Accuracy verification of impulse voltage measuring systems by convolution methods

This paper presents the effect of convexity of lightning impulse voltage waveforms on accuracy of HV measuring systems. The effects of different three convexities on wave front are analyzed by simulation tests with some standard waveforms. The simulation tests have two aspects. First one is consideration in frequency domain by using FFT with standard waveforms and transfer function of measuring system and second one is consideration in time domain by using time convolution method or Duhame's integration method for computing waveform outputs standard testing waveforms and unit step responses of the sample measuring systems. The standard waveforms under investigations are full lightning impulse voltage waveforms, tail-chopped of lightning impulse voltage waveforms, front-chopped of lightning impulse voltage waveforms according to IEC standards 60060-2. This paper considers two samples of different types of the measuring systems. The results show that the convexity has effect on accuracy of measuring systems.

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.

The standard impulse voltage calibrator is the key equipment for impulse voltage traceability, and its accuracy directly affects the measurement accuracy of impulse voltage measurement system. International comparison is best important method to ensure the unification of national quantities. In this paper, the developed standard impulse calibrator is compared with the standard digitizer of the Physikalisch-Technische Bundesanstalt (PTB), The standard calibrator can generate three kinds of full-wave of lightning and full-wave of operation with different time parameters. The measurement error of the output voltage of the calibrator measured by PTB's digitizer is less than (+0.1%) and the measurement error of the time parameter is less than (+0.5%). The digitizer of National Center for High Voltage Measurement (NCHVM) is also calibrated by standard calibrator, and the comparison results are evaluated. From the calculation results, it can be seen that the comparison results are satisfactory, and the measurement level evaluation of the digital recorder of the two laboratories are accurate.

Whereas high resolution digital recorders are used in recording the impulse voltage tests in prominent accreditation laboratories worldwide, a usage of an 8 bit recorder is also allowed by IEC publication. An 8 bit recorder is, due to its nature, known to record a waveform with 0.4% vertical resolution and it has not been appreciated for determining a peak value of lightning impulse in the reference measuring system where the scale factor is often evaluated with 0.1% or less uncertainty. This paper demonstrates simulation in which an 8 bit record with an internal noise is fed into the lightning impulse parameter determination software and the computed parameters were compared with theoretical values. The results show that, if suitable software is used, errors in parameters deduced from an 8 bit record is as small as those derived from a 12 bit record, suggesting an inexpensive 8 bit recorder can replace a 12 bit in impulse voltage measurements.

The goal of this work is to study the transient behavior of the cable against the application of standard and non-standard lightning impulse voltage waveforms. A 66 kV cable model has been developed in MATLAB Simulink and standard and non-standard impulse voltages are applied to it. A preliminary comparative study on the obtained voltages indicated that non-standard impulse voltage waveform developed higher voltage stress in the cable. Simulation results helped to investigate which impulses (standard or non-standard) represent the worst possible voltage stresses on the cables. This study provides the basis for further study of effects of non-standard impulse voltage waveforms and make necessary correction in the existing impulse testing standards.

Transient voltage measurement is not only the design basis of insulation coordination of power equipment, but also related to the safe and stable operation of power grid. The transient voltage waveform in the actual power system is often the superposition of overvoltage and power frequency voltage. In order to measure this kind of superposition waveform, it is necessary to develop the high voltage test equipment which can produce the superposition waveform. Therefore, based on the circuit theory, this paper puts forward a parallel superposition circuit, respectively carries out mathematical analysis and simulation verification of the circuit principle, and determines the specific structure and key parameters of the circuit. On this basis, a set of high-voltage test equipment is set up by designing and purchasing high-voltage components and the overall control system of the equipment. The voltage waveform is observed by using voltage divider and oscilloscope. The test results show that the superposed voltage generator can superpose 500 kV positive or negative impulse voltage at any phase of 120 kV AC voltage.

