Logo IEEE HOLM CONFERENCE ON ELECTRICAL CONTACTS

2019 Technical Program

The final program is available in pdf : Holm Final Program 2019.

2018 Holm Conference papers

The 2018 conference papers are now available in the IEEE Xplore database: Click Here.

2019 Technical Areas

Automotive Degradation Mechanisms
Hybrid/Electric Power
Hot Plugging
Switching and Connectors
Environmental Effects
Switching Performance
Environmental Effects
Welding
Reliability
Breakdown
Diagnostics
Fretting
Electronics connectors Arc Interruption
High Frequency
High-Speed Data
Telecommunications
Lubricants
Corrosion Inhibitors
DC/AC Switching
Circuit Breakers
Vacuum Interrupters
Hybrid Switching
Micro-Arcing
Power connectors Modeling
Crimp Connections
Bolted Connections
Plating/Lubricants
Glowing Contacts
Degradation Effects
Fundamentals
Dielectric Breakdown
Arc Simulation
Dynamic/Static Welding
Contacts Materials New Technologies
Air and Vacuum
High Frequency Relays
Ultra Miniature Relays
Carbon Fiber Degradation
Mechanisms
Reed Relays
Material Development
Switching Performance
Electroplating
Lead Free
MEMS
Micro Switches
RF Connectors
Arc Fault/Safety
Nanotechnology
Superconductors
Higher DC Voltage Switching

2019 Preview of the accepted abstracts

A Novel Crimp Connector Technology
Roland S Timsit and Dmitry Ladin
The primary criteria for a reliable electrical crimp/compression connection are (i) a low electrical contact resistance between the attached conductors and the connector body, and (ii) maintaining this low resistance by sustaining a sufficiently large contact force on the conductors during the connector service life. Conventional crimp connectors are particularly susceptible to loss of mechanical contact force with attached conductors because the connector is permanently deformed over the conductor(s), thus preventing the use of an external energy storing device. This paper describes the use of an internal elastic-spring insert in a tubular compression connector of the type used in the electrical utility industry, to maintain a large mechanical contact force with the conductor(s). The results of preliminary thermal cycling tests on a high-power compression connector attached to an aluminum conductor, using such an internal elastic-energy storing device, are described.
The Impact of Micro-protrusions on Field Emission of Electrons
Robert Malucci
Field emission of electrons is a quantum mechanical process. Solutions in this case show that the field emitted electron currents are greatly affected by the intensity of the electric fields at the surface of the cathode. Since micro-protrusions at the surface enhance the electric field at these locations, it is of some interest to analyze the impact of various structures, such as spherical and elliptical protrusions. In the present paper, the latter is done using electrostatic theory to estimate the maximum electric field at these locations. This is done by using image charge methods to calculate electric potentials. Consequently, by choosing optimum locations and magnitudes for the image charges, the boundary conditions at the surface of the cathode and anode can be imposed on the solution for this case. This provides a valid solution that meets the conditions for this case. This gives some insight into the affects one would expect in various cases where micro-structures are expected to occur. It is believed that this phenomenon greatly affects the breakdown in arcing contacts. This is especially true in vacuum contacts but may impact the initiation of arcing in gaseous contacts as well.
Effect of Additives on the Switching Performance of Ag/SnO2 under AC-3 Conditions
Timo Muetzel and Christian Hubrich
Silver tin-oxide (Ag/SnO2) contact materials as applied as switching contacts for contactors are typically doped with different types of additives to tailor and optimize the behavior for different types of applications. Typically, different types of metal oxides e.g. WO3, In2O3, CuO, Bi2O3 and others, as well as combinations thereof are used. In this work the interaction of the electric arc, as it appears during AC-3 endurance, with the contact material itself and the resulting impacts on erosion and contact resistance were scrutinized. Powder metallurgical type Ag/SnO2 materials with different additives were studied by an experimental approach performing AC-3 endurance test with a commercially available contactor. By novel approach contact voltages could be evaluated for every contact pair during contactor test, deeper insights into the contact material - device interaction could be achieved. Experimental results will be further explained by post analysis of the contacts via metallurgical routines such as optical microscopy of cross sections and EDX/WDX analysis.
An improved model of electrical contact resistance for pad-probe interaction during semiconductor wafer test
Oliver Nagler, Tobias Krebs and Michael Heuken
State-of-the�art semiconductor wafer test requires a stable electrical contact resistance between each individual I/O pad and the probe needle. Due to the strong sensitivity of modern IC�s to mechanical stress, low contact force probe cards are used. Those probe cards face the challenge of a randomly increased and instable electrical contact resistance during multiple insertions, whose root cause is not fully understood yet. We investigated Holm�s theory for an individual probe on different pad metal alloys and film thicknesses. We could confirm the force and material dependency of the constriction resistance for Au and Al pad metallization�s but we did observe a much stronger pad metal hardness influence. The root cause for an increased and instable electrical contact resistance was identified as geometrical factors and time dependent oxidation effects. Besides electrical tests, this was proven by high-resolution 3D microscope inspection. Strong variances regarding probe tip shape and roughness within a probe card were observed. All findings were used to develop an improved model which describes the increase and stability of the electrical contact resistance. Based on the results of this investigation, the qualification and process optimization of pad-probe interaction during wafer test is much more precise and less time-consuming.
Arc movement investigations of break arcs of AgSnO2 contacts under applied external magnetic field in inductive DC load conditions
Makoto Hasegawa and Seika Tokumitsu
For better understandings of influences of magnetic field application on arc movements and magnetic blowing, AgSnO2 contacts were operated to break inductive DC currents of 14V-7A, 14V-12A, 14V-20A, 20V-7A, and 20V-17A with applied external magnetic field of about B=120mT at contact opening speeds from 1mm/s to 200mm/s. Break arc movements were observed with a high-speed camera, and arc voltage/current waveforms were simultaneously obtained. In some conditions especially with smaller current levels and slower opening speed levels, magnetic blowing was not observed, while arc reductions were still realized. Lorentz force to be applied onto arcs were calculated based on the measured arc current waveforms. The obtained results indicate that in the cases where magnetic blowing was observed, arc movement started almost at the maximum level of the calculated Lorentz force. The required Lorentz force levels for starting arc movements were dependent on load current levels and contact opening speeds. Even when magnetic blowing was not observed, the calculated Lorentz force levels were found to follow the same trace up to the maximum level as the blown cases. Thus, some factors other than the Lorentz force level seem to have critical influences on realization of magnetic blowing. In the non-blowing cases, arc was found to move in the direction opposite to the Lorentz force direction. When the magnetic field in the opposite direction was applied, the arc movement direction was also switched in the opposite direction. These phenomena are being further investigated.
Contact Resistance Development of High Current Non-Overlapping Butt Contacts During a Large Number of Mechanical Switching Operations
Henrik Menne and Christian M. Franck
Over the last years, the need for HVDC Circuit Breaker became obvious. The first HVDC grid is in operation and more grids are planned. To fully utilize the advantages of a grid, fast and reliable Circuit Breaker technology is needed. One technology that fulfills these requirements is the Hybrid HVDC Circuit Breaker. The key component of such a breaker is an Ultra Fast (mechanical) Disconnector (UFD). Such a disconnector must have a very short opening time and very low resistance in closed position. The goal of the present work is to develop a completely novel UFD platform. To minimize the opening time, non-overlapping butt contacts are used. Even though no fault current need to be interrupted, the surface of the contacts will wear off and the contact resistance will increase. It is likely that the contact material and the contact geometry will influence the aging. A test bench is developed to investigate this behavior. It is designed to allow easy testing of different contacts, change of contact force and test current. This contribution will report on the test bench details and on systematic aging studies using different contact materials.
