A persistent current switch (PCS) is used for superconducting applications, such as superconducting magnetic energy storage (SMES) system. The authors have proposed a mechanical switch of Y-Ba-Cu-O (YBCO) bulk as a mechanical PCS. In previous study, the authors have successfully reduced a residual resistance by depositing with metal on contact surface. This paper focused on a current carrying area (called a-spot) on contact surface and presented an effect of deposited metal on electrical contact characteristics in order to clear the contact mechanism. As the results of experiments and simulation using FEM, it became clear that it was effective for reducing the residual resistance from a view point of increasing the a-spot by depositing with metal.

Eddy-current type proximity sensor is a non-contact type sensing device to detect the approach of a conductor by increase of coil resistance due to eddy-current loss. This paper proposes to add the cap-shaped magnetic flux shield at the top of the ferrite core for the actual sensor. In conventional proximity sensors, main magnetic flux path passes through the air between the target conductor and ferrite core. Proposed sensor, in contrast, has closed magnetic circuit geometry. It means that main magnetic flux path is almost completed by the core and the shield. Therefore, it is predicted that flux does not reach the target conductor and it causes debasement of sensing property. However, it is shown that the calculated results by FEM and measured results of sensing property of the proposed sensor is enhanced compared with the actual sensor. This paper quantitatively accounts the electromagnetisms of the proposed sensor from sensing property, flux distributions and eddy-current loss in each part of the sensor body. Moreover, material characteristics for the proposed shield, such as relative permeability and conductivity, are found.

This letter presents a newly developed automatic data-acquisition system for contact resistance in which a personal computer is used for control and data processing. And the experimental results on Ag-Pd alloy contacts are reported, especially concerning the relation between Pd contents and resistance.

Arc discharge at switching contacts is one of the key phenomena, because it strongly affects material wear/transfer, contact resistance and electromagnetic interference (EMI). The arc discharge is classified into various types from the viewpoint of its sustaining mechanism and voltage waveform. They are mainly steady arc, showering arc and initial arc. Furthermore, a steady arc consists of two stages named metallic phase arc and gaseous phase arc. In the metallic, phase arc, metal ious from the electrodes mainly sustain the arc. On the other hand, gas ions from the surrounding atmosphere play an important role in the gaseous phase. Each phase arc has different influence on contact performance and EMI. The purpose of this paper is to review the arc discharges at light duty electrical contacts, and to survey the effects of arc discharges on material transfer and EMI.

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 behavior 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. And the following results are made clear. The fluctuation of voltage waveforms, especially peaks of pulse-like fluctuation more easily occurs for minus rings than for plus rings. Further, peak values of the pulse-like fluctuation rapidly decreases and disappear at lower rotation speed as mentioned in the previous works. In addition, each peaks of the pulse-like fluctuation is identified at each position of the ring periphery. From these results, it can be assumed that lubricant film exists between brush and ring surface and electric conduction is realized by tunnel effect. In other words, it can be made clear that the fluctuation would be caused by the lubricant layer, not only by the ring surface. Finally, an electric conduction model is proposed and the above results can be explained by this model.

Carbon brushes for starters are used under severe conditions of high electric current density, high contact pressure and high sliding velocity. Lead has traditionally been added to carbon brushes to improve their performance and durability. Because lead is an environmentally hazardous substance, after January 2005 the EU will prohibit adding lead to carbon brushes for electric motors installed in vehicles. The purpose of our current study is to develop materials of lead-free carbon brushes for starters. Analyzing the effects of adding lead has shown that lead inhibits the brush resistance from increasing under high temperatures, or a combination of both high temperature and high humidity. This is because corrosion of lead precedes that of copper, which is one of the materials comprising the brush, and this prevents the copper from corroding. Moreover, lead functions as a solid lubricant and reduces brush wear. We developed the lead-free brush material, by adding soft metallic substances that corrode prior to copper and are also oxidation-resistant, as well as possessing low hardness and solid lubricant properties. The developed lead-free brush surpasses the conventional lead-added brush in durability and permanence.

