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.

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.

Break arcs are rotated with a radial magnetic field formed by a permanent magnet embedded in a fixed contact. The break arcs are generated in a 48VDC resistive circuit. The circuit current is 10A when the contacts are closed. The polarity of the fixed contact in which the magnet is embedded is changed. The rotational radius and the difference of position between the cathode and anode spots are investigated. The following results are obtained. The cathode spot is moved more easily than the anode spot by the radial magnetic field. The rotational radius of the break arcs is affected by the Lorentz force that is caused by the circumferential component of the arc current and the axial component of the magnetic field. The circumferential component of the arc current is caused by the difference of the positions of the rotating cathode and anode spots.

Various DC power supply systems such as photovoltaic power generation, fuel cell and others have been gradually spreading, so that DC power distribution systems are expected as one of energy-saving technologies at houses and business-related buildings as well as data centers and factories. Under such circumstances switches for electric appliances are requested to interrupt DC current safely in DC power systems (DC 300-400V). It is well-known that DC current is much more difficult to be interrupted than AC current with current-zero. In this paper a model switch is developed and fundamental characteristics of DC current interruption in a resistive circuit is experimentally and theoretically examined. Consequently arc duration is found to be approximately a function of interrupted power rather than source voltage and circuit current. In addition arc length at its extinction is obtained by the observation of a high-speed camera. Then the arc length is found to be decided only by interrupted power like the gap length, independent of separation velocity. From these results it can be made clear that the arc form becomes arc-shaped at its extinction when the interrupted power is larger than about 500W. In addition the effect of magnetic blow-out on arc extinction is examined.

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.

Break arcs are rotated with the radial magnetic field formed by a magnet embedded in a fixed cathode contact. The break arcs are generated in a 48VDC resistive circuit. The circuit current when the contacts are closed is 10A. The depth of the magnet varies from 1mm to 4mm to change the strength of the radial magnetic field for rotating break arcs. Images of break arcs are taken by two high-speed cameras from two directions and the rotational motion of the break arcs is observed. The rotational period of rotational motion of the break arcs is investigated. The following results are obtained. The break arcs rotate clockwise on the cathode surface seen from anode side. This rotation direction conforms to the direction of the Lorentz force that affects to the break arcs with the radial magnetic field. The rotational period gradually decreases during break operation. When the depth of magnet is larger, the rotational period becomes longer.

Silver electrical contacts are separated at a constant speed and break arcs are generated in a DC300V-450V/10A resistive circuit. The transverse magnetic field formed by a permanent magnet is applied to the break arcs. Alumina pipes are placed around the contacts to restrict the motion of break arcs. The dependences of the arc lengthening time and arc length just before arc extinction L on the strength of the magnetic field and supply voltage are investigated. It was found that the arc lengthening time increases with increasing supply voltage E and tends to decrease when the magnetic flux density Bx is increased. The arc length just before arc extinction L increases with increasing E and decreasing Bx. It also increases linearly with increasing arc lengthening time tm when no reignitions occur.

Silver electrical contacts are separated at constant speed and break arcs are generated in a DC100 V–450 V/10 A resistive circuit. The transverse magnetic field of a permanent magnet is applied to the break arcs. Dependences of the arc duration, arc dwell time and arc lengthening time on the strength of the magnetic field and supply voltage are investigated. The characteristics of the re-ignition of the break arc are also discussed. Following results are shown. The arc duration D is increased due to the increase of the arc lengthening time tm when the supply voltage E is increased for each magnetic flux density Bx, because the arc dwell time ts is almost constant. The arc duration D is increased due to the increase of both of the arc lengthening time tm and the arc dwell time ts when the magnetic flux density Bx is decreased. The arc lengthening time tended to become long when the re-ignition of the break arc is occurred. The lengthening time tends to become longer when the duration tm1 from the start of the arc lengthening to the start of the re-ignition is increased. Re-ignitions occurred frequently when the magnetic flux density of the transverse magnetic field is increased and the supply voltage is increased.

