Study on ultrasonic detection system for defects inside silicone rubber insulation material

In order to solve the problem that it is difficult to detect the local ice layer debonding when the thermal protection system is working, an on-line ultrasonic detection method for the melting degree of interface between skin and ice layer based on the theory of ultrasonic transmission in multi-layer media was studied. A multi-layer medium acoustic model including skin, water film, ice water transition layer, ice layer and air layer is constructed. Ultrasonic pulse waves with different center frequencies are used as excitation sources, and the echo signals of multi-layer medium interface are obtained by using the numerical calculation. The ultrasonic signal processing algorithm for ice melting and debonding measurement is developed. The original echo signal is processed and the characteristic parameters of the echo signal of interface between skin and ice layer are extracted. The ultrasonic reflection coefficient of interface between skin and ice layer is proposed to evaluate the degree of ice melting. The ultrasonic ice detection system was built, and the low-temperature ultrasonic sensor was designed and fabricated. The ability of the system to measure the degree of ice melting under the action of electric heating was verified in the low-temperature environment. The ultrasonic ice detection system was built, and the low-temperature ultrasonic sensor was designed and fabricated. The ability of the system to measure the degree of ice melting under the action of electric heating was verified in the low-temperature environment. The theoretical results show that when the ice on the skin melts and produces a thin water film, the degree of ice melting can be reflected by the change of ultrasonic reflection coefficient at the skin-attachment interface. In this paper, the ultrasonic reflection coefficient more than 0.8 is used as the criterion of ice melting. With the increasing of center frequency of the ultrasonic signal, the thinner water film can be identified. The identification thickness of the water film corresponding to 7.5 MHz center frequency signal is 10 μm. The experimental results show that under the conditions of clear ice, mixed ice and frost ice, the ultrasonic detection system can out-put the ice layer debonding signal at the initial stage of electric heating. The propagation characteristics of ultrasonic pulse wave of interface between skin and ice layer in the thermal protection are preliminarily explored. The present method for detecting the degree of ice melting is expected to further reduce the energy consumption of thermal protection.

Internal defects and uneven density can reduce the mechanical and insulation performance of basin insulators. At present, the defect detection methods for basin insulators have low sensitivity, low resolution, and challenging localization, especially for the cone area that is prone to defects and has a complex structure. This seriously impacts the operating reliability. Therefore, in this article, the ultrasonic longitudinal wave reflection propagation model is established for the cone area of basin insulators. The ultrasonic detection range of the epoxy and conductor interface in the cone is calculated based on the principle of ultrasonic longitudinal wave reflection. An ultrasonic nondestructive detection method for the localization and quantification of defects in the cone is proposed. The defect’s vertical distance from the sloped surface of the cone and its projection area on the sloped surface are studied by detecting the abnormal ultrasonic propagation time and its corresponding position on the sloped surface under the same propagation path. A 126-kV three-phase basin insulator retired due to abnormal partial discharge during operation is subjected to ultrasonic tests using the method proposed in this article and the density uniformity method. The ultrasonic detection for locating and quantifying found that there is a defect in the A-phase cone of the basin insulator. Also, there are no defects in the flat area. The ultrasonic image of the defect in the cone and the ultrasonic clouds of density in the flat area are drawn by Kriging interpolation. It is compared with X-ray imaging and partial discharge tests. The results prove that the ultrasonic detection method proposed in this article can effectively locate and quantify small size and complex shape defects in the cone of three-phase basin insulators. It has a good application prospect in the factory test and fault analysis field test of basin insulators.

Gas-insulated transmission lines are very long with the length over 100 meters for each single chamber and there are no non-metal connection parts between two chambers, which leads to a poor detect effect when using the UHF method. Because of the attenuation of the propagation process, the ultrasonic detection method has many measuring points and a large workload of manual detection. To solve these problems, an automatic detection device and diagnostic location method based on ultrasonic method for the partial discharge of GIL were proposed in this paper. By combining the ultrasonic partial discharge detection device with the inspection robot, the robot performs the partial discharge inspection and transmits the data to the background diagnostic system for analysis. The overall structure of the system, the method of automatic diagnostic and location are introduced. The effectiveness of detection, diagnostic and location of the system is verified by simulation of the discharge signal in the laboratory. The application of the system can avoid the possible limitations of manual inspection in GIL Partial Discharge Ultrasonic testing, improve the work efficiency and guarantee the safe operation of power system.

