Observed results of arc discharges generated between the brush and commutator are reported. The motion of the arc discharges was observed by a high-speed camera. The brush and commutator were installed to an experimental device that simulated the rotational motion of a real DC motor. The aim of this paper is to investigate the occurring position, dimensions, and moving characteristics of the arc discharges by means of high-speed imaging. Time evolutions of the arc voltage and current were measured, simultaneously. The arc discharges were generated when an inductive circuit was interrupted. Circuit current before interruption was 4A. The metal graphite or graphite brush and a copper commutator were used. Following results were obtained. The arc discharge was dragged on the brush surface and the arc discharge was sticking to the side surface of the commutator. The positions of the arc spots were on the end of the commutator and the center of the brush in rotational direction. The dimensions of the arc discharge were about 0.2 mm in length and about 0.3 mm in width. The averaged arc voltage during arc duration became higher and the light emission from the arc discharge became brighter, as the copper content of the cathode decreased.

Dependences of arc duration D and contact gap at arc extinction d on contact opening speed v are studied for break arcs generated in a 48VDC resistive circuit at constant contact opening speeds. The opening speed v is varied over a wide range from 0.05 to 0.5m/s. Circuit current while electrical contacts are closed I0 is varied to 10A, 20A, 50A, 100A, 200A, and 300A. The following results were obtained. For each current I0, the arc duration D decreased with increasing contact opening speed v. However, the D at I0=300A was shorter than that at I0=200A. On the other hand, the contact gap at arc extinction d tended to increase with increasing the I0. However, the d at I0=300A was shorter than that at I0=200A. The d was almost constant with increasing the v for each current I0 when the I0 was lower than 200A. However, the d became shorter when the v was slower at I0=200A and 300A. At the v=0.05m/s, for example, the d at I0=300A was shorter than that at I0=100A. To explain the cause of the results of the d, in addition, arc length just before extinction L were analyzed. The L tended to increase with increasing current I0. The L was almost constant with increasing the v when the I0 was lower than 200A. However, when I0=200A and 300A, the L tended to become longer when the v was slower. The characteristics of the d will be discussed using the analyzed results of the L and motion of break arcs. At higher currents at I0=200A and 300A, the shorter d at the slowest v was caused by wide motion of the arc spots on contact surfaces and larger deformation of break arcs.

In this paper, experimental data of non-arcing circuit breaking phenomena in electrical contacts are presented. A dark bridge that is a non-luminous bridge between electrical contacts is an effective factor for the non-arcing circuit break. A facility of a cantilever system was established to precisely control a position of an electrode. By using this facility, dark bridges between contacts were made and the dark bridges were observed by a microscopic camera system.

In order to realize better understanding of influential order sequences of surrounding atmospheres on break arc durations of electrical contacts in DC load conditions, a quantitative mathematical model, which aims to indicate dependences of break arc durations on several gas parameters such as molecular mass, viscosity, specific heat capacity, thermal conductivity, electro-negativity, and ionization potential, was analyzed. Break arc durations of AgCdO contact pairs were measured in several kinds of surrounding atmospheres (N2, Ar, He, air, O2 and CO2) under different DC voltage and current conditions, and data fitting processes were conducted. As a result, a candidate mathematical model was established, which could indicate possible influential order sequences of surrounding atmospheres on break arc durations in the range of the tested conditions.

When AgSnO2 contacts were operated to break an inductive DC load current of 14V-12A, 20V-7A or 20V-17A at a contact opening speed of 10mm/sec or slower, application of an external magnetic field resulted in reductions in break arc durations even without magnetic blowing. Simple estimation of Lorentz force to be applied onto arc column revealed that a certain minimum magnitude of Lorentz force seems to be required for initiating arc blowing. Certain relationships between the Lorentz force magnitude and the timing of metallic-to-gaseous phase transition were also found to exist.

Break arcs are generated in a 48VDC resistive circuit. Circuit current I0 when electrical contacts are closed is changed from 50A to 300A. The break arcs are observed by a high-speed camera with appropriate settings of exposure from horizontal direction. Length of the break arcs L is measured from images of the break arcs. Time evolutions of the length L and gap voltage Vg are investigated. The following results are obtained. By appropriate settings of the high-speed camera, the time evolution of the length L is obtained from just after ignition to before arc extinction. Tendency of increase of the length L is similar to that of increase of the voltage Vg for each current I0.

