Ultra High Frequency Technique Research Articles

Design of a Pediatric Rectal Ultrasound Probe Intended for Ultra-High Frequency Ultrasound Diagnostics.

It has been shown that ultra-high frequency (UHF) ultrasound applied to the external bowel wall can delineate the histo-anatomic layers in detail and distinguish normal bowel from aganglionosis. This would potentially reduce or lessen the need for biopsies that are currently mandatory for the diagnosis of Hirschsprung's disease. However, to our knowledge, no suitable rectal probes for such a use are on the market. The aim was to define the specifications of an UHF transrectal ultrasound probe (50 MHz center frequency) suitable for use in infants. Probe requirements according to patient anatomy, clinicians' requests, and biomedical engineering UHF prerequisites were collected within an expert group. Suitable probes on the market and in clinical use were reviewed. The requirements were transferred into the sketching of potential UHF ultrasound transrectal probes followed by their 3D prototype printing. Two prototypes were created and tested by five pediatric surgeons. The larger and straight 8 mm head and shaft probe was preferred as it facilitated stability, ease of anal insertion, and possible UHF technique including 128 piezoelectric elements in a linear array. We hereby present the procedure and considerations behind the development of a proposed new UHF transrectal pediatric probe. Such a device can open new possibilities for the diagnostics of pediatric anorectal conditions.

Study of Ultra High Frequency Measurement Techniques for Online Monitoring of Partial Discharges in High Voltage Systems

Partial Discharge (PD) activity is a pre-cursor for insulation degradation which may eventually lead to catastrophic failure of the electrical equipment with severe social and economic consequences. It is therefore imperative that PD is detected at its early stages to permit repair or replacement, prior to total failure. The bulky non-planar construction of existing ultra-high frequency (UHF) sensors coupled with the lack of proper feeding techniques and the ultrawide signal bandwidth of PD signals which necessitates the use of digital storage oscilloscope have restricted field deployment of UHF technique for online PD detection. In this work, we present a compact ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.58 \boldsymbol {\lambda } $ </tex-math></inline-formula> ) wideband (0.5-3 GHz) dual arm Archimedean slot spiral with coplanar waveguide feed for PD detection, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda } $ </tex-math></inline-formula> is the wavelength at center frequency. Numerical simulations of the antenna were compared with the measurements of the fabricated antenna. The fabricated wideband antenna was used to detect PD emissions from a mineral oil test cell connected to 10 kVA 50 Hz transformer. We also present different UHF signal measurement techniques ranging from PD pulse detection to reconstruction of the bandlimited PD signal in the digital domain for online structural health monitoring of high voltage systems. The proposed UHF PD measurement techniques are low cost compared to the conventional approach and indicate the feasibility of an embedded system for online PD monitoring using the fabricated UHF sensor.

Diagnosing Technosphere Pollution to Form Environmental Policy

All The technosphere pollution with various substances has been analyzed considering their impact on human health, depending on the hazard degree. The most frequently occurring in nature hazardous substances have been classified by the degree and class of hazard. The impact of exhaust gases emitted by the recently growing motor vehicle fleet on human health is shown. A new ultrahigh-frequency technique is proposed to monitor the concentration of exhaust gases emitted by vehicles into the atmosphere. Measures are specified that allow reducing the environmental footprint by pursuing a sound environmental policy and introducing innovative technologies.

Combined application of ultrasonic and ultra high frequency techniques in the partial discharge detection and positioning of gas insulated switchgear

Partial discharge live detection of GIS can effectively find internal defects, but it is often interfered by surrounding environmental noise, which affects the correct identification and judgment of defect signals. This paper introduces the application of AE and UHF technique in the live detection of GIS, which successfully recognizes the external interference signal, analyzes the cause of abnormal partial discharge signal based on signal characteristics, and uses the method by calculating time difference to locate the source of the signal. An internal checking on the equipment were conducted based on the test results while the equipment were stopped, and verified the existence of floating fault inside GIS.

Investigation on electrical, thermal and mechanical properties of thermally aged pressboard impregnated with mixed mineral oil and synthetic ester fluid

The proposed study compares the electrical, thermal and mechanical performances of thermally aged cellulose pressboard material impregnated in mineral oil, synthetic ester fluid and mixed oil. The electrical insulation characteristics of oil-impregnated pressboard (OIP) are studied by means of surface discharge inception voltage (SDIV) using an ultra-high frequency technique and surface potential measurement analysis. It indicates that OIP aged in mineral oil has higher surface potential due to higher charge trap density compared to that of the mixed oil and synthetic ester fluid. Mechanical and thermal characteristics of the aged OIP are studied by means of tensile strength measurement and thermo-gravimetric analysis, respectively. The change in the chemical composition of OIP is studied by means of laser-induced breakdown spectroscopy, which indicates lower plasma temperature with mineral oil-based OIP indicating higher degradation state. To further understand the microscopic structure of the thermally aged OIP in different oils, scanning electron microscopy and X-ray diffraction studies have been performed. The pressboard thermally aged in synthetic ester fluid and the mixed oil has better electrical, thermal and mechanical properties as compared with the pressboard aged in mineral oil.

