Lightning flashover test on pipeline: Effect to conducting material

Mechanical and electrical performance characterization of partial mock-up of the ITER PF6 coil tail

Overload and High Voltage Tests of Witness Samples of 200m HTS Power Cable

The flashover voltage test results under laboratory atmospheric condition of external insulation are usually converted to the standard atmospheric condition by international or national standard. Thus, this thesis presents the study of the conversion of flashover voltage of Pin-post and Line-post insulator under atmospheric conditions in high voltage laboratory to standard atmospheric conditions recommended by international standard: IEC 60060-1:1989/IEEE4:1995, IEEE4 Amendment1 Std4a:2001 and national standard: ANSI C29:1 1988. For the high humidity of Thailand, the studies show that the humidity correction factor recommended by ANSI C29:1 1988 is suitable, while those recommended by IEC 600060-1: 1989 is appropriate only for negative impulse voltage. For positive impulse and AC voltage test according to IEC 60060-1: 1989, a new humidity correction factor is proposed.

Sulfur hexafluoride (SF6) has excellent insulating and arc quenching properties, but it has strong greenhouse effect which is 23900 times of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Nitrogen (N2) is an environmental-friendly gas with good insulation performance and is developed to use in gas insulated equipment in recent years. In this paper, the effect of humidity and purity on N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> insulated switchgear was researched. A 40.5 kV N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> insulated switchgear was taken as the test object. Short-duration power-frequency withstand voltage test and lightning impulse voltage test were carried out under different gas purity and humidity. The test results showed that N2 mixed with 20% O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> can pass both tests. N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> containing 650 ppm, 1200 ppm and 2380 ppm water can pass both tests. While the water content increased to 12700 ppm, the switchgear cannot pass the test. From the aspects of ionization energy and electronegativity, the test results were analyzed. The results can provide guidance and basis for the maintenance and operation of N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> insulated switchgears.

Partial discharge (PD) activities are a major factor in insulation failure, accounting for over 60% of damage to high voltage transformers. Common causes of PD are manufacturing defects, environmental stress, and high-voltage surges. In this study, the effect of PD has been examined on minor and major insulation of a Power Transformer subjected to high voltage surges. The considered test voltages are high voltage operational surges like the Standard Lightning Impulse (SLI), Standard Switching Impulse (SSI), Oscillating Lightning Impulse (OLI), and modified SLI with tail chopped or additional overshoots. The OLI and modified SLI with superimposed oscillations or tail chopped are used to simulate the real-world like stresses on the transformer. To analyze the insulation conditions, the coherence function (CF) of the winding current is calculated at the neutral end of the transformer. CF is a statistical tool that measures the linear relationship between two signals in the frequency domain. The CF values are calculated for the simulated winding current obtained when partial discharges of varying magnitude are present versus when they are absent under different high frequency test voltages. From the results, it is found that when PD occurs across the main insulation, superimposed voltages consistently show the strongest correlation, while SLI with tailchopped voltages show minimum coherence with PD activity. The effect of varying the PD magnitude is negligible for minor insulation. This preliminary simulation study establishes a foundation for future experimental research to study the interaction of PD and test voltages on winding insulation, ultimately aiming to improve transformer performance, safety, and cost-effectiveness.

Very fast transients (VFTs) in a grounding circuit of a 1000 kV class high speed grounding switch (HSGS) were investigated. Referring to the VFT voltage levels estimated by the investigation, the structure of their grounding circuit was designed. The suitability of the design was confirmed by a low voltage test and a high voltage test, which were carried out using the HSGS for a field test.

Electrical test results are reported characterizing the dielectric properties, insulation capability, and equivalent circuit parameters of a 1.8 m OD, 24 turn IR&D dummy coil built by the Westinghouse TPX Team to address magnet coil manufacturing issues and to verify electrical insulation design for TPX PF and TF magnet coils. Induced voltage tests at 77 K were performed at the National High Magnetic Field Laboratory (NHMFL) to 200 V per turn without dielectric failure. High voltage testing was performed at Everson Electric under room temperature factory conditions. The coil turn insulation was surge tested to 21 kV without failure. The coil groundwall insulation was hipot tested up to 58 kV with 48 kV minimum withstand to the imbedded groundplane screen electrode. The coil was sectioned and examined for insulation impregnation quality and manufacturing tolerances.

