Jonathan Swingler

Intermittency phenomena in electrical connectors

Fretting is known to be a major cause of contact deterioration and failure, particularly in tin-plated contacts. During fretting the contact resistance generally increases slowly with time. Superimposed on this slow increase in contact resistance are rapid changes in contact resistance within fractions of a second, called intermittences or short duration discontinuities. Although intermittences have been reported by several authors, they are frequently overlooked in traditional fretting experiments and not much is known about their origin. The present study aims at filling this gap. A test apparatus has been built to measure the contact voltage-drop profile during an intermittence and fretting experiments on tin-plated copper contacts have been carried out. The results lead to a set of requirements for a model to explain intermittency phenomena.

Fretting corrosion and the reliability of multicontact connector terminals

The harsh operating environment of the automotive application makes the semi-permanent connector susceptible to intermittent high contact resistance which eventually leads to failure. Fretting corrosion is often the cause of these failures. However, laboratory testing of sample contact materials produces results that do not correlate with commercially tested connectors. A multicontact (M-C) reliability model is developed to bring together the fundamental studies and studies conducted on commercially available connector terminals. It is based on fundamental studies of the single contact interfaces and applied to commercial multicontact terminals. The model takes into consideration firstly, that a single contact interface may recover to low contact resistance after attaining a high value and secondly, that a terminal consists of more than one contact interface. For the connector to fail, all contact interfaces have to be in the failed state at the same time.

The erosion and arc characteristics of Ag/CdO and Ag/SnO/sub 2/ contact materials under DC break conditions

Break operation studies have been conducted upon Ag/CdO and Ag/SnO/sub 2/ contact materials under dc conditions between 1-16 A. The apparatus used allows contact materials to be continually tested with a controlled break velocity. Results are presented on erosion data in terms of mass transfer. Surface analysis methods are used, scanning electron micrographs reveal distinct structures and areas on the contact surface, and elemental analysis (EDS) shows migration of metal species with current. The metal-oxide used in the contact is shown to influence the arc and erosion characteristics of break only operations. The Ag/CdO contacts exhibit lower erosion than Ag/SnO/sub 2/ contacts under these controlled conditions.

Modelling of energy transport in arcing electrical contacts to determine mass transfer

This paper presents a model which calculates the amount of erosion of an electrical contact undergoing arcing for a range of contact opening conditions. The model assumes all vaporised material is lost from the contact and is related to the energy received by the contact. It is proposed that two processes occur which transport energy to the contact surface from the arc discharge. These have been called the Radial Transport Process and the Channelled Transport Process. Calculations at different ratios of the transport processes are compared to experimental data at 9A, 64V DC. The modelling procedure consists of several stages: (a) the arc discharge is divided into three regions which generates energy for dissipation; (b) the energy from each region is dissipated through the arc and delivered to the contact surface by Radial/Channelling Transport Processes; (c) heat flow through the contact from the surface is calculated using an explicit numerical finite difference scheme dependent upon energy input, contact dimensions and material properties-this is then used to determine the temperature gradient of the surface and any phase changes; (d) knowing the condition of the contact surface, and contact separation, the erosion/deposition rate is calculated assuming all evaporated material is removed from the surface.

Micro-Arcing and Arc Erosion Minimization Using a DC Hybrid Switching Device

Hybrid switching devices utilize the advantages of both conventional electrical contacts and solid state electronics to minimize arcing during opening and closing operations. This can result in higher reliability and reduces the need for high cost specialist contact materials. The hybrid switch does not eliminate arcing completely, due to the inductive nature of circuits; micro-arcing is known to occur. An experimental dc hybrid switching device is introduced which minimizes arcing for 42 V applications. The characteristics of micro-arcing are investigated to determine the factors which influence the duration of micro-arcs. Surface profiling techniques are used to determine low level contact erosion. The magnitude of contact erosion is related to the micro-arcing.

