Guofu Zhai

Experimental Study on Arcing Process and Contact Erosion under Transverse Magnetic Field

Arc characteristics and contact erosion of Ag, AgNi and Ag/SnO2 contacts were studied when the opening arcs were driven by transverse magnetic field. The experiments were carried out with a DC 28V/10A pure resistive load. The opening velocity varies from 10 mm/s to 50 mm/s. The transverse magnetic fields are provided by magnets and their flux density on the contact axes varies from 0 to 200 mT. The experiments were conducted in a hermetic chamber filled with pure nitrogen. Time variations of arc images were recorded by using a high speed camera. Relationships between flux density and arc parameters, such as arc durations, 2-dimensional distribution of arc positions and arc velocities, were obtained for those contacts. Contact erosion was observed and material transfer mass was measured after breaking operations. Decline ratio of the arc durations and alleviation of the mass transfer by the magnetic field no longer increase with the increment of the flux density, so the critical flux density for each contact material were finally obtained. The results can be used to design magnetic blow contacts in hermetic relays.

Thermal Analysis of Sealed Electromagnetic Relays Using 3-D Finite Element Method

Up to now, it is difficult to test the inner temperatures of sealed electromagnetic relays. In this paper, the temperature distribution of a sealed electromagnetic relay is obtained by using 3-D finite element analysis. The quality of thermal simulation results depends on the accuracy of both the modeled heat sources and heat sinks. Due to the high performance requirements of sealed electromagnetic relay it is interesting to know not only the temperatures of the conducting parts but also the thermal impact on the plastic components. Therefore, the non-metallic parts of the sealed electromagnetic relay (including the air within the device) are now part of the model. In order to improve the accuracy of simulation, the contact radius is calculated in advance. The relationship between convection heat transfer coefficient and temperature and how to consider connecting wires boundary condition are also researched here. Finally, the temperature distribution of a sealed electromagnetic relay is obtained by this method. Comparisons with experimental results confirm its validity.

Study on feasibility of storage accelerated testing based on parameter degradation for aerospace relays

It is difficult to obtain the failure data of long-lifetime and high-reliability aerospace relays, even based on the traditional storage accelerated life testing method. Aiming at this issue, based on the reliability test, the feasibility of accelerated degradation test for aerospace relays was studied. The performance degradation mechanism of the aerospace relays was analyzed during the storage and the possibility of the performance degradation of aerospace electromagnetic relay was illustrated. The storage reliability pre-research test was utilized to study the accelerating ability of aerospace electromagnetic relay performance degradation with temperature environment stress. The testing system of relay storage parameters was developed. And, by analyzing the performance data which was acquired with test system of relay storage parameters under temperature-accelerated stress, the acceleration of performance degradation was illustrated. Finally, the degradation physical equation of aerospace relays under temperature stress was deduced based on Arrhenius equation. The result demonstrated that storage accelerated testing based on parameter degradation for aerospace relay is feasible. And, these studies provide the basis and reference for aerospace relays in storage with the method of Prognostics and Health Management (PHM) approach based on Physics-of-Failure (POF).

Reliability research on power MOSFET using coupled electrical-thermal-mechanical analysis

As an integral component of electronic equipments, power MOSFET with its degenerate performance affects the reliability of the whole system. The modeling of power device based on structural geometry, material properties, and boundary conditions can reduce the repetition test and shorten the failure analysis cycle. In this paper, coupled electrical-thermal-mechanical analysis based on finite element model of TO-247 package power MOSFET was performed. First, electrical-thermal simulation was accomplished to obtain the distribution of temperature under power cycling. Then, thermal-mechanical analysis was carried out to calculate the inelastic strain range generated by the thermal stress. Finally, on the basis of simulations above, the fatigue path can be achieved to predict the thermal fatigue life of MOSFET by Coffin-Mansons law.

Research on Accelerated Storage Degradation Testing for Aerospace Electromagnetic Relay

It is difficult to obtain the failure data of high-reliability and long-lifetime aerospace electromagnetic relay, even if based on the traditional accelerated storage life testing method. Aiming at this issue Based on the reliability test technique, the scheme of accelerated degradation testing for aerospace relay was designed. The test system of aerospace electromagnetic relay storage parameters under temperature-accelerated stress was designed and developed. Taking a certain aerospace electromagnetic relay as the research object, the accelerated storage degradation testing was carried out. The most past research on storage reliability of relay only focuses on the measurement of relay contact resistance. And, the relay time parameters (closing time, opening time, overtravel time, rebound duration time.) which reflect main performance function was not monitored. So, in this paper the relay time parameters and relay contact resistance were detected simultaneously. The test system of relay storage parameters could be implemented the function that the contact resistances and time parameters of 40 aerospace relays under several temperatures were monitored automatically at the same time. And, the test system transmitted the test data to the host computer for processing. According to the analysis on experiment results of contact resistance, relay time parameters, the degradation phenomena and degradation mechanism of aerospace electromagnetic relay in long-term storage are investigated. These studies provide the basis and reference for latter aerospace electromagnetic relay storage life prediction and using the method of prognostics and health management.

Method for Identification of Nonlinear Parameters and Its Application to Data Analysis for Aerospace Relay Reliability

A method which uses the moving time and the over travel time of contact to discover the characteristics of contact and the reliability of aerospace relay is proposed. The Gauss-Newton method and its improved form (Macalto method) are used to identify the nonlinear mathematical model of the parameter during armature initial moving period, which is from the coil is energized at a rated voltage to the moment the armature begins to move. The validity of the method is verified by results of actual experiments and analysis.

The effect of mechanical parameters of switch-type contact on relay operation characteristics

Electric arc erosion during contact break/make cause contact resistance degradation, material transfer, non-closing and non-opening, above failure modes affect relay operation characteristics greatly. A relay model testing device which could simulate relay parameters of: initial contact force between N.C. contacts, contact gap and N.O. over-travel mechanical parameters assembly was used to study arc erosion. During breaking and closing operation, contact resistance, pick-up/release voltage, pick-up/release/arc duration were recorded explicitly during test. The optimal matching mechanical parameters assembly of switch-type contact was determined by test results comprehensively. Therefore the contradiction between reducing arc duration and lower bouncing time was solved in maximum extent. The conclusions drawn in this paper are meaningful for optimization of mechanical parameters of switch-type contact in relay.

Research on the Starting Points of the Combined Subsection Permanent Magnet

One of the important parts for the polarized magnetic system design is the equivalent processing of the permanent magnet (PM) in polarized relay, which affects the design accuracy of the system directly. Based on the combined subsection permanent magnet (CSPM) in the condition of the open magnetic circuit, this paper concludes that the starting points of PM are different, by setting up the equivalent magnetic circuit, and analyzing the relationship between the starting points of PM in theory. Meanwhile, it provides the method of solving the starting points. Finally, the conclusion is validated by the analysis example.