Slip Ring Research Articles

4D Imaging of Two‐Phase Flow in Porous Media Using Laboratory‐Based Micro‐Computed Tomography

AbstractDynamic three‐dimensional computed tomography (CT) imaging of liquid transport in porous media has primarily been conducted at high brilliance synchrotrons thus allowing fast, sometimes sub‐second, temporal resolution to be obtained. University laboratory CT instruments lack the photon flux available at synchrotrons, limiting the obtainable spatiotemporal resolution. Here, we discuss our experiences with instrumentation and software methods to conduct time‐resolved micro‐computed tomography (4D‐CT) experiments of flow in porous media, based on a conventional CT instrument operated with a highly undersampled number of projections. An experimental stage outfitted with syringe pumps placed on a slip ring allowed two‐phase flow experiments to be carried out with continuous unidirectional rotation and without obstruction of the liquid supply lines. An iterative reconstruction algorithm based on a priori information was used to provide high image quality and ∼30 s time resolution despite the few and low‐exposed projections compared to standard protocols. The experimental technique was demonstrated with imbibition and drainage in glass bead‐pack and Bentheimer sandstone samples with sub‐minute temporal resolution, allowing the liquid configurations just before and after fast dynamic phenomena such as cooperative pore‐filling events and Haines jumps to be captured. Power law scaling exponents for burst volumes associated with imbibition and drainage were estimated and compared with the literature. That 4D‐CT experiments can be carried out using conventional CT instruments to challenge contemporary permeability models is of high importance for many geo‐, bio‐ and environmental physics challenges.

Ultrahigh Critical Current Density across Sliding Electrical Contacts in Structural Superlubric State.

In conventional sliding electrical contacts (SECs), large critical current density (CCD) requires a high ratio between actual and apparent contact area, while low friction and wear require the opposites. Structural superlubricity (SSL) has the characteristics of zero wear, near zero friction, and all-atoms in real contact between the contacting surfaces. Here, we show a measured current density up to 17.5 GA/m^{2} between microscale graphite contact surfaces while sliding under ambient conditions. This value is nearly 146 times higher than the maximum CCD of other SECs reported in literatures (0.12 GA/m^{2}). Meanwhile, the coefficient of friction for the graphite contact is less than 0.01 and the sliding interface is wear-free according to the Raman characterization, indicating the presence of the SSL state. Furthermore, we estimate the intrinsic CCD of single crystalline graphite to be 6.69 GA/m^{2} by measuring the scaling relation of CCD. Theoretical analysis reveals that the CCD is limited by thermal effect due to the Joule heat. Our results show the great potential of the SSL contacts to be used as SECs, such as micro- or nanocontact switches, conductive slip rings, or pantographs.

Fast Arc Detection Technology Based on Fractal Dimension for SADA Slip Ring in Satellite Power System

The solar array drive assembly (SADA) slip ring is a critical link that provides electrical power and electric signal transmission between solar arrays and satellite power systems, which is prone to arc faults in the space environment. If these arc faults cannot be detected and eliminated quickly enough, they will seriously threaten the safety of the satellite power system and the satellite. In this paper, a fast arc detection method based on fractal dimension is proposed that adapts to different operating modes of power systems. The detection method collects the current differential signal data flowing through the SADA slip ring, and, according to the trend of the fractal dimension change in this signal, the fault identification algorithm is designed for different operating modes of the power system to achieve real-time and rapid identification of arc faults. Finally, the effectiveness of the proposed method is demonstrated using test data under several different fault conditions.

Design and Performance Research of a Novel Iron-Core Permanent Magnet Compensated Pulsed Alternator With Segmental Squirrel-Cage

Compensated pulsed alternator (CPA) can realize transient high current discharge by compressing magnetic field through compensating element, which has important application in pulse power field. The compen- sation shield and short circuit compensation winding are usually used as compensation elements, but the local compensation effect will be affected by the opposite eddy currents or conductor currents under other poles at maximum discharge time. To solve this problem, a novel iron-core permanent magnet CPA (PMCPA) with segmental squirrel-cage is proposed in this paper. At the time of maximum discharge, the bars' current of each segmental squirrel-cage segment will not be affected the bars' currents in opposite direction of other segments, which has better local compensation effect. In addition, the permanent magnet (PM) excitation eliminates the brush and slip ring and improves the reliability of operation. First, the design basis and scheme of the PMCPA are introduced. Second, the dynamic mathematical model of the PMCPA is presented. Third, the finite-element model of the PMCPA is established to analyse. Fourth, the prototype is manufact- ured to test and validate. Through analysis and verification, the superiority of segmental squirrel-cage compensation is proved, which provides a new idea for the optimization and development of compensation elements.

