Breakdown Voltage Test Research Articles

Life Estimation of Thermally Stressed Insulating Papers of Rotating Machines by Using Arrhenius Model

Abstract In the present study, life estimation of accelerated aged insulating papers used in rotating machines is estimated by Arrhenius model. Various types of insulating papers used in rotating machines such as Mylar, Nomex-Mylar-Nomex(NMN), Leatheroid, Dacron-Mylar-Dacron(DMD), Mica Tape, and Kapton are thermally aged at 90°C, 130°C and 170°C with 300hrs duration of each sample. These insulating materials wrapped on copper conductor with single and double layer. Then, breakdown voltage test is performed at each temperature for both single and double layer papers to determine their dielectric strength. Further, correlation analysis between breakdown voltage and different applied temperatures is performed for all paper samples. Popular Arrhenius plot is drawn by short term test data on breakdown voltage for an extrapolation to long term performance of various types of insulating paper used in rotating machines. The results showed that the performance of double layer insulation is almost twice than single layer performance. The aging analysis and testing of insulating papers was performed in TIFAC-Core centre of NIT Hamirpur, H.P., India.

Comparison of the AC breakdown voltage of various polymers intended to the conception of a new generation of piercing connectors – influence of geometrical, electrical and climatic factors

The AC breakdown voltage (BDV, 50 Hz) of various polymers is investigated regarding the influence of several constraints: (i) the effect of the electrodes geometry (namely cylindrical, spherical or pyramidally capped point/point) that simulates the interaction between the metallic constituents of the connector (piercing teeth and metallic plates) and those of covered cables (such as the conductor or the presence of voids); (ii) the rate-of-rise of voltage (RRV) and the connection of electrodes to the H.V. source; (iii) the thermal ageing at higher temperatures (namely, 100, 130 and 150 °C) and; (iv) the thermo-hygro ageing under salt rain. The aim of such a study is to identify suitable organic materials that could be intended for the conception of a new generation of piercing connectors that will be used on overhead covered cables. Regarding BDV tests, used polymers cover (i) thermoplastics (namely, polyamide 6, polyamide 66, polyarylamide, polycarbonate, high density polyethylene and polyphenylene sulfide); and (ii) unfilled/fireproofed EPDM rubbers. The obtained results clearly show that breakdown voltage (BDV) with spherical electrodes exhibits the highest values. It is also evidenced that the connection to the H.V. source and the influence of the electrode dimension to the BDV value is significant. Results show that the spherical–pyramidally capped point electrodes exhibit higher BDV than that for the spherical–cylindrical ones for PA 66/50 PC/40, PARA/50 and HDPE. Furthermore, thermal ageing affects seriously BDV of EPDM based materials while polyphenylene sulfide is less damaged due to its highest thermal stability. As concerns thermo-hygro ageing, the moisture absorption is responsible for the significant BDV decrease of polyamide materials (PA 6/50 and PA 66/50).

Analysis of the Dielectric Characteristics of Gaseous Nitrogen According to Various Temperatures and Pressures for a Magnet System

Gaseous nitrogen (GN 2) is used as an insulation and pressurization material for developing a high-voltage superconducting magnet system utilizing liquid nitrogen (LN 2) cooling. In a LN 2 cooling system, current leads for a high-voltage superconducting magnet are exposed to GN 2 to temperatures that can range from 65 to 300 K. Therefore, a study on the electrical breakdown and partial discharge inception voltage test was performed considering the temperature and pressure variation of GN 2. The dielectric characteristics of GN 2 were observed to improve as the temperature and pressure increased. In addition, the partial discharge inception voltage was similar to the behavior of dielectric breakdown voltage with respect to temperature and pressure. To confirm a functional relationship between the breakdown voltage and effect of the electrode surface area, experimental results were summarized using a field utilization factor. The dielectric breakdown voltage was found dependent on the field utilization factor. Consequently, the dielectric breakdown voltage of GN 2 could be expressed as a function of field utilization factor according to temperature and pressure.

