nan Suwarno

Partial discharges due to electrical treeing in polymers : phase-resolved and time-sequence observation and analysis

We have investigated the partial discharge (PD) due to electrical treeing degradation in low-density polyethylene (LDPE), ethylene - vinyl acetate copolymer (EVA) and ethylene - acrylic acid copolymer (EAA) by a computer-aided partial discharge measurement system which allowed us to obtain phase-resolved PD pulse data. The experimental results revealed that the PD magnitude was strongly affected by the instantaneous applied voltage and that the occurrence of a PD was determined by the time derivative of the applied voltage (). The PD pulse-sequence analysis revealed the following: (i) a PD occurs in a discharge path which consists of a tree trunk and branches extending from the trunk; (ii) in each discharge path at most one PD occurs per half cycle. Based on these facts, a model of PDs due to electrical treeing was proposed. The influences of applied voltage and frequency were investigated by applying a triangular voltage. The number and average magnitude of PDs increased linearly with applied voltage whereas the PD charge per cycle increased quadratically. These results are in good agreement with the model.

Leakage Current Waveforms of Outdoor Polymeric Insulators and Possibility of Application for Diagnostics of Insulator Conditions

This paper reports the investigation results on the leakage currents (LC) on polymeric outdoor insulators. The samples used were EPDM (ethylene prophylene diene monomer) insulators used at 20 ㎸ distribution lines. AC voltage was applied and the LC waveforms were measured under various environmental conditions (humidity and pollution). Digital data of the LC was transferred from a digital storage oscilloscope to a computer for further analysis. The LC waveform parameters such as magnitude and harmonic content (as indicated by the total harmonic distortion (THD)) were analyzed. The experimental results showed that 3rd, 5th and 7th harmonics and higher odd harmonics were observed for symmetrical-distorted LC waveforms while for unsymmetrical-distorted LC waveforms, odd and even harmonics were observed. The LC analysis indicated that there are 5 stages of insulator conditions from normal condition up to flashover correlated with different kind of LC waveforms. The results also showed that in general the magnitude of LC was good enough to show the condition of the insulators. However, under discharge condition (for example as a result of dry band arching) the LC magnitude should be combined by the THD to show a better correlation with the insulator condition. The product between THD and LC magnitude may be used as a diagnostic parameter.

Study on the characteristics of palm oil and it's derivatives as liquid insulating materials

Insulation is one of the most important parts in a high voltage apparatus. Petroleum-based mineral oils have been used as insulation for power transformer since long time ago. Recently, peoples pay attention on the environmental aspects of the oils. Researchers are now searching new types of insulating materials, which are friendly to environment. We have investigated the dielectrics-short term characteristics of Palm Oil and its derivatives in attempt to find the environmental friendly insulating materials. The samples used including CPKO (Crude Palm Kernel Oil, CCO (Crude Coconut Oil, RCO (Refined Coconut Oil) and RBDPO (Refined, Bleached and Deodorized Palm Oil). The losses factors and breakdown voltages of the oils as function of temperature were investigated. The values of flash point, viscosity, specific heat and pour point are presented. The comparison of the properties of the oils with that of mineral and silicone oils is also done. According to the existing standard such as IEC, ASTM or British Standard, some of the oils such as RCO and RBDPO may be used as alternatives for liquid insulating materials in the future. However, long-term performances of the oils have to be investigated.

Partial discharge patterns of electrical treeing in polyethylene

The partial discharge pattern of electrical treeing in polyethylene was investigated by using a computer aided partial discharge measurement system. It was found that partial discharge from an electrical tree is characterized by the so-called wing-like pattern. By using the wing-like patterns, treeing degradation was successfully diagnosed. It is likely that each PD from a tree occurs in a different channel and the number of discharges in each half cycle in one channel is one or less. Negative discharges occur more easily than positive ones.<<ETX>>

Properties of RBDPO Oleum as a candidate of palm based-transformer insulating liquid

This paper presents properties of RBDPO Oleum to be used as an insulating liquid. RBDPO stand for Refined, Bleached and Deodorized Palm Oil. Electrical properties like breakdwon voltage, dielectric dissipation factor and relative permitivity of RBDPO Oleum were measured for three different temperature and compared to that of ASTM D-6871 standard. Physical and chemical properties like viscosity, acid number and water content are also investigated. Experimental results show that RBDPO oleum can be considered as an initial material for developing palm oil based-transformer insulating liquid. Breakdwon voltage of sample at room temperature, 25°C, is 57kV. The relative permtivity is 3.1, very closed to that of strandard, 3.2, while the dissipation factor is 0.03. Viscosity and water content of oil are significantly lower then those of ASTM D-6871 standard value. The remaining problems are reducing acid number wich are stil slightly above standard value.

