Patrick Schweitzer

Arc Fault Analysis and Localisation by Cross-Correlation in 270 V DC

This article is focused on low-frequency, spectral and correlation analysis to serial arc fault electrical system in order to detect arc fault. This analysis can be used to improve the security of power supplies in the automotive, aerospace and photovoltaic systems. More precisely, we study the influence of arc ignition on the signal characteristics. The experimental test bench is composed by an arc generator, a robotic cylinder and different loads. Three types of arcs ignitions are considered: carbonized path, contact opening and over-voltage. 0.5 kHz - 500 kHz spectrum is measured before and during the start phase of the arc and stabilization. The results show the possibility to determine the cause of the arc fault ignition. The shape of low frequency arc voltage is estimated from the current measurement with a very high fidelity where the load is known. Finally we study the possibility to locate series arcs by analyzing the correlation function of the Radio Frequency (RF) signals from two Rogowski coils inserted at two distinct points of the circuit. The calibration procedure performed reveals a mean velocity in the system of about 24 cm/ns.

Arc Fault Model of Conductance. Application to the UL1699 Tests Modeling

Differents types of arc faults can be responsible for the start of an electrical fire. Depending on the power system and the application (photovoltaic, vehicule, aircraft, residential wiring) the arc fault may involve contact or non-contact arcing with eventually semi-conductive materials in the vicinity. Other characteristics such as the gap distance or the electrode material and geometry may also strongly differ. An electrical model was developed to fit with the arc fault scenarios described in the standard for AFCI UL1699. The contact arcing copper-graphite electrodes produced by the arc generator and the non-contact arcing on carbonized track produced with the arc clearing time tester were observed and their electrical characteristics (restrike and burning voltage, time constant and stability) could be verified thanks to the electrical model with a very good agreement. A qualitative study showing the various parameters used for fitting shows that the model is applicable regardless of the arc ignition principle.

Measurement of liquid density by ultrasound backscattering analysis

The ultrasound pressure backscattered by a wire depends on the density of the liquid in which it is immersed in which ultrasound waves propagate. To express this dependence, the classic resonant scattering theory (RST) is used. This theory shows that the influence of the liquid density on the backscattering ultrasound pressure is weak in absolute value but important in relative value. So, in this paper, we propose a new method of liquid density measurement based on the relation given by the RST in a relative way. The spectrum of the ultrasound pressure backscattered by a wire immersed in a liquid of unknown density is compared to the spectrum obtained from the same wire immersed in a benchmark liquid (water). The comparison of these spectra gives a curve which is a characteristic of the relative density of the test liquid with regard to the benchmark liquid density. Experimentally, a measurement is performed in four stages and needs two different wires. The first wire allows effective measurement, the second wire is used to calibrate the instrumental chain. The four stages consist in acquiring an echo for each wire in each liquid (the benchmark liquid and the test liquid). In this paper, the theory and the methodology of the measurement are developed. Some preliminary experimental results are also presented. These results confirm the theory.

Frequency Analysis to Arcing Detection and Prototyping FPGA Approach

Several authors propose different methods to arc fault detection based on time or frequency characteristics. Among those, some papers present the arcing fault detection using a specific frequency band on the current or voltage. This paper presents an overview of the different frequencies bands proposed by the authors that allow the detection of an arcing fault. To compare these proposed methods, we make a frequency analysis to obtain the frequencies characteristics of arcing fault for different loads signatures (resistive, inductive and nonlinear load). The method we have developed for arcing detection are based on five criterions: Analysis of the current low frequency, the voltage high frequency, the 5th harmonic current and current and voltage magnitude variations. Hardware in the loop approach allows us to test the methods of detection. Finally, our architecture of arcing detection is implemented on Field Program Gate Array (FPGA) prototyping board.

Ultrasonic scattering technique for target size measurement

We present in this paper a new ultrasonic method for sizing immersed wires (or more generally any kind of target shape). By extracting the first part of its backscattered echo, which gives what we call the quasi-rigid backscattered echo (QRBE), the size of a wire can be found by comparing its QRBE spectrum with the quasi-rigid form function (QRFF). The principal advantage of the QRFF in comparison with the form function is to be almost insensitive to the targets acoustical properties. After some theoretical aspects, we present step by step our sizing method using ultrasonic scattering. Some experimental results of wire sizing are presented.