Currently, the high voltage testing method is widely used to detect pinholes and porosity defects in dielectric coatings. However, most modern coatings also have requirements for the minimum allowable coating thickness. Conducting tolerance tests on the thickness of dielectric coatings concurrently along with monitoring integrity within a single technological process appears promising. Additionally, mitigating the impact of various interfering parameters is crucial. This paper conducts a theoretical and experimental examination of spark formation processes in both gas and dielectrics. This analysis takes place during the identification of both through and non-through defects in dielectric coatings on conductive substrates. The principles of selecting the test voltage for the investigated dielectric coatings, considering the need to detect both through defects and inadmissible thinning, are theoretically and experimentally justified. It is suggested to utilize a probabilistic approach for evaluating the detectability of the mentioned defects. It is demonstrated that, when the dielectric strength of the coating is known, it is feasible to identify both through and non-through defects in coatings with a calculated probability under a specified test voltage. The conditions of occurrence of partial discharges in the process of testing are investigated, and measures to suppress their influence on the inspection results are proposed. The influence of the substrate surface roughness on the magnitude of the breakdown voltage during testing is considered.

This paper presents application of a resonant power frequency converter for high-voltage (HV) and partial discharge (PD) test of a voltage transformer. The rating voltage, power, and frequency of the system are 70 kVrms, 40 kVA, and 200 Hz, respectively. The testing system utilized the converter feeding to an HV testing transformer connected to a conventional partial discharge detection system. The converter system comprising a rectifier and insulated-gate bipolar (IGBT) switches with the H-bridge configuration was applied as a low-voltage source instead of a conventional motor-generator test set which requires large space and high cost. The requirements of the test according to the standards are quality of the test voltage and the background noise level. The required voltage must have the different voltage (DV) and total harmonic distortion (THDv) in the acceptable values of less than 5%. The DV is defined as the difference of the root mean square and peak voltages in percent. The required background noise level must be lower than 2.5 pC. Simulations and experiments were performed for verification of the developed system performance in comparison with those of the previously developed system based on the pulse width modulation converter. It is found that the developed system can provide the testing voltage with the DV and the THDv of lower than 1% and the background noise level of lower than 1 pC. Considering this achievement of promising performance, the developed system is an attractive choice for the HV and PD testing of voltage transformers in real practice.

The paper presents the experimental results on a 15kV composite insulator for outdoor functioning on distribution systems. An Aging study is performed on 15 kV polymeric insulators using a rotating wheel dip test according to the ANSI C29.13-2000 standard for distribution dead-end type polymer insulators. Based on the test analysis, the performance of the aged composite polymer insulators is evaluated and compared with a new composite polymer insulator as reference at macroscopic and microscopic levels. The evaluation of the insulators was done by tracking and erosion test under accelerated aging test conditions. A steep front impulse test and power frequency voltage test is next for analyzing the insulator design technological faults and dielectric strength. The accelerated aging performed on the insulators shows the changing properties of polymer compounds at electrical and chemical levels. The primary aim of the work is to know the interrelation between surface conditions for the tracking, erosion and puncture of the housing and sheds of polymeric insulators.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> With the rapid growth of energy generation by regenerative decentralized sources and the continuous replacement of overhead power lines by subterraneous distribution grids, the amount of power supply cables is increasing. In consequence, a large demand for mobile high-voltage cable test systems is expected within the coming years. This contribution deals with modeling and control design of a novel high-voltage test system based on a zero-voltage switching series-parallel resonant converter and a three-stage Cockcroft–Walton voltage multiplier rectifier, generating a true sinus test voltage of 85 kV (rms) at 0.1 Hz. Due to the inherent high dynamics of the power supply as compared to the slowly varying output test voltage, a cascaded control scheme relying on a fast inner current control loop combined with an outer voltage control is established. In order to derive the relevant waveforms, the complex rectifier was significantly simplified to a one-stage voltage doubler rectifier. By applying a suitable generalized averaging method in combination with an extended describing function, a steady-state solution along with the corresponding small signal model can be established, which is utilized for the current control design. The cascaded control strategy using an observer enables substitution of voluminous and costly high-voltage current sensors. The total high-voltage test system was implemented and validated by experimental tests. </para>

