Cable Test Research Articles

An improved local maximum synchrosqueezing transform with adaptive window width for instantaneous frequency identification of time-varying structures

Civil engineering structures usually exhibit time-varying characteristics under operational conditions due to changes in environment and loads. The identification of instantaneous frequencies (IFs) from measured responses of time-varying structures is a challenge when using the local maximum synchrosqueezing transform (LMSST) due to the difficulty in selecting the appropriate window width. In this study, an improved LMSST with adaptive window width (ALMSST) is proposed to circumvent the limitations of LMSST. The window width of ALMSST can be adaptively determined by combining the autoregressive power spectrum-based variational modal decomposition (AR-VMD) and a window width optimization algorithm. The AR-VMD is used to decompose the multi-component signal into mono-component signals. The Rényi entropy is adopted as an evaluation index in the window width optimization algorithm for selecting the optimal window width for each mono-component signal. Therefore, ALMSST can provide a highly concentrated time–frequency (TF) representation for all mono-component signals. Two simulated signals demonstrate that the ALMSST improves the accuracy of identified IFs compared with LMSST. Numerical simulation of a three-story shear building model with time-varying stiffness shows that ALMSST can accurately identify the IFs of time-varying structures under heavy noise. A cable test with linear and sinusoidal varying tension forces and a vehicle-bridge interaction (VBI) model system with different vehicle weights are investigated to verify the applicability of ALMSST to track the IFs of time-varying structures. Numerical simulation and experimental results illustrate that ALMSST performs well in identifying the IFs of time-varying structures.

Cable vibration measurement based on broad-band phase-based motion magnification and line tracking algorithm

Cables are important components of cable-supported bridges and the measurement of cable vibration is very useful for the condition assessment of bridges. The recently developed computer vision (CV) based vibration measurement method has many merits over the traditional contact method. However, most existing CV-based methods require installing the artificial targets on the structure and are only suitable for situations with large vibration amplitude. Therefore, this study proposes a method based on the broad-band phase-based video motion magnification (BPVMM) and the line tracking algorithms for the vibration measurement of cables with small-amplitude vibration. The BPVMM algorithm is used to magnify the small vibrations and the line tracking algorithm is used to extract the vibration displacement from the magnified video for the final identification of cable frequencies. The proposed method is then verified by the laboratory cable test and the field test of a cable-stayed bridge. The results indicate that using the BPVMM algorithm to magnify the small vibration can significantly improve the identification accuracy of displacements and frequencies. The proposed method performs motion magnification over a wide frequency band including all the frequencies of interest, without prior knowledge of the structure frequencies, which greatly improves the computational efficiency and facilitate the measurement of cable vibration under environmental excitation in practical applications.

Common OECD/NEA FIRE and PRISME Cable Benchmark Exercise

This paper deals with the common OECD/NEA FIRE and PRISME Cable Benchmark Exercise conducted for a realistic cable fire scenario in an electrical system of a nuclear power plant. The major goal was to simulate a real cable fire event in order to assess the behaviour of fire models for a complex and real fire scenario with the current state of knowledge. Since a numerical Benchmark Exercise on a real fire event is quite challenging, a three-step methodology was adopted: (1) a calibration phase of the cable fire models, (2) a blind simulation of a cable fire test, and (3) the real cable fire event simulation. The selected fire event from the FIRE Database occurred in 2014 in a heater bay of a nuclear power plant. Thirteen institutions from nine NEA member countries participated in this Benchmark Exercise. Simulations were performed using computational fluid dynamics codes, a lumped parameter code, and zone codes. The simulations have provided a wide range of results which reflect the difficulty for fire simulation codes to correctly predict the development of the fire heat release rate over time of a cable tray fire, even under simple, open atmosphere conditions.