Fluorescence Fiber Based Identification of Partial Discharges in Liquid Nitrogen for High-Temperature Superconducting Power Apparatus

Partial discharge (PD) in liquid nitrogen (LN2) insulation is a key issue in cryogenic or high-temperature superconducting power apparatus. In this letter, we experimentally demonstrate PD identification in LN2 using a fluorescent optical fiber sensor and compare its sensitivity to the conventional ultrahigh frequency (UHF) technique. The Corona inception voltage (CIV) in LN2 is studied under fundamental ac and harmonic ac voltages with different values of total harmonic distortion (THD). It is observed that CIV reduces with the increase in harmonic voltage with higher THD. Phase resolved partial discharge pattern, peak-to-peak voltage, and the energy content due to corona discharges measured by both fluorescence-based and UHF techniques follows the same trend, indicating the viability of the new technique.

On the Electromagnetic Wave Behavior Due to Partial Discharge in Gas Insulated Switchgears: State-of-Art Review

The rapid growth of gas insulated switchgears as a compact, efficient, and reliable device has recently been given great attention. Albeit gas insulated switchgears can seldom suffer from failure due to the high resiliency and robustness, some severe damages have been experienced by such devices particularly in the event of partial discharge. Thus, monitoring such accidents has become a vital part of power systems reliability. The ultra-high frequency techniques have recently shown superior performance in the detection and classification of electromagnetic waves produced by partial discharge. This is mainly due to the great immunity to the noise of the ultra-high frequency detection techniques compared with the very-high-frequency counterparts. This review paper highlights the mathematical aspects of the electromagnetic waves generated by partial discharge. It also delivers an overview of the electromagnetic wave behavior in the complex structure of gas insulated switchgears, and outlines the important characteristics of the internal and external partial discharge detection using ultra-high frequency methods.

Field Applications of Ultra High Frequency Techniques for Defect Detection in GIS

The reliable and stable operation of power apparatus is important for the development of GIS. It is important to utilize condition monitoring technologies and anticipate possible failures in advance. Many papers have been published about the partial discharge detection with UHF or X-ray in laboratory, but seldom in field application. Thus, many engineers at project sites are not familiar with the current professional diagnosis techniques. Recently, during the GIS routine data analysis obtained by partial discharge online monitoring system, it was found that the UHF monitoring signals’ developing trend of the 220 kV GIS No. 2 high-voltage side of transformer in phase C at an actual station was abnormal and needed further detection. In order to precisely investigate the problem and then guide the operation and maintenance activities, a series of professional diagnoses were conducted. Three new types of partial discharge detection and positioning methods were applied for accuracy, including UHF partial discharge detection based on multi-stage amplified signal demodulation and multiple weighted averages processing; the partial discharge detection based on the signal radiation hole of insulation disk at the ground connection; and the positioning method based on UHF-SHF. After a series of troubleshooting works, the partial discharge defects have been diagnosed, and the case can be referred in the field monitoring of GIS.

Experimental Investigation on Propagation Characteristics of PD Radiated UHF Signal in Actual 252 kV GIS

For partial discharge (PD) diagnostics in gas insulated switchgears (GISs) based on the ultra-high-frequency (UHF) method, it is essential to study the attenuation characteristics of UHF signals so as to improve the application of the UHF technique. Currently, the performance of UHF has not been adequately considered in most experimental research, while the constructive conclusions about the installation and position of UHF sensors are relatively rare. In this research, by using a previously-designed broadband sensor, the output signal is detected and analyzed experimentally in a 252 kV GIS with L-shaped structure and disconnecting switch. Since the relative position of the sensor and the defect is usually fixed by prior research, three circumferential angle positions of the defect in cross section are performed. The results are studied by time, statistics and frequency analyses. This identifies that the discontinuity conductor of DS will lead to a rise of both the peak to peak value (Vpp) and the transmission rate of the UHF signal. Then, the frequency analysis indicates that the reason for the distinction of signal amplitude and transmission rate is that the mode components of the PD signal are distinctively affected by the special structure of GIS. Finally, the optimal circumferential angle position of the UHF Sensor is given based on the comparison of transmission rates.