Comparison of typical damages from multivariable life tests and field vehicles
Jian Song, Christian Koch and Haomiao Yuan
This paper introduces an approach to answer the question whether a multivariable life test conditions are relevant for field operation.
Modelling of Transient Heating and Softening Behaviour of Contact Points during Current Pulses and Short Circuits
Toni Israel, Stephan Schlegel, Steffen Grossmann, Tom Kufner and George Freudiger
In this paper, electrical connectors for high power applications such as gas-insulated switchgear or charging stations are investigated. Recent findings show that the contact points in these connectors are heated up rapidly during current pulses and thus, they soften and their contact resistance drops instantly. The contact points are a major source of power losses in the electrical connector. Therefore, a precise estimation of the drop in contact resistance is needed for an accurate estimation of the maximum temperature during a short circuit. In this paper, a new multiphysic calculation model is presented which aims at a better understanding of these transient processes. For this calculation, the influence of contact temperature, contact hardness and contact force on the contact resistance is evaluated. The contact hardness is highly temperature-sensitive. Therefore, pulse current tests were done to evaluate the contact hardness depending on temperature. The contact force is given by design but can be reduced by high current pulses. For the contact points, this blow-off force is estimated analytically. With these data, the effective contact resistance for every moment of a short circuit is calculated with a transient electric-thermal FEM model. Finally, the calculations are compared to results of short circuit tests.
An active limit baffle for alleviating arc instability and re-ignition in relay
Xue Zhou, Yuxin Zhou, Huimin Liang and Guofu Zhai
The arc instability and re-ignition refers to the arc cannot maintain a stable state or the arc extinguished but re-burn quickly. When a normally open relay releases, its movable contact, static contact, as well as their reeds are free, especially the movable contact of which energy cannot be dissipated immediately. In this case, the contacts will experience a short period with sharply swing that will cause the contact gap change periodically and the arc burns unsteadily. By conducting plenty of experiments, the failure mode and the failure principle are proven to be arc reigniting with contact welding. We introduce a method of an active baffle that the backwards extend of the spring can be limited effectively. Finally, we confirm arc erosion alleviation with Scanning Electron Microscope.
Effect of Vibration Induced Fretting on Contact Failure in a Coaxial Connector
Qingya Li, George Flowers, Jinchun Gao, Michael Hamilton and Sherman Peek
Impact of Cross Modulation in Coaxial Connectors on Signal Distortion
Lingyu Bi, Jinchun Gao, George Flowers and Gang Xie
Radio frequency (RF) connectors generally exhibit nonlinear characteristics even the connectors are pristine. In addition, there are phase noise and Additive White Gaussian Noise (AWGN) in broadband communication systems. All of these factors cause different levels of signal distortion and negatively impact the reliability of communication systems. In this paper, a polynomial behavior model was developed to describe the nonlinear characteristics of RF connectors. Based on the two-tone continuous wave (CW) testing procedure, a series of experiments were conducted to obtain the model coefficients. The Error Vector Magnitude (EVM) was selected as the index to quantify the level of signal distortion. The impacts of nonlinearity, phase noise and AWGN on EVM were theoretically calculated. Simulations were conducted to compare the impacts of different factors. The results show that the nonlinearity of RF connectors is a significant factor causing signal distortion in broadband communication systems. This study serves to provide a theoretical basis for evaluating the impacts of nonlinearity, phase noise, and AWGN on signal distortion.
Modeling and Analysis of the Effect of Signal Frequency on the Contact Surface Temperature of Coaxial Connectors
Yuqi Zhou, Jinchun Gao and George Flowers
Increases in signal frequency can result in contact surface temperature rises in coaxial connectors. Such increases in temperature on the contact surface of coaxial connectors may negatively impact the quality of high frequency signal transmission in communication systems. In this paper, the effect of signal frequency on the contact surface temperature of coaxial connectors at high frequency was modeled and analyzed. A model was developed of the structural characteristics of the contact surface of a connector designed for high frequency applications. Using this model, finite element analysis (FEA) simulations were conducted to evaluate the influence of surface roughness on the resistance, capacitance and inductance of the connector contact surface. From these simulations, the relationship between the signal frequency and temperature rise of the connector contact surface was obtained. This study provides a reference for the selection of coaxial connectors and the development of low temperature rise connector designs.
The Performance Degradation Comparison Test and Failure Mechanism of Silver Metal Oxide Contact Materials
Shang Shang, Zhaobin Wang, Weiyan Li, Cunyang Han and Zhan Wang
In order to evaluate the electrical contact performances of silver metal oxide contact materials more accurately, and perfect the optimum selection of contact materials, the electrical contact simulation testing method was used to analyze the degradation parameters of the contact materials in this paper. An innovative type of electrical contact simulation test system was designed and developed, which can easily replace dynamic and static contact materials. The contact resistance, static pressure and rebound energy degradation parameters of AgSnO2, AgCdO and AgNi contact materials under the same load conditions were obtained through experimental research, the contact resistance and arcing energy degradation parameters of AgSnO2 under different load levels were acquired at the same time. The result indicated that the more accurate data are received by the electrical contact simulation testing method than the traditional electrical simulation method. Finally, based on the test data, the degradation performance of the selected test materials were sum
Opening high voltage resistive circuit in arc chamber with magnetic field and splitter
Huimin Liang, Xiaoyu Liao, Xue Zhou, Guangcheng Ma and Dan Chen
DC high power contactors find their potential application with the development of DC distribution system, which raises a claim on high voltage and long lifetime contactors. Specific designs on arc chamber are necessary for arc quenching and meeting requirement of DC high power break. In this paper, arc extinguishing performance in different kinds of arc chamber equipped with magnets and arc-splitters are studied by analyzing arc voltage and current, as well as arc profiles. The source voltage varies from 300V to 750V, load current varies from 30A to 100A. Two cuboid permanent magnets are used to accelerate arc quenching. The durations of the arc lengthening and blowing can be obtained as the source voltage increases from 300V to 750V, the current increases from 30A to 100A. The results are of practical value for designing arc chambers in high power and long life DC contactors.
A Standardized Reliability Evaluation Framework for Connectors � Stress Levels and Test Recommendations
Holly-Dee Rubin, Jyoti Gupta, Seven Cheng, Phillip Conde, Robert Druckenmiller, Cindy Han, Michael Lipschutz, Yen-Han Oon, Vincent Pascucci, Jeffrey Toran and Vasu Vasudevan
The iNEMI Connector Reliability Test Recommendations Project was organized to address the need for standardized reliability qualification methods for connectors. In previous work, the team reviewed current standards and defined connector interconnect levels. Using existing standards as a basis, a generalized protocol for evaluating connector reliability based on the defined connector interconnect levels and stresses expected in use was proposed. In the current work, the team makes recommendations for specific stress level definitions for connectors used in office/consumer, high end systems, and portable and wireless applications. The stress levels are mapped to those expected for one of the connector interconnect levels, Level 4, defined in the previous work. Recommendations are made for test conditions associated with each of the stress levels. In addition, the project group concluded that with some modifications, the EIA-364-1000 standard, Environmental Test Methodology for Assessing Performance of Electrical Connectors and Sockets used in Controlled Environment Applications, can be extended to connectors intended for use in uncontrolled environments. These modifications would include adding dust preconditioning, thermal shock preconditioning, and mechanical shock to the test sequences. The group also identified gaps in current standards/knowledge to help guide future improvement in the recommended testing.
