IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 4; August 2011 1307 1070-9878/11/$25.00 © 2011 IEEE Analysis of Electrical Contact Temperature Rise in Spark Gap Switches with Graphite Electrodes Lee Li, Cai Li, Yu Feng, Nan Jing, Zhou Zheng-Yang and Lin Fu-Chang State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology, Wuhan, China ABSTRACT Electrode replacement is an effective method to extend the useful lifetime of the spark gap switch with graphite electrodes. In order to perform electrode replacement, suppressing temperature rise and preventing static welding/erosion should be considered for the static electrical contact interface between the electrode and the holder. In this paper, a mathematical model of contact temperature rise is proposed based on the Holm model and heat-conduction equations. This mathematical model can quantitatively prove that some material properties of the metal holder and some mechanical characteristics of the spark gap switch are key parameters affecting temperature rise. Material properties of the metal holder include thermal conductivity, specific heat, density, electrical resistivity, elasticity modulus, and the Poisson ratio. Mechanical characteristics of the spark gap switch include contact radius/area, contact pressure, and contact surface roughness. Optimum configuration of these key parameters reduces temperature rise and prevents static welding/erosion. Index Terms — Spark gap, electrical contact, temperature rise, graphite. 1 INTRODUCTION HIGH voltage, high current and high coulomb transfer closing switches are required for many high power systems employing capacitive energy-storage, such as the power supply for a high power laser pump [1]. There are two competitive, alternative solutions. One is to use solid-state switches [2-3] such as thyristors, whose attractive merit is a very long service time. However, the limited electrical characteristics of individual thyristor requires a stacked architecture with several series-parallel connections. This brings about high costs and low integrated reliability. Another solution is to use spark gaps due to their relatively simple design, robustness, and easy field maintenance and repair [4-6]. Graphite electrodes are used in many popular spark gap switches [6]. The main drawback of spark gaps is the limited lifetime due to electrode erosion. If using the number of discharge shots as a performance standard, the engineering lifetime of a spark gap is usually around 10 3 shots [7]. A practical method of extending the switch lifetime is to replace eroded electrodes with new electrodes, allowing significantly longer service lifetimes. However, the metal electrode holders might be eroded too. A seriously eroded holder can not support the electrode replacement. In the case of high current and high coulomb transfer, it is necessary to examine the electrical contact between the electrode and the electrode holder. This will directly determine the possibility of electrode replacement. The heating effect of the electrical contact under pulse discharge is inevitable, bringing about temperature rise. Once the temperature of the contact interface rises to the phase-transition temperature of the metal holder, erosion or welding might happen. Therefore, suppressing temperature rise of the metal holder should be very important to implementing electrode replacement. This paper focuses on establishing the mathematical principle affecting the temperature rise of the electrical contact interface firstly, and then puts forward a quantifiable model of temperature rise based on electrical contact theory and heat conduction theory. Further, some numerical calculations and experiments are presented to test and verify the analysis of electrical contact temperature rise. Organization of this paper is as follows. In section 2, the structure of the graphite spark gap switch is reviewed. Section 3 forms the temperature rise model of the static electrical contact interface. Section 4 proposes the temperature rise formula under pulse current effect. The simulations and testing of several holder materials are implemented in section 5. Concluding remarks are given in section 6. Manuscript received on 28 September 2010, in final form 4 January 2011.