulation System

This paper deals with the discharge time lag of partial discharge in insulation-gap-insulation system with different levels of relative humidity. The sample was polymethylmethacrylate (PMMA) plate with 1 mm thickness. The PD patterns and the PD time lag with various levels of relative humidity were measured and discussed. The increasing of relative humidity brings significance change in PD time lag. The PD magnitude decreased by 50% when relative humidity changed from 33% to 98%. The change in relative humidity brought about 1.2 ms of characteristic time lag. In the vicinity of crossing point, 1.2 ms of time difference is equivalent to 0.5 time PD inception voltage. This can be an explanation that, PD intensity goes down as much as 50 %

Induced voltage on objects under six-phase transmission line

This paper presents results of an experimental investigation on voltage induced on objects under a six-phase transmission line due to line switching incidences. In this work, the voltage induced on a vertical receiver and a pipeline due to line energization and de-energization in a six-phase power transmission line system is reported. The research was carried out using a six-phase transmission line mock-up system with ratio of 5/132 kV. The results showed that the induced voltage on the objects is less than 4 kV. In addition the high induced voltage experienced by the vertical receiver was from the left side of the phase composition while the pipeline experienced higher induced voltage from the right side phase composition.

The self-healing property of silicone rubber after degraded by treeing

Early damage of insulation systems is indicated by the existing of partial discharge within it. It is a release of electrical charges that occur locally at some parts of insulation, which leading to completely insulation failure. A measurement is conducted to knoe its mechanism in insulation. This research deals with the correlations of self-healing properties (i.e. the decrease of tree length and the partial discharge inception voltage (PDIV) of silicone rubber material. This researcu is carried out in high voltage engineering laboratory, Tanjungpura University, using silicone rubber material without filler. The results data show that electrical treeing grew after the voltage was applied exactly at its inception level (6 kV for 45 minutes). Silicone rubber specimens could self-heal after the occurrence of electrical treeing in the range of 0 to 72 hours. The PDIV was getting higher as the process of self-healing in electrical treeing. This means that the physical self-healing of the specimen (by the decrease of tree length) would be followed by its electrical self-healing (by the increase of PDIV).

Surface resistance effect on dielectric breakdown characteristic of LDPE film

Low density polyethylene is widely used in electrical apparatus such as power cables and capacitors because of the excellent electrical and mechanical properties. The long life of these materials is greatly affected by temperature and humidity. In this paper we investigated the surface resistance due to humidity change and the correlation with dielectric breakdown characteristics. The experiments were made on low density polyethylene films with 50 /spl mu/m thickness without evaporated electrode under AC voltage application. The result showed that the surface resistance becomes lower when the humidity increases and has significant correlation between the surface resistance and dielectric breakdown of the low density polyethylene film.

Evaluation and mitigation of underground gas pipeline coating stress due to nearby lightning stroke

Rapid economic developments have forced power networks and pipeline networks to share the same pathway. Induced voltages and currents appear on pipelines running parallel with high voltage transmission line when the transmission line is hit by lightning strike. In this study, a simulation had been carried out to determine the first lightning stroke effect on an underground pipeline coating stress. CDEGS software was used to solve Maxwell equations; in particular, HIFREQ and FFTSES tools were utilized. A 2-km underground pipeline and a 345-kV transmission line (TL) tower had been modeled. A suitable TL-pipeline distance need to determined based on lightning current, surrounding soil properties, and coating withstand voltage. In addition, horizontal and vertical rods are able to reduce the overvoltage across the coating. The first layer soil resistivity and thickness are important factors to be considered when carrying out mitigation in a non-uniform soil.

AC breakdown strength enhancement of LDPE nanocomposites using atmospheric pressure plasma

Polymer nanocomposites have been identified to possess superior electrical insulation properties compared to its base polymer. However, weak interfacial interaction between the nanoparticles and the host polymer matrices would result in poor insulation properties. In this study, the surfaces of Boron Nitride (BN) nanoparticles were treated with atmospheric pressure plasma discharge to strengthen the interface between the low density polyethylene (LDPE) matrices and BN nanoparticles. Furthermore, AC breakdown strengths of the untreated and treated LDPE nanocomposites were measured according to ASTM D149 standard. The obtained results were analyzed with 2-parameter Weilbull distribution. Moreover, the treated and untreated nanocomposites were characterized using Fourier Transform Infrared (FTIR) Spectroscopy in order to characterize the functional groups in LDPE nanocomposite samples after subjected to plasma discharges. It is shown that hydrogen bonds are created in the functional groups of the plasma treated LDPE nanocomposites. The results also show that the AC breakdown strength of plasma treated LDPE nanocomposites sample was improved compared with the untreated LDPE nanocomposites.

