UHF Sensor Research Articles

Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide

Recently, diagnosis of gas insulated switchgears (GIS) is important because number of aged GIS is increasing and maintenance method of GIS is changing from TBM (Time Based Maintenance) to CBM (Condition Based Maintenance). In this paper, the mechanism of electromagnetic wave propagation in a GIS tank is investigated for understanding of fundamental characteristics for partial discharge detection using UHF method. In this paper, the output characteristics of UHF sensor in non-reflection coaxial waveguide are obtained under the various parameters of installation and shape of UHF sensor. The mechanism of electromagnetic wave propagation is investigated with comparison of the experimental result and EMTP (Electro-Magnetic Transients Program) analysis of equivalent circuit. In consequence, it is found that the mechanism of electromagnetic wave propagation can be treated as an equivalent electric circuit in the frequency region below cutoff frequency of TE11 mode, and another mechanism of electromagnetic wave with higher mode dominantly propagates.

Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide (2) -Output Characteristics of UHF Sensor above Cut-off Frequency-

It is necessary to consider the TEM-mode, the higher TE and TM-mode and resonance phenomena in GIS to describe the propagation and detection characteristics for partial discharge measured with the UHF-method. Measurements on the non-reflection coaxial wave-guide simulating GIS were carried out with changing installation and shape of UHF sensor and wave-guide length. This paper describes the output characteristics of UHF sensor above cut-off frequencies, when reflection and resonance phenomena are taken into account. In the frequency region above the cut-off frequencies of the TE11 mode, the output characteristics of UHF sensor shows resonant by reason of the electromagnetic reflection of TE mode at the both ends of wave-guide. At the resonant frequency, the output characteristics of UHF sensor are different by wave-guide length, shape of sensor and sensor installation, distance from end of tank, angle at circumference. The resonant frequencies are function of tank-length and cut-off frequency of tank, and expressed with equation of cylindrical cavity resonator.

Recognising multiple partial discharge sources in power transformers by wavelet analysis of UHF signals

Partial discharges (PD) in a transformer generate transient UHF signals that resonate within the tank. Where more than one source of PD or interference is present, the ability to separate incoming signals depending on their point of origin would enhance the diagnostic process. A wavelet-based method for recognising UHF signals from PD sources at different positions in the transformer tank, even when the signal is received at only one UHF sensor, is described. Time-frequency characteristics of the UHF PD signals are established using the wavelet transform, providing a means of mapping the energy distribution of the signal. A similarity function is then defined to provide a measure of the similarity between the various wavelet coefficient distributions. The procedure is demonstrated by means of laboratory experiments and application of the technique to data obtained from a transformer in the field.

電力機器におけるセンシング・監視・診断・保守技術の動向

This article deals with trend of sensing, monitoring, diagnostics and maintenance technology in electric power apparatus, especially, gas insulated switchgear (GIS). Partial discharge measurement is one of key technology and the most promising method for developing highly reliable diagnostics for insulation performance of the high voltage apparatus. The review is made by focusing UHF sensors and acoustic method for detecting electromagnetic and ultrasonic waves caused by partial discharges in GIS, respectively.

UHFセンサの周波数応答特性およびGISハンドボール定在波の解明

UHFセンサの周波数応答特性およびGISハンドボール定在波の解明

A pulsed GTEM system for UHF sensor calibration

A system for measuring the sensitivity of electric field sensors at UHF using a novel gigahertz transverse electromagnetic (GTEM) cell is described. The system was developed to enable calibration of UHF couplers that are used to detect insulation defects in gas insulated substations. The frequency response of a sensor is determined using fast Fourier transform (FFT) processing of its output voltage when it is subjected to a step electric field with a rise time of less than 300 ps. Provided the step response of the sensor is relatively short, the absorbing termination of the GTEM cell can be dispensed with, simplifying its construction. The need for impedance matching at the cell input can be eliminated by using a signal source that absorbs the reflected energy. In addition, the use of a wire septum offers the potential for improving field uniformity. A description of the measurement system is given, and some typical results are presented.

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Part 1 Principles and techniques: basic phenomena formulas, definitions, and theorems circuit principles information and communications theory systems engineering reliability of components and systems computer-assisted design standards, units, and symbols. Part 2 Materials and hardware: properties of materials discrete components integrated circuits and microprocessors UHF and microwave devices transducers and sensors microsensors and actuators opto-electronics and lasers. Part 3 Circuits and functions: filters and attenuators amplifiers and oscillators modulators, demodulators and converters power electronics pulsed circuits (logic circuits), waveform generators measurement and control antennas and wave propagation. Part 4 Systems and applications: audio systems video and facsimile systems broadcasting systems telecommunications systems digital computer systems industrial electronics systems electronic navigation and detection systems medical electronics systems resources.