Experimental Evaluation of Tool Geometries for the Ultrasonic Crimping Process for Tubular Cable Lugs
Johannes Seefried, Tobias Glaessel, Alexander Kuehl, Andreas Mayr and Joerg Franke
In the production chain of electric drives, the electrical and mechanical contacting of the winding ends with a contact element forms a time-consuming and cost-intensive process step. The most common processes, e.g. hot crimping, are characterized by high tool wear and enormous energy consumption. An innovative and at the same time energy-efficient process is the ultrasonic crimping process which also combines the two process steps of skinning and contacting in a single process. The thermal energy required for skinning is based on the damping of oscillation energy in the cable lugs used. Due to the direct heat generation in the cable lug and the oscillations coupled in, the process has high potentials with regard to process stability, contacting of high-frequency litz wires and energy consumption. However, some disadvantages like the occasional occurrence of fatigue fractures in the tubular cable lugs and unclear dependencies reducing process reliability have to be investigated. One possibility to avoid these cracks and to further increase the process stability of ultrasonic crimping is the evaluation of adapted tool geometries. In context of this paper, different sonotrode and anvil geometries are compared and evaluated with regard to electrical, mechanical and optical connection quality.
Fretting corrosion behavior of various contact surfaces under diverse operating conditions
Haomiao Yuan and Jian Song
The electrical contact is a component in LED lamps. During their operation, the temperature increases, and the difference in thermal expansion coefficient of materials connected to the two parts of electrical contacts can result in micro-motions between these parts. Consequently, these electrical contacts can suffer fretting corrosion, which causes the LED lamps to fail. Under various operational conditions, various contact surfaces can be used. Bare base material can be directly applied to reduce costs, if the electrical contacts work in a clear environment, where corrosion is not a large issue. Tin coatings can be applied on the base material to improve the solderability when soldered to a printed circuit board (PCB). If the electrical contacts operate in a high temperature environment, nickel coatings can be employed. In order to compare the reliability of the various contact surfaces, the lifetime of electrical contacts with bare base materials, tin coatings and nickel coatings is investigated using fretting corrosion tests in this paper. To simulate the various operational conditions, the fretting corrosion tests are conducted at different fretting amplitudes and temperatures. The results gained from these investigations, provide a guideline for surface selection.
The Method of Majorant Functions for the Calculation of the Arc Erosion
Stanislav Kharin
Dynamic model based temporary arc fault analysis method for contact system in SHSR
Jiaxin You, Bo Li, Ding Ding, Delin Bi and Huimin Liang
The temporary arc fault often appeared in life test for small hermetically sealed relay (SHSR). In many applications, this type of fault is strictly prohibited. To analyze and solve this problem in design stage, a dynamic model is established with a spring system core including key parameters of the contact pair. Contact resistant and kinetic speed are compared between spring designs of different contact deflection. The comparison for the performance of the movement difference in orthogonal direction for spring and the speed difference of end points are issued. Test system for the dynamic performance of contact system is designed and established to test the different contact system. The arc is photographed by high speed camera. The whole SHSR is tested following IEC standard to compare the anti temporary arc fault ability between different spring design. The validity of this dynamic model based analysis method is verified.
Break kinetic energy based overload dynamic model for a small hermetically sealed relay
Jiaxin You, Bo Li, Ding Ding, Delin Bi and Huimin Liang
As one of the important components of the electronic systems, the requirements for the overload capacity of the small hermetically sealed relay (SHSR) is rising with the development of the multi-application. The experiments for SHSR based on IEC standard is carried out, the arc and dynamic characteristic is analyzed firstly. There exist some disadvantages for the improvement using the force-velocity improve method: anti-vibration performance decrease, operate voltage rise and so on. In order to improve these shortcomings, a novel break kinetic energy model (BKEM) is presented in this paper to improve the overload capacity of SHSR. The BKEM is established, and the new structure of the spring and the contact system of the relay have been improved according to BKEM. The FEM model for electromagnetic system and the dynamic model for contact system are built, then simulate the effect for the improved design, therefore carry out the comprehensive improvement of the resisting surge capacity. Overload tests are carried out to examine the correctness of this model. Compared with the original design of the SHSR, the validity of the BKEM for resisting surge performance improvement has been verified.
Study of Silver-graphene Tungsten Material For Low Voltage Electric Contact
Hai Chen, Pengpeng Wang and Jesus Hernandez
Silver Tungsten composite material is widely applied in low voltage circuit breaker. AgW50, consisting of 50% silver and 50% Tungsten in weight is a typical and popular contact material. Advantages of this contact composition is its low arcing erosion, high current interruption, and switching capabilities but it still has some disadvantage in electrical conductivity, potential welding, and higher electrical resistance. This paper is study a novel electric contact material, (AgGr)W50 made with Silver-graphene nanocomposite material. Instead of silver in the conventional electric contact, (AgGr), a nanocomposite material replaces silver Ag in AgW50 material. The study focuses two different percentage of graphene nanocomposite materials, (Ag Gr0.3) W50 and (AgGr0.5)W50 for our initial work. The electrical and mechanical properties of both nanocomposite materials are measured in comparison with conventional AgW50 material. The surface morphology of Ag-graphene-tungsten contacts show their unique microstructure compare with traditional Ag-tungsten material. This study will also look into the influences of (AgGr) in performance according to standard test from some low voltage circuit breakers.
Influence of Terminal Lubrication on Crimp Reliability
Jessica Hemond, Marcos Pajuelo and Suvrat Bhargava
TE Connectivity considers the use of terminal lubrication or oil to be an important component to ensure a consistent, high quality end crimp. While not required for all crimps, past investigations have shown that lubrication can provide benefits in terms of reducing tool wear and corrosion. Additionally, lubrication can provide a greater consistency and uniformity in the crimping process. TE Connectivity�s research in this topic has been both substantial and varied. TE Connectivity researchers have studied various aspects of this technology from crimp type, the performance of solid versus stranded wires as well other factors, including contamination. These factors were identified and studied to ensure that any variable that may influence the process or crimp, itself, was well understood. In the development of crimp tooling, this body of research has provided guidance to the development of reliable tooling. It is understood through this prior work that terminal lubrication has an influence on crimp force. The addition of lubricant can result in a decrease of crimp force and impact the final crimp height. The end recommendations from this work include the use of crimping lubricants, adjusting the crimp height regularly and changing the crimp tooling when signs of wear are seen. These recommendations are not new to the industry, but with the passage of time the supporting data for these recommendations and the relationship to the known influence of crimp lubrication have become obscure. This effort relates the influence of crimp lubricant in creating a consistent high-quality crimp and ensuring consistent die tool performance.
