Extended Aging of Ag/W Circuit Breaker Contacts: Influence on Surface Structure, Electrical Properties, and UL Testing Performance (original) (raw)
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Surface Degradation of Ag/W Circuit Breaker Contacts During Standardized UL Testing
Journal of Materials Engineering and Performance, 2015
The near-surface microstructure of Ag/W contacts from 120 V, 30 A commercial circuit breakers in the asmanufactured condition and after standardized UL overload/temperature-rise, endurance, and short-circuit testing have been investigated using a combination of x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, focused ion beam milling, and transmission electron microscopy. The as-manufactured contacts comprised three constituents: sintered Ag/W composite particles with finegrained Ag and coarse-grained W, coarse-grained pockets of Ag infiltrate, and a nano-crystalline surface Ag layer. There are also WO 3 and Ag 2 O phases at the surface. After UL overload/temperature-rise testing, there is Ag loss giving a porous W-rich layer at the contact surface. In addition to binary oxides, we observe the formation of Ag 2 WO 4. After UL endurance testing, material is swept across the surface by the breaker action giving a W-rich eroded porous surface on one side and a build-up of mixed oxides on the other. After UL short-circuit testing, a W crust forms due to melting and re-solidification of W and vaporization of Ag, and mid-plane cracks form due to the severe thermal gradients. There is a strong correlation between the observed microstructural features and the contact resistance measurements obtained from these samples.
Journal of Energy and Power Engineering, 2014
The DRM (dynamic contact resistance measurement) in high voltage circuit breakers is a manner of evaluating the internal ageing condition of the chamber. DRM is similar to static contact resistance measurement testing, but instead of measuring a single value when the breaker contacts are closed (static value), the ohmic resistance is measured at various contact positions, from the beginning of the contact opening until a complete separation of the contacts. The relationship between the contact resistances of the new circuit breaker and the ageing circuit breaker in operation provides subsidy for the evaluation of both the main and arcing contact conditions. This research aims to analyze the correlation between the various levels of degradation of the contacts and the configuration of the DRM curve. This work considers curve samples from new breaker chamber contacts and different levels of degradation by acceleration tests.
Impact of Surface Morphology on Arcing Induced Erosion of CuW Contacts in Gas Circuit Breakers
2018 IEEE Holm Conference on Electrical Contacts, 2018
In this paper, the impact of surface morphology of contacts, in particular different microstructural parameters like size and distribution of contact ingredients, on contact erosion in high voltage gas circuit breaker is investigated. It is demonstrated that the size and contiguity of copper and tungsten zones play a key role in contact erosion so that the mass loss in one specific contact after interruption of the rated short-circuit current is 2.5 times higher than that of another one, with the same dimensions and material composition. It is shown that the arc roots tend to be formed on larger copper zones and if the zones are not confined by tungsten area, the arc cross section expands resulting in a higher evaporation rate of copper areas. In addition, it is emphasized that ejection of tungsten particles after evaporation of surrounding copper areas is another mechanism leading to more contact erosion, which has to be taken into consideration in contact erosion modeling along with molten contact splash and vaporization. Index Terms-arc contacts, contact erosion, contact morphology, microstructural image of contact surface.
Degradation of power contacts in industrial atmosphere: silver corrosion and whiskers
2002
Degradation of power contacts in corrosive atmosphere leads to significant increase of the contact resistance and consequently to a rise in temperature, and eventually to the failure. In electrical apparatus, both base metal copper and silver plating heavily corrode in environment containing sulfuric gases. In addition, expansive growth of silver filaments (whiskers) has been often found on primary current conductors of circuit breakers. This paper describes extensive whisker growth found in switchgear at paper recycling mill. The major environmental factor to initiate the growth is relatively low concentration of Hydrogen Sulfide (H 2 S). As soon as a thick enough layer of silver sulfide has been formed, metal filaments start to grow virtually everywhere but most intensely in locations usually having elevated temperature while electrical units are energized. Though hazardous phenomenon has been seen from 1920s and caused a number of violent failures, but it was practically neither studied nor understood. Just in two months after previous cleaning, we found the filaments up to several inches (6-8 cm) long and up to 0.04 in (1 mm) thick. Using SEM/EDS analysis we have determined chemical composition and morphology of the whiskers. Most of the whiskers are made of silver with 1-3 % of copper. The surface of the whiskers long exposed to atmosphere is contaminated with silver sulfide. After thoroughly investigating the factors that initiate and accelerate whiskers' growth we have determined effective means eliminating extremely hazardous phenomenon For more information, contact:
Comparison of Reignition Properties of Several Ag/W, Ag/WC, and Ag/Mo Electrical Contact Materials
IEEE Transactions on Components, Hybrids, and Manufacturing Technology, 1986
A/&rucl-The reignition properties of several Ag/W, AI/WC, and A&MO electrical contacts were compared, in a static gap discharge system. The effects of refractory particle size, composition, and processing method wetie studied. Silver-molybdenum was found to have the least tendency to restrike. Silver-tungsten carbide contacts generally restruck more frequently than Ag/Mo and Ag/W and the number of restrikes increased 6jth the refractory content. Restrike in dilver-tungsten contscts was not as sensitive to the refractory content; however, the use of coarse tungsten increased the tendency to restrike. The processing method had a significant influence on. the number of restrikes of Ag/W contacts. In particular the press-sinter contacts processed at below the melting temperature of silver showed a high probability of reignition.
