Ishida Lab.
 
Research on electric contacts
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Simultaneous−parallel measurements of physical quantities concerning the arc phenomena
Fig.3 Simultaneous-parallel-automatic measurement system.
*Phenomena in contacts (contact phenomena) include the phenomena in solid, the phenomena in liquid and the phenomena in gas. Researches on contact phenomena have the relationship to the progress of the science.
*Contacts are the materials used in switches, relays and connectors. High performance has been required.
*The contact phenomena have been studied with the attention to the basic studies in Ishida laboratory.
*The purpose of the studies have been the investigations of the relationships between the arc phenomena and the phenomena before arcs. Wears are mainly caused by arc discharges in contacts. Thus, the arc phenomena should be elucidated.
*It is effective to measure some physical quantities simultaneously in order to investigate the relationships between those phenomena. Computers are the tools to measure quantities simultaneously.  
*The photograph of the system developed by us is shown in Fig.3. Three computers are connected to have the timing to control the moving stage and to measure the voltage waveform between contacts.
 
*Measured data are compared each other as is shown in Fig.4 as an example. Arc durations and arc distinction gaps concerning arc phenomena were simultaneously measured every opening operations with contact resistances and bridge distinction gaps concerning to the phenomena before arcs.
*The experiments were carried out at the different conditions such as separating speeds of contacts.
*As a result of the experiments, the arc phenomena must be influenced by the phenomena before arcs.
Fig.4 Measured data(comparisons between physical quantities)
Digital separation (micro-step separation) and contact voltage waveforms
*Contact voltage waveforms before arcs have been observed.
*The micro-step separation system developed by us was realized as the system by which the characteristics of  the materials were investigated.
*As is shown in Fig.5, the electrode separates step by step (0.5µm/step)
*As is shown in Fig.6, the shape of the contact voltage waveform is convex.
*Transients start from each micro-step separations ( voltages rise and falls), and the situations approach to the steady state ( voltages approach to the certain value).  
*The contact voltage waveform was influenced by the micro-step separation.
*The transient occurs in the area around the contact spot due to the micro-step separation(0.5µm), while the situation approaches to the steady state due to the electrode halt.
*Thus, the characteristics concerning the contact phenomena could be expected to be investigated in the state of each step by step separation, as each separation starts at thermal steady state ( step by step temperature in the area around the contact spot).
 
Why does the contact voltage fall at a certain gap fixed? Some investigations have been made to elucidate this phenomenon. The result of the investigation will be shown soon.
Fig.5 Stroke image of the electrode at digital separation (micro-step separation).
Fig.6 Typical contact voltage waveform under digital separation (micro-step separation).
Hiriyuki Ishida, Masanari Tanuguchi and Tasuku Takagi:” Observation of Contact Voltage by Using Micro-Step Separating System in Very Slow Opening Ag and Pd Contacts”, proc. of the 21st International Conference on Electrical Contacts, pp.238-241(September 2002) Zurich, Switzerland(p.240, Fig.7)
Observation of a dark bridge generated under very slow separating speed.
Contact opening speed is extremely slow by using the separation machine developed by us. For example:
 
                50nm/s (0.05µm/s)
 