Arc runners are fixed on silver electrical contacts. Break arcs are generated between the contacts in a 450VDC circuit. Break arcs are magnetically blown-out and air is blown to the break arcs. The air flow was not used to our previous reports with runners. Circuit current when contacts are closed is 10A. Flow rate of air Q is changed from 1 to 10L/min. Supply voltage E is changed from 200V to 450V. The following results are shown. Arc duration D tends to decrease with increasing flow rate Q. The number of reignitions N increases with increasing supply voltage E for each flow rate Q. The number of reignitions is the least when the flow rate Q is 2L/min.

Silver contacts are separated at constant speed and break arcs are generated in a 300V-450V DC and 10A resistive circuit. The transverse magnetic field of a permanent magnet is applied to the break arcs. Motion of the break arcs, arc duration and the number of reignitions are investigated when side surfaces of the contacts are covered with insulator pipes. Following results are shown. The motion of the break arcs and the arc duration when the anode is covered with the pipe are the same as those without pipes. When the cathode is covered with the pipe, the motion of break arcs change from that without the pipes and reignitions occur more frequently. The arc duration becomes longer than that without the pipes because of the occurrence of reignitions. The number of reignition increases with increasing the supply voltage in 300V-400V. The period of occurrence of the reignition with pipes is shorter than that when the cathode is covered with the pipe.

Copper arc runners are fixed on silver electrical contacts. Break arcs are generated between the contacts in a DC resistive circuit. Circuit current when contacts are closed is 10A. Supply voltage is changed from 200V to 450V. The following results are shown. Cathode spots stay on the cathode surface but anode spots run on the runner when the supply voltage is 250V and over. In cases of the supply voltage is greater than 250V, the break arcs run on the runner when the arcs are successfully extinguished, and stays on the runner in cases of the failure of arc extinction. The arc lengths just before arc extinction with or without the runners are also investigated. The arc lengths are the same with or without the runners for each supply voltage.

Break operations of DC inductive (L=20mH) load currents up to about 5A with 14V were conducted in air with AgSnO2 contact pairs under different contact opening speeds, first up to 20mm/s and then to 200mm/s. Average break arc duration at each current level was calculated under the respective opening speeds. While break arc durations became shorter with increases in the opening speeds at larger current levels, such reduction tendencies were less significant with an increase of the contact opening speed from 20mm/s to 200mm/s, even when operated to break a load current of 5A. Both load current levels and contact opening speed levels seem to exhibit certain roles for realizing arc shortening effects.

For break arcs occurring between Ag and Ag/SnO$_2$ 12,wt% electrical contact pairs, the electrical conductivity, viscosity and specific heat at constant pressure are calculated as thermodynamic and transport properties. Mixture rates of contact material vapor are 0%, 1%, 10% and 100%. Influence of the contact material on the properties is investigated. Temperature for the calculation ranges from 2000,K to 20000,K. Following results are shown. When the mixture rate is changed, the electrical conductivity varies at lower temperature (< 10000,K), and the viscosity and specific heat vary widely at all temperature range. The electrical conductivity is independent of the mixture rate when the temperature is exceeding 10000,K. The thermodynamic and transport properties are independent of the kind of the contact materials.

High voltage DC contactors, for operation at voltage levels up to at least about 300,volts, find their increasing markets in applications such as electrical vehicles and aircrafts in which size and weight of cables are of extreme importance. The copper bridge-type contact, cooperated with magnetic field provided by permanent magnets and sealed in an arc chamber filled with high pressure gases, is a mainly used structure to interrupt the DC arc rapidly. Arc characteristic in different gases at different pressure varies greatly. This paper is focused on the arc characteristics of the bridge-type contact system when magnetic field is applied with nitrogen and gas at different pressure. The pressure of the gases varies from 1,atm to 2.5,atm. Arc characteristics, such as arc durations at different stages and arc motions in those gases are comparatively studied. The results are instructive for choosing the suitable arcing atmosphere in a DC bridge-type arc chamber of a contactor.

Break arcs are generated in a DC48V and 12A resistive circuit. Silver electrical contacts are separated at constant opening speed. The cathode contact surface is irradiated by a blue LED. The center wavelength of the emission of the LED is 470nm. There is no spectral line of the light emitted from the break arcs. Only the images of contact surface are observed by a high-speed camera and an optical band pass filter. Another high-speed camera observes only the images of the break arc. Time evolutions of the cathode surface morphology being eroded by the break arcs and the motion of the break arcs are observed with these cameras, simultaneously. The images of the cathode surface are investigated by the image analysis technique. The results show that the moments when the expanded regions on the cathode surface are formed during the occurrence of the break arcs. In addition, it is shown that the expanded regions are not contacted directly to the cathode roots of the break arcs.