The circuit switching device by the electrical contact needs the high reliability and long lifetime. The very important factor for the high reliability, long lifetime and electromagnetic noise of the electrical contact is to suppress the duration and electromagnetic noise of arc discharge. Usually, the suppression of arc duration method is applying the external magnetic field. But, this method was not able to suppress the metallic arc duration and increased the voltage fluctuation at arc duration. Therefore, the new method for suppressing the duration and noise for electrical contact is expected. In this paper, a new method for suppressing duration and EM noise of arc discharge by applying housing pressure is proposed. To investigate the availability of proposed method, the measurement and some considerations on arc duration, voltage-fluctuation and current noise up to GHz frequency band generated by breaking contact in the applied pressure relay housing are reported. Firstly, voltage waveform and duration of the arc are measured. The effects of the pressure in the relay housing on the duration of the metallic and gaseous phase arcs are discussed. Secondary, voltage fluctuation, the spectrogram of contact voltage and current noise up to GHz frequency band are discussed. In the results, the proposed method with applying pressure makes shorter both durations of metallic and gaseous phases. The shorter duration of metallic phase is an advantage of the proposed method beyond the applying external magnetic field. As the housing pressure is increase, the voltage fluctuation and current noise becomes smalls. The proposed method can suppress the voltage fluctuation as well as arc duration. Consequently, the proposed method is on of the good solution to suppress the duration and electromagnetic noise of the arc discharge from electrical contact and result of this study indicates the basic considerations necessary to ensure good lifetime and EMC designs for electrical contacts.

In order to study the influences of contact opening speeds on arc extinction gap length characteristics, Ag contacts were operated to break DC inductive load currents from 0.1 A to 2.0 A at 14 V with contact opening speeds of 0.5 mm/s, 1 mm/s, 2 mm/s, 5 mm/s and 10 mm/s in a switching mechanism employing a stepping motor, and arc voltage waveforms were observed at each opening of the contacts. From the results, the average arc durations were determined at each current level under the respective contact opening speeds, and the average arc extinction gap lengths were calculated by multiplying the average arc duration value and the contact opening speed value. It was found that average arc durations showed no significant differences with increasing contact opening speeds. Thus, arc extinction gaps became larger at faster opening speeds in the inductive load conditions of this study.

Break arcs are generated between electrical contacts in a DC 42 V resistive circuit. Contact materials are Ag/SnO2 and Ag/ZnO. Circuit current when contacts are closed is varied from 5 A to 21 A. The radial magnetic field to drive break arcs is formed between the contact gap with a permanent magnet embedded in the cathode. The arc motion is observed with a high-speed camera. Experimental results with the magnet are compared with those without the magnet. Following results are shown. Similar experimental results to pure silver contacts are obtained for Ag/SnO2 and Ag/ZnO contact pairs. The rotational motion of the break arcs and the shortening effect of the arc duration are confirmed. The ring-shaped, wide and uniform traces are observed on the contact surfaces after break operations. This result shows the prevention effect of local erosion of electrical contacts and the reduction of total amount of contact erosion. The rotational frequency f is increased with the increase of the arc current Iarc. These results for Ag/SnO2 and Ag/ZnO contact pairs are similar to the results for pure silver contacts in our previous experiments. The rotational frequency of the break arc for the Ag/SnO2 and Ag/ZnO contacts is lower than that for the pure silver contacts.

Motion of break arcs driven by external magnetic field is observed using a high-speed camera. The magnetic field is applied with a permanent magnet. Experimental circuit is DC42 V-10 A resistive circuit. Material of electrical contacts is silver. Following results are shown. The break arcs are driven in the direction according to Lorentz force. The arc duration decreases with decrease of the distance between the electrical contacts and the magnet. When the external magnetic-flux density at the position of the break arc is lower than a certain value, the effect of the magnetic field to drive the break arc becomes ineffective to shorten the arc duration. The result is explained with a relationship between the motion of break arc and the distribution of the external magnetic field.

Arc discharge generated by breaking electrical contact is considered as a main source of an undesired electromagnetic (EM) noise. To clarify mechanism of generation of the EM noise, feature extraction of bridge and short-time arc waveforms generated by slowly breaking Ag contact was discussed experimentally. The short-duration time arc before the ignition of the continuous metallic arc discharge was observed. The highest probability density voltage is defined as short-arc sustainable voltage (SASV). The relationship between SASV and duration of short-time arc was quantified experimentally. It is revealed that as the arc voltage of the short-time arc is higher, its duration becomes longer.

