E. Carvou

Electrical contact behaviour of power connector during fretting vibration

It is well known that vibration of contact interfaces is the main cause of contact degradation by the so called fretting corrosion phenomena. In fact the process of generated particles by mechanical wear produce the increase of contact voltage frequently assimilated as high contact resistance in low power and signal connector. In high power connector, this degradation is expected to be accentuated by thermal effect generate by increasing contact voltage to melting and arcing voltage. The main objective of this work is to examine conjointly the wear amount and electrical behaviour of connector terminal under vibration and higher current stress. The spring lamellas of an automotive connector are submitted to high number of vibrations (10 to 10 ) whereas the pin is firmly attached to a fixed support. High frequency oscillation (100 Hz) with amplitude of 50 mum is used. The contact is made with copper alloy and coated with 2 mum of tin. The contact is inserted in resistive circuit supplied by 20 V and 3 A. The contact voltage is measured with fast sampling oscilloscope and the voltage histogram is built in real time. So, the removed mass in the track are evaluated by micro weight (1 mug). The main results show that at low level of wear observed during the earlier stage of fretting corresponds to pure constriction voltage <20 mV. However after this initiation period as the wear is increased, the contact voltage is increased and reaches few hundred millivolts (melting and fritting voltage). Finally in later stage of degradation, arcing voltage due to bounce phenomena is detected close 12 V. This short arc, observed for the first time in fretting area under power could accentuate the wear and the degradation process by erosion and mass transfer.

Statistical Study of Voltage Fluctuations in Power Connectors During Fretting Vibration

It is well known that vibration of contact interfaces is the main cause of contact degradation by the so called fretting corrosion phenomenon. In fact the process of generating particles by mechanical wear produces an increase of contact voltage, frequently manifested by a high contact resistance in low power and signal connectors. In high power connectors, this degradation is expected to be accentuated by thermal effects generated by increasing the contact voltage up to melting and arcing voltages. The main objective of this work is to examine conjointly the electrical behavior and amount of wear of a connector terminal under vibration and higher current stress. In order to reproduce harsh vibration conditions, spring with lamella shape from an automotive connector, made from a copper alloy and coated with 2 mum of tin, are submitted to a high number of oscillations (103 to 106) where the pin is firmly attached to a fixed support. High frequency oscillations (100 Hz) with an amplitude of 50 mum is used. The contact is inserted into a resistive circuit supplied by 20 V and 3 A. The contact voltage is measured with a fast sampling oscilloscope and the voltage histogram is built up in real time. The losses of mass in the erosion track are evaluated by micro weighing. The main results show that at the low level of wear observed during the earlier stage of fretting, the contact voltage corresponds to pure constriction voltage < 20 mV. However, after this initiation period as the wear is increased, the contact voltage is increased and reaches a few hundred millivolts (melting and fritting voltage). Finally in last stage of degradation, an arcing voltage due to bounce phenomena is detected. These short arcs, observed for the first time in fretting under power, could accentuate the wear and the degradation process by erosion and mass transfer.

An arc study at high DC current levels in automotive applications

In order to fulfill the increasing electric power needs in automobiles and to satisfy new environmental requirements and security, the currently used 14 VDC electrical power systems must either supply higher currents (up to 100 A) or be changed to 42 V. Considering the difficulties of operating with this new 42 V system, we have focused our interests on higher currents by extending our previous 14 VDC study. The arc parameters such as break arc duration and extinction gap for different materials and circuit loads are investigated. We have established that these main arc parameters are greatly influenced by load (inductance) and contact materials. The behavior of the material is investigated according to the composition, oxide content, and doping agent in silver. As found for low currents, the material transfer direction from the anode to the cathode is maintained at high current and neither opposite transfer direction or bilateral erosion was observed.

Small angle x-ray scattering and electron microscopy of nanoparticles formed in an electrical arc

Small Angle X-ray Scattering has been used to characterize nanoparticles generated by electrical arcing between metallic (AgSnO2) electrodes. The particles are found to have diameters between 30 and 40 nm and display smooth surfaces suggesting that they are either in liquid form or have solidified from the liquid state. Particles collected around the electrodes were analyzed by Transmission Electron Microscopy and were seen to be much larger than those seen in the SAXS measurement, to be spherical in form and composed of silver metal with irregular tin oxide particles deposited on their surface. Mixed metal nanoparticles can have important practical applications and the use of mixed sintered electrodes may be a direct method for their production.

Time and Level Analysis of Contact Voltage Intermittences Induced by Fretting in Power Connector

It is well known that vibrations of contact interfaces are the main cause of contact degradation by the so called fretting corrosion phenomena. In fact the process of generated particles by mechanical wear produce either the increase of contact voltage accompanied with rapid fluctuations. The main objective of this work is to examine the electrical behaviour of contact interface under vibration and characterize theses fluctuations during the fretting. A single point contact is submitted to high number of vibrations (103 to 107) at 100 Hz with an amplitude of 50 mum. The contact is in a resistive circuit supplied by 14 V and 10 A. The contact voltage is acquired with fast sampling oscilloscope and fluctuations are analysed by real time FFT module. We have found that, depending on the degradation stage, the apparition of these fluctuations is attributed to electro-mechanical phenomena. Some slow fluctuations are well correlated to vibration period while the rapid ones are linked to electrical conduction perturbation in granular interface by movement. Furthermore, the self-heating by such high contact voltage at high current levels is examined.