Automotive fuel pumps are driven by small DC motor. Commutation is carried out in gasoline, and arc voltage and duration are different from that in air. Our laboratory have analyzed commutation phenomenon in gasoline quantitatively and we have considered brush materials. To develop high power motor, we need to examine materials that are less arc abrasion and good sliding condition. In this research, we attend to characteristics of flat carbon commutator. As a result, it is possible to drive longer time, like established cylindrical copper commutator.

Many DC commutator motors are widely used in automobiles. In recent years, as compact and high output DC motors have been developed due to advanced technology, the faster the rotational speed is required and the commutation arc causes a high rate of wear/erosion of brush and commutator. Therefore, it is important how the motor speed influences commutation phenomena such as arc duration, residual current and erosion and wear of commutator and brush in order to achieve high reliability and extensive lifespan. In this paper waveforms of commutation voltage and current are measured at the rotation speed of 1000 to 5000min-1and the relation between rotation speed and arc duration / residual current is obtained. In addition long term tests are carried out at the rotation speed of 1000 to 5000min-1 the change of arc duration and effective commutation period is examined during the test of 20hours. Further, brush wear is evaluated by the difference of brush length between before and after test. Consequently, it can be made clear that as the speed increases, the effective commutation period decreases and the arc duration is almost same at the speed up to 3000min-1 and is around 42µsec.

We proposed a new electric contact device that suppresses the arc phenomena. The functions of electric contacts are divided into energizing and switching for arc suppression. Switching contacts consist of multielectrodes and each electrode current is suppressed by the series resistance. For realization of multicontacting, cantilever beam array electrodes were formed on a silicon substrate using micro-electromechanical systems (MEMS) technology. The finite element method was used to optimize the structure. The fabrication process of the cantilever was examined. Au-Au contact current of 0.97 A was broken without arc ignition.

This paper reports the development of a lead-free brush material for a high-load starter. These brushes are used in much more extreme conditions -- at the PV-value (the product of brush contact pressure and sliding velocity) approximately three times that of other starter brushes, and double the electrical current density. The major technical requirement of this development was to decrease the electrical wear in brushes caused by commutation sparking. We developed a brush material that reduces electrical wear by adding zinc phosphate. Because zinc phosphate can improve the lubricity at high-temperature and the contact stability of brushes, the developed brush reduces commutation sparks. The life of the developed brush is about 1.5 times longer than that of conventional brushes containing lead.

At the sliding contact of brush and rotating slip-ring or commutator, it has been recognized that the brush wear is influenced by brush pressure, current density and atmosphere nearby contact part. However, little is known about the relation between brush wear and atmosphere condition in detail. In this paper, the experiments are carried out with a great attention to the effect of surrounding temperature and humidity on brush wear. The sliding part of brush and slip-ring is put on the sealed box and the atmosphere in the sealed box is kept on the specified condition by temperature and humidity control system. The brush wear, contact voltage drop and slip-ring surface morphology are observed after the sliding test. From these results, in both cases of the high humidity (nearby 80%) and low humidity (nearby 20%), the brush wear are large. And the brush wear rate is the lowest around 60% relative humidity. However, the characteristics of brush wear under the 15C is not similar to others. When the surrounding temperature is changed, in case of the 20% humidity, the brush wear increases with increasing surrounding temperature. On the other hand, in case of 80% humidity, the brush wear increases with decreasing surrounding temperature. Consequently, the results clearly shows that the temperature and humidity not only affect the brush wear but also change the condition of the film formation on slip-ring.

Electromagnetic relays were developed in the first half of 19th century. At the beginning, they have been mainly used for telecommunication systems, afterwards, their uses were expanded, they have been applied to various systems such as industry products, traffic control equipment, household appliances and so on. During this time, international standardization on them became active, Japan took part in the auxiliary relay committee in the International Electrotechnical Commission (IEC). Recently, Japan is playing an important role in the committee activities. In this paper, transition and the present circumstance on technical trends of the electromagnetic relays and their activities on international standardization are described, talking about some future prospects.