Carbon nanotube-reinforced metal matrix composites as novel electrodes for low-voltage switching applications: a surface degradation analysis
Sebastian Suarez, Rafael Puyol, Christian Sch�fer and Frank M�cklich
Arcing is one of the major degradation mechanisms of electrical contacts. Currently, the most suitable materials to minimize this are composed of oxide particles dispersed in a me-tallic matrix. Due to their outstanding thermal and electrical properties, carbon nanotubes (CNT) might be appropriate candidates to replace the aforementioned ceramic particles and provide an enhanced overall behavior. To evaluate this, low voltage (13.5 V) DC single break operation tests were performed on pure Ni and CNT-reinforced Ni composites to investigate their suitability as electrode materials. Arc energy and duration was assessed and a thorough morphological and microstructural characterization was performed with the aid of high-resolution techniques. It is observed that the addition of CNT positively influences the behav-ior by reducing the arc duration and, therefore, the energy input. Furthermore, the resulting erosion craters are generally smaller in size when compared to a pure Ni electrode. A signifi-cant fraction of the CNTs were able to withstand the arc discharge, playing a fundamental role in removing the heat contribution and increasing the molten pool viscosity and conse-quently, reducing the total material removal. Summarizing, our results show that it would in-deed by viable to utilize CNT as a reinforcing phase in composite electrodes.
Observation of metallurgical changes induced by an electric arc on Ag-SnO2 electrodes
Aur�lien Fouque, Georges Cailletaud, Vladimir Esin, Romaric Landfried, Philippe Test�, Fr�d�ric Houz�, Alexandre Bonhomme, Jean-Luc Ponthenier, Fran�ois Chaudot and Marina Lysniak
Understanding the erosion of contact materials caused by electric arcs is a major challenge to improve the lifetime of switching devices. The main purpose of this study is to determine how the silver-tin oxide material (Ag-SnO2 12%w.) evolves under the action of a unique arc impact, as well as to estimate the power and power flux density brought by the arc to the material. Pairs of electrodes with flat or curved surfaces were submitted to an opening arc at room atmosphere for current intensity of 150, 300 and 600A rms and typical duration of 5ms. In a first step, the resulting craters were all characterized by optical profilometry. Then further investigations were performed on two samples - a flat anode and a flat cathode stemmed from the 300A tests. Metallographic cuts along the diameter of the craters were analyzed by electron backscatter diffraction; they revealed a wide and deep volume with resolidification crystals, attesting that a large area surrounding the crater actually underwent a melt. The frontier between this area and the untransformed material can be considered as a fusion isotherm. These isotherms have been used to estimate from numerical simulations the power flux characteristics of the arc.
The evolution of wear in a hot switched (200 mW) Au on Au coated MWCNT electrical contact for a MEMS switch application
John McBride and Thomas Bull
A key benefit of metal-metal MEMS switches is their ability to carry signals from DC to GHz frequencies. The contacts in these switches are often made from thin (< 1 �m) gold (Au) films. Au is used as it has low resistivity and is resistant to oxidation. A problem is the low contact force available in a MEMS device only gives a small area for conduction. A solution is the use of a composite contact material engineered to increase the compliance between contacts. The use of Au film with a sublayer of elastic vertically-aligned multi-walled carbon nanotubes (Au-MWCNT) has been shown to increase contact area and extend switching lifetime by orders of magnitude. Hot switching the contact is more demanding than cold switching as the electrical signal can itself cause wear. Hot switching at low current DC conditions below the arcing voltage (~12 V) is linked to microscopic surface wear caused by the molten metal bridge (MMB) phenomenon. In the Au-MWCNT contact the MMB causes a microscopic fine-transfer of contact material. In this study a Au-MWCNT composite contact is paired with a Au coated hemisphere contact under a constant contact closure force of 100 �N, in an In-situ Contact Evolution (ICE) apparatus. The apparatus allows the measurement of surface wear during the hot switching of a DC 4 V, 50 mA (200mW) signal. The surface is measured every 10 Million cycles over 150 Million cycles. It is shown that contact surface is gradually deformed, with the volume of Au transfer linked to the switching current. Eventually regions form where the Au is entirely removed from the surface. The switch maintains stable and low contact resistance (~400 mO) throughout the experiment. In a new observation, when the Au surface has depleted, a previously unreported transient voltage waveform is seen as the contacts separate. The waveform is characterised by discrete steps in the contact potential above the level associated with Au boiling. These voltage steps are discussed and related to the pyrolysis of the carbon nanotubes.
Nanoscale Measurements of the Real Area of Contact and Comparison to Theoretical Models
Yang Xu, Robert L. Jackson, Yan Chen, Anqi Zhang and Barton Prorok
In this study, a new experimental method is proposed to measure the real area of contact between a ceramic sphere and an Al surface based on the adhesive transfer of the Au film and the Scanning Electron Microscope (SEM) in the back-scattered mode. A thin film of Au is sputtered on the ceramic sphere before the indentation with the Al surface. After indentation, the interfaces of the ceramic sphere and Al surface are observed by SEM. The contact area can be identified based on both the distributions of the ceramic and Au on the ceramic sphere and Al surface, respectively. The measured contact area at different nominal pressures are compared to predictions made by several popular theoretical elastic-plastic rough surface contact models.
Contact Resistance and Arc-free Commutation Current of Tungsten-clad Copper Contacts for a Hybrid DC Switch
Koichi Yasuoka, Yuta Yamada and Mo Chen
Hybrid DC switches have been intensively developed due to the increasing demand for DC power distribution systems. A hybrid switch consists of high-speed mechanical contacts, semiconductor power devices, and metal�oxide varistor elements. The contact voltage increases during the opening of contacts, and it turns on the power device connected in parallel to the contacts. The DC circuit current subsequently commutates from the contacts to the power device, and is interrupted by the power device with varistors. The arc-free commutation is achieved in case that the contact voltage is always below the boiling voltage of the contact metal. The tungsten material is suited for arc-free commutation due to the highest boiling-voltage, however, the higher contact resistance increases the contact voltage by Joule heating, particularly at high current operation. Newly developed contacts that have tungsten-clad copper electrodes, show the features of lower contact resistance and high boiling temperature. The copper part removes the Joule heat fast from the tungsten part during the current commutation. The contact resistance of copper (Cu), tungsten (W), and tungsten-clad copper (W-Cu) were 0.40, 1.68, and 0.68 milliohm, respectively. While, the maximum arc-free current increased as 120 (Cu), 225 (W), 400 (W-Cu) A. These results show that the tungsten-clad copper contacts are the most suitable for the arc-fee hybrid DC switch because of its low on-state energy losses and large current capacities of the arc-free current commutations. Key words: Hybrid DC switches, tungsten-clad copper, SiC-MOSFET, Arc-free commutation, contact material
On the aging of electrical joints with a copper and an aluminum contact member
Marcella Oberst, Stephan Schlegel and Steffen Gro�mann
Aluminum and copper are the two commonly used conductor materials in electrical power engineering. If these two materials are connected in an electrical joint without material closure, long-term stability of the connection is not reliably achieved. Previous research has attributed the witnessed rise in resistance to the formation of intermetallic compound between aluminum and copper. However, Pfeifer has shown in her work that this cannot be the main aging mechanism for joints of the mentioned material combination. This paper explores the influence of other aging mechanisms by examining the aging of bolted joints with one aluminum and one copper busbar. Several test parameters are varied, such as the joining elements, the torque at assembling, and the surrounding atmosphere. The results lead to the conclusion that oxygen entering the contact plain during the aging process causes the formation of aluminum oxide in the a-spots. Due to its high resistivity, the joint resistance increases, leading to a failure of the connection. Selected test parameters were repeated for a model geometry consisting of a flat and a conically reduced cylinder, thus generating a point contact in contrast to the flat surface contact of the bolted joints with busbars.