Model test of negative Poisson's ratio cable for supporting super-large-span tunnel using excavation compensation method

Model test of negative Poisson's ratio cable for supporting super-large-span tunnel using excavation compensation method

Partial Discharge Measurement of GIS With Damped AC (DAC) Voltage: Case Study for the Particle on Insulator

Off-line PD measurement is important for GIS. Interference signal generated by frequency-tuned resonant test set has a huge impact on PD measurement. Damped alternating current (DAC) voltage has been widely used in field testing of power cable and has no power interference. Whether the DAC can be used for PD testing of GIS still needs to be studied. The particle on insulator can greatly reduce the dielectric strength compared to clean condition, which is a very destructive defect. In this paper, the PDIV of AC and DAC were measured, the number of discharges per cycle was counted, and the PRPD pattern was obtained. For the defect model we set up, test results show that PDIV is independent of waveform and frequency; PD distribution area and the number of PDs per cycle increase with frequency. This is because SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gap needs to recover its dielectric strength after discharge. When the recovery time and discharge interval are on the same order, it's possible to excite PD at a lower voltage, thereby increasing the number of PDs in each cycle. DAC is effective for detecting the defect of particle on insulator in GIS, and the PD activity of DAC is more obvious.

Development of an Instantaneous Loading Impact Test System for Containment of a Nuclear Power Plant during Aircraft Impact on Steel Bar Joints.

As major projects such as nuclear power plants continuously increase, it is inevitable that loopholes will arise in safety precautions. Airplane anchoring structures, comprising steel joints and acting as a key component of such a major project, directly affect the safety of the project due to their resistance to the instant impact of an airplane. Existing impact testing machines have the limitations of being unable to balance impact velocity and impact force, as well as having inadequate control of impact velocity; they cannot meet the requirements of impact testing for steel mechanical connections in nuclear power plants. This paper discusses the hydraulic-based principle of the impact test system, adopts the hydraulic control mode, and uses the accumulator as the power source to develop an instant loading test system suitable for the entire series of steel joints and small-scale cable impact tests. The system is equipped with a 2000 kN static-pressure-supported high-speed servo linear actuator, a 2 × 22 kW oil pump motor group, a 2.2 kW high-pressure oil pump motor group, and a 9000 L/min nitrogen-charging accumulator group, which can test the impact of large-tonnage instant tensile loading. The maximum impact force of the system is 2000 kN, and the maximum impact rate is 1.5 m/s. Through the impact testing of mechanical connecting components using the developed impact test system, it was found that the strain rate of the specimen before failure was not less than 1 s-1, meeting the requirements of the technical specifications for nuclear power plants. By adjusting the working pressure of the accumulator group, the impact rate could be controlled effectively, thus providing a strong experimental platform for research in the field of engineering for preventing emergencies.

An Analytical Approach to Locate Short Circuit Fault in a Cable Using Sweep Frequency Response Analysis

In this paper, analytical methods are proposed for the location of a short circuit fault in a power cable using sweep frequency response analysis (SFRA). The impedance spectroscopy is estimated using classical transmission line (TL) theory whereas the driving point impedance function (DPIF) of the cable is proposed to be constructed either by using experimental SFRA data or analytically from the knowledge of the frequency-dependent parameters, material properties, and dimensions of the cable. Finally, an analytical formula is proposed for the estimation of the location of a short-circuit fault using the location of poles and zeros of the impedance function before and after the fault. The formulae are validated using FEM software simulations as well as experimentally on a test cable.

Target-free recognition of cable vibration in complex backgrounds based on computer vision

The cable system is a critical load-bearing member and a vital factor of cable-stayed bridges; its health condition indicates the operation safety of these structures. The cable force estimation based on vibration is a major indicator for assessing the safety of cable-bearing bridges. Contact sensors are used to collect vibration in traditional cable systems. Recently, computer vision-based non-contact remote monitoring has gained popularity due to its cost, efficiency, and safety advantages. However, the cable is a unique structure with poor vision imaging, a low pixel share, and susceptibility to ambient interference. To address these issues, this study proposes a deep learning-based cable vibration recognition system. In complex environments, this system provides reliable recognition of cable vibration without the necessity of markers. The system consists of a composite model based on Resnet-34 (Residual Neural Network of 34 layers) and Swin-B (the base model in Swin Transformer), a linear rigid body motion recognizer based on Hough linear detection, and data processing. The pre-trained composite model performs cable segmentation on the video captured by the camera; this new video contains only cable data and is then transmitted to the linear rigid body recognizer, which recognizes cable vibration in the new video, and the cable force is determined by processing vibration data. As a result of the model experiments conducted in the laboratory and the cable test of cable-stayed bridges under complex outdoor conditions, the effectiveness and robustness of the system have been verified. The error of the proposed method in this study is found to be less than 2.0% comparing the results with that calculated from conventional sensors employed in the tests. The test results indicate that the system proposed in this paper is capable of conducting cable detection in complex environments.

