We propose a new electric contact device that greatly improves arc discharge characteristics. Electric contact functions are divided into an energizing operation and a switching operation. A capacitor is connected in series to a contact for switching contact. Using two conventional relay contacts, no arc operation is confirmed for a 42 V/3 A break operation. Contact resistances are measured over many operations, and the surfaces of electrodes are observed. A chip capacitor is arranged at one side of the contact electrodes of a twin relay, confirming the possibility of miniaturization.

The authors have been interested in a Scanning Laser Microscope (SLM) and applied it to studies of contact phenomena. In particular, a digital SLM is being currently used, and confirmed to be a successful tool for investigating the contact phenomena. In this paper, the theory and mechanism of a digital SLM are briefly explained, and some actual data obtained with the digital SLM are presented for demonstrating its usefulness for studies of contact phenomena.

AgCdO12wt% contacts mounted on electromagnetic relays are tested in a DC 42 V-8.4 A resistive circuit as make-only contacts and break-only contacts. In this experiment, the arc duration has been measured for each operation and the shape of the transferred pip on each contact has been observed using photograph records taken every 1000 operations. The transferred pip grows markedly at make-only contacts. Furthermore, as a few samples with the long arc duration have the flat hill transferred from the cathode on the anode surface of break-only contacts, we believe that the transferred direction reverses at a certain arc length.

Even in today's industries that are predominated by solid-state switching devices, electromechanical devices with electrical contacts are still widely used for switching and/or conveying electrical signals and power. In this paper, some interesting topics in the investigation of electrical contacts, which were selected mainly from those presented at recently held international conferences or submitted to the related Transactions of IEEE and IEICE, are introduced. Specifically, some topics related to investigation regarding contact materials, new techniques for evaluating electrical contact phenomena, new understanding of the contact phenomena, and new applications of electrical contacts are briefly explained.

Sticking is one of dominant characteristics of reliability in relays for medium current loads from several amperes to several dozen amperes, which are used for relays for automobiles, industrial control units or power supplies of household electrical appliances. Correlations between the release failures due to sticking and contact characteristics such as arc discharges, material parameters and design factors in relays have never been always made clear. This puts difficulty in the way of reasonable development of contact materials and rational design of relays. So, dependence of electrical load conditions on sticking characteristics are investigated, using the Ag-CdO contacts which have had high practical use to relays for medium current loads. Furthermore, relationship among the sticking characteristics, arc discharge characteristics and contact surface properties after operations are studied. Mechanism of sticking is considered on the basis of those data. The results are as follows: (1) Sticking phenomenon occurs intermittently from initial operations and lasts to the end. (2) The µ + 2 σ value (the sum of the mean value and the integral multiple of the standard deviation of sticking force) increases in proportion to the circuit current. On the other hand, it has the maximum value at a circuit voltage, slightly less than the minimum arc voltage. (3) Factors causing the sticking are considered to be divided into direct factors and its root factors. It is considered that a dominant direct factor is welding, and that its root factor is bridge or welding by Joule's heat. On the other hand, the sticking force becomes rather lower as the circuit voltage increases, in the circuit voltage range where regular arc discharge occurs.

The applicability of composite materials containing laminar solid lubricants to sliding contacts was studied. Performances of several composite materials prepared by incorporating solid lubricants with the basic alloys of the Cu-Nb system and Cu-Sn system were investigated to test the suitability of the composite materials as sliding contacts. As a result, it was clarified that the composite materials based on Cu-Sn alloy were superior to those based on Cu-Nb alloy and those containing only WS2 and not MoS2 were more effective in reducing both the contact resistance and the coefficient of friction. Based on the relationship between the contact resistance and the coefficient of friction obtained in this experimental study, the author proposed a new model for electric contact of composite materials.

In a DC 50 V/3.3 A circuit, the spatial distributions of the spectral intensities of breaking arcs near the cathode for silver contacts were measured on the contact surfaces of three different shapes: flat and spherical (1 mm radius and 2 mm radius) and the arc temperature and the metal-vapor quantity were calculated from the spectral intensities. The influence of the contact shape on the arc temperature and the metal-vapor quantity were also examined, as well as the arc tracks on the contact surfaces and the gain and loss of the contacts. Findings show the distributions of spectral intensities are non-symmetrical from the beginning to the extinction of the breaking arc for the flat contact: However, they are symmetrical in the latter half of the breaking in spite of the number of breaking arcs and the shape of contact surface for the spherical contact. The relationship between the area of the arc tracks on the cathode and the shape of contact surface is the same as the relationship between the existent areas of measured spectra and the shape of the contact surface. For the spherical contacts, the arc temperature and the metal-vapor quantity are affected a little by the radius of the curved of contact surface and the number of breaking arcs. However, the longer the arc duration, the higher the metal-vapor quantity is in the latter period of the breaking arc. For the flat contacts, the metal-vapor quantity is lower than those for the spherical contacts. The gain and loss of the contacts are less and the arc duration is shorter for the flat contact than for the spherical contact.