Minimization of arc extinction gap in the opening speed range 1 cm/s - 1 m/s

Speed separation in switches and relays is a fundamental parameter to improve breaking devices performances by reducing extinction gap and arc duration. It is commonly admitted, that with resistive load, high speed separation produces lower arc duration and keeps constant extinction gap, whereas with inductive load, the extinction gap is enlarged. The objective of this paper is to minimize the gap in a wide opening speed range (from 1 cm/s to 1 m/s) covering the main application of breaking and disconnecting devices. The results reveal a minimum arc extinction gap that occurred at an opening speed close to a few cm/s. Contrary to the common idea, this new result shows that high separation speeds are not always required to minimize the gap. In addition, this minimum gap value is highly affected by load and current, while contact materials seem to have a minor action. Based on arc shape and plasma examination, some attempts are made to explain this gap contraction.

Characteristics of Arcs Between Porous Carbon Electrodes

Arcs between carbon electrodes present some specific differences compared with metallic arcs. The arc voltage is higher, but does not attain a stable value displaying large fluctuations. Indeed, the arcs are produced by the direct sublimation of the electrodes, without passing through a molten phase. The arc production is also facilitated by both circuit breaking and electric field breakdown. In this paper, arcing has been examined under various conditions (voltage, current, and opening or fixed interelectrode gap) and particular attention has been given to the ability of the system to sustain the arc due to reignition. Small-angle X-ray scattering has been used to examine the formation of particles within carbon arcs and again the results are different from what is found with metallic electrodes, the particles being larger with rougher surfaces. The ultimate aim of this paper was to gain new knowledge concerning these arcs and their consequences for electrical safety (arc faults in wires).

Electrical Arc Characterization For Ac-Arc Fault Applications

The improvement of security in relation to hazardous disconnections and deteriorated connections requires a deeper knowledge of the characteristics of the ensuing arcs and their subsequent damage to the contact materials, insulation and wiring. Numerous studies have been performed on arcs for the DC power supplies used in telecommunications, and more recently in automotive fields. Furthermore, there is an important demand in the sense of safety and reliability in the areas of domestic applications, i.e. in the domain of alternative current. The purpose of this study is to extend our knowledge of AC-arc characteristics and consequences (e.g. risk of fire ignition). The electrical and physical characteristics of arcs that can appear in carbonized paths in domestic wires have been studied for alternative currents with the objective of comparing European and US electric loads on their characteristics. The arcs are produced by separating electrodes made with graphite, in order to reproduce the carbonized path environment. A very low separation speed (50μm/s) allows arcs to reinitiate, as in arc fault in wires. Arc voltage and current are measured and arc characteristics (voltage and current level, arc duration, power and energy) are defined at each cycle. The main result shows that, because of the constancy of arc voltage, the electrical energy consumption at each cycle does not depend on the voltage supply level. However, a large voltage make more probable the arc re-ignition, thus making higher, the total amount of consumed energy, with consequences for fire ignition.

Fretting corrosion in power contacts: Electrical and thermal analysis

Fretting corrosion phenomenon is known as the main cause of contact resistance increasing in signal contact. But for power connectors this undesirable phenomenon in embedded systems is more complex because high current induces high voltages and subsequent Joule overheating can be expected during vibration. Our study deals with contact similar power connectors, ones submitted to vibration amplitudes up to 25 micrometres at frequencies of a few 10Hz under a current ramp from 0.1 to 40A under 14VDC. The main measured parameters are the contact voltage during vibration up to a hundred thousand cycles. The average voltage by micro-voltmeter and its fluctuations during one cycle are acquired permanently by oscilloscope. Thermal aspects are also investigated by the use of miniature thermocouples placed as close as possible to the contact zone. It was found that a limiting voltage is reached, similar to the fritting voltage in a tarnished metal film reported by Holm. So contact resistances and the power brought by Joule effect are reduced and the temperature rise is limited. The main factors which playing a role are current, contact materials and its susceptibility to wear and debris oxidation at the interface. This behaviour is confirmed by the SEM-EDX analysis of fretting zone at different steps of fretting.

Vibration induced at contact point of a tighten-up connector system

For automotive field, the vehicle vibrations induce movements of connector systems, composed of a female part system (springs) which is connected and tighten up with the male part system (pin). There is relative movement of the contact zone between spring and pin which can lead to the fretting corrosion phenomena. Several studies have been performed to investigate vibration consequences on electrical connectors. This work aims to address the influence of a variety of factors such as fretting amplitude, frequency and current on the performance of automotive connectors. An original bench has been designed in order to measure the three dimensional displacements of the connector and the electric contact characteristics at the same time. The velocity is measured with a laser Doppler vibrometer within the excitation-axis and the displacements within the two other axes are measured with laser displacement while a vibration is applied to the system. In this study, a measurement of induced relative displacements for different types of connector systems is undertaken as an analysis of the influence of the connector shapes and the dynamic parameters on the contact area damage and on the connector threshold of use.