Investigation of the attachment transition from anode spot type 2 to anode plume of vacuum arcs depending on current density
Diego Gonzalez, Sergey Gortschakow, Steffen Franke, Ralf Methling and Dirk Uhrlandt
The characteristics of the discharge mode transitions of vacuum arcs on Cu/Cr electrodes as a function on current density was investigated using high-speed camera technique and pulsed DC-currents. The time required for a given transition mode was related to total transferred charge and corresponding current amplitude and separation speed of the electrodes. The arc voltage and current � gap characteristics from the recorded waved and the radiating characteristics of the observed arcs permit to identify the conditions for the transition of the arc attachment from diffuse over footpoint onto the high-current anode modes. Comparison to previous works regarding gap � current diagrams indicate differences for the classification of attachment modes.
Realistic Time-Domain Simulations of Arc Faults in Low-Voltage Installations
Matija Varga, Yannick Maret, Stefano Maran�, Luca Ghezzi and Agostino Butti
Electric arc faults that appear in home installations pose a significant safety hazard that may result in an outbreak of fire. Such events can be prevented using an arc fault detector device (AFDD) that interrupts the electrical circuit upon detecting an arcing event. Nevertheless, commercial AFDDs are still facing the challenge of false trips caused by home appliances. In this work, we propose a realistic model of arcs for electrical simulations of low-voltage installations. We model an arc as a circuit component whose parameters dynamically change to account for the stochastic behaviour of electric arcs. The model uses a black-box representation that consists of a set of mathematical equations that link current and voltage. The proposed model goes beyond the state of the art by dynamically adapting the arc parameters after each current zero crossing. The parameters and their statistical distributions are extracted from laboratory measurements using optimisation methods. In addition to that, we implement a noise source within the arc model with a 1/f characteristic during the arcing phase. Power spectral density and noise source impedance are derived from actual noise measurements. Finally, transient behaviour of the modelled arc is implemented in an analog and mixed signal simulator VHDL-AMS.
Spectroscopic investigation of DC-arcs between parallel rails under the influence of external magnetic fields
Diego Gonzalez, Ralf Methling, Steffen Franke, Sergey Gortschakow and Dirk Uhrlandt
The effect of transverse magnetic fields on the spectral characteristics of low current DC-arcs on air was investigated. The setup consists of parallel copper rails. The arc radiation with or without external magnetic field was analyzed using high-speed spectroscopy as well as high-speed imaging. Results confirm further changes of the arc geometry and arc behavior as well as changes on its radiation characteristics, voltage and duration under the influence of the external magnetic field. The observed strong influence of the external magnetic fields lead to conclusions regarding its further application for arc-extinction and limiting of fault currents.
Experimental Characterisation of Contact Resistivity for CFRP Wind Turbine Spars' Equipotential Bonding
Antonio Andrea Maria Laudani, Igor O. Golosnoy, Jochen Kremer, Evangelos C. Senis, Ole T. Thomsen and Paul L. Lewin
The aim of this study is to characterize the contact resistance of several equipotential bonding interfaces for CFRP wind turbine spars. The contact resistance plays a key role since elevated values might result in high temperatures, which in turn cause resin evaporation around the bonding points and consequent delamination within the joint.
Research on composite fretting behavior of Au plated copper connectors
Sanqiang Ling, Le Xu and Guofu Zhai
Gold-plated copper alloy wire spring connector is widely used in the electrical interconnection system of aviation and aerospace engineering due to its advantages of high quality, high reliability and long life. In order to improve the contact stability, there is a certain angle in the axial direction between the pin and wire spring. When in the vibration environment, this design structure will lead to the phenomenon of composite fretting at the contact interface. In this paper, the variation of contact resistance is recorded at the different angles between the pin and wire spring under fretting condition based on the vibration test system. Surface characteristics of fretted area are also analyzed by SEM/EDX. The variation of contact area in the process of composite fretting is analyzed by finite element simulation. It is clearly revealed that the included angle is an important factor for the electrical connector degradation and the failure mechanisms of connectors. Key words-Wire spring connector, Composite fretting, Angle, Surface characteristics, Contact area.
The Effect of Convection on Electro-thermal Modeling of Whisker Shorting
Robert L. Jackson and Erika R. Crandall
Whisker growth from metal surfaces of electrical connectors and other components has shown itself to create reliability issues. If a whisker grows in a location that bridges between two conducting surfaces not previously electrically connected, a short can occur, resulting in faulting components. The current passing through the whisker will cause its temperature to rise due to Joule Heating. This can eventually cause the whisker to melt, which can than disconnect the short circuit. Therefore whisker shorts are limited by this melting current. Previous works have examined the coupled electro-thermal model of a solid whisker conductor, but most neglect the convection of heat into air, which dissipates some of the heat, reducing the temperature rise of the whisker. This work examines the influence of convection on the melting of a shorted whisker. This is done using a finite difference model that considers the temperature dependent conductivities when solving the coupled one-dimensional heat and electrical conduction equations. Since there exists a variety of metals capable of whiskering, various metal whiskers will be modeled here for comparison purposes.
Simulation of Electric Arcing in HVDC Relays During a Short Circuit Situation
Crispin Masahudu Ewuntomah and Jens Oberrath
Electric arcing in high voltage direct current (HVDC) relays is an undesirable phenomenon that many manufacturers seek to fully understand and control. In short circuit situations, the rapid increase of direct current causes the arcs to excessively heat, melt, boil, and vaporize the contact spots of the relays. This situation may end in explosion of the relays. In this work, the arcing process of such a short circuit situation is simulated based on time dependent current and voltage measurements at the relay. To analyse the electric arcs in detail, and estimate the resulting vaporization from the increasing current, a multiphysics model which couples current flow, fluid flow, and heat transfer to the magnetohydrodynamics equations is established in COMSOL. The simulation results will show the electric arc formation and time dependent arc evolution. It is expected that; the temperatures of the arcs are high enough to melt, boil, and vaporize the contact materials, which has to be quantified to understand the pressure increase within the relay chamber. The authors acknowledge the funding of the European Regional Development Fund (ERDF), and the collaboration with Panasonic Industrial Devices Europe GmbH, as part of the ARKE project.
Investigation on Electrical Contact Resistance of NiPdAu-Plated CPU Package Pads and NiAu-Plated Second-Level Interconnect Socket Contacts Interface
Feifei Cheng and Jiwei Sun
In this paper, a modeling framework combining electrical contact and electronic magnetic theories is developed to investigate and quantify some potential high contact resistance contributing factors for CPU package pads and socket contacts interface.
Analytical Methods to Identify Root Causes for Early Failure of an AC Contactor with Heavy Load Service Life Test
Volker Behrens, Havva Cinaroglu, Bernd Meidel, Sandra Fuchs and Thomas Honig
Recently developed Silver/Tin oxide contact material Ag/SnO2 14 WPA has been proven to fulfill AC contactor switching requirements as service life, make capacity, and overtemperature behavior in a very satisfactory way. Based on these experiences early failures with an additional AC4 electrical endurance test at app. 50% of service life goal were unexpected and triggered in depth analytical evaluations to fix root causes. Applying microsections, microtome sectioning, ultrasonic analysis, optical and scanning electron microscopy (SEM) combined with energy dispersive x-ray spectroscopy (EDS) three different possible root causes could be identified. Joining area between contact carrier and contact tip showed voids indicating non-perfect brazing. In addition compound substances based on phosphorous as well as some iron oxide particles were detected on the contact surface, probably originating from excess braze alloy rising the contact tip side and splitter plate splashing and evaporation, respectively. Additional tests proved that optimization of brazing technique led to substantially improved AC4 service life results.