Floating photovoltaic systems: photovoltaic cable submersion testing and potential impacts

Background: Floating photovoltaics (FPV) is an emerging technology that is gaining attention worldwide. However, little information is still available on its possible impacts in the aquatic ecosystems, as well as on the durability of its components. Therefore, this work intends to provide a contribution to this field, analysing possible obstacles that can compromise the performance of this technology, adding to an increase of its reliability and assessing possible impacts. The problem under study is related to the potential submersion of photovoltaic cables, that can lead to a degradation of its electrical insulation capabilities and, consequently, higher energy production losses and water contamination. Methods: In the present study, the submersion of photovoltaic cables (with two different insulation materials) in freshwater and artificial seawater was tested, in order to replicate real life conditions, when FPV systems are located in reservoirs or in the marine environment. Electrical insulation tests were carried out weekly to assess possible cable degradation, the physical-chemical characteristics of the water were also periodically monitored, complemented by analysis to detect traces of copper and microplastics in the water. Results: The results showed that the submersion of photovoltaic cables with rubber sheath in saltwater can lead to a cable accelerated degradation, with reduction of its electrical insulation and, consequently, copper release into the aquatic environment. Conclusions: The test results pointed a probable relationship between submersion of cables with rubber outer shell and water freezing temperatures and the occurrence of accelerated degradation of the cable insulation layer. Reduced insulation resistance values were measured in this cable type after the occurrence of such temperatures, both in salt and freshwater, the cable presented visible exterior degradation signs. For this case copper residues were detected in the water.

Practical Approach to Underground Distribution Power Cable Fleet Management

With the growing requirements imposed by regulatory authorities, grid operators and power utilities firms are confronted with the challenging task of ensuring the reliability, safety, and resilience of distribution networks amid aging asset infrastructure and a lack of resources. Over the past 15 years, the health index (HI)-based analysis has become an increasingly popular asset management tool for several power utilities. This strongly focuses on HI-based analysis to consider not only factors such as the cable vintage, type, and operating conditions, but also maintenance testing data. In this regard, the best industry practices for cable maintenance testing, including VLF Tan-Delta, partial discharge (PD), and time domain reflectometry (TDR), are outlined. Moreover, online tests, such as infrared thermography, ultrasonic PD scan, and temperature monitoring, are discussed. This paper also summarizes the classic asset management strategies for underground (UG) distribution power cables. The paper offers a practical approach for cable fleet management based on authors’ experience dealing with distribution power utility cable management for North American power utilities firms in the past 10 years. The proposed approach ensures reliable cable management at the lowest total life cycle cost. The topic of fleet management for UG power cables considering various condition parameters and an overall risk assessment is outlined. The fleet management guideline of UG power cables covers both cables and their accessories, such as terminations and joints. The main contributions of the paper are to: (1) determine the key parameters and testing factors for condition assessment of cables; (2) offer a practical approach to cable management that is not only based on technical issues, but also considers risk and impact costs, such as financial impact, reliability impact, etc.; and (3) propose a methodology for translating the HI/calculated risks into GIS, making it possible to identify major degradation patterns for fleet assessment. Considering budget and resource limitations around testing UG cable installations, this paper aims to assist asset managers, engineers, and asset owners in developing an effective cable fleet management strategy.

