IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 38, NO. 3, MAY/JUNE 2002 825 The Effect of Silicon Avalanche Diodes on Fuse Behavior in LV Power Networks Andreas Beutel, Student Member, IEEE, and John Van Coller, Member, IEEE Abstract—The effect of silicon avalanche diodes (SADs) on the behavior of fuses in low-voltage (LV) power networks is shown, as well as the effect of the fuses on the energy dissipation in the SADs. In order to achieve this, an existing model developed for medium- voltage fuses was adapted for LV fuses operating in the presence of SADs. An SAD model was also developed. Both models were validated by laboratory measurement. The effects of fault closing angle and fault level on SAD energy dissipation are shown, and a general method for determining the SAD energy rating for any given situation is derived. Index Terms—Coordination, current-limiting fuse, energy, low- voltage power networks, silicon avalanche diode, simulation. I. INTRODUCTION T WO FORMS of protection that are included with elec- trical equipment operating on low-voltage (LV) power networks are current-limiting load fuses and surge protective devices (SPDs). Fuses and SPDs behave differently when used together, so they must be correctly coordinated. Several sources have studied the subject of coordination in the context of medium-voltage (MV) distribution systems [1]–[3]. In contrast, there is very little literature available on coordination on LV systems. Many of the aspects identified by the studies on MV networks also hold true for the LV situation. However, there are also several important issues which occur only in LV networks. These concern SPDs with protective levels very close to the peak of the normal power frequency voltage waveform, and the comparatively low energy ratings of these devices in comparison with other SPDs. The SPD concerned is the silicon avalanche diode (SAD). It is the purpose of this paper to show the effect that SADs have on the behavior of current-limiting load fuses used on LV power networks. Consequently, the effect of the relatively low energy rating of the SADs on their ability to survive the surges generated by the operation of the fuses during fault conditions is shown, as the surges generated by fuse operation have been identified as having large energy contents [4], [5]. In Section II of this paper, the theory of operation of current-limiting fuses is Paper IPCSD 02–51–1, presented at the 2001 Industry Applications Society Annual Meeting, Chicago, IL, September 30–October 5, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Power Systems Protection Committee of the IEEE Industry Applications Society. Manuscript submitted for review October 15, 2001 and released for publication March 1, 2002. This work was supported by Eskom through TESP and DTI through THRIP. The authors are with the School of Electrical and Information Engi- neering, University of the Witwatersrand, Wits 2050, South Africa (e-mail: a.beutel@ee.wits.ac.za; j.vancoller@ee.wits.ac.za). Publisher Item Identifier S 0093-9994(02)04505-X. Fig. 1. Reduction of fault current by the operation of a current-limiting fuse. reviewed, as well as modeling techniques that have been used in the past to predict fuse behavior. In Section III, the SAD and the problem of coordination between SADs and fuses is introduced. Section IV presents the results of laboratory tests carried out to determine the effect of SADs on fuses. Simulation results illus- trating this are also shown. Based on these findings, a revised model for current-limiting fuses operating under the influence of SADs is developed. In Section V, a general method for deter- mining SAD energy dissipation is presented. The system voltage used throughout this study is 230 V, with a frequency of 50 Hz. Similar trends to those shown here will be observed for systems of other ratings. Simulations were performed using Simulink—in particular, the Power System Toolbox. 1 II. CURRENT-LIMITING FUSE Overvoltages result from reduction of the fault current to a value substantially lower than the peak available fault current by the fuse, as shown in Fig. 1. This is achieved by the generation of an arc voltage of polarity opposing the flow of the fault current. The phenomenon is explained using the equivalent circuit of Fig. 2 and [5] and [6]. The peak arc voltage of the fuse is given by (1) 1 MATLAB Simulink Power System Toolbox, Version 5.3.0.10183 (R11), The MathWorks Inc., Natick, MA, 1999. 0093-9994/02$17.00 © 2002 IEEE