Preliminary experimental study on the insertion and withdrawal characteristics of blade and receptacle pair
Wanbin Ren, Yuan Meng and Tengyu Wang
The structure and dimensions of blade and receptacle pair directly influence the insertion and withdrawal process and current carrying capability of electrical connectors. In this paper, a commercial blade and receptacle pair is selected for analytical and experimental studies. Firstly, the relevant mathematic model for insertion and extraction force calculation is presented. Next, the typical waveforms of insertion/extraction force, contact resistance and deflection of receptacle are measured simultaneously and interpreted explicitly. The effects of motion speed and assembling position on the insertion characteristics are compared and analyzed. Finally, under the repetitive mechanical insertion and withdrawal experiments, the degradation behavior and associated physical mechanism are determined.
Printed copper connexions on flexible substrates
nataliya kalashnyk, Sophie Noel, pascal chretien, aurore brezard oudot, frederic houze, fanny hauquier, vincent derycke, thomas berthelot and didier rousseau
We describe here the first results of a study aiming at realizing printed copper connexions on flexible polymeric substrates. The ink under investigation is not a nanopartcle ink but is is based on copper salts combined to ligands and additives. The aim is to print with an industrial type inkjet printer conducting and adherent connexions on PET substrates. Several obstacles were met and we show that with a proper Intense Pulse Light post treatment low conductivity patterns can be achieved. Several electrical characterizations are realized and commented with additionnal mophological and composition.
Measuring joint resistances of power connections with stranded conductors � fundamentals, principles and common reasons for measurement errors
Christian Hildmann, Stephan Schlegel, Steffen Gro�mann and Carina Schmidt
Measuring the joint resistance of power connections with stranded conductors may be a challenging task. Generally, to apply four terminal sensing is state of the art. Depending on the type of conductor and connection, the suitable type of current feed-in and potential tap has to be considered carefully. Especially tapping the potential correctly is one of the main issues for an accurate and repeatable measurement of joint resistance. The paper therefore summarizes the common methods for joint resistance measurements on power connections with stranded conductors. Further, it presents options for the electric modeling of connections as well as conductors and compares the measurement methods theoretically. By the means of chosen examples, differences between the measured and the actual joint resistance are shown and discussed. Thereby, the influence of the coaction of conductor and connections as well as of the test setup is considered. The paper reviews these principle considerations in experiments on newly installed and aged power connections. This publication aims to reveal common reasons of errors in the joint resistance measurement and gives recommendations how to avoid them.
The Influence of Film Area on Sn Whisker Growth
Zekun Wang, Michael Bozack and George Flowers
An important question in Sn whisker research is the role of lateral Sn diffusion in the film to the whisker root in providing the feedstock for whisker growth. In this current work, the effect of limiting the lateral extent of the Sn feedstock available during whiskering by employing extremely thin, micron-sized patterned Sn deposits is investigated and compared to whisker growth from an essentially infinite thin film of Sn. A series of metal, mesh grids of varying sizes was used to define the area of sputtered tin deposited on a Si substrate. The square areas varied in size from 1um to 150um. A thickness of ~500� of sputtered Sn was deposited on each specimen. The samples were divided into three comparison groups and subsequently incubated for 34 days under three incubation conditions: 23oC (isothermal); 100oC (isothermal); and thermal cycling over -40
Development and application of a multifunctional nanoindenter: coupling to electrical measurements and integration in-situ in a Scanning Electron Microscope
Sol�ne Comby-Dassonneville, Fabien Volpi, Chaymaa Boujrouf, Guillaume Parry, Muriel Braccini, Sol�ne Iruela, Annie Antoni-Zdziobek, Yannick Champion, Marc Verdier, Fr�d�ric Charlot, Rachel Martin, Francine Roussel-Dherbey, Laurent Maniguet and Didier Pellerin
Nanoindentation is a well-known characterisation technique dedicated to local mechanical testing of materials at small scales. The present submission reports the development of a home-made multifunctional characterisation device based on a commercial nanoindentation head. This device combines mechanical to electrical characterisations, and can be integrated in-situ in a Scanning Electron Microscope (SEM). Different applications will be presented: electrical contact monitoring, leakage current through insulators subjected to mechanical load, multifunctional property mapping, local dielectric permittivity determination,etc.
3D Printing of Functional Electrical Contacts
Greg Pawlikowski, Anthony Ventura, Wojciech Misiolek and Martin Bayes
Process parameters for 3D printing and precipitation hardening have been developed for an electrically conductive alloy of CuNiSi. Optimized printing parameters achieved part densities approaching 99 % (relative to the wrought alloy), enabling the ability to create contacts in their formed state without the need for costly and time-limiting forming tooling. A simplified precipitation hardening process has been shown to yield properties comparable to those of the wrought alloy of C70250 (TM03), with a conductivity of 35 % IACS and a tensile strength above 700 MPa. It has been demonstrated that direct 3D printing can create functional contacts in a fraction of the time compared to traditional stamping/forming, meaning that the formation of the contacts is no longer the time-limiting step in the production of connector prototypes. In addition, 3D printing can offer greater design freedoms, and overcome the limitations associated with stamping/forming to fabricate contacts where the 3D geometries and feature thicknesses are not limited by the 2D real estate and single stock thickness of a blank wrought strip.
Research on the electrical contact status of 1000kV GIL and its contact resistance degradation effect on temperature rise
Huidong Tian, Zehua Wu, Lilan Liu, Shoufeng Jin, Qingyu Wang and Zongren Peng
Good electrical contact status is an important guarantee for the stable operation of gas insulated line (GIL). Loop resistance is a key parameter which can characterize the contact condition of the current-carrying system in GIL. Generally, the conductor and metal liner cast with insulator are connected by the contact fingers. The degradation of contact status can cause severe temperature rise near the insulator, which will reduce the insulation and mechanical properties of insulator and cause discharge accidents. In this paper, firstly, the loop resistance measurement and temperature rise experiment were conducted on 1000kV AC GIL model machine. Then, the regular effect of contact resistance degradation on local overheating was simulated based on the computational fluid dynamics (CFD). Finally, according to the thermal analysis and the heat resistance of materials used in GIL, the permissible contact resistance degradation lever was proposed. The results indicated that the temperature near the contact structure is 7? higher than that at other locations on the conductor under current load of 6930A. The contact resistance degradation will cause the overheating on the adhered interface between insulator and metal liner and reduced its bond strength. This research can basically provide a reference for 1000kV GIL engineer application.
A Supplement to Deterioration Process of AgPd Brush and Au-plated Slip-ring System with Lubricant
Koichiro Sawa, Yoshitada Watanabe, Takahiro Ueno and Hiroyasu Masubuchi
The authors have been investigating the deterioration process of Au-plated slip-ring and Ag-Pd brush system with lubricant to realize stable and long lifetime. Through the past tests, it can be made clear that lubricant is very important for long lifetime, and a simple model of the deterioration process was proposed. However, it is still an issue how the lubricant is deteriorated and also what the relation between lubricant deterioration and contact voltage change is. In this paper, the contact voltage waveforms were regularly recorded during the test, and analyzed to obtain the time change of peak voltage and standard deviation during one rotation. Based on these results, it is discussed what happens at the interface between ring and brush with the lubricant. Consequently, from the analysis of the voltage waveforms it can be made clear that the fluctuation would be caused by the lubricant layer, not by the ring surface. In other words the fluctuation means that there would be enough lubricant between ring and brush. Further, the element analysis and laser microscope observation of the ring surface were made after the test. From these results, the Au plating layer is found to still remains on the surface of good rings, while it was worn out from the surface of the ring, the lifetime of which ends. The wear depth of good rings is less than 2 micrometers even after the operation time of about 6000 hours.
