APPENDIX I Analysis of the Switching Behaviour of Solid State Power Controllers (SSPCs) The purpose of the following investigations is to study transient responses when a simple electrical circuit consisting of input filter and resistive load is switched on by means of a linear SSPC. The linear SSPC is an electronic switch with current limitation feature. Due to its thermal self-protection it can maintain overload situations for a limited time TF (trip-time) only. When using such ‘switches' it is of interest to know up to which extent they can cope with inrush currents as they will occur for example when a. m. loads shall be connected to the bus. By establishing the energy balance of the SSPC during switch-on, constraints will be derived which relate sizes of reactive filter elements to the limitation current of the SSPC. In order to have a reference against which SSPC performance can be measured, switch-on of the considered electrical circuit by means of a mechanical relay contact will be analysed first. 1. The Relay Contact as Switching Element The corresponding circuit diagram reflecting this case is shown in Fig. A.l. At the time t=0 the switch S is closed and a unit step of the bus voltage is applied to the input filter. The task is to determine input current iff) and load voltage uff) as response to this unit step. By introducing the abbreviations The Laplace transforms of i(t) and u(t) are given by:
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