On the interaction of 132 kV transmission system with communication line: Street cabinet resistivity evaluation

Occurrence of surge voltages and surge currents in low-power circuits is initiated primarily because of two sources, i.e, natural lightning and switching phenomena; the other source of surge occurrence is possibly due to the interaction of power systems and communication system. Results have indicated that soil resistivity is crucial in determining the adequacy of an earthing system. In region with the highest resistivity, the EPR and the scalar potential of the cabinet are very high. Remarkable low induced voltages at 200 m away from the power line when subjected to a single phase-to-earth fault was observed. At 50 m away, step and touch voltages could be dangerous due to the nature of soil in the vicinity. In addition, a 132 kV double circuit transmission line sharing the same corridor with a telecommunication line was also investigated and have also shown the induced voltages in the order of thousand volts on the cable due to a single phase-to-earth fault. Cables must be protected from such dangerous voltages. During normal peak load conditions voltages are considered not to inflict any damage to equipment and livestock.

AC breakdown strength performance of plasma treated mineral oil-based nanofluids

Nanofluids have been identified to be one of the suitable approaches to increase the breakdown strength of transformer oil. However, the nanofluids tend to form sediment which nullifies its full capabilities in increasing the electrical properties such as higher AC breakdown strength. In view of foregoing, this paper presents an approach to enhance the AC breakdown strength of the transformer oil by using plasma treated silica nanoparticles to form plasma treated nanofluids. The surface of silica nanoparticle was functionalized by using atmospheric pressure plasma discharge to enhance the interfacial interaction in order to improve the sedimentation issue in nanofluids. Plasma treated nanoparticles with desired surface functionality can strongly interact with liquid molecules with better dispersed into the base fluid to form a stable suspension. The AC breakdown strength of oil samples before and after surface modification of nanoparticles were measured accordance to IEC 60156 standard. Based on obtained results, it was found that the plasma treated nanofluids had higher AC breakdown voltage compared to the pure oil and the untreated nanofluids.

Comparison of the effect of fixed metallic defects in coaxial gas insulated switchgear condition monitoring

Gas insulated switchgear assumes an indispensable equipment for high voltage transmission of electrical energy because of its focal points of high unwavering quality and execution, smaller in measurements and extraordinary compatibility with the environment. It utilizes sulphur hexafluoride gas as its insulant and coolant in view of its high dielectric quality and superb circular segment extinguishing capacity. Gas insulated switchgear in operation suffers the challenge of its insulation deterioration that leads to its failure due to the activities of partial discharge that is caused by defects. This failure is calamitous and it will prompt to whole power out stage that will affect all classes of human exercises. In order to monitor the condition of GIS, in this studies a simulated coaxial decomposition chamber was designed and used to simulate the decomposition of SF6 under the effect of fixed copper (Cu) and aluminium (Al) foil metallic artificial defect on the surface of the spacer in the chamber at the pressure of 0.2MPa when energizing with high voltage for a period of about 50 hours. The decomposition products of Cu and Al foil fixed defects detected offline by FTIR spectrometer are HF, SOF2, SOF4, SO2F2, SO2F10, SiF4, SO2, CO, C2F6, CF4 and SO2, SO2 F2, C3F8 and C2F6 respectively. These decomposed products and its concentration identify the type and the magnitude of fault in switchgear (contamination fault) and it shows that Cu fixed defect is more harmful to GIS than fixed Al foil defect.

Sulphur hexafluoride gas decomposition products of fixed metallic defect in coaxial gas insulated switchgear

A reliable diagnostic technique of Gas insulated switchgear condition monitoring is used in this research for the detection of Sulphur hexafluoride gas (SF6) decomposition products due to its high sensitivity and anti-electromagnetic interference; it is known as decomposition by-product method. A simulated coaxial decomposition chamber was designed and used to simulate the decomposition of SF6 under the effect of fixed metallic artificial defect on the surface of the spacer at the pressure of 0.2MPa when the chamber is energized at a 45KV experimental voltage over the period of 30 hours due to the presence of partial discharge caused by the artificial defect. The decomposition products (HF, SOF<inf>2</inf>, SOF<inf>4</inf>, SO<inf>2</inf>F<inf>2</inf>, SO<inf>2</inf>F<inf>10</inf>, SiF<inf>4</inf>, SO<inf>2</inf>, CO, C<inf>2</inf>F<inf>6</inf> and CF<inf>4</inf>) were detected offline by FTIR spectrometer. These decomposed products and its concentration can be used detect and identify the type and the level of fault in switchgear (contamination fault) before failure for purpose of preventive maintenance.