Characterization of UHF PD sensors for power transformers using an oil-filled GTEM cell

Common reasons for local failures in power transformers are partial discharges (PD) in the electric insulation. The ultra-high frequency (UHF) PD measurement method gained in importance for transformer diagnosis and monitoring within the last years. Due to its robustness against external noise, it is suitable for both, factory acceptance tests (FAT) and site acceptance tests (SAT). For the application at acceptance tests, it is necessary that the UHF technique is a reliable testing method and also comparable between different UHF measurement systems. Therefore, the UHF sensor's characteristic has to be included in a calibration procedure by using its antenna factor (AF). This contribution implements a custom-built oil-filled Gigahertz-Transversal-Electromagnetic cell (GTEM cell) for the AF evaluation. In the first part, the GTEM cell's design and dimensioning are illustrated and the cell is evaluated in terms of its high frequency behavior. The second part determines the AF of two different UHF sensor types: UHF Drain Valve Sensors and UHF Plate Sensors using the GTEM cell. Additionally, the influences of insertion depths and standardized gate valves on the Drain Valve Sensor's AF are taken into account.

Study on the Application of an Ultra-High-Frequency Fractal Antenna to Partial Discharge Detection in Switchgears

The ultra-high-frequency (UHF) method is used to analyze the insulation condition of electric equipment by detecting the UHF electromagnetic (EM) waves excited by partial discharge (PD). As part of the UHF detection system, the UHF sensor determines the detection system performance in signal extraction and recognition. In this paper, a UHF antenna sensor with the fractal structure for PD detection in switchgears was designed by means of modeling, simulation and optimization. This sensor, with a flat-plate structure, had two resonance frequencies of 583 MHz and 732 MHz. In the laboratory, four kinds of insulation defect models were positioned in the testing switchgear for typical PD tests. The results show that the sensor could reproduce the electromagnetic waves well. Furthermore, to optimize the installation position of the inner sensor for achieving best detection performance, the precise simulation model of switchgear was developed to study the propagation characteristics of UHF signals in switchgear by finite-difference time-domain (FDTD) method. According to the results of simulation and verification test, the sensor should be positioned at the right side of bottom plate in the front cabinet. This research established the foundation for the further study on the application of UHF technique in switchgear PD online detection.

A generic knowledge-based approach to the analysis of partial discharge data

Partial Discharge (PD) diagnosis is a recognized technique to detect defects within high voltage insulation in power system equipment. A variety of methods exist to capture the signals that are emitted during PD, and this paper focuses on the ultra high frequency (UHF) and IEC 60270 techniques. Phase-resolved patterns can be constructed from the PD data captured using either of these techniques and due to the individual signatures that different defects generate, experts can examine the phase-resolved pattern to classify the defect that created it. In recent years, knowledge regarding PD phenomena and phase-resolved patterns has increased, providing an opportunity to employ a knowledge-based system (KBS) to automate defect classification. Due to the consistent physical nature of PD across different high voltage apparatus and the ability to construct phase-resolved patterns from various sensors, the KBS offers a generic approach to the analysis of PD by taking the phase-resolved pattern as its input and identifying the physical PD processes associate with the pattern. This paper describes the advances of this KBS, highlighting its generic application through the use of several case studies, which present the diagnosis of defects captured through both the IEC 60270 and UHF techniques. This paper also demonstrates, in one of the case studies, how a limitation of previous pattern recognition techniques can be overcome by mimicking the approach of a PD expert when the pulses occur over the zero crossings of the voltage waveform of the phase-resolved pattern.

Understanding the partial discharge activity of conducting particles in GIS under DC voltages using the UHF technique

AbstractThe major cause of failure of DC‐GIS is due to presence of foreign particles causing partial discharges in the insulation structure. The particle movement in gas insulated system (GIS) radiates electromagnetic waves and the bandwidth of the signal lies in the range 1–2 GHz. Increase in applied DC voltage/pressure has not altered the frequency content of the ultra high frequency (UHF) signal generated due to partial discharge formed by particle movement. The UHF sensor could recognize the breakdown of sulfur‐hexa‐fluoride (SF6) gas under DC and Lightning impulse voltages and the frequency content of the signal captured by the UHF sensor lies up to 500 MHz. Mounting UHF sensor in GIS could allow one to classify internal partial discharges from breakdown, at the time of testing/during operation. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Partial discharge measurement in the ultra high frequency (UHF) range