Authors have studied degradation phenomenon on electrical contacts under the influences of an external micro-oscillation. A new micro-sliding mechanism 2 (MSM2) has developed, which provides micro-sliding driven by a piezo-electric actuator and elastic hinges. The experimental results are obtained on “minimal sliding amplitudes” to make resistances fluctuate on electrical contacts under some conditions which are three types of inputwaveform (sinusoidal, rectangular, and impulsive) and three levels of frictional force (1.6, 1.0, and 0.3 N/pin) by using the MSM2. The dynamical characteristics are discussed under the conditions. The simple theoretical model on the input signal and the output of the mechanism is built and the theoretical expressions from the model are obtained. A natural angular frequency (ω0=12600[s-1]) and a damping ratio (ζ=0.03[-]) are evaluated using experimental dynamical responses. The waveforms of inputs and outputs are obtained and the characteristics between inputs and outputs are also obtained on the theoretical model using the above. The maximal gain between the input and the output in rectangular or impulsive (24.4) is much larger than that (0.0) in sinusoidal. The difference on the output-accelerations between in sinusoidal and in rectangular (impulsive) is discussed. It is shown that it is possible to cause the degradation phenomenon in sinusoidal only when the output displacement are enlarged. It is also shown that it is possible to cause the phenomenon in rectangular or in impulsive, in addition to the above, when the external force has sharper rising and falling waveforms even if the displacement and the frequency of the force is small. The difference on the output-amplitudes between in rectangular and in impulsive is discussed. It is not clear that there is the difference between the effect in rectangular and that in impulsive. It is indicated that it is necessary to discuss the other causes, for instance, another dynamical, thermal, and chemical process.

A new scheme for evaluation of shapes of pips and craters formed by arc discharges on electrical contact surfaces is proposed. Measuring a height of a pip or a depth of a crater as well as an average diameter thereof with a scanning laser microscope and then putting a plot having the measured values as its vertical and horizontal coordinates enable us to numerically and briefly evaluate shapes of those pips and craters on arc-damaged contact surfaces. Some exemplary results obtained by this evaluation scheme are presented here.

Some experimental results on the contact phenomena that have been observed with electrical contacts operated to break an inductive DC load current in nitrogen atmosphere and in air (laboratory atmosphere) are presented. When Ag, Pd and Cu contacts were operated to break an inductive DC load current in the range of 1.0 A to 3.0 A in nitrogen atmosphere, more stable contact resistance characteristics were obtained, as compared to the case where operated in air, or at least the occurrence of unstableness and increase in contact resistance was delayed. The arc duration in nitrogen atmosphere became shorter in general than in air, especially with the Pd and Cu contacts. Voltage waveforms of arc discharges in the Ag and Pd contacts operated in nitrogen atmosphere showed a relatively clear step-like transition from the metallic phase to the gaseous phase as compared to the case where operated in air, while the Cu arcs did not show such significant differences due to the surrounding atmosphere. Although any apparent differences on the contact surface conditions in connection with the surrounding atmosphere were not clearly observed after the switching operations, the anode mass change characteristics were found to be more significantly affected by the difference of surrounding atmospheres than the cathode mass changes. The obtained experimental results suggest that the difference in the surrounding atmosphere introduce some difference in the anode surface morphology, possibly through the deposition of arc products in different deposition patterns, which will then result in differences in the contact resistance characteristics.

This letter presents the results of Auger analysis of surface products by steady arc on Ag/Pd contacts. Black products formed on Ag contact surfaces, which make contact resistance high and unstable, are silver oxide. In the case of Pd contacts, contact resistance of which remains low and stable, white-colored products seen after operations seem to be powdery palladium.

In this letter the formation of palladium-oxides on AgPd 70 and AgPd50 contacts caused by mechanical switching actions is reported. Further, palladium-oxides are found to show non-linearity of contact resistance when contact potential drop gets over about 0.3 V.