The contact resistance force relationship of an intrinsically conducting polymer interface

Investigations on contact connector materials for different applications such as in the automotive industry have focused toward the increasing interest of using conducting polymers, as compared to conventional metallic contacts. The aim is to achieve overall improvements in performance as well as cost effectiveness. Currently, extrinsic conducting polymers (ECPs) are employed as conductive coats or adhesives at contact interfaces. However, frictional abrasion within the metal doped polymer (ECP) causes fretting corrosion, which leads to instability in the contact resistance. To overcome this, intrinsically conducting polymers (ICPs) are explored. Hemispherical contact coatings were fabricated using poly(3,4-ethylenedioxythiopene) (PEDOT) or polyaniline/polyvinylchloride (PANI/PVC) commodity blends. Contact resistances were taken using four-wire resistance measurement techniques. The conductivities of in-house fabricated ICP contacts were found to be in the range of 10-2 Smiddotcm-1. The response relating the change of contact resistance under varying compression force appeared to be repeatable with minimum deviation of 2%. The surface profiles of the ICP contacts were also recorded by an optical confocal system. The initial investigation results presented in this paper were used to evaluate and validate the hypothesis of employing ICP contacts to eliminate or minimize wearing and fretting effects

The net zero erosion phenomena on opening switching contacts with AC loading

Studies have been conducted of silver metal oxide contacts on a purposed built apparatus to investigate the extent of erosion under opening (break) operations. The investigation focused on opening the contacts under AC loading of up to 30 A rms and opening these contacts at particular points in the current duty cycle (or Point-On-Wave, POW). A number of erosion and deposition mechanisms have been observed to dominate at particular current loading which were also dependent on the point-on-wave opening. These mechanisms were found to balance at particular current values and point-on-wave opening leading to a net zero mass transfer between the two contacts. This paper presents data on mass transfer against these two parameters of current and point-on-wave showing the net zero mass transfer curve. It was found that the curve was the same for both silver tin oxide and silver cadmium oxide. However, in the case of silver tin oxide the magnitude of erosion and deposition was larger than in the silver cadmium oxide case. The metal and gaseous ion phases of the arc discharge are presented as mechanisms behind this phenomena.

Influences on the length and severity of intermittences in electrical contacts

This paper deals with short-duration high contact voltage-drops in static electrical contacts during fretting experiments on tin-plated terminals. The focus lies on the rate of high voltage-drop events over the fretting cycle, the maximum level of voltage-drops, the influence of current and the influence of the direction of relative movement. The parameters used for measuring the contact voltage-drop are an open circuit voltage of 14 V, a nominal current of 9 mA, 29 mA, 54 mA and 92 mA, an amplitude of fretting motion of 0.2 mm and a maximum velocity of relative movement between the contact partners of 100 /spl mu/m/s. The contact force is 500 mN+50 mN. It is shown that high voltage-drop events occur in clusters, not as isolated events. The nominal current through the contact as well as the open circuit voltage have an influence on the occurrence of these events. Two different shapes of events have been identified, suggesting different conduction mechanisms.

A comparison of the erosion and arc characteristics of Ag/CdO and Ag/SnO 2 contact materials under DC break conditions

Break operation studies have been conducted upon silver metal-oxide (Ag/MeO) contact materials under DC conditions between 1-16 Amps. The materials used in this study are Ag/CdO and Ag/SnO/sub 2/ typically used in low voltage switching. The apparatus used in the study has been previous presented and allows contact materials to be continually tested with fully controlled break velocity. The results presented include erosion data in terms of mass transfer and surface analysis using scanning electron microscopy. Scanning electron micrographs reveal distinct structures and areas on the contact surface. Elemental analyses (EDS) was also conducted which show migration of metal species in the Ag/MeO, with various current loads. It is shown that the type of metal-oxide used in the contact significantly influences the arc and erosion characteristics on break operations. Contacts have been shown to exhibit different erosion/deposition characteristics at particular current on break operations. Erosion and deposition of the contacts on break have been related to two parameters: arc energy and arc duration.

The effects of porosity, electrode and barrier materials on the conductivity of piezoelectric ceramics in high humidity and dc electric field

Prolonged operation of piezoelectric ceramic devices under high dc electric fields promotes leakage currents between the electrodes. This paper investigates the effects of ceramic porosity, edge conduction and electrode materials and geometry in the development of low resistance conduction paths through the ceramic. Localized changes in the ceramic structure and corresponding microscopic breakdown sites are shown to be associated with leakage currents and breakdown processes resulting from prolonged operation in harsh environments. The role of barrier coatings in mitigating the effects of humidity is studied, and results are presented on improved performance using composite diamond-like carbon/polymer coatings. In contrast to the changes in the electrical properties of the ceramic, the measurements of the piezoelectric properties showed no significant effect of humidity.