Experimental investigation of interfacial behavior of fiber optic cables embedded in frozen soil for in-situ deformation monitoring

Deformation monitoring of frozen soil is essential to prevent ground settlement problems and geological disasters in cold regions. Fiber optic sensing offers an effective tool for this purpose. However, the interfacial behavior of fiber optic strain sensing cables embedded in frozen soil remains elusive, leading to uncertainty in monitoring data analysis. This study presents an experimental investigation of cable-soil interfacial behaviors with different initial water contents and freezing durations. The results from the cable pullout test show that interfacial progressive failure conforms to the elastoplastic model under low water content conditions, while the softening model is applicable with higher water contents. Interfacial shear strengths and characteristic displacements are positively correlated with initial water contents and freezing durations. Freezing front migration and water redistribution during soil freezing were effectively characterized by shear strength profiles along the cable. These findings provide important references for implementing fiber optic-based deformation monitoring in frozen soil.

Inline reinforcement of steel cable in 3D concrete printing

In recent years, there has been a significant expansion of 3D printing technologies for construction applications. However, a recurring difficulty with these processes is the lack of tensile strength in the resultant product. An innovative approach to enhance the tensile strength is the addition of reinforcement as followed in the conventional concrete casting technology. In this work, an extrusion device is therefore developed to entrain flexible steel cable within extruded concrete layer during the printing process. The device was fabricated to entrain the steel cable of different diameters during concrete extrusion with the help of a wire feeder in a controlled way. A printable material was used and the structural performance of the 3D printed samples was characterizedbased on the tensile, three-point bending, and cable pull-out tests. The results reveal that the flexural strength of the steel cable-reinforced printed sample was significantly increased, by 77% and 240% for 1 mm and 1.5 mm diameter wire, respectively.

Inversion of dynamic displacement response of cable in the whole field based on single vibration measurement

Aiming at the problem that the dynamic displacement at critical positions of the cable cannot be measured due to economic or difficult installation, this paper proposes a method to invert the dynamic displacement of the cable in the whole field by using the dynamic displacement of a single measuring point. The method can realize the inversion of the lateral dynamic displacement response (L-DDR) and angular dynamic displacement response (A-DDR). Firstly, the exact mode shape functions of the L-DDR and A-DDR, considering bending stiffness, sag, inclination angle, and boundary conditions, are derived from the cable vibration control differential equation. The exact mode shape functions are a closed-form solution; thus, it can accurately calculate the cable mode shape at any frequency in real time. Then, an inversion method of the dynamic displacement of the cable in the whole field is proposed based on the amplitude ratio of the exact mode shape. This method can be used to invert the dynamic displacement of the cable in the frequency domain and time domain. Finally, through a numerical simulation and an actual cable test, it is verified that the accuracy of the proposed method is satisfactory. The cable dynamic displacement components at modal and external load frequencies are the main contributors to the dynamic displacement of the cable.

Non-Contact Measurement Method of Phase Current Based on Magnetic Field Decoupling Calculation for Three-Phase Four-Core Cable

As one of the important parameters characterizing the cable’s operation status, an accurate measurement of the current is particularly important for the cable’s reliable operation and status monitoring. Aiming at the problem that the sum of the current phasors of multiphase cables is 0 when running in a steady state, and that the traditional mutual inductance current measurement method cannot be used for the phase current measurement of such cables, or that the insulation layer needs to be damaged, this paper proposes a non-contact measurement method of three-phase cable current, based on the magnetic field decoupling calculation. When combined with the actual parameters of the three-phase cable, the analytical calculation model of the magnetic field distribution of the three-phase cable is established. The relationship between the output ratio of the sensor and the deflection angle is obtained through theoretical derivation, the magnetic field coupling coefficient matrix is determined, and the transfer relationship between the output of the magnetic sensor and the current of each phase is clarified; an array magnetic field sensor is designed, which can sense the information of the adjacent magnetic field independently and is used for the reconstruction of three-phase currents. The effectiveness of the proposed method was tested on the built three-phase four-core cable current measurement test platform. The experimental results show that under the three-phase current balance, the measurement error of phase A, phase B and phase C is less than 2.8%, and the waveform and phase angle of the three-phase current can be well restored, which verifies the three-phase current measurement method proposed in this paper.