Most of the existing ultrasonic detection systems for pipeline defects require coupling agent assistance. These systems have problems such as low detection efficiency, poor adaptability to pipe diameter, and limited coverage to pipeline media, making them difficult to apply. In this paper, a new ultrasonic detection system is designed to detect pipeline defects. On the basis of pulse reflection technology, this paper designs a wheel type ultrasonic probe structure. Furthermore, the dry coupling between the ultrasonic transducer and the inner wall of the pipe is realized. The system has the advantages of in-pipe detection, not affected by the pipeline medium, supporting multicaliber pipeline detection, and high detection efficiency. According to the characteristics of the ultrasonic echo signal, the FIR digital filter is designed to process the ultrasonic echo signal. Finally, the feasibility of the method in this paper is verified through experiments.

Partial discharge (PD) detection and measurement is one of the main nondestructive techniques in high voltage cable systems to verify the quality of the manufactured bulk insulation product and to check the integrity of installed cable accessories. To have confidence in the installation and to ensure system reliability, more sensitive on-site testing and on-line pd monitoring is required particularly for transmission class cables. Over the last ten years significant developments have been made and several techniques, including capacitive, dual capacitive, directional coupler, sheath interruption and inductive methods, have been proposed and partially put into practice Due to advances in material processing, manufacturing and factory test procedures, it is unlikely that the cable itself will normally exhibit pd activity. It is the cable accessories (the, joints and terminations) that are the most likely source of PD. Placing a capacitive coupler inside or close to the cable accessory is an attractive PD monitoring option However, a, full understanding of the technique is essential in order to maximise its potential application. This paper reports on some aspects of the theoretical characteristics of the capacitive coupler. Based on an equivalent circuit model, simulations to investigate the influence of different parameters on the performance of the coupler have been undertaken. Experimental results show good agreement with theoretical predictions.

There exists many reasons for the partial discharge in switchgear such as the insulation defect, insulation aging, and bad contact and so on, so the judgment of partial discharge type is important for the evaluation of switchgear operation status. The types and causes of switchgear are analyzed, discuss the advantages and disadvantages of transient earth voltage detection method, ultrasonic detection method and ultra high frequency detection method. The applicability of different detection methods are summarized under the different insulation defects and partial discharge types according to the partial discharge detection data for the heavy duty area and pivotal substation. The location methods are analyzed for partial discharge source. Base on the four typical defects in switchgear, as for the employed detection method, the amplitude, types and reason of partial discharge are discussed. It can provide a practical application basis for condition based maintenance and technical guarantee for tester.

A novel ultrasonic sensor is presented which has the ability to determine the angle of incidence of sound waves by evaluating simultaneously different vibration modes of a single transducer. Since signals from the main lobe and sidelobes are discernible, side reflections can be identified and suppressed. Combining angle and distance measurement allows a detailed characterization of object scenes. The signal evaluation is performed by an adaptive algorithm incorporating Wiener filtering to improve the angular and axial resolution. The principle of the sensor is described and results for different object scenes are presented. Investigations on level measurements in silos proved the practical applicability of the method.

Insulation defects in high-voltage cable accessories easily induce partial discharge and even severe faults under sustained electrical stress, threatening cable line safe operation directly. However, existing defect detection methods are difficult to accurately identify early latent defects and are susceptible to electromagnetic interference. This study aims to clarify the influence law of insulation defects on ultrasonic characteristics, reveal the propagation mechanism of ultrasonic waves in insulating materials with defects, and establish a correlation relationship between ultrasonic characteristics and insulation performance. The research takes XLPE (cross-linked polyethylene), SIR (silicone rubber), and SEMI (semiconductive material) as objects, artificially prepares single-layer (XLPE, SIR) and double-layer composite (XLPE/SIR, XLPE/SEMI, SIR/SEMI) insulation samples with bubble defects. The experimental results show that samples with bubble defects produce obvious defect echoes, with amplitudes of 10% to 20% of the incident wave, and the ultrasonic amplitude attenuation of XLPE is greater than that of SIR. Defects cause the leakage current of insulating materials to increase by 67.22% to 81.49%, and the breakdown strength to decrease by 11.53% to 30.33%, which is closely related to the accumulation of charges at the defect site. The simulation results reveal that the semi-crystalline structure of XLPE enhances ultrasonic absorption attenuation, and the generation of defect echoes is due to the significant difference in acoustic impedance between the defect and the insulating material. The correlation relationship between ultrasonic characteristics and insulation performance in this study provides a theoretical basis for the early identification and state assessment of insulation defects in cable accessories.