IEEE Transactions on Power Delivery
In this paper, an effort has been made to evaluate the online condition of arc contacts as a vital component of interruption chamber in high voltage puffer type SF6 circuit breakers. The relationship between eroded mass caused by shortcircuit current interruption and different thermal stress indices such as transferred electrical charge, current squared, and arc energy is investigated, by performing many experiments with different current amplitudes and arcing times. It is demonstrated that none of the known indices can solely determine mass erosion caused by the current interruption. Therefore, the equations including two of defined parameters are proposed to evaluate mass erosion. The method using arc energy and transferred electrical charge owns the highest accuracy in evaluating mass loss. However, considering the complexity of arc voltage measurements, a second method using current and arcing time can be also utilized. In addition, the development of erosion during the lifetime of arc contacts is studied. It is shown that arc roots tend to form on new uneroded areas of the contacts during current interruption, resulting in different erosion rates between the first few and subsequent interruptions due to change of morphology of the contacts after the first few switching operations.
Metallurgical study of Ag-Cd and Ag-CdO alloy electrical contacts
IEEE Transactions on Components, Hybrids, and Manufacturing Technology, 1988
Ag-Cd and Ag-CdO contacts, made both by sintering and post-oxidation, were evaluated as to their durability by inductive and capacitive overcurrent tests according to IEC 328 and NBR 6269 standards. Materials transfer during electric tests was monitored at 10 000,20 000,30 000, and 40 000 switching operations by SEM, EDAX, and chemical analysis. Better performance, in regard to erosion, was found for Ag-CdO post-oxidized contacts as 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 post-oxidized contacts have, also, different structures. Sintered Ag-CdO contacts show a matrix with pulverized droplets while post-oxidized Ag-CdO show very little change. Results from the present work show that SEM, in connection with EDAX, is useful for studying electrical contacts, and should be increasingly used.
Corrosion Resistance of Copper-Coated Contacts
Journal of The Electrochemical Society, 2006
Corrosion of electronic components can produce a wide range of failure signatures, from intermittent electrical faults to complete functional breakdown. This paper presents an investigation on the exposure of a simple connector-coating system. The system consists of a copper contact coated with a nickel layer underneath a gold finish layer. The system was characterized using the following techniques: optical microscopy, atomic force microscopy ͑AFM͒, scanning electron microscopy ͑SEM͒, energy dispersive X-ray spectroscopy ͑EDAX͒, secondary ion mass spectroscopy ͑SIMS͒ and focused ion beam ͑FIB͒. After initial characterization, the connector was exposed to 2, 4, 7, 15, and 30 days in an aggressive environment consisting of 90% relative humidity, 40°C, and 4 ppm H 2 S. Digital images of the corrosion products that developed on the contacts after exposure clearly demonstrated localized corrosion by-products present on the connector surface. SEM, EDAX, and SIMS analysis of the corrosion sites demonstrated the presence of copper sulfide and nickel sulfur corrosion product, which suggest a two-step mechanism: first, the Ni layer is attacked by the aggressive environment at the sites where the gold layer is not available, followed by the diffusion of copper through the nickel layer. FIB cross-sectional analysis revealed that surface defects in the gold layer resulted in sites for corrosion initiation and subsequent development of a thick copper sulfide layer of approximately 5 m. It is concluded that this copper connector coating system does not prevent the formation of insulating corrosion products on the surface of the connector in a very aggressive environment.
Recent Advancements in Production Testing of AC High-Voltage Outdoor Circuit Breakers
Production tests are performed when an AC HV circuit breaker is fully assembled, after the completion of the manufacturing process and prior to shipment. A general description is made of tests applicable to modern outdoor SF 6-insulated, single-pressure, dead-tank circuit breakers as prescribed by IEEE standards. The background for various production tests and test parameters is discussed. This is followed by a description of recent advancements in testing at a manufacturing facility. Associated facility design features and capabilities are presented. These include state-of-the-art power frequency withstand voltage and leakage detection test processes. Test and data collection automation as well as process improvements that allow for greater efficiency and safety of personnel are covered.