The paper provides essentially a summary of PD measurements applying the UHF range in order to increase the detection threshold, to improve the localization accuracy and to perform on-line measurements of Partial Discharge (PD) in noisy environments. The electromagnetic UHF technique offers good signal to noise ratios, because external PD signals and disturbances can be shielded effectively. A new developed method allows the localization of PD in gas-insulated substations (GIS) by frequency domain measurements. The basic idea is the displacement law of Fourier transformation. The interference phenomena of superposed signals from two sensors give information about the time delay of the sensor signals. On-site PD measurements are made at cable connectors by means of monopole antennas housed in a barrel sleave, while the cable is in service. Thus a sensitive PD measurement even in noisy environment is possible. PD measurements on several 72 kV cable connectors were performed in an unshielded laboratory. On-site measurements during operation showed the great potential for condition assessment. For decoupling sensitive UHF PD signals from the inner of a power transformer tank UHF sensors applied through drain/oil valves are used. Experimental studies indicate that all relevant types of PD possibly occurring within a transformer emit high frequency spectra to be detected with UHF sensors. Furthermore in laboratory experiments and on-site measurements very moderate UHF signal attenuations have been observed.

UHF technique for identification of discharges initiated by liquid droplet in epoxy nanocomposite insulation material under ac voltages

In this work, an attempt has been made to understand the feasibility of using a ultrahigh frequency (UHF) technique for identification of any corona discharge/ arcing in insulating material due to water droplets. The sensors of broadband type are useful for the identification of such discharges. It is realized that corona discharges/arcing initiated by liquid droplet radiates UHF signals in the entire bandwidth up to 2 GHz. The frequency content of the UHF signal generated due to corona/arcing is not much varied in epoxy nanocomposites with different weight percentage of clay content. The exfoliated/intercalated properties were analysed through TEM studies. It is realized that corona initiated discharges are of intermittent process. It is observed that the permittivity and tan(δ) reduces with increase in percentage of clay in epoxy nanocomposite material up to 3 wt%. The hydrophobicity of the material is characterized through contact angle measurement. It is realized that low weight percentage of nanoclay content in epoxy resin reduces the surface carbonization due to arcing.

Using the UHF technique to investigate PD produced by defects in solid insulation

The partial discharges produced by internal defects in solid insulation have been investigated using the ultra high frequency (UHF) technique. The work has shown that the discharges produced by a virgin cavity generate a UHF signal that may be detected using this UHF technique. The discharges are observed as a series of UHF pulses that occur less frequently as time progresses. The reduction in the number of UHF pulses has been attributed to a progressive change from the streamer discharge mechanism, that is observed with a virgin cavity, to the Townsend mechanism, which occurs when the cavity has been exposed to prolonged discharge activity. It also has been shown that the discharges associated with tree formation generate a detectable UHF signal. The paper describes a method of distinguishing between the streamer discharges and the discharges that cause treeing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

UHF detection of leader discharges in SF/sub 6/

The ultra-high frequency (UHF) technique of partial discharge detection has been used to study the partial discharges produced by electrode protrusions and surface contamination in a gas insulated substation (GIS). The paper describes the stages of discharge development from inception to breakdown. The work has shown that the UHF technique may be used to identify distinct phases of discharge activity corresponding to discharge inception and a prebreakdown condition. The prebreakdown activity is detected as an increase in the UHF signal magnitude which has been attributed to the formation of leader-type discharges. These discharges form an essential part of the breakdown process, and their detection can be used to identify when the system is close to breakdown. The paper describes a filtering technique that may be employed to optimize the sensitivity of UHF leader detection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Assessing the risk of failure due to particle contamination of GIS using the UHF technique

The ultra high frequency (UHF) technique has been used to study the partial discharges produced by free conducting particles in gas insulated substations (GIS) with a view to predicting the probability of particle-triggered breakdown. Statistical techniques have been developed to describe the motion of a single particle. It is possible to identify whether the particle is capable of crossing to the busbar, which is a necessary condition for particle-triggered breakdown. In addition, the technique can be used to assess the size of the particle, which is useful for making a qualitative assessment of the breakdown risk. The implications for the continuous discharge monitoring of GIS are discussed. >

Radar techniques in an industrial control

The elementary electronics circuits familiar to radar men are not limited to one field, as is shown by this description of a typical industrial electronics application. Ultrahigh frequency techniques are described as used for register control in the printing and paper industries.

Radar Technique in an Industrial Control

The elementary electronics circuits familiar to radar men are not limited to one field, as is shown by this description of a typical industrial electronics application. Ultrahigh frequency techniques are described as used for register control in the printing and paper industries.