Break arcs are generated between carbon contacts in a DC48V and 10A resistive circuit. The external transverse magnetic field formed by a permanent magnet is applied to break arcs. The position of the cathode spot region of the break arcs occurring between carbon contacts is investigated and the following results are shown. The cathode and anode spot regions moves together with and without the magnetic field. The position of the break arcs just before arc extinction tends to shift upward with increase of the magnetic flux density of the transverse magnetic field.

Break arcs are generated in a DC48V resistive circuit. The circuit current is varied from 1A to 6A. The contact resistance distribution on the anode surfaces eroded by break arcs is investigated. The following results are shown. When the current is 2A, 3A and 6A, the contact resistance at the center region of the anode surface is higher than that around the center region. The contact resistance around the center region decreases with the decrease of the circuit current. When the current is 1A, the contact resistance is very low at all positions on the contact surface. The lower contact resistance may be caused by the occurrence of the short arc that is extinguished in the metallic phase arc.

Bridge-type contacts are mainly used in high voltage direct current contactors for their performance of arc extinguishment and break capacity. It is also easy to add external magnetic field in them to blow the arc. Experiments on the arc behaviors were carried out when a copper bridge-type contact pair opening a 270V resistive circuit in the air. Influences of the shape of the movable contact, the opening speed and the magnetic flux density on the key behaviors, such as the arc duration, the arc re-ignition and the stability of arcing process, were investigated by using an oscilloscope and a high-speed camera. It was revealed that a uniform magnetic field with proper density could extinguish the arc stably and could reduce the arc re-ignition.

Break arcs are rotated by the radial magnetic field formed by a magnet embedded in the pipe-shaped cathode. The arcs are generated in switching a DC42 V resistive circuit. The closed contact current varies from 5 A to 21 A. The curvature of the anode surface is varied to study the dependence of the arc length and the positions of the break arcs in the contact gap. The following results are obtained: (i) as current decreases, there is more difference in arc duration among different curvatures; (ii) as current decreases, the arc duration decreases with decrease of the radius of curvature; (iii) in each contact curvature, the anode spots region is located nearer to the center axis than the cathode spots region; (iv) the arc length just before arc extinction is independent of the curvature of the contacts.

In this paper, a contactless measurement technique of passive intermodulation (PIM) using a coaxial tube excited with standing waves is proposed. The principle of the proposed method is described using a two-port network model with the lumped resistances representing the losses of a specimen and test equipment. To show its validity, a test using nickel wires producing high PIM is carried out, and its PIM-dependency on DUT-position in the coaxial tube is simulated using the FDTD method. The simulated result shows a good agreement to the experiment. Through the examination, it is found that the power consumption by the PIM source in a specimen is essential in PIM production, and sensitive PIM detection does not require good matching condition. Finally, the relation between PIM-source size and generated PIM level is also examined. The result shows that at least 18 dB-PIM reduction is obtained by PIM source size in a half-wavelength conductive wire.

Tin (Sn) contacts are widely applied to connector contacts. Surfaces of plated tin layer are covered with an oxide film that results in high contact resistance. However, it is possible to obtain low contact resistance by using high contact load. Current downsizing trends often make it difficult to obtain high contact loads. Therefore, it is important to conduct basic studies of the contacts resistance characteristics under low contact load conditions. In this study, relationships between contact resistance and the changes of contact traces were examined. When a platinum (Pt) hemisphere contacted to tin plated flat coupon, it was found that the hemisphere surface sank into the softer tin plated flat surface during loading resulting in a piling up tin crystal grains along the periphery of the contact trace. During this process, sudden decrease in contact resistance was observed. To clarify the phenomenon, morphology changes of contact traces were observed by AFM, SEM and EBSD. FEM analysis was also used to analyze the mechanical stress distribution in the tin plated layer. Due to the peculiar distribution of stress, the crystal grains are separated and push out the contact area. This phenomenon is very different from commonly observed decrease in contact resistance due to elastic and plastic deformation inducing mechanical fracture of the surface oxide film.

Break arcs are rotated with the radial magnetic field formed by a magnet embedded in the fixed contact. They are generated in a DC42 V resistive circuit. The circuit current when the contacts are closed varies from 5 A to 21 A. The strength of a radial magnetic field for rotating break arcs changes. Arc duration is investigated. Then rotational frequency, arc length and Lorentz force when the periodic rotation of break arcs starts are analyzed to investigate the conditions required to rotate break arcs. The following results are obtained. The arc length L when the rotational motion of the break arc starts is almost constant at a constant magnetic flux density with an increase in circuit current. The arc length L decreases with an increase in the magnetic flux density of the radial magnetic field. The rotational motion of break arcs starts when the arc length L reaches a certain value determined by magnetic flux density. Rotational frequency and Lorentz force increase linearly with an increase in circuit current.