The author's reply to the discussion on “The influence of irradiation on the measurement of impulse voltages with sphere-gaps”

The field lightning impulse withstand voltage test is an important step to ensure the safe operation of the gas insulated switchgear (GIS). The oscillating lightning impulse voltage is recommended in field test by IEC standard due to its high generating efficiency and lower impulse ratio. The insulation condition of GIS can be evaluated overall by detecting the partial discharge (PD) when conducting the field impulse withstand voltage test. In this paper, the protrusion defect was set in a 330 kV real GIS to study the PD characteristics under lightning impulse voltages, including SLI (standard lightning impulse) voltage and OLI (oscillating lightning impulse) voltages with different oscillating frequencies. The PD under impulse voltages was effectively detected by using the internal UHF sensor. The 50% probability PD inception voltage (PDIV50), maximum discharge amplitude, and discharge number were analyzed based on the measurement results. It was concluded that the PD number is significantly larger and the PDIV50 of OLI voltage is lower when the oscillating frequency is low by comparing the results of oscillating and standard impulse voltage. The PDIV50 increases and discharge number decreases with the increasing of oscillating frequency of the OLI voltage.

Invasive high voltage dividers are usually used for the measurements of high voltage x-ray tube and x-ray generators. Because of the diversity of the pulses it is usually difficult to establish a measurement set up for all the waveforms without determining a test procedure for the calibration and characterization of the measuring system. For example in X-ray diagnostic application, the voltage level is up to 150 kV, the time duration is varying between 50 µs (fast transient over voltages) to several seconds (temporal over voltages), the rise time is varying between 10 µs and 500 µs, the waveforms are usually superposed by DC voltage, spikes and a high frequency ripples up to 200 kHz. To overcome these difficulties, LNE (The National laboratory of Metrology in France) and LCOE (the Designated Institute for High Voltage measurements in Spain) have developed, in the frame of 15NRM02 UHV EMPIR European project, a technical procedure to measure with accuracy this large type of pulses using one reference system. An invasive resistive divider (with bandwidth adapted to the measured waveforms) combined with a storage calibrated digitizer is used as a reference standard for the evaluation of the impulse parameters (PPV, Average peaks value, Rise time, duration of the pulse and the fall time). Firstly, high voltage measurements technics have been used to determine the linearity of the reference system for known, traceable and standardized waveforms. Secondary, to ensure a best accuracy while performing the calibration of pulse parameters, we have decided to use a FFT and inverse FFT based technique (deconvolution technics) before the main calibration to correct the frequency non-linearity of the measuring system. The uncertainties of measurements are 0.4% for Voltage measurements and 2% for time parameters measurements.

The phenomena of Lichtenberg figures has been known and studied for many decades. Photographic recording of the discharge figures has been used for impulse voltage measurement. They are produced by breakdown from a point or cylinder end over the surface of an insulating barrier above a ground plane. The diameter of the discharge pattern, which is recorded on a photographic film under the electrode, is related to the impulse voltage applied. This voltage measuring device has become known as a Klydonograph.

Since their inception [1,2], micro-size light emitting diode (µLED) arrays based on III-nitride semiconductors have emerged as a promising technology for a range of applications, including single-chip high voltage AC-LEDs for solid-state lighting [3], self-emissive microdisplays [1,2,4,5] and light sources for optogenetic neuromodulation [6]. This talk provides an overview on recent progresses on single-chip AC-µLEDs that can be plugged directly into standard high AC voltage power outlets. These single-chip AC-LEDs integrate arrays of μLEDs on-chip for high voltage AC operation. We also discuss the successful integration of III-nitride µLED array with Si CMOS to accomplish a high-resolution solid-state self-emissive microdisplay operating in an active driving scheme. The fabricated blue and green video graphics array (VGA) microdisplays (640 x 480 pixels) have a pixel size of 12 µm, a pitch distance of 15 µm and are capable of delivering real time video graphics images [5]. The luminance level of III-nitride microdisplays is much higher than those of liquid crystal and organic-LED displays. The present study indicates that III-nitride microdisplays are a favorable competing technology for ultra-portable products such as next generation pico-projectors, wearable displays, and head-up displays. Other possible future applications of nitride µLED arrays will also be discussed.