Study on the performance of reciprocating seals under the coupling effect of elastohydrodynamic lubrication and rubber wear

Due to the lack of research on the sealing performance of reciprocating combined seals under the coupling of elastohydrodynamic lubrication and rubber wear, this paper uses the UMESHMOTION user subroutine and the improved Archard model to realize the dynamic wear process of the combined seals and the adaptive meshing of the local area to simulate the wear of the seals. At the same time, combined with the elastohydrodynamic lubrication model of the toothed slip ring combined seal ring, the sealing performance of the reciprocating combination under mixed lubrication conditions is studied. Finally, the accuracy of the model is verified by building a two-cylinder reciprocating seal test bench with more accurate measurement. The results show that the influence of the change of fluid pressure on the wear of the seal lip is greater in the fast wear stage than in the stable wear stage. The influence of the change of interference on the wear of the sealing lip is small at different wear stages. The wear of the sealing lip has a significant effect on the sealing performance of the instroke, but has little effect on the sealing performance of the outstroke.

Maximum Power Control of DFIG Based Grid Connected Wind Turbine Generator System

This paper presents a simulation model of variable speed wind turbine with a doubly fed induction generator developed in Matlab/simulink. Vector control of a doubly fed induction generator (DFIG) drive for variable speed wind power generation is described. A slip ring (wound rotor) induction generator with back to back three phase PWM converter between its rotor and the grid forms the electrical system. A vector control scheme for the PWM converters results in independent control of active and reactive power. Line (supply) voltage oriented reference frame has been used to independently control the active and reactive power. Results are provided at the end for sub synchronous and super-synchronous operation of the DFIG.

Tribo-electrical properties of copper matrix composites in salt-fog environment

To enhance the reliability of floating offshore wind platforms exposed to salt-fog environment, a new material, CNTs-MoS2/Cu, was developed for slip rings. Tribo-electrical properties of composites in salt-fog environment were explored. A novel method for characterizing current-carrying stability, based on correlation dimension, was proposed. When compared to copper, the correlation dimension decreased by 31.43%. It reveals that composites exhibit superior current-carrying stability compared to copper in salt-fog environment. The wear mechanism is further revealed. CNTs enhance the damage resistance of friction film, while MoS2 contributes lubrication. The appropriate addition of CNTs and MoS2 leads to the formation of an intact conductive lubrication anti-corrosion film on the surface, reducing the erosive impact of salt fog.

Fractal contact resistance model of wind pitch slip ring considering wear and self-excited vibration

Purpose The purpose of this paper is to reveal the dynamic contact characteristics of the slip ring. Dynamic contact resistance models considering wear and self-excited were established based on fractal theory. Design/methodology/approach The effects of tangential velocity, stiffness and damping coefficient on dynamic contact resistance are studied. The relationships between fractal parameters, wear time and contact parameters are revealed. Findings The results show that the total contact area decreases with the friction coefficient and fractal roughness under the same load. Self-excited vibration occurs at a low speed (less than 0.6 m/s). It transforms from stick-slip motion at 0.4 m/s to pure sliding at 0.5 m/s. A high stiffness makes contact resistance fluctuate violently, while increasing the damping coefficient can suppress the self-excited vibration and reduce the dynamic contact resistance. The fractal contact resistance model considering wear is established based on the fractal parameters models. The validity of the model is verified by the wear tests. Originality/value The results have a great significance to study the electrical contact behavior of conductive slip ring. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0300/

Piezoresistive Sensor for Strain Measurement on Turbine Blade with Wireless Telemetry Data Acquisition