Comparative Study on the AC Brekadown Voltage of Palm Fatty Acid Ester Insulation Oils Mixed With Iron Oxide Nanoparticles

Mineral oils are are derived from petroleum which is a non-renewable and non-sustainable source, and therefore there is a critical need to develop alternative insulation oils for use in transformers. Ester oils offer a number of benefits over mineral oils such as good biodegradability, high cooling stability, good oxidation stability and excellent insulation performance. Nowadays, nanotechnology has become one of the most important research fields in both the academia and industry and it has been shown in previous studies that nanoscale materials are beneficial for transformers. In this regard, the objective of this study is to compare the AC breakdown voltage of palm fatty acid ester (PFAE) oils mixed with iron oxide (Fe<sub>3</sub>O<sub>4</sub>) nanoparticles. The PFAE-based nanofluids are prepared using two methods: (1) Method I (weight-based method whereby the concentration of the Fe<sub>3</sub>O<sub>4 </sub>nanoparticles is 0.01 g/l) and (2) Method II (volume-fraction method whereby the concentration of the Fe<sub>3</sub>O<sub>4 </sub>nanoparticles is 0.01, 0.02 and 0.03%). The AC breakdown voltage test is conducted on the PFAE-based nanofluids in accordance with the ASTM D1816 standard test method. Weibull statistical analysis is carried out to analyse the AC breakdown voltage of fresh PFAE oil and PFAE-based nanofluids. It is found that there is enhancement of the AC breakdown voltage for all PFAE-based nanofluids with the exception of with the exception of one sample prepared using Method II (0.01% Fe<sub>3</sub>O<sub>4 </sub>nanoparticles).

Scatter reduction of the 50-60 Hz breakdown voltage test for insulating liquids

There are several reasons to test the breakdown voltage of insulating liquids: acceptance tests on new deliveries, testing of treated liquids prior to or during filling into electrical equipment, and monitoring and maintaining oil-filled apparatus in service. Among others, the test for the determination of breakdown voltage at 50 or 60 Hz is one of the most important. In fact, it is worldwide accepted that this test gives quickly very useful information even if mainly related with moisture and particle content than the intrinsic properties of the insulating liquids. This test is standardized by IEC and ASTM but has some limitations in terms of the statistical scatter of mean value of the breakdown voltage. The present paper presents an improvement on the scatter of the mean values of the breakdown voltage by increasing the number of requested shots and discarding the most disperse results. In addition, it is presented as a revised test cell having stirring device on the top and round edges at the bottom may further reduce the standard deviation of the same breakdown voltage. Others experimental parameters which may still influence the scatter of the same standardized test are also examined and discussed.

Design of Post Metal Shields Through Electric Field Distribution Analysis for a 154-kV SFCL

Korea Electric Power Corporation has developed a 154-kV superconducting fault current limiter (SFCL). This report is a part of the design process of the SFCL, particularly for fixation of posts supporting the superconducting element on the cryostat wall side. For supporting the superconducting element, the use of a post insulator is inevitable; however, the post insulator and cryostat with liquid nitrogen (L-N2) during operation of the SFCL form three junction points where electric field is intensified. In this study, we aim to design the metal shield in order to relax the electric field intensity at triple points (TPs) through numerical analysis of electric field distribution. For the electric field distribution analysis, a commercial software based on the finite-element method was employed. Each design for the metal shield was checked whether it makes the electric field intensity at the TP sufficiently lower than dielectric strength in L-N 2 for 750-kV input and whether there is any electrically weak point on the metal. The designs of the metal shields were improved through four critical steps where thermal contraction, manufacture tolerance, and insulation distance in L-N 2 were considered. It was experimentally verified that there was no electric breakdown in L-N 2 between the metal shield and the fiber-reinforced plastic post insulator for the lightning impulse test and the ac breakdown voltage test according to the IEC 60137 standard.

Correlation between DC electric field intensity and electrical breakdown of butt gap in LN2/PPLP composite insulation system

In the design of DC superconducting cables, the electrical insulation design is a critical factor in the cable's performance and reliability. To evaluate the insulation design of DC superconducting cables, DC electric field analysis and experimental verifications should be performed. Wrapped polypropylene laminated paper (PPLP) tape has generally been used to insulate superconducting cable. During the wrapping process, butt gaps are inevitably introduced, and these are filled with liquid nitrogen (LN2) during normal operating conditions. Therefore, the insulation characteristics of the resulting combination of PPLP and liquid insulation should be carefully verified. The objective of this work was to determine the DC electric field transitions when a butt gap is present in a LN2/PPLP composite insulation system. DC electric field distribution and transition were simulated by using COMSOL Multiphysics® software. Also, to verify the characteristics of DC electric field transitions, two kinds of breakdown tests were performed: a ramp voltage breakdown test and a step voltage breakdown test. In both the experimental and analytical works, it was observed that the electric field distributions were totally different while the DC field transition. And, due to the different distributions of electric field, the breakdown characteristics of LN2/PPLP composite insulation systems could be altered.