Hardware Implementation of Series Arc Fault Detection Algorithm for Different DC Resistive Systems
Silei Chen, Qishen Lv, Yu Meng, Xingwen Li and Ning Xu
DC series arc faults result in much more serious safety threats without zero-crossings. With the increasing DC voltage and capacity, series arc faults appear in DC systems more frequently. To eliminate their damages, specific arc fault circuit interrupters (AFCI) should be developed. In this paper, two kinds of DC systems are considered in the designed experimental setup. Firstly, a simulated DC source with the ac-DC-DC structure is connected to a resistor. This source could act as a constant voltage or photovoltaic (PV) source by operating in different U-I output curves. Then a real PV array outputting the nonlinear U-I output curve is also conducted as a comparison. Next, a simple detection algorithm is proposed based on time domain detection variable. Finally, this series arc fault detection algorithm is implemented using a digital signal processing (DSP) chip. The performance of this hardware behaves satisfying under arc fault conditions with different arc ignition methods, current levels, arc gap lengths, operation points and prevents false judgments from system transitions.
Analysis on Arc Evolution Process of Double-breaker DC Miniature Circuit Breaker
Yin Nan, Lichang Wang, Jinbao Zhu, Yijun Deng, Fang Liu, Jianning Yin, Tian Tian and Xingwen Li
Direct current (DC) miniature circuit breaker (MCB) is a crucial component for controlling and protecting the DC power system, especially in photovoltaic power generation system. In this paper, a 3-D magneto-hydro-dynamic (MHD) model for a double-break MCB is developed, where the nonlinear characteristic of splitter plates is considered. Based on the model, the effects of arc current, arc ignition position, arc quenching chamber on the arc evolution process are analyzed. Also, relevant experiments are carried out in order to verify the model. Except arc current and voltage waveforms, the arc images during the interruption process are recorded by CCD. It shows that the developed model could be used to optimize the design of the arc quenching chamber and contact system of DC MCB.
Investigation on the thermal and electrical properties of Ag-based electrical contact materials
Ohjib Kwon, Jae Soung Park and Joohyeon Park
Electrical Contact are critically important for a wide variety of applications, automotive, manufacturing and renewable energy technologies. Especially for contact materials, Silver (Ag) is the best electrical and thermal conductor of all metals. That�s why it is used in many electrical contact materials. Among them, Silver Cadmium Oxide (Ag-CdO) has been widely used as an electrical contact material because of its excellent electrical and thermal characteristics. In recent years, the use of Cd has been restricted in many countries due to human and environmental hazards. In addition, since Ag, which is a precious metal, despite these excellent properties, manufacturers and users were forced to pay a high price. In general, Ag is characterized by limited alloying with other metals. Thus, the electrical contact material is manufactured through the powder metallurgy method. However, when the content of other elements mixed exceeds 20wt%, the electrical conductivity decreases sharply and the use of it as an electrical contact material is limited. And the current electrical contact material used is mainly Ag-based. Ag has a thermal conductivity of 429 W/mK in pure state, and the thermal conductivity decreases with the addition of other elements. As the thermal conductivity decreases, it affects the reliability of the electrical contact material, and affects the service life such as welding and consumption during use. In this study, we focused on two key things. First, we aimed to reduce the use of Ag along with the development of alternative materials for Cd. The present invention also provides a method for manufacturing a powder which is a new electrical contact material which does not decrease electric conductivity even when 30wt% or more of other elements. Second, we aimed to reduce the use of Ag by developing high thermal conductivity composites. We have developed a high thermal conductivity (over 450 W/mK) composite that has more than the thermal conductivity of Ag and tried to apply it as an electrical contact material. When the Ag-C powder was prepared through DC non-transferred plasma equipment, it was possible to produce a nano-sized powder in C particles of 20? in size were uniformly dispersed in Ag particles of about 200?. In addition, Ag-Ni-C was able to produce nano-sized powders in the same manner, and the material of the electrical contact was manufactured using this raw material powder and compared with the commercial electrical contact material. The Ag-C and Cu-C composites were prepared by the chemical reaction method, in which Ag and Cu were coated on the C particles, respectively. The prepared powders were oriented by applying ultrasonic waves to the C particles and then sintered to form bulk materials. Electrical contact materials made of micrometer sized powders exhibited an electrical conductivity of below 50% IACS, while those of electrical contact materials made of nano powders had an electrical conductivity of over 80% IACS. Also, it showed good electrical, thermal and mechanical properties, which was maintained below 50? in temperature rise evaluation. The Cu-C and Ag-C high thermal conductivity composites with C particles with longitudinal microstructures showed thermal conductivity of 533 W/mK and 487 W/mK at room temperature, respectively.
Partial Discharge Testing for Low Voltage Switchgear at high temperatures
Nicholas Hill, Michael Hilbert and Michael Kurrat
Low voltage switch- and control gear product standards of IEC, UL and CSA usually do not consider partial discharge testing. The creepage and clearance dimensions, material categories mainly described through CTI and RTI values, are the tools subjected to insulation coordination. However, in principle, PD measurements are required for rated voltages exceeding 500 VAC. IEC 60664-2 delivers rules for consideration and electrical dimensioning of solid insulation. Operation conditions changed due to two trends: miniaturization and increased application of power electronics. The first trend leads to increasing power densities as well as higher operational temperatures. Furthermore, lower dimensions of molded cases reduce the clearances in conjunction to solid insulation. The second trend addresses the use of pulse width modulation (PWM) converters for variable frequency drives (VFD) connected by long cables or lines. The dielectric stress and behavior of solid insulations changes when the time characteristic of the applied voltage becomes non-sinusoidal. For instance, one additional stress appears through reflected voltage waves. As result, these changing operation conditions enable partial discharges (PD) processes and insulation damages. Therefore, reconsideration of PD testing of low voltage switchgear is an essential item. PD processes are well known and the transfer to low voltage switchgear design is the prerequisite to evaluate the changed operation conditions. The paper presents two basic arrangements, which reflect typical design cases of insulating structures with solid insulation. The use of these test cases enables the calculation of PD inception conditions at higher ambient temperatures and the comparison with PD measurement results. AC voltage sources supply sinusoidal test voltages for the PD measurements. The temperature dependent PD characteristic delivers an additional parameter for comparison. Room temperature and elevated temperature up to the maximal operational temperature are specified as test conditions for the PD measurements. The interpretation of the PD measurement results under consideration of low voltage switchgear allows concluding the test procedures and parameters. PD measurement and simulation results of the test cases provide a first assumption for limiting values of the PD characteristics. Therefore, a PD test procedure is now available for future PD test considerations of low voltage switchgear.
Comparison of equations of the VI characteristics of an electric arc in open air
Jonathan Andrea, Erwann Carvou and Patrick Schweitzer
This paper presents a comparison of VI characteristics of an arc. Many VI characteristic equations can be found in papers on the subject, though they all vary slightly in form and are obtained through empirical processes. We will present a non-exhaustive list of these empirical equations and identify the one which is most suitable by comparing it with the result of an arcing VI characteristic measurement. This identification was made possible by calculating the absolute difference between measures and fitted equations. The subsequent data is presented in a radar plot.