The aim of this paper is to point out the advantages of the use of the time-frequency analysis in the digital processing of waveforms recorded in high voltage impulse tests. Impulse voltage tests are essential to inspect and test insulation integrity of high voltage apparatus. On the other hand, generated impulse currents are used for different test applications such as investigation of high current effects, electromagnetic interference (EMI) testing, etc. Obtained voltage and current waveforms usually have some sort of interferences originated from the different sources. These interferences have to be removed from the original impulse data in order to evaluate the waveform characteristics precisely. When the interference level is high enough, it might not be possible to distinguish signal parameters from the recorded data. Conventional filtering methods cannot be useful for some interference like white noise. In that case, time-frequency filtering methods might be necessary. In this study, the wavelet analysis, which is a powerful time-frequency signal processing tool, is used to recognize the noise of impulse current and voltage data. Thus, the noise sources can be determined by short time Fourier Transform, and a coherence approach is used to determine the bandwidth of noises.

Power transformer is the important equipment in power system, once the occurrence of faults may bring serious harm to power grid, and even cause great losses. This paper proposes a transformer winding insulation defect detection method. The method only uses the impulse voltage test. It can obtain the diagnosis signal source which contains a lot of harmonic. This paper can judge the insulation defects in the location according to compare the extreme value distribution of every winding voltage and currents correlation coefficient .and can determine the coordinate values. The method does not need large or complex additional equipment, can realize the detection and diagnosis of transformer winding insulation defect location. It is image, intuitive, convenient and practical. This paper studies the insulation defects and the severity of transformer winding, puts forward the method for changing winding current and voltage detection winding insulation defects. And it uses a large number of experiments to verify the insulated and reliability of transformer winding according to different position, different types of insulation defects.

Fiber grating sensors have been widely used in industry and has been an important research topic in power systems due to their small size, satisfactory electric shielding ability, and high compatibility with optical fibers. Voltage is a crucial parameter that must be monitored in the power system. Existing PZT-FBG voltage sensors are small, inexpensive, and present acceptable linearity in the range of 50 Hz-20 kHz. However, voltages in power systems cover signals with a frequency from DC to MHz and the existing frequency range is insufficient. Finite element method is adopted to improve frequency characteristics of the PZT-FBG sensor and choose the optimal basic structure by initially calculating resonant frequencies. Structural parameters are then selected via dielectric spectrum analysis. The test platform is established to verify amplitude response, frequency response, three-wave response, temperature characteristics, and impulse voltage response of the frequency-optimized PZT-FBG sensor. Test results showed that the sensor presents satisfactory linearity and the temperature-independent demodulation method improves its stability with temperature changes. Impulse voltage tests indicated that the sensor can respond to impulse waveforms with a wave front time of 250 and 10 μs. Hence, the sensor can respond to a voltage signal of 100 kHz with acceptable consistency. The optimization achieved in this study can provide a reference for further improvement of this sensor and other similar sensors with PZTs.

The philosophy behind the development of Rogowski-type test objects and the aging and test procedures used in the Norwegian Electric Power Research Institute (EFI) test method are presented. Some of the results obtained during almost eight years of the use of this method are briefly reviewed. The great advantage of the method is that a model of a cable insulation system consisting of semiconducting screens and extruded insulating materials can be tested. After production, the test objects are screened in a high-voltage test (50 kV/mm) in order to exclude production errors. After aging, water tree analysis and breakdown tests can be performed on the same test objects. The effect of differing aging conditions and materials on water treeing and breakdown strength can easily be determined. The objects are manufactured from extruded insulation tapes. The EFI test method has been demonstrated to be well correlated with cable test results provided the same batch of materials is used for comparison. >