Visualization of multi-factor changes in HTV silicone rubber in response to environmental exposures

In this paper, we present a tool for visualizing multi-factor changes in HTV silicone rubber using results from ATR-FTIR, color coordinates, contact angle, and voltage breakdown test. Experimental works were performed on samples collected from a 22 KV silicone rubber insulator. The specimens were subjected to accelerated degradation using an Accelerated Weathering Tester (QUV). The proposed 3D scatter plot based on the obtained data shows a clear trajectory on how a new specimen degrades over time and eventually leads to complete failure. In addition, the application of Multiple Linear Regression method provides linear plane equation which quantitatively describes the changes in silicone rubber in response to environmental exposures over time.

Experimental and analytical study of the DC breakdown characteristics of polypropylene laminated paper with a butt gap condition considering the insulation design of superconducting cable

It has been reported that the insulation design under DC stress is considered as one of the critical factors in determining the performance of high-voltage direct current (HVDC) superconducting cable. Therefore, it is fundamentally necessary to investigate the DC breakdown characteristics of the composite insulation system consisting of liquid nitrogen (LN2)/polypropylene-laminated-paper (PPLP). In particular, the insulation characteristics under DC polarity reversal condition should be verified to understand the polarity effect of the DC voltage considering the unexpected incidents taking place at line-commutated-converters (LCC) under service at a DC power grid. In this study, to examine the variation of DC electric field strength, the step voltage and polarity reversal breakdown tests are performed under DC stress. Also, we investigate the electric field distributions in a butt gap of the LN2/PPLP condition considering the DC polarity reversal by using simulation software.

Vertical finFET with Salicide Contact for Potential Power Applications

We report a vertically diffused finFET with high-κ gate dielectric and metal gate for potential power applications. Electron beam lithography and deep silicon reactive ion etching (RIE) were utilized to form the fins, followed by atomic layer deposition of Al2O3 high-k dielectric and TiN to form the metal gate. Self-aligned silicide (salicide) was formed on the top of the fins to lower the contact resistance. The devices exhibit excellent performance with steep sub-threshold swing (SS), low drain-induced barrier lowering (DIBL) and a high ION/IOFF ratio. The breakdown voltage test (BVDSS) was also characterized for potential power applications.

Effects of SiO2 and TiO2 Nano Fillers in Enhancing the Insulation Breakdown Strength of Epoxy Nano Composite Dielectric under Divergent Electric Fields

The proper mixing of nanoscale fillers in conventional dielectric materials leads to an enhancement in the breakdown strength and voltage endurance. In this study experimental investigations are carried out to compare the breakdown characteristics of epoxy nano-composites with that of a base epoxy resin under the influence of divergent electric fields so as to obtain inferences on its breakdown performances. This would in turn enable providing solutions to acquire more effective electrical insulation systems and explore the prospect of tapping the merits of utilizing the rapid strides made in field of fabrication of nano-dielectrics. The main objective is such studies are to enhance the electrical properties of the epoxy dielectric by employing nano-fillers such as SiO2, TiO2 etc. This research envisages the use of epoxy resin mixed with nano-fillers for ascertaining the ability of the nano-composite to be utilized as a dielectric/ insulator in power apparatus. The epoxy resin is mixed with appropriate proportion of SiO2 and TiO2 and experimentation is carried out under the influence of divergent electric fields. Classical breakdown voltage withstand tests such as AC power frequency, DC voltage, lightning impulse and switching impulse test is carried out on epoxy dielectrics (with and without nano-fillers) and the results are compared. In addition, a non-classical breakdown voltage test (high frequency high voltage) is also devised to analyze and ascertain the breakdown characteristics due to varying frequencies so as to investigate the possibility of utilizing such nano-composites in applications related to high speed switching devices.

Solid Dielectric Barrier in Oil Insulator under Uniform and Non-Uniform Electric Fields

This paper presents the dielectric barrier (PVC, PMMA, and glass) breakdown voltage test in transformer oil in uniform field, slight non-uniform field and highly non-uniform field generated by plate-plate, plate-point, and point-point electrodes, respectively. It was found that PVC can withstand the maximum breakdown voltage that is higher than PMMA and glass. The dielectric barrier with 1 mm thick placed next to the high voltage electrode and ground electrode can withstand the higher breakdown voltage than dielectric barrier with 2 mm thick placed next to the ground electrode and at the middle of electrodes. PVC for point-point, plate-point and plate-plate electrodes can withstand the maximum breakdown voltage of 216.5, 195.7 and 181 kV, respectively. The breakdown voltage of solid insulations is different because of the shape of electrode. These results lead to design the solid insulator in transformer oil under uniform and non-uniform electric fields.