Pre-tensioned SMA cable tests and its application in a novel self-centering viscoelastic damper

The elastic modulus of superelastic NiTi shape memory alloy (SMA) is between normal structural steel and viscoelastic materials. To enhance the initial stiffness and self-centering capability of viscoelastic (VE) dampers, an innovative self-centering high-damping rubber damper (SC-HRD), which is parallel composed of an SMA-cable-controlled self-centering system and a traditional high-damping rubber damper, was proposed and investigated in this study. The influence of initial strain, loading amplitude, and strain rate on the behavior of SMA cables after training and pre-tensioning was also tested for the SC-HRD application. Configuration and working principles of the SC-HRD were subsequently illustrated, followed by numerical studies on the behavior of the novel damper. Parametric analyses were then carried out on several design parameters of the SC-HRD to optimize its mechanical performance. Results show that the initial stiffness and residual self-centering strength of the SMA cables, which are essential for the SC-HRD application, can be enhanced with the increasing initial strain and loading strain rate. Compared with traditional VE dampers, the SC-HRD has better initial stiffness and self-centering capacities. Initial strain and relative area ratio of the pre-tensioned SMA cables in the proposed SC-HRD are suggested to be designed as about 2% and 0.123%, respectively, to achieve appropriate initial stiffness, energy dissipation, and residual deformation of the proposed SC-HRD.

Multifrequency-based tension intelligent identification for cables with unknown end-restraints using a metaheuristic algorithm

Vibration frequency methods are widely used for cable tension identification; however, calibrated a priori knowledge of the flexural stiffness, axial stiffness and end-restraints of cables cannot always be obtained in advance, leading to the inabilities of these methods in the identification from theoretical or empirical formulations. In this study, a multifrequency-based intelligent multiparameter identification method is proposed for the tension identification of a cable equipped with a single sensor. The framework of the method establishes an optimization objective function with the theoretical and on-site frequencies based on a cable dynamic model considering the effects of inclination, sagging, flexural stiffness and end-restraints. The identification domain is obtained from empirical formulas and dimensionless characteristic parameters, and the model is solved using a finite difference method. An efficient metaheuristic algorithm is introduced as an engine for the simultaneous identification of the cable tension and the parameters supposed to be calibrated first. The accuracy and efficiency of the method are demonstrated through comparative studies consisting of algorithm tests, tension identification tests of laboratory rigid short cables and some stay-cables of an on-site bridge.

Study on the Dynamic Characteristics of Bit Anchor Cable Drilling in the Gravel Sediments of a Soft Rock Bottom Hole

During the pore-forming stage of floor heave treatment, the phenomenon of gravel sediment accumulation in the bottom hole often occurs, which causes great difficulties in the normal installation of the anchor cable. Based on this observation, a new anchor cable installation method was proposed, which involves installing a drill bit at the front end of the anchor cable to assist its drilling. With the help of an anchor cable drilling test bench, the influence of the bit, motion parameters, and hole environment on the performance of anchor cable drilling was studied. Through the co-simulation of the discrete element method (i.e., multibody dynamics (DEM-MBD)), the drilling process of the bit anchor cable was simulated, and the dynamic characteristics of the bit anchor cable drilling in the bottom hole gravel sediment were analysed. The results show that installing a drill bit in front of the anchor cable can greatly reduce the drilling resistance and hamper torque during anchor cable drilling. When the rotational direction of the bit anchor cable is consistent with the spiral direction of the anchor cable, the bit anchor cable can exhibit better drilling performance. The drilling resistance and hindering torque of the bit anchor cable are the largest when drilling in soaked particles, followed by drilling in dry particles, and the smallest occurs when drilling in moist particles. The research results can provide reference for the parameter setting of anchor cable auxiliary installation equipment.