An optimization design strategy is developed for ultrasonic transducer (UT) with multimatching layer to improve its performance. The piezoelectric equivalent circuit model is used to determine the optimization interval of matching layer, and the PiezoCAD software is used to simulate the performance of UT with multimatching layer. The neural network (NN) models are trained by the simulation data to characterize the relationship between the thickness of matching layer and performance of UT. Then, the multiobjective optimality criteria for UT is established based on its performance parameters, including center frequency (CF), -6 dB bandwidth (BW) and pulsewidth (PW). The thickness of matching layer is optimized by particle swarm optimization (PSO) algorithm. According to the designed performance, the optimized copper thickness and parylene thickness are about 17.76 and [Formula: see text], respectively. The simulation results of UT with the optimized multimatching layer well agree with the designed targets. Also, CF, -6 dB BW, and PW of the fabricated UT with the optimized multimatching layer are 5.672 MHz, 50.08%, and [Formula: see text], respectively, which nearly achieve the designed performance. In addition, the performance of UT with the optimized multimatching layer is much better than that of UT without matching layer. Moreover, compared with UT with single or double matching layers determined by the quarter wavelength theory, the UT with the optimized multimatching layer has better comprehensive performance. Finally, the fabricated UT with the optimized multimatching layer is used to measure the thickness of testing block, and the relative errors are all less than 1.0%, which implies that the optimized UT has excellent performance.

Inversion layer technique can increase the centre frequency ( f 0 ) and the −6 dB bandwidth of the ultrasound transducer without reducing thickness of active material. However, it suffers from the reduced −6 dB bandwidth when the centre frequency is increased more than 1.5 f 0 . A modified inversion technique is proposed and applied it to high‐frequency intravascular ultrasound (IVUS) transducer. The performance was computationally verified by using finite element method (FEM) simulation. The proposed IVUS transducer consists of two sub‐elements with each aperture size of 0.6 × 0.6 mm, and each sub‐element has different types of inversion layer using PMN‐PT and PZT‐5H. The initial thickness of overall active material was designed for 40 MHz centre frequency and the FEM simulation showed that the centre frequency was increased by about 1.8 f 0 maintaining the −6 dB fractional bandwidth compared with the conventional transducer.

The detection of partial discharge (PD) in transformers is of great significance for preventing insulation defects from developing into insulation failures. Transformer partial discharge detection technology includes pulse current method, radio frequency measurement method, UHF method, ultrasonic detection method, gas chromatography, and optical detection method. Among them, the optical detection method has the characteristics of strong anti-electromagnetic interference ability, and the signal can be transmitted and received without loss. The optical detection method has unique advantages. In this paper, an optical signal measuring device for partial discharge inside the transformer is designed and fabricated, the typical insulation defect inside the transformer is simulated, and the optical signal characteristics of typical partial discharge are obtained. Compared with the pulse current method, it is found that the magnitude of partial discharge can be characterized by the integral of the optical signal. The characteristic of the optical signal phase resolved partial discharge (PRPD) spectrum of typical insulation defects is obtained. The PRPD spectrum of the optical signals of different defects is obviously different. It is feasible to draw the PRPD spectrum and identify the defect types according to the optical signal, which can be further applied to the identification of internal faults in transformers.