This research reviewed the effect of induction voltage resulting of the electromagnetic induction from the thunderbolt attack to the electronic equipment especially if the induction effect to the component has a high sensitivity rate that was IC CMOS component. In this study the experiments done in the laboratory of High Voltage Technique where the impulse voltage as a simulation to the thunderbolt external voltage surge for the Electronic circuit. Experiment I the distance component of the test article to the test point was 5 cm with the impulse voltage of 99.3 kV, induction voltage 158.41 V, Experiment II with the distance of 7.5 cm, the impulse voltage 88.3 kV so the induction voltage 105.62 V IC, in the experiment III the distance of the test article was 10 cm from the test point. The impulse voltage 88.3 kV and the induction voltage was 79.2 V, In the experiment IV the component distance was 15 cm. the impulse voltage 88.3 kV and the induction voltage as big as 52.74 V.From each experiment IC make damage, where distance component from each experiment settled more distant so component no make damage. From the measurement and calculation yields then the induction voltage resulted will damage the IC component conformed to the yield presented by Hasse in the table 2.1 where the component CMOS 70-100V. Where the study results proved that the electromagnetic induction from indirect thunderbolt attach can result an interference and damage to the electronic component tested, as the distance between the component and the ball gap to the impulse tension was very influential in determining of damaged mechanism of IC in self.

The impact of high velocity air flow on discharge characteristics generated in strongly inhomogeneous electrical fields has been investigated under DC and combined DC + impulse voltages. In the laboratory, a needle plane electrode configuration with a gap distance of 20 cm was exposed to high voltages and a laminar air flow up to 22 m/s. In the first setup, the gap was exposed to a variable DC potential of up to 100 kV in order to create space charges in the vicinity of the electrode. The impact of the air flow on partial discharges and the dynamic behavior of the space charges is evaluated by means of partial discharge measurement and ultraviolet photography. The results show that the air flow increases the frequency of partial discharges in the gap due to an increased rate of space charge removal in the high field area around the tip of the electrode. The partial discharge behavior shows higher dependency on air flow at positive tip polarity as compared to the negative polarity. In the second setup, the standard impulse voltage created by a multistage impulse voltage generator was superimposed to a DC voltage, which continuously created corona and space charges around the tip of the electrode. Breakdown of the gap was triggered by means of the impulse voltage. The DC offset was varied from 0 kV to 100 kV in 20 kV steps and the 50 % flashover voltage was determined for both polarities. The results show that the impact of the air flow is highest at negative DC potential with negative impulse voltage, with an increase in flashover voltage of 40 % when air flow is applied. At positive polarity, the impact of air flow is only observable at 100 kV when the wind extinguishes the stable streamer stem.

Investigations into machining accuracy and quality in wire electrochemical micromachining under sinusoidal and triangular voltage pulse condition

This paper focuses on the electrical tree growth characteristics in epoxy resin with dc-impulse voltage caused by line fault and switching surges in liquid nitrogen (LN2). Electrical tree initiation tests were conducted on molded epoxy resin with a needle–plate system. The test samples were stressed with a dc voltage amplitude of 10 kV and an impulse voltage amplitude of 24 kV at 77 K. With a wide range of voltage frequencies and different impulse polarities, four different waveforms of dc-impulse voltage were used as applied voltage. Result shows that the electrical tree tends to grow longer when the dc and the impulse are of the same polarity. The impulse frequency plays a crucial role in tree initiation and growth process. The tree initiation probability increases with the frequency rising from 50 to 400 Hz in epoxy resin. Different charge transportation processes are discussed based on four different voltage waveforms. The collision ionization and charge recombination have a decisive effect on electrical tree initiation. The impulse voltage is worth regarding in the operation of a superconducting cable system.