The impact of pressure on electric arcs switch-off
Mohamed Boukhlifa, Jonathan Andrea, Thomas Klonowski, Romaric Landfried and Philippe Teste
The evolution towards the more electric aircraft leads to the increase of the electrical embedded power and network voltage (+/- 270 V DC) in the aircraft. An important issue facing professionals in the aeronautics sector, is the implementation of a functioning cut-off device capable of ensuring a galvanic insulation under the new voltage conditions and standard aeronautical pressure conditions. Recently, studies concerning electric arc properties in aeronautical conditions of pressure in the DC regime, have shown that the arc voltage is a decreasing function of the pressure. The aim of this paper is to provide a study concerning the properties of an electric arc under 540 V DC supply voltage in sub-atmospheric pressure. In the first part, we present research regarding the influence of various parameters on the extinction properties of the arc (arc energy, arc duration, extinction gap, etc.) on a simple configuration. In the second part, we focus on the cut-off tests undertaken at sub-atmospheric pressure. These tests were carried out using an industrial device that operates reliably at atmospheric pressure and under voltage conditions comparable to those encountered in the aircraft of the future (540 V DC).
Critical Experiments Leading to a Novel Test Fixture Assembly for Microcontact Reliability and Performance Research
Protap Mahanta, Ronald Coutu and Farhana Anwar
In microelectromechanical systems (MEMS) ohmic switches, reliability is of paramount concern for the applications where billions of switching cycles are required. Microcontact surface tribology plays a critical role in determining their reliability and performance. In this work, a novel, simple, quick and efficient test fixture has been designed and assembled to study the contact resistance, contact force, adhesion force, and contamination associated with the microcontact. In support of developing the test fixture, we evaluate the performance limitations of each component (i.e. piezoelectric actuators, force sensors, nanomax stage) independently. Position versus voltage, force versus voltage, and force versus position data have been collected for each test fixture components at the cycle rates of ~5 KHz. A customized stage has been 3D printed for holding the microcontact support structure. We use Thorlab�s state-of-the-art nanomax stage to provide nanometric positioning and precise alignment between the microcontact support structure and the force sensor on three orthogonal axes. We fabricate a novel contact support structure to test the feasibility of our test fixture and collect force and resistance data simultaneously using LabView. Data obtained from the test fixture will provide significant information for designing a reliable MEMS switch for future DC and RF applications.
Fretting Performance Comparison between PFPE and PAO Based Lubricants for Lightly-Loaded Gold Plated Electrical Contacts
Lovlesh Kaushik, Michael Azarian and Michael Pecht
Organic lubricants, such as perfluoropolyether (PFPE) and polyalphaolefin (PAO) based oils, have previously been found to reduce fretting wear in gold plated electrical contacts operating at loads higher than 50 cN. A film of such lubricant might negatively affect the contact performance in applications, such as RF electromechanical switches, in which contact loads are only several centiNewtons. This study compared a PFPE and a PAO based lubricant in terms of the fretting performance of lubricated, lightly-loaded gold plated contacts. Lubricated flats contacted pins at 10 cN load, with fretting amplitude of 80 �m and fretting frequency of 5 Hz, for up to 1.2 million cycles or until contact failure (defined as contact resistance greater than 1 O). No failures were observed for unlubricated contacts or PAO lubricated contacts, whereas 2 out of 4 PFPE lubricated contacts did fail. The latter exhibited failures due to hydrodynamic lift that was caused by the lubricant film. Unlubricated contacts sustained a low coefficient of friction of around 0.1 for only about 1% of the total number of fretting cycles achieved by PAO or PFPE lubricated contacts at that level of friction. Both PFPE and PAO lubricated contacts showed evidence of lubricant degradation near the contact zone.
Test categories for characterization of sliding electrical contacts
Christian Holzapfel
For sliding electrical contacts a variety of material combinations and principles are being used. Field tests with real sip rings in real applications have the advantage that real load and environmental conditions are used. However, these tests are complex and expensive. This is also the case if real sip rings are investigated in the laboratory with full load at a variety of climatic conditions e.g. within a climate chamber. On the other hand, tribometer technology exists that is relatively easy to set-up and additional parameters such as friction force of individual contacts can be measured. This paper presents different configurations of test categories in an exemplary screening test sequence that elucidates how new material combinations can be efficiently developed.
Analysis on the Stress Corrosion Characteristics of the Torsion Spring Contact in SF6 Environment
Shoufeng Jin, Huidong Tian, Shiyi Zhou, Zehua Wu, Qingyu Wang and Zongren Peng
Torsion spring contact are widely used in the high voltage SF6 insulated power equipment. They carry the full current and suffer from strong mechanical stress. Due to the thermal expansion and contraction, etc., the continuously fretting wear occurs on the contact interface, which increase the contact resistance and cause local overheating. When the temperature of the contact interface exceeds the SF6 decomposition temperature, the by-product such as SO2F2, SO2 and H2S will corrode the contact fingers and accelerate the fretting corrosion, which finally cause the overheating fault of power equipment. In this paper, taking the corroded torsion spring contact used in an overheating faulted extra high voltage (EHV) bushing as example, the corrosion process was researched. Firstly, the SEM and EDS were conducted on the overheating contact fingers to analyze the chemical reaction dynamics of the corrosion process. Then, the mechanical stress analysis based on the finite element method were conducted. Combining the SEM image with first principle stress distribution contour, the place where the first principle stress of the finger is the largest is consistent with the place where the corrosion begins on the non-contact area, which explains why there is also severe corrosion in the non-contact zone.
An Estimation Method of Cu-W Arcing Contact Electrical Life of SF6 Circuit Breakers in Making Capacitor Bank
Can Ding, Chengxi Li, Zhao Yuan and Chunhua Fang
For an SF6 circuit breaker in capacitor bank making operation, the inrush current may cause serious erosion to its arcing contacts. In order to observe the contact erosion property and electrical life under making process, an arc extinguish chamber of SF6 circuit breaker with Cu-W arcing contacts was designed, and experiments of capacitor bank making were carried out under different experimental conditions. In the experiment under various conditions, the arcing time and inrush current have been recorded, the mass loss has been measured after 100 times of operation, and the mass loss rate and friction coefficient have been calculated. Based on the failure mode of reversed order contacting between arcing and main contacts, an estimation method has been proposed to calculate the electrical life of arcing contact in making operation. This method can be used to support the design of the arcing contacts. Changing the arcing contact geometry and reducing arc energy in making operation will improve electrical life of arcing contact.
A statistical approach to electro-thermal simulations with contacts
Joerg Ostrowski, Marcelo Buffoni, Michael Gatzsche and Boguslaw Samul
The aim of this contribution is to predict the transient temperature distribution inside an earthing switch of a gas insulated switchgear during a short time current test. The high electric current heats up the device and the test is only passed if the temperature stays below the melting point throughout the device. It is crucial to consider the electrical contacts for simulations of this process, because a large amount of heat is generated there. We developed a Finite Element based simulation tool that is capable of calculating this, see [1, 2]. The temperature maximum that is reached is very sensitive with respect to the electric contact resistances. However, measurements of the individual contact resistances are often not available, because it is mostly impossible to access them in an assembled device. We therefore rely on a statistical approach and use intervals for each contact resistance of the earthing switch. Scanning these intervals in the simulations yields a probability distribution of the maximum temperature.
Inside the Aluminum Contact Spot
Magne Runde