Daily monitoring of internal tissues with shape-conformable and breathable ultrasound (US) imaging probes is promising for early detection of diseases. In recent years, textile substrates are widely used for wearable devices since they satisfy both conformability and breathability. However, it is not currently possible to use textile substrates for US probes due to the reflection or attenuation of US waves at the air gaps in the textiles. In this paper, we fabricated a shape-conformable and breathable US imaging probe by sandwiching the US elements between two woven polyester textiles on which copper electrodes were formed through electroless plating. The air gaps between the fibers at the electrode parts were filled with copper, allowing for high penetration of US waves. On the other hand, the non-electrode parts retain air gaps, leading to high breathability. The fabricated textile-based probe showed low flexural rigidity (0.066 × 10−4 N m2 m−1) and high air permeability (11.7 cm3 cm−2 s−1). Human neck imaging demonstrated the ability of the probe to monitor the pulsation of the common carotid artery and change in the internal jugular vein diameter, which led to the early detection of health issues such as arteriosclerosis and dehydration, and the capability of stable 24-hour monitoring.

We present recent progress in our development of fibre-optic sensors for the detection of partial discharge (PD) in silicone cable accessories, based on detecting related low-level optical emission. We experimentally show that the sensitive optical detection of PD can dramatically enhance the performance of conventional electrical PD measurement in electromagnetically noisy environments, and that it can yield high sensitivity and specificity even when no synchronous electrical PD measurement is conducted. This is demonstrated using a real-scale model of a high voltage cable accessory with a surface-attached conventional thermoplastic fluorescent polymer optical fibre (F-POF) sensor. In order to increase light collection efficiency, as a prerequisite for a commercially competitive implementation using cost-efficient detectors, sensing fibres will have to be integrated into the silicone rubber insulation, close to the potential origin of PD-induced damage. This is the rationale for our efforts to develop elastomeric fluorescent sensing fibres, tailored to the requirements of the application. We discuss specific challenges to be tackled and report on the successful implementation of all-silicone rubber fluorescent POF, to our best knowledge for the first time.

The study of production, transfer and accumulation of space charge in silicon rubber (SIR) under direct current (DC) is significant for the research of new high voltage (HV) DC cable accessories and the accessories' stable operation. In this paper, based on SIR materials used for cable accessories and the actual low working stress, the accumulation of space charges in SIR was measured under low DC stresses (6-15kV/mm), different temperatures (room temperature and the 40? temperature difference) and different applied voltage patterns (independent voltage and stepped voltage). The results show that the major polarization type in SIR is the dipole's steering polarization when the voltage is applied. Moreover the higher the applied stress the stronger the dipole's polarization. As a result, the amount of charges near the electrode is reduced. Besides, the form of injection channel under the step voltage indicates the presence of large numbers of deep traps in SIR, the deep traps are easy to trap charges and to form conductive channels. The channels are helpful for migration and dissipation of local injected charges. In addition, Temperature gradient facilitates to enhance charge injection from high temperature electrode, weaken dipole moment and lead to more injected charges in SIR bulk.

At present, the partial discharge(PD) detection of high voltage power capacitor usually employs a resonant circuit which requires a very bulky reactor, and a PD detector with ultrasonic sensors. One of the problems with this approach is difficult experimental setup. Another is the limitation of PD signal analyze and get further valuable information, due to the properties of ultrasonic signal itself. This paper reports on a new user-friendly and effective way to carry out PD test of HV power capacitor. This system contains a supply module, a specially made sampling impedance and a PD pulse collector. The supply module, consists of high voltage DC power generator, protection resistance, damping resistance, semiconductor switch, which is integrated designed, characterized by small size, light weight, and low power consumption. The specially made sampling impedance which is employed to obtain PD signals could be applied to the detection of capacitor samples with different capacity, and the impedance can be directly connected to the end of the capacitor without the influence of large current signal. And the PD pulse collector is different from PD detectors under stable voltage, which needs to grasp the PD signal accurately in several cycles of the test loop oscillation, and the signal acquisition is required to be continuous. Compared with the previous approach, the oscillating wave circuit with specially made impedance reported in this paper, showed much more portability for large power capacitors PD detection, and the results provided chances for time and frequency domain spectrum analysis, which could be helpful to identify the PD type of HV power capacitors.