Ag-CdO Contacts Research Articles

The evaluation of arc erosion on electrical contacts using three-dimensional surface profiles

Three-dimensional surface profiling is a useful technique for the evaluation of electrical contact erosion. A review is given of the various methods by which a 3-D surface profile can be measured, and numerical techniques are described which can be used to analyze electrical contacts to define erosion in terms of volume and height changes. Experimental data on the rate of change of mass of Ag-CdO contacts are used to compare with volume and height changes over a number of switching cycles. Emphasis is given to the evaluation of 3-D surface profile in the particular condition where the change of mass of the contacts is nearly zero after a large number of break only switching cycles, and it is shown that in this condition the contacts exhibit volume changes both above and below the datum surface of a new contact.

Metallurgical study of Ag-Cd and Ag-CdO alloy electrical contacts

Ag-Cd and Ag-CdO contacts, made both by sintering and postoxidation, were evaluated as to their durability by inductive and capacitive overcurrent tests according to the IEC 328 and NBR 6269 standards. Materials transfer during electric tests were monitored at 10000, 20000, 30000, and 40000 switching operations by scanning electron microscopy (SEM), energy-dispersive X-ray analysis, and chemical analysis. Better performance with regard to erosion was found for Ag-CdO postoxidized contacts, compared with sintered ones. Structural changes on the surface of Ag-Cd and Ag-CdO contacts were studied by SEM. The surface of Ag-Cd contacts changed rather uniformly, while Ag-CdO contacts developed considerable inhomogeneity. Sintered and postoxidized contacts also have also different structures. Sintered Ag-CdO contacts show a matrix with pulverized droplets while postoxidized Ag-CdO show very little change. >

Metallurgical Study of Ag-Cd and Ag-CdO Alloy Electrical Contacts

Ag-Cd and Ag-CdO contacts, made both by sintering and postoxidation, were evaluated as to their durability by inductive and capacitive overcurrent tests according to the IEC 328 and NBR 6269 standards. Materials transfer during electric tests were monitored at 10000, 20000, 30000, and 40000 switching operations by scanning electron microscopy (SEM), energy-dispersive X-ray analysis, and chemical analysis. Better performance with regard to erosion was found for Ag-CdO postoxidized contacts, compared with sintered ones. Structural changes on the surface of Ag-Cd and Ag-CdO contacts were studied by SEM. The surface of Ag-Cd contacts changed rather uniformly, while Ag-CdO contacts developed considerable inhomogeneity. Sintered and postoxidized contacts also have also different structures. Sintered Ag-CdO contacts show a matrix with pulverized droplets while postoxidized Ag-CdO show very little change.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Arc-Erosion Studies of Matrix-Strengthened Silver-Cadmium Oxide

A matrix-strengthening agent has been added to Ag-CdO material in order to reduce it's susceptibility to arc erosion. The matrix-strengthening agent, added to Ag-CdO as an additional oxide component, was chosen to enhance the wetting of liquid silver on the Ag-CdO surface. The erosion characteristics of Ag-CdO containing various matrix-strengthening additives have been investigated under static-gap conditions and in switching devices. The statlc-gap erosion measurements showed a lower material loss rate for Ag-CdO materials that euntained a matrix-strengthening additive compared to conventional Ag-CdO. The lowest erosion rate was obtained with a material containing the additive exhibiting the lowest interfacial energy against silver. Electron microscopy of the eroded surface of matrixstrengthened Ag-CdO revealed a smooth surface morphology indicative of good wetting between molten silver droplets and the contact surface. The erosion characteristics of materials containing the two most promising additives GeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and Ta <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 0 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> were evaluated in switching devices. Even though the material loss rate of the matrix-strengthened Ag-CdO was higher than that of conventional Ag-CdO under some test conditions, the surfaces of the matrix-strengthened materials consistently showed a uniform distribution of damage over the contact surface in contrast to the more severe localized damage observed on the conventional Ag-CdO contacts. Metallographic sections of the tested contacts revealed a significant reduction in thermal stress cracking for materials containing the additive. The reduced cracking tendency and more uniform erosion pattern are shown to result in extended cycle life under heavy arcing conditions for matrix-strengthened Ag-CdO compared to conventional Ag-CdO.

The Effect of Lithium Upon the Erosion Kinetics of Ag-CdO Contacts

The erosion kinetics of metallurgically similar Ag-CdO contacts with and without Li have been investigated. Time-resolved spectroscopic measurements reveal significant differences in the temporal development of the temperatures and metal species concentration in the arc, associated with the presence or absence of lithium in the supporting contact. These differences correlate well with bulk erosion measurements and are consistent with a physical model involving greater spatial or temporal dispersion of the arc root in lithium-containing materials.