*It was noted that thermal steady state nearby the bridge might be held under very slow separating speed of contacts.  
*The machine to open contacts together very slowly was developed in order to investigate the steady state of the bridge.
*The photograph is shown in Fig.7. The cantilever of which length was 1m was used.
*This cantilever has high mechanical performance ( mechanical resolution ).
Fig.7 Machine to slowly separate contacts by using a cantilever.
Fig.8 Typical non-luminous bridge ( dark bridge ) between contacts.
Yoshitomo Watanabe, Hiroyuki Ishida, Masanari Taniguchi, Hideaki Sone, Hiroshi Inoue and Tasuku Takagi : “ Observation of Contact Bridge Generating at Extremely Slow Opnening Speed “, Thechinical Report of IEICE, EMD2004-118, pp.37-40, (Mar. 2005 ), p.38, Fig.5
*As is shown in Fig.8, the non-luminous single bridge was observed between the contacts under the separating speed of 50nm/s. It was confirmed that the steady state of the bridge was held, even if the contacts separated  together under very slow speed.  The separating speed of 2µm/s could be sufficiently slow to hold the steady state [Tasuku Takagi, Masanari Taniguchi, Hiroshi Inoue and Hiroyuki Ishida: “ Bridge Phenomena in Slow Opening Electric Contacts in a State of Thermal Equilibrium Conditon “, Technical Report of IEICE, EMD2004-29, pp.45-48, ( Jul. 2004 )].
Initial state of the single bridge growing in contacts
*There are microscopic asperities on the surfaces of contacts as is shown in Fig.9.
*The currents flow through microscopic contact spots [ R. Holm: "Electric Contacts, Theory and Application, 4th ed., 3rd printing 2000.", Springer (1967)].
*We have taken a notice of the research concerning the relationship between the contact resistance and the surface roughness [ Seiki Harada and Kunio Mano:” The Effects of Surface Roughness on Contact Resistance”, Proc. of the Third International Research Symposium on Electric Contact Phenomena, pp.39-48, (June, 1966)].
*It has been noticed that the size of the single bridge must be depend on the surface asperity that is the highest mountain.
*If the movable contact could stop as soon as contacting together approaching to the another contact under very slow speed, a few contact spots could be formed.
 
 
*We have investigated the initial state of the contact phenomena that must influence on the arc phenomena.
 
 
  We will have to use electric energy without petroleum in the near future. Therefore, we must study electric phenomena and find new phenomena in order to supply energy fully.    
  Electric contact (contact) is a releasable junction between two conductors.  These conductors are called contacts. Contacts are used in electro-mechanical devices such as switches and connectors. There are very small contact spots through which current is able to flow. The current concentrates to the contact spot [ Ragnar Holm: “Electric Contacts, Theory and Application, 4th ed, 3rd printing 2000”, Springer (1967)].
  Strange phenomena have been found. For example, as is shown in Fig.1, the contact resistance has a strange relationship to the  electrode temperature. Electric resistance (resistance) of Palladium (Pd) must become high with temperature. However, contact resistance does not become high with temperature. The result is very important, because it may tell us the method to reduce resistance. That is to say, energy loss due to Joule heat may be suppressed.
  The reason why contact resistance becomes low with temperature has not been understood. More precise measurement shall be carried out. A new measurement system has been developed by using a cantilever as is shown in Fig.2.
Fig.1 Relationship between contact resistance and electrode temperature.
(Fig.8 in the proceeding. : Hiroyuki Ishida, Hiromichi Kubota: “Measurement of the Constriction Resistance in Palladium Contacts Heated by a Heater”, IEICE technical reprot, EMD2012-4, pp.19-22 (May 2012))
Fig.2 Precise measurement system for contact phenomena by using a cantilever.
Probability of reducing the electric energy loss
Study on the relationship between phenomena in contacts and temperature
Fig.11 An example of the calculated temperature around the single contact spot in Palladium contacts.
 
Fig.9 Simplified contact model.
Calculation of the temperature rise by Joule heat in the electrode
A simulation program was developed for calculating the temperature rise due to arc by using the electrode model as is shown in Fig.10.  The electrode is cylindrical and its tip is flat. The cylindrical electrode is inserted into the cylindrical holder.
We can apply this model to the model for a single contact spot that is shown in the area surrounded by the dotted box in Fig.9.  One of the calculated temperature rise around the single contact spot in Palladium contacts is shown in Fig.11. The current through contacts was 2A, and the emery papaer (#1500) were used to polish the contact surface. The simulation program should be revised. This is because, the phenomenon such as shown in Fig.1 could not be explained by the past theory and the results of experiments. A new phenomenon may influence the phenomenon as is shown in Fig.1.
 
                    Fig.10 An electrode for calculating the temperature rise due to arc.