Break arcs are generated in a DC 42 V-10 A resistive circuit. The contact material is Ag or Ag/ZnO. The number of break operations is two hundreds for each contact material. The motion of break arcs is observed with a high-speed camera. Relationship between the dependence of arc duration on the number of operations and the motion of arc spots is investigated. The following results are shown. For Ag contacts the arc duration is almost constant independent to the number of break operations. For Ag/ZnO contacts, on the other hand, the arc duration changes irregularly to short (59 ms) or long (69 ms) arc-duration after 30th break operation. The moving range of arc spots on contact surfaces is broad for the case of short arc-duration and is narrow for the case of long arc-duration. The cause of the results for Ag/ZnO contacts is considered that the difference of the boiling points of Ag and ZnO leads to the porous structure on the contact surface.

To clarify the mechanism of the generation of electromagnetic (EM) noise, current and radiation noise up to the GHz band generated by slowly breaking silver-compound contacts were investigated experimentally. The current and radiation noise at the GHz band were observed. It was demonstrated that the frequency spectrums of the current and radiation noise correspond to the frequency responses of the circuit admittance and radiation efficiency of the experimental setup, respectively. It was revealed that even if current noise at the GHz band is very small, it can cause a large EM radiation noise because of the high radiation efficiency. From the time-frequency domain characteristics of current noise, it was clarified that the peaks of current noise at 10 MHz band arise immediately after the initiation of the arc discharge and the transition from metallic phase to gaseous phase. On the other hand, the peak current noise above 100 MHz arises immediately after the initiation of the arc discharge.

Arc occurrence rates were measured for Ag contacts in DC resistive and inductive load circuits. In inductive load conditions, arc occurrence rates in general came close to 100% at around 0.4 A, the conventional minimum arc current level of Ag. In resistive load conditions, the similar results were obtained with 30 V, while arc occurrence rates close to 50% were still obtained at around 0.4 A with 14 V and 10 V. Careful attention should be paid to the term "minimum arc current" to avoid misinterpretation thereof.

We proposed a method for suppressing arc ignition in mechanical contact devices using a transient current switch and a capacitor. We applied the method to conventional reed switches. For the electric circuit analysis, we clarified the momentary voltage-current characteristics at breaking operation of reed switches by FEM analysis. We could also estimate the capacitance of the contact electrodes at the metal bridge rupture by FEM analysis, and would derive the non-arcing condition using SPICE simulation. The suitable capacitor value in the transient current circuit for arc ignition suppression would be depend on the load impedance, the power supply, the time depending contact resistance R(t)s, the contact capacitance, and the minimum arc voltage and current.

In this paper, the separation of heat generation and heat transfer related to temperature rise of silver palladium contact was investigated experimentally in order to predict the temperature rise of contact by the use conditions such as voltage range between 25 to 40 V, current range between 3.2 to 5.0 A and silver palladium alloy (AgPd) materials. Firstly, relationship between temperature rise of contact and supply power was discussed. The effects of heat generation and heat transfer on temperature rise were separated and quantified by least squares method. Secondly, effects of durations and integral powers of bridge and arc on temperature rise were also discussed by changing supply power. Results show that the integral power of the bridge increases when supply power increases. As the supply power increases, integral power of arc also increases. The temperature rise is dominated by integral power of bridge. Remarkable difference of bridge duration can not be seen in the five materials (AgPd30, AgPd40, AgPd50, AgPd70 and Pd). The supply power is increased, arc duration gets longer. As weight percent of Pd content increases, the effect of supply power on arc duration becomes larger. Consequently, the integral power of arc increases. This study is a basic consideration to realize methods predicting temperature rise of contact.

Breaking arcs occurring between silver electrical contacts are observed in DC42 V resistive circuit using a high-speed camera. The motion and current densities of the cathode and anode spot regions are investigated for different interrupt currents (I=7 A, 10 A and 14 A). Results indicate that the arc length at which the motion of arc spots becomes stable depends on the interrupt current, and the current densities of the cathode spot region are almost constant immediately before arc extinction for each interrupt current.