Electrothermal lifetime prediction of polyimide wire insulation with application to aircraft

ABSTRACTThis work investigates the electrothermal lifetime of a commonly used polyimide wire insulation material, Kapton®, through the use of thermogravimetry (TG) and breakdown voltage testing. From TG, an isoconversional model‐free kinetic evaluation was used to obtain a relationship between the activation energies of degradation for Kapton as a function of weight loss. By relating the electrical life theory and the TG theory through the model defined by Toop (IEEE Trans. Dielectr. Electr. Insul. 1971, 6, 2), the electrothermal lifetime of Kapton has been calculated for conditions of 12 and 14.7 kV over a temperature range of 250–400°C. The resulting model can be used to make lifetime predictions for wire insulation degradation in aging aircraft for improved safety and risk assessment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1639–1644, 2013

The Lightning Impulse Properties and Breakdown Voltage of Natural Ester Fluids Near the Pour Point

Recently, researchers have become interested in natural ester fluids, as they are an environmentally friendly alternative to mineral oils. Natural ester fluids are a natural resource made from plants; they have higher biodegradability, flash, and fire points, and a greater permittivity compared to conventional mineral oils. However, natural ester fluids also have a higher pour point, viscosity, and water content. These characteristics can hamper circulation and impair the electrical properties of an oil-filled transformer. A large amount of data has been accumulated over the years in regards to mineral insulating oil involving dielectric breakdown voltage and lightning impulse tests. However, natural ester fluids have not had their electrical properties sufficiently characterized. In this paper, we present an investigation into the characteristics of the electrical discharge development in natural ester fluids and in an oil-filled transformer near the pour points. The experiment results show that the electrical properties decreased according to a decrease in the ambient temperature and freezing time. It was found that the pour point and water content of natural ester fluids have a significant effect on the electrical properties.

Adaptive neuro-fuzzy inference system approach for simultaneous diagnosis of the type and location of faults in power transformers

Electrical, mechanical, and thermal stresses can degrade the quality of the insulation in power transformers, causing faults [1]. Several methods are used for fault diagnosis in transformers, e.g., dissolved gas analysis (DGA), measurement of breakdown voltage, and tan ��, pollution, sludge, and interfacial tension tests [2]. Of these, DGA is the most frequently used. Thermal and electrical stresses result in fracture of the insulating materials and the release of several gases. Analysis of these gases may provide information on the type of fault. Various standards have been suggested for the identification of transformer faults based on the ratio of dissolved gases in the transformer oil, e.g., International Electrotechnical Commission (IEC) standards [3]���[7], and these standards has been quoted in many papers, e.g., [8]���[15]. However, they are incomplete in the sense that, in some cases, the fault cannot be diagnosed or located accurately. Intelligent algorithms, e.g., wavelet networks [16], neuro-fuzzy networks [17], [18], fuzzy logic [8], [12], and artificial neural networks (ANN) [2], [9], [10], [19], [20] have been used to improve the reliability of the diagnosis. In these algorithms, the type of fault is diagnosed first, and the fault is then located using the ratio of the concentrations of CO2 and CO dissolved in the transformer oil [21], [22]. The algorithms are not entirely satisfactory. The wavelet network has high efficiency but low convergence, the fuzzy logic method has a limited number of inputs and, in some cases, it is very difficult to derive the logic rules, and the ANN need reliable training patterns to improve their fault diagnosis performance. In this paper, we present a new method for simultaneous diagnosis of fault type and fault location. It uses an adaptive neuro- fuzzy inference system (ANFIS) [23]���[27], based on DGA. The ANFIS is first ���trained��� in accordance with IEC 599 [3], so that it acquires some fault determination ability. The CO2/CO ratios are then considered additional input data, enabling simultaneous diagnosis of the type and location of the fault. The results obtained by applying it to six transformers are presented and compared with the corresponding results obtained using ANN and some other standards and methods.