Enhanced bowtie UHF antenna for detecting partial discharge in gas insulated substation

UHF method to detect partial discharge (PD) phenomenon has been proven to be an effective way. Many types of UHF antenna have been developed in order to achieve a better sensitivity and accuracy in certain bandwidth (300 MHz-3.0 GHz) for detecting the ultra-high frequencies generated by partial discharge. Bowtie antenna is proven to be sensitive, accurate and easily designed and fabricated. This paper focuses on the enhancement of bowtie antenna to achieve better performance in detecting partial discharge using UHF method. Characteristics of antenna both on the simulation result prior to the fabrication and measurement using a network analyzer show the good agreement. Experiment was carried out in a gas insulated switchgear (GIS) model with a protrusion on the conductor as PD source and antenna located at different positions with applied voltage range from 20-25 kV. EM wave intensity and frequency captured by antenna were observed. The relation between the distances of PD source to antenna, either from one spacer aperture to others, or distance from one spacer aperture were investigated. Antenna mounted 55 cm from the closest spacer aperture to the PD source can still detect EM wave intensity very well. The lowest EM wave peak envelope intensity measured at 30.03 mV from the same spacer aperture compared to 1.952 mV peak-peak EM wave intensity from internal GIS UHF sensor demonstrates a sufficient sensitivity performance.

Study on the wave form of leakage current on the 20 kV post-pin ceramic insulators under various conditions

This paper reports the results of investigation on the wave forms of leakage current (LC) on the 20 kV-post-pin ceramics insulators under various conditions. The measurement was conducted by utilizing a computer-based measurement system. analysis of LC harmonics was done by applying fast Fourier transform (FFT). Total harmonic distortion (THD) was used to quantify the harmonics content of the LC. The results show that the magnitude as well as the wave form and THD of the LC were significantly correlated with the condition of the insulator surfaces.

Study On The Electrical Equivalent Circuit Models of Polluted Outdoor Insulators

During operation, an outdoor high voltage insulator may come under various stresses. One of them is environmental pollution, where pollutants stick to the insulator surface. The polluted condition may produce leakage currents or even electrical discharges. Their waveforms are normally non-pure sinusoidal. To understand the correlation between insulator condition and its leakage current phenomenon, we will, in this study, investigate various equivalent circuits for representing insulator under different conditions. This paper presents the proposed equivalent circuit models of three main conditions of insulator, i.e. clean, polluted and polluted with dry-band discharge. In general, the model consists of capacitor(s) and non linear resistor(s). By using the models, the leakage current simulations have been done using ATP/EMTP software package. The simulations show that a clean low capacitance insulator yielded a pure sinusoidal current waveform, whereas that of a high capacitance yielded an oscillating sinusoidal current waveform. On the other hand, the polluted insulator simulations produced distorted sinusoidal current waveforms. At the end, the polluted insulator with dry-band discharge simulations showed chopped sinusoidal current waveforms. It was also showed the harmonic amplitudes, where third harmonics were usually the second highest amplitudes, a part of the fundamental ones

Effects of temperature on the breakdown voltage and partial discharge patterns of biodegradable oil

A power system with high voltage transmission is necessary to transmit a large amount of electrical energy from generating stations to consumers. High voltage transformers are widely used in electric power systems. Oil insulation is important component in the transformers. The oil serves as electrical insulation and coolant in transformers. The integrity of the oil insulation is important factor in keeping the normal operation of the transformer. In particular condition an excessive electric field may occur and partial discharges may take place in the oil insulation which may degrade the performance of the insulation. The occurrence of the partial discharge (PD) is also an indication of insulation abnormality. There are 3 kinds of oil insulations. They are mineral, synthetic and natural oils. Due to environmentally friendly, the last oil is being popular. This paper reports the effects of temperature on the breakdown voltage and partial discharge patterns of natural oil. The oil used was BIOTEMP. The range temperature used was from room temperature to 60o. The breakdown voltage was measured using Liquid Dielectric Cell Test, LD 60 from Phenix. The bi-spherical electrodes with the separation of 2.5 mm was used in accordance with IEC 156 standard. The AC voltage was applied to the electrode filled with BIOTEMP at the rate of 2 kV/s. The partial discharges were generated using needle-plane electrode system under sinusoidal voltage. Partial discharge measurement was conducted using phase-resolved measurement system which able to measure the PD magnitude (q), phase of PD occurrence (ϕ)as well as PD number (n). The analysis of the PD data was conducted by utilizing ϕ-q-n and ϕ-n pattern. The experimental results showed that in the experimental temperature range the breakdown voltage increased significantly with temperature. The relative water content may play an important role. Partial discharge measurement results indicated that negative PD appear early than those of positive PD. The inception of negative PD slightly lower than those of positive PD. The inception voltage decreased with temperature. PD took place at around the peak of the applied voltage. Phase-resolved analysis indicated that PD magnitude as well as PD occurrence were strongly dependent on the instantaneous applied voltage.

Evaluation of surface degradation of silicone rubber under natural tropical aging using thermogravimetric and thermomechanical analysis

Silicone rubber is a new insulating material for HV outdoor insulators. In order to know the long term of its performance we investigated the aging of the material under a natural tropical environment. This paper reports the investigation results on surface degradation of silicone rubber with different filler content which were installed in the open air in Bandung city, Indonesia, for 120 weeks by using thermogravimetric analysis (TGA) and thermomechanical analysis (TMA). The test results showed that adding a higher filler content improved the surface of RTV and HTV silicone rubber. The RTV with 29,2% filler content showed less surface degradation than RTV with 18% filler content; RTV with 22,9% filler content, and HTV with 72% filler content also showed less surface degradation than HTV with 48% filler content and also less surface degradation than HTV with 60% filler content. SEM photographs confirmed the results that both RTV with 29,2% filler content and HTV with 72% filler content had a little difference from those virgin samples.