Modeling of an ultrasonic auto-controlled frequency generator in VHDL-AMS language

In this paper, we present the structure of digital generator feedback which is controlled for the optimal excitation of ultrasonic high efficiency narrow band transducers. In the first phase, simulations allow various excitation signal forms to be compared in terms of efficiency. A burst of sine waves has been selected because there is no excitation of the transducers harmonic and anharmonic resonances. In order to exploit this type of excitation without knowing the central frequency of the transducer, we propose that the generators architecture includes an automatic search of the antiresonance frequency of a piezoelectric ceramic. Our strategy is based on studying the electric voltage at the transducers output, and the iterative algorithm we have developed looks for the maximum value of this voltage which is validated by a modeling in VHDL-AMS language (IEEE standard 1073–1993), including the transducer. We present the results of modeling in terms of the time setting and the frequential precision obtained with two different piezoelectric ceramics.

Method to Design Arc Fault Detection Algorithm Using FPGA

Abstract-The object of this paper is to present a method to design and to improve arc fault detection algorithm using FPGA devices. When designing an arc fault detection prototype, criteria such as detection reliability, detection speed and silicon occupation must be extracted to compare detection algorithm performances. We have developed a device which can execute and test the performances of algorithms with differents kind of power sources (AC and DC for domestic and aeronautic applications) and any loads. This prototype includes an analog part to carry out line voltage and current measurements (up to 270 V, up to 50 A, up to 1.5 MSPS). The digital part is built with an Altera Cyclone III FPGA circuit. An interface is added to control a contactor which protects the electric line. Algorithm implementation is carry out with VHDL We describe the algorithms in VHDL. The board architecture is characterized by low power consumption, high fonctionality and fast prototyping. Our prototype gives an effective and inexpensive means to design arc fault detection algorithms.

The temperature influence on the piezoelectric transducer noise, measurements and modeling

In many case, the SNR limit the performance of a transducer. The understanding of the nature and the behavior of the noise allow to increase this SNR. First, we present the noise and impedance real part measurement results in air and in water. We show the link between them. The second part is a temperature study which confirms this influence. We show the little evolution of the total output noise in a conditioning chain. Finally, we use a derivate of Redwood electro-acoustical model to estimate the noise. The measurement results agreed with this one.

Repeatable and calibrated arc fault generator

This article describes the design and use of a repeatable and calibrated arc fault generator. We have developed a test bench which can generate AC and DC currents and series and parallel arc faults on variable loads and have chosen a method which consists in producing an overvoltage in arc initiation, obtained with a step-up transformer; a line generator (AC or DC) then sustains the arc. We show the initial measurement results relating to arc current/voltage characteristics for all possible scenarios, thus enabling us to extract those indicators which are useful for fault detection (such as, for example, arc time constant). This device can also be used to test the arc fault detectors.

Wavelet-based estimator versus spectral correlation method for acoustic target sizing

This paper presents two different methods for estimating the diameter of an immersed wire insonified by an ultrasonic plane wave. The first part of the backscattered echo, called the quasi-rigid backscattered echo (QRBE), and the quasi-rigid form function (QRFF) are described first. It is shown that the QRBE contains the size information (diameter) of the target. In the first method, this size is obtained by associating a pattern recognition procedure with a spectral correlation. The second method is based on a continuous wavelet analysis of the QRBE at a particular scale with a judiciously selected wavelet. After a brief description of the wavelet tool, we present in detail the wavelet-based approach for target sizing. Results thus obtained are compared with experimental measurements using copper and steel wires. They show that for the largest diameters, the results are similar. On the other hand, the more the diameter decreases, the more the wavelet-based estimator is distinguished by giving a better relative precision. In terms of the cost of calculation, the second method is better since it requires only one wavelet transform at only one single scale against a Fourier transform and an iterative correlation procedure, necessary in the first technique.