In a DC 50 V/5 A circuit, the relationship between the number of breaking arcs and the spatial distribution of the spectral intensity of breaking arcs of long duration near the cathode in palladium contact were examined through substitution of the contact surfaces of three different shapes: flat and spherical (1 mm radius and 2 mm radius). Findings show the distribution of spectral intensity in Pd arcs to be influenced remarkably by the shape of contact surface and the number of breaking arcs. However, the temperature of Pd arcs was affected neither by the shape of contact surface nor by the number of breaking arcs. The metal-vapor quantity present differed for flat and spherical surface contacts; however, it was not affected by the radius of the curved contact surfaces or by the number of breaking arcs. Additionally, the longer the duration of the breaking arc, the more metal-vapor was presented in the beginning of the arc. Furthermore, arc tracks on contact surfaces were observed with microscopes, clarifying that the relationship between the area of the clouded white metal on the cathode and the shape of contact surface is the same as the relationship between the existent area of measured spectra and the shape of the contact surface.

Arc and contact resistance characteristics of Ag and Pd contacts were determined in several kinds of dielectric liquids, such as distilled water, methanol and n-hexane, under the inductive load condition. The experimental results showed that arc discharge types are dependent on dielectric liquids. A steady arc develops in air under this test condition. However, it was found that not the steady arc but the showering arc occurs in distilled water and methanol at a low load current. It was demonstrated that this phenomenon is caused by the high capacitance generated by the ambient dielectric liquid. Also, in almost all cases, the contact resistance behavior in dielectric liquids is satisfactory because metal spots remain on the contact surface. However, in n-hexane, the contact resistance tends to deteriorate, particularly for the Ag contact, with increasing load current. It seems that the deterioration of contact resistance is caused by carbon included in n-hexane.

The effect of silicone vapour concentration on the contact failure was examined by using micro relays and motor brush-slip ring(commutator) contacts, [(CH3) 2SiO]4: D4 was used as a vapour source of silicone contamination. Because the influence of the vapour of the silicone on the contact surface can not be avoided at all times due to its gradual evaporation in the atmosphere. The contact failure caused by the silicone vapour was confirmed as formation of SiO2 on the contact surfaceby analysis of EPMA and XPS. A minimum limiting concentration level which does not affect contact reliability was found. This limiting level was 10 ppm(O.13mg/l). Validity of the limiting level was confirmed by the relationships among concentration, temperature, SiO2 film thickness and contact resistance. Furthermore, the effect of the degree of silicone polymerization on the limiting concentration was derived by an empirical formula. This silicone is found to have polymerization degree larger than D7: n=7. These results were confirmed by the contact failure data due to the silicone contamination.

The former experimental results have already shown that it is oxide films formed on contact surface causing the contact resistance to degrade in dc. breaking arcs for Ag and Pd materials. In order to understand the detailed information about it, the experiments are performed to break dc. inductive load at 20 V, 0.5 A and 1.0 A in nitrogen gas with different oxygen concentrations. The contact surface morphology and surface contamination are evaluated by SEM and AES, respectively. The tested results demonstrate that, for Ag contact, the severe oxidation occurs with increasing oxygen concentration, and the critical value of oxygen concentration is found to be about 10% and 5% in 0.5 A and 1.0 A, respectively, above those values the contact resistance degrades due to the oxide films formed on the contact surface, especially on the anode surface. While, for Pd contacts, a remarkable contact resistance degradation is not found even at 1.0 A in oxigen. Evidence shows that the arc duration, in particular the gaseous phase arc duration affects the anode oxidation, which in turn causes the significant fluctuation of contact resistance.

The authors have studied mechanism of transition from metallic phase to gaseous phase in contact break arc. For further elucidation of the mechanism, we have carried out spectroscopic measurement. The spectrum measurement system which had high time resolution was composed using two monochromators and a bifurcated image fiber, which had one input port and two output ports. The input port received the arc light, and the two monochromators received the arc light from the two output ports, respectively. The spectral sensitivity of the two monochromators was corrected with a standard lamp. We have measured simultaneously two spectra of break arc for Ag in laboratory air, under the condition where source voltage E=48 V, load inductance L=2.3 mH, and closed contact current I0=6 A. As a result, the time-varying tendency of spectrum intensity is similar for the same element, even if the wavelength is different. And from the comparison of time average spectrum intensity, it is clarified that average intensity for gas spectrum does not attain to 10% of that for metallic atomic spectrum (Ag I, 520.91 nm). In addition, the decrease point of Ag II (ion) spectrum has been found to correspond with the peak of Ag I (atom) spectrum.

Arc discharge between electrodes of relays and switches often causes contact surface damage through material transfer and arc erosion. Especially, material transfer sometimes occurs and brings serious failure even under lower load that is quite smaller than the minimum arc current value of contact material. In this paper, contact surface configuration, material transfer, and arc erosion characteristics of Ag and AgPd 60 contacts were experimentally studied after 0.5 or 1 million switching operations at various load levels. The followings can be made clear. Firstly, it was confirmed that the arcs and material transfer occurred even under such current that was lower than the minimum arc current. Therefore, the definition of the arc occurrence boundary current was newly determined. Secondly, the relation between load conditions (current and power supply voltage) and contact surface configuration (craters and pips) caused by material transfer was studied. The arc erosion behaviors of tested samples could be classified into two types: material transfer type and wear-out type. As one of the primary factors of transition from the former type to the latter one, contact activation was considered. The influences of load conditions and organic gas emitted from relay structure on arc characteristics was experimentally examined. The results indicated that load current greatly influenced the amount of material transfer and that power supply voltage affected the occurrence of the wear-out type significantly. The activation behavior of the contact surface could be found through observing the bridge voltage waveform.