The Motor Control Switching Performance of Cu-CdO Contacts in a Helium Atmosphere

An investigation of the arc rupture capacity and electrical endurance of Cu-l0 weight percent CdO and Ag-l0 weight percent CdO in motor control gear. In addition, the arc rupture capacity and electrical endurance of Cu-l0 weight percent CdO in helium at 1 atm is presented. Cu-CdO contacts in a helium atmosphere are observed to perform motor control switching duty with similar electrical performance to that registered by Ag-CdO contacts operated in air. The theoretical aspects of the electrical switching of typical motor control loads in contained environments, such as helium, and the possible applications of this type of switch are discussed.

Dielectric Recovery and Interruption Variability of Air Arcs at Atmospheric Pressure

The dc dielectric recovery method has been used extensively to study processes in post-current-zero arc columns in circuit breakers. This paper describes recovery experiments in air at atmospheric pressure following arcs drawn between butt and cone-shaped electrodes of different materials and surface profiles for contact gap spacings of 2 mm and 1 cm. The experiments were carried out with 400 pusec duration current pulses between 10 A and 1000 A for reignition voltage between 300 V and 30 kV. A statistical recovery experiment was performed using the Normal Approximation to the Binomial and Probit analysis methods to determine the standard deviation of the recovery data. The experiments show that recovery is faster: (i) with Ag-CdO contacts than with any other material tested, (ii) with flat contacts than with those having a high-point at the contact center and (iii) with cone-shaped rather than butt contacts. These results are then related to ac interruption, and are explained in terms of physical processes related to: (i) the electrodes, such as thermal properties of electrode materials or contact surface properties; (ii) the gas, such as density reduction and ionizing and electron-attaching processes; and (iii) magnetic pumping and looping effects.

Effect of Arcing on the Microstructure and Morphology of Ag-CdO Contacts

The changes in the microstructure, the composition, and the morphology of internally oxidized Ag-CdO contacts after high current arcing were investigated. The contacts were always opened on the same half cycle (60 Hz ac); thus one electrode was always the cathode, the other always the anode. Qualitative spectra of the arc at its midpoint were also taken, The results indicate that during arcing, there is a much higher concentration of Cd vapor than of Ag vapor in the interelectrode region. It is also found that the erosion of the cathode is more severe, and that the metal in the interior of the cathode craters is depleted of CdO, while a layer of Ag-Cdo is built up in the anode craters.

Ag-CdO接点の耐溶着性ならびに接触抵抗におよぼす移転層の影響

The structure and composition of migrated layer formed on the surface of internally oxidized Ag-CdO contacts were observed by an electron probe X-ray microanalyser and a microscope. Changes in welding resistance and contact resistance with growth of the migrated layer were also measured.The results obtained are as follows:The migrated layer formed by switching the d.c.circuit is deposited in the form of a laminar structure which consists of Cd-and Ag-rich phases on the contact surface. The amount of Cd in the migrated layer depends on the Cd content in the anode materials, and is hardly influenced by the circuit condition. As the current flows through the migrated layer, the contact resistance increases and the welding resistance remarkably decreases with increasing Cd content. In this case, the direction of material transfer is from anode to cathode, so that the migrated layer is made on the cathode contact surface. The welding resistance and the contact resistance are therefore influenced by anode materials.On the other hand, the migrated layer formed by switching the a.c. circuit is not in the form of a laminar structure and, moreover, it deposits around the contact area. Therefore, the welding resistance and the contact resistance are hardly influenced by the migrated layer.

Electric Ag-CdO contacts obtained by the internal oxidation method

Electric Ag-CdO contacts obtained by the internal oxidation method

Erosion Phenomena of Silver-Base Contacts (Part I)

The erosion manner of Ag, Ag-W (6500) and Ag-CdO (100') contacts under large current (D. C.) was examined mainly from the view point of the micro-structural changes of their contact surface layers. In the first place the result of a single making operation of large current on each virgin contact surface shows more spreaded arc-foot and shallower erosion-depth in the case of Ag-matrix containing W or CdO than in the case of pure Ag-contact. Then as to the structural changes due to the repeated operations, it is found that in the case of Ag-W contact the composition of the surface layer is converted into the mixture of W and W-oxide by the dissipation of Ag, while in the case of Ag-CdO contact into Ag-rich by the dissipation of CdO.In view of the fact that the micro-structure has an important function in contact operation, the Ag-CdO contacts of uniform composition (10% CdO) but of different micro-structures were compared. From these experiments it is found that properly minute distribution of CdO tends to leave the contact at but slight rate of erosion, but expra-ordinarily minute distribution increases the dissipation amount of CdO.The operating condition in this experiment included in addition to the normal swi-tching on-off test, other loading systems such as exclusively to make and exclusively to break the circuit.