Design of a $\hbox{SF}_{6}$-Gas-Filled Spark Gap Switch for High-Voltage Application

It is our endeavor to develop switching technology for the breakdown reliability and reproducibility at extremely high voltages above 1 MV. One of the key objectives of the endeavor is to derive precise breakdown criteria for use in high-voltage applications. We have developed empirical criteria by which the breakdown field strength of a high-pressure SF_6-filled spark gap can be computed. The validity of the computed result has been verified with several experimental data from different investigators. The computed result has shown good agreement in an extended range of pd (pressure times gap distance) and field enhancement factor of the spark gap geometry. Furthermore, a spark gap has been designed and constructed with particular intention of generating a high-pulsed-power source in Pohang Accelerator Laboratory. In parallel, field modeling has been performed to verify the appropriate shape of the highly stressed insulator and electrode design in the spark gap and to evaluate their field enhancements. A series of breakdown voltage tests has demonstrated the function of the spark gap switch as intended up to 9 bars of SF_6. Aside from this, the limitation of the switching behavior has been examined with an aim of operating the designed spark gap to its maximum capability.

Study on the lightning impulse breakdown characteristics of gaseous insulation media for the design of a high voltage superconducting apparatus

In general, the current leads of high voltage superconducting apparatuses cooled by liquid nitrogen are exposed to gaseous insulation media. Therefore, the investigation on the electrical breakdown characteristics of gaseous insulation media should be performed to develop electrically reliable high voltage superconducting power apparatuses. In this study, the lightning impulse breakdown tests on gaseous insulation media are conducted by using sphere-to-plane electrode systems made of stainless steel. Also, the lightning impulse breakdown voltage tests on gaseous insulation media according to various pressures are performed. The experimental results show that the electrical breakdown characteristics under lightning impulse voltage are affected by the gap length between electrode systems, the size of electrodes, and the field utilization factors. From these results, the electrical insulation design criteria to estimate the electrical breakdown voltage are established. The results are expected to be applicable to the design of current leads for high voltage superconducting apparatuses.

An Amendment of the VLF tanδ Criteria to Improve the Diagnostic Accuracy of the XLPE-insulated Power Cables

VLF diagnosis technology is introduced in IEEE Std 400 and proposed as evaluation criterion in an effective way of detecting water tree which mainly causes the failure of XLPE insulated cables. In order to inspect the accuracy of the VLF method for XLPE insulated power cables in Korean distribution system, diagnosis for 41 cables which were being serviced in the fields has been carried out and they were removed for AC breakdown voltage test after. Regarding the 41 cables, it was hard to confirm any relation between the VLF values and AC breakdown voltages and also water tree in the insulation was not detected. However, the other cables were failed several days after the diagnosis of the 41 cables. Water trees were found and their VLF values were also much higher than the criterion of IEEE standard. It has been ascertained that we need to change the IEEE criteria in order to improve the accuracy of detecting water trees by additional analyzing of field examples of failure and case studies from overseas countries and therefore amended VLF test voltage and evaluation criteria have been proposed.

DETECTION OF MILK FAT ADULTERATION USING DIELECTRIC PROPERTIES

Nowadays, milk adulteration and, in particular, milk fat adulteration represents a big problem. Because of its high price, ghee and butter has always been the object of adulteration by adding less expensive vegetable oils or animal fat. The determination of fatty acids by gas chromatography (GC) followed by calculation of suitable ratios is commonly used to detect extraneous vegetable oils or animal fats, but with the introduction of some lipids sources in cow's and buffalo's diets, the detection of extraneous fat become difficult. The dielectric properties (Breakdown voltage (KV) test) of oils are electrochemical and thermo-physical property widely used to determine the shelf life of mineral oils used in transformers. This property was determined in some vegetable oils, some animal fats, milk fats and margarine oil to see whether there is a big variation between them easy to be used to distinguish between these oils and fats or not. Also, this property was determined in mixture of milk fat with different edible oils and animal fat in different ratios. The obtained results indicated that it could be possible to depend on the dielectric breakdown voltage as a rapid and easy method to detect milk fat adulteration with other vegetable oils and animal fats.

Dielectric Strength, Breakdown Voltage and Acidity Test with Respect to Transformer Insulating Oil

This paper presented the qualitative assessment of transformer insulating oil. The breakdown voltage, dielectric and acidity tests were electrically and chemically carried out on sixteen samples of transformer insulating oil collected from various serving distribution transformers in Ilorin Metropolis in Nigeria, through the supply authority. The adequacy of the obtained results was determined by comparing experimental values with America Society for Testing and British Standard (BTA4705) pre-requisites. About seventy five percent (75%) of the tested samples failed at least one of the tests, indicating inadequacy in the routine checks. Economic impacts of the obtained results and major causes and prevention of insulation oil degradation were also presented.