A novel broken wire evaluation method for bridge cable magnetic flux leakage testing under lift-off uncertainty

Magnetic flux leakage (MFL) is one of the most commonly used techniques for detecting broken wires of bridge cables. In practical testing, the sensor and magnetizer lift-off variations caused by mechanical vibration, sheath surface roughness and thickness nonuniformity significantly affect the accuracy of the estimated defect size. To address this problem, the theory of ratio of adjacent peaks (RAP) is developed based on the magnetic dipole model, which reveals the nonlinear relationship between RAP vector and broken-wire width. Based on the RAP theory, a radial sensor array (RSA) configuration and an evaluation method are further proposed in this paper. The RSA consists of four sensors along the bridge cable radial direction with a fixed interval and is employed to acquire RAP vector, which is identified as a spatial characteristic of MFL signal. An artificial neural network (ANN) algorithm is employed to develop the nonlinear defect width evaluation method based on the RAP vector. The effectiveness of the RSA configuration and the evaluation method is verified by finite element method (FEM). The results indicate that the broken-wire width can be accurately estimated utilizing RAP vector obtained by RSA without considering the lift-off variation.

Frequency-Based Cable Tension Identification Using a Nonlinear Model with Complex Boundary Constraints

Accurate estimation of the cable force affects the bridges’ long-term integrity and serviceability directly. The frequency method is often used for cable tension testing in bridge engineering. However, the generally used cable tension calculation formulae are based on “ideal hinge” or “ideal fixed” boundary conditions. The inclination, bending stiffness, and sag-extensibility of the cable are not properly considered, which results in non-negligible errors. A frequency-based method for precisely determining the tensile force of a cable with unknown rotational and support constraint stiffnesses at the boundary was proposed. A nonlinear mathematical model of the vibration of the cable was established. In addition to parameters such as inclination, sag, and bending stiffness, the effects of unknown rotational and support constraint stiffnesses at both ends of the cable were also considered. The finite difference method was employed to discretize and solve the mode equation of the cable vibration. A frequency-based sensitivity-updating algorithm was applied that can identify simultaneously several system parameters using multiorder measured natural frequencies. Calculation of the matrix eigenvalue derivatives was the key to obtaining the system sensitivity matrix. Numerical examples indicated that the algorithm can be used efficiently and precisely to identify multiple system parameters of the cable, including its tension, bending stiffness, and boundary constraint stiffnesses.

Operability evaluation of electrical wires and cables subjected to simultaneous fire and current loadings

Introduction. Intumescent coatings are used as a means of protection from heat flows, and their mission is to preserve the operability of wires and cables under fire conditions coupled with simultaneous current loading. However, the effect of insulation destruction on the operability of cables has not been studied for the case of a real fire regime.Goals and objectives. The purpose of the article is to evaluate the experimental operability of electrical wires and cables subjected to simultaneous effects of fire and current loadings.To achieve this purpose, an experimental testing unit was applied to conduct the experimental testing of wires and cables manufactured by various producers. At the same time, the temperature effect of the heated environment on electrical parameters of wires and cables, such as resistivity, inductance and capacitance, was evaluated.Theoretical background. In real fire conditions, dependence of indoor temperature, affecting the heating of cable insulation, differs essentially from the same dependencies in cases of various standard fire conditions. Therefore, the insulation destruction process may occur before the coating intumescence starts.Results and discussion. An experimental testing unit has been developed. This unit allows for the gradual cable heating with a pre-set temperature measurement interval and cable electrical characteristics. Dependencies of resistivity, inductance and capacitance of standard electrical cables on the temperature of the air surrounding the cable are obtained. It’s been discovered that the gradual heating of an electrical conductor or cable eventually leads to a short circuit between its conductive cores and further electric current transmission in electrical wires and cables. It is shown that phases and amplitudes of an input electrical signal can drastically change before the short circuit.Сonclusions. The simultaneous effect of fire and current loadings on standard electrical wires and cables causes a short circuit in the temperature range, in which no intumescence of flame retardant coatings is initiated on the insulation surface. Therefore, these coatings can ineffectively maintain the operability of electrical wires and cables.