In the paper, strain-gauge sensor design and its application for wireless measurement of blade deformations and strains are presented. The strain sensor was designed using FEM (Finite Element Modeling) and uses piezoresistive strain sensitive boron doped nanocrystalline layers or insulated silicon layers (SOI). Nanocrystalline Diamond (NCD) is a very promising material for fabrication of harsh-environment devices because of its unique mechanical and electrical properties. The prospective of using diamond is not only in sensors (MEMS) but in RF and power electronic as well. Selection of method for data transfer is the key problem in rotating mechanisms. Traditional approach is using the slip ring, but it is not suitable for multisensor applications due to the requirement of one slip ring per sensing element. Telemetry can be related to transfer a data over any media, but is typically applied on wireless communications. A basic telemetry system consists of a measuring element or sensor, a device for sending the transmission, a receiver, and an output controller which records and displays data.

Arc Fault Diagnosis Method for Brush Slip Ring System of Doubly-Fed Induction Generator Based on Image Recognition

Arc Fault Diagnosis Method for Brush Slip Ring System of Doubly-Fed Induction Generator Based on Image Recognition

Mechanism of the Sliding Contact of a Ag-Graphite Brush against a Au-plated Slip Ring for Varying Ag Content

Mechanism of the Sliding Contact of a Ag-Graphite Brush against a Au-plated Slip Ring for Varying Ag Content

Dual Side Field Oriented Control of Slip Ring Induction Motor

Dual Side Field Oriented Control of Slip Ring Induction Motor

Hybrid lubrication model study of slip ring combination seal under the influence of frictional heat

This paper presents an experimental and theoretical investigation into the factors influencing the sealing performance of combined slip rings. Factoring in the frictional heat from micro convex bodies and convective heat exchange between the slip ring, oil film, and air, we formulate a thermoelastic flow hybrid lubrication model for the combined slip ring seal. This model calculates the distribution of oil film thickness, pressure, temperature, velocity, and viscosity in the sealing zone, drawing on the generalized average Reynolds equation and the transmembrane average energy equation, in conjunction with the heat conduction equation of the slip ring. Utilizing the Archard wear model, we also examine the wear characteristics of the combined slip ring seal, providing insights into seal wear under these conditions. The model enables an analysis of the interplay between parameters and their impact on seal performance. The method proposed accurately predicts friction and leakage in line with experimental data, thereby providing a theoretical foundation for further numerical investigation of seal characteristics.

Intravascular Optical Coherence Tomography Utilizing a Miniature Piezoelectric-Driven Probe.

Intravascular optical coherence tomography (IV-OCT) is crucial for evaluating lumen dimensions and guiding interventional procedures. However, traditional catheter-based IV-OCT faces challenges in achieving precise and full-field 360° imaging in tortuous vessels. Current IV-OCT catheters that employ proximal actuators and torque coils are susceptible to non-uniform rotational distortion (NURD) in tortuous vessels, while distal micromotor-driven catheters struggle with complete 360° imaging due to wiring artifacts. In this study, we developed a miniature optical scanning probe with an integrated piezoelectric-driven fiber optic slip ring (FOSR) to facilitate smooth navigation and precise imaging within tortuous vessels. The FOSR features a coil spring-wrapped optical lens serving as a rotor, enabling efficient 360° optical scanning. The structurally-and-functionally-integrated design significantly streamlines the probe (with a diameter of 0.85 mm and a length of 7 mm) while maintaining an excellent rotational speed of 10,000 rpm. High-precision 3D printing technology ensures accurate optical alignment of the fiber and lens inside the FOSR, with a maximum insertion loss variation of 2.67 dB during probe rotation. Finally, a vascular model demonstrated smooth probe insertion into the carotid artery, and imaging of oak leaf, metal rod phantoms, and ex vivo porcine vessels verified its capabilities for precise optical scanning, comprehensive 360° imaging, and artifact elimination. The FOSR probe exhibits small size, rapid rotation, and optical precision scanning, rendering it exceptionally promising for cutting-edge intravascular optical imaging techniques.

Magnetic Coupling Effect and Performance Analysis of Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Power Generation

To eliminate slip rings, brushes, and terminate gear-box mechanism, ferrite permanent magnet (PM) based counter rotating dual rotor PM flux switching generator (CRDRPMFSG) for direct drive counter rotating wind turbine (D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> CRWT) application is proposed in this paper. Initially, the mechanism of gearless and brushless counter rotating wind power generation is discussed, and a simplified formulation opted for the slot/pole combinations. The proposed CRDRPMFSG encapsulate inner and outer machines with circumferentially magnetized PM enclosed by non-overlapped armature windings; thus, offering reduced overhang with compact design. However, co-axially linking the inner and outer machines through a shared stator yoke results in serious issues of magnetic coupling due to dual air-gap fields. To this end, eight topologies with various slot/pole combinations are comprehensively investigated using finite element analysis (FEA) for magnetic coupling effects and its influence on electromagnetic performance. From the analysis, it is shown that magnetic coupling level influence electromagnetic performance i.e., average torque, ripple rate, power factor, efficiency, losses, and output power. Moreover, it is noted that coupling level can be reduced by adopting same stator teeth in inner and outer machines or same stator teeth with different rotor poles. Finally, the predicted FEA calculations are verified experimentally with four benchmarked CRDRPMFSG prototypes.

Study on the Influence of Structure and Material Parameters on Dynamic Sealing Characteristics of Composite Seal Ring

Aiming at the failure problem of composite sealing ring, the influence of elastic modulus of carbon fiber content, groove width and number of grooves on dynamic sealing characteristics of sealing ring was analyzed by finite element method. The results showed that the maximum stress after precompression was located in the middle of the contact between slip ring and O ring, and the maximum contact pressure was located to the left of the inner circle of slip ring. After applying the fluid pressure, the maximum stress is located at the right side of the contact between the slip ring and O ring and the middle part of the contact between the slip ring and O ring, and the maximum contact pressure is located at the middle part of the inner circle of the slip ring. In dynamic sealing state, the magnitude and position of the maximum contact pressure and the maximum stress of left and right stroke are basically the same; The width and number of grooves increase the contact pressure and stress, but the width of groove interval is opposite.

Study of ordered phase precipitation behaviour and hardening mechanism of Au-20Ag-10Cu alloy during deformation-aging treatment

With the rapid development of aerospace technology, the demand for a longer service life of Au-Ag-Cu alloy as conductive slip rings is increasing. Therefore, it is important to improve the hardness of the alloys in order to prolong their service life. Deformation-aging can improve the hardness of many alloys. The effect of the deformation-aging process of Au-20Ag-10Cu (wt%) alloy was investigated on the microstructure and properties, which characterized by DSC(Differential Scanning Calorimeter), XRD(X-ray Diffraction), EBSD(Electron Backscatter Diffraction), TEM(Transmission Electron Microscope) characterization techniques, microhardness and electrical conductivity testing methods. The results indicated that the microhardness increases and the conductivity decreases gradually with the increase of deformation rate. As the aging time increasing, the content of face-centered tetragonal AuCu I ordered phase increases, and thus the hardness increases gradually. The maximum hardness value of 307.44 HV was obtained after undergoing 70 % deformation and then aged at 300 ℃ for 16 h with the electrical conductivity values of 8.40 MS·m−1. This result indicated that both higher hardness and higher electrical conductivity of Au-20Ag-10Cu (wt%) alloy could be obtained, which ensures the requirements in the field of electrical contact materials.

Contactless Rotor Ground Fault Detection Method for Brushless Synchronous Machines Based on an AC/DC Rotating Current Sensor.

Brushless synchronous machines (BSMs) are replacing conventional synchronous machines with static excitation in generation facilities due to the absence of sparking and lower maintenance. However, this excitation system makes measuring electric parameters in the rotor challenging. It is highly difficult to detect ground faults, which are the most common type of electrical fault in electric machines. In this paper, a ground fault detection method for BSMs is proposed. It is based on an inductive AC/DC rotating current sensor installed in the shaft. In the case of a ground fault in the rotating parts of the BSM, a fault current will flow through the rotor's sensor, inducing voltage in its stator. By analyzing the frequency components of the induced voltage, the detection of a ground fault in the rotating elements is possible. The ground faults detection method proposed covers the whole rotor and discerns between DC and AC sides. This method does not need any additional power source, slip ring, or brush, which is an important advantage in comparison with the existing methods. To corroborate the detection method, experimental tests have been performed using a prototype of this sensor connected to laboratory synchronous machines, achieving satisfactory results.

Research on a Transverse-Dislocated Magnetic-Field Modulated Brushless Contra-Rotating Machine Adopting Different Core Material Combinations

This article proposes a transverse-dislocated magnetic-field modulated brushless contra-rotating machine (TDMFM-BCRM) with multiunit structure for the contra-rotating propulsion system. Compared with the existing contra-rotating machines, it has the advantages of equal and opposite torque at any time, no brushes and no slip rings. The improved three-dimensional (3D) magnetic-field modulation principle by considering multiunit structure of the TDMFM-BCRM is investigated. Then, due to the structural complexity of the TDMFM-BCRM, there are some challenges about its manufacturing. Therefore, the performance of the TDMFM-BCRM adopting different core material combinations including electrical steel (ES) and soft magnetic composite (SMC) material is investigated. Meanwhile, a prototype is manufactured and tested to validate the theoretical analysis, finally more manufacturing methods for the TDMFM-BCRM are comparatively studied.

First Demonstration of the Commissioning of a New Multi-Modality Radiotherapy Platform

A new multi-modality radiotherapy platform was developed and introduced into clinical application, which has received US FDA 510k(K210921) and National Medical Products Administration (NMPA) clearance in China (20223050973). This study, for the first time, presents the technological characteristics and commissioning results of the new platform. The platform consists of 3 modules: linear accelerator, rotating gamma system, and a kV imaging system within an O-ring gantry. The O-ring gantry can rotate continuously achieved by using a slip ring. The Linac delivers a 6 MV FFF photon beam with a variable dose rate of 50 to 1400 MU/min. The delivery techniques include 3D-CRT, IMRT, and VMAT. The rotating gamma system utilizes 18 Co-60 sources with a reference dose rate of 350 cGy/min. The image-guided techniques consist of kV-kV pairs and kV-CBCT. The X-ray intensity-modulated radiotherapy and γ-ray stereotactic radiotherapy can be delivered on the same platform. The acceptance test and commissioning were performed following the vendor's customer acceptance tests (CAT) and several AAPM Task Group reports/guidelines. Regarding the Linac, all applicable validation tests recommended by the MPPG 5.a (basic photon beam model validation, IMRT/VMAT validation, E2E tests, and patient-specific QA) were performed. For the rotating gamma system, the absorbed doses were measured using a PTW31014 and PTW60016. EBT3 films were employed to measure the relative output factors (ROFs). The E2E tests were performed using a PTW31014 and EBT3 films. The coincidence between the imaging isocenter and the Linac/gamma treatment isocenter was investigated using EBT3 films. The image quality was evaluated regarding the contrast-to-noise ratio (CNR), spatial resolution, and uniformity. All tests included in the CAT met the vendor's specifications. All MPPG 5.a tests complied with the tolerances. The confidence limits for IMRT/VMAT validation were achieved according to TG-119. The point dose differences were below 1.68% and gamma pass rates (3%/2 mm) were above 95.9% for the Linac E2E tests. All plans of patient-specific QA had point dose differences below 1.79% and gamma pass rates (3%/2 mm) above 96.1% suggested by TG-218. For the rotating gamma system, the differences between the calculated and measured absorbed doses were below 1.86%. The ROFs calculated by the TPS were independently confirmed within 2% using EBT3 films. The point dose differences were below 2.57% and gamma pass rates (2%/1 mm) were above 95.3% for the E2E tests. The coincidence between the imaging isocenter and the Linac/gamma treatment isocenter was within 0.5 mm. The image quality fully complied with the vendor's specifications regarding the CNR, spatial resolution, and uniformity. This is the first report about the commissioning of a new multi-modality radiotherapy platform. The platform has been successfully commissioned and exhibits good performance in mechanical and dosimetry accuracy.