Conclusions of Section 1 When considering Table I, it can be easily recognized that input current and output voltage show high overshoots for small values of the damping coefficient. Since overshooting of the voltage may damage the load, it is important to select filter components such that O.4<<5< 1 which keeps the voltage overshoot smaller than 25%. When the bus provides a sufficient inrush capability, the current overshoot does not represent a problem because mechanical relay contacts can easily cope with such a situation. Hence, the only design condition to be observed when the considered load shall be switched on by means of a relay contact is the above restriction for d. However, such a simple design procedure leads to undesired consequences when the mechanical switch is combined with a protection function. The trip threshold is to be adjusted such that it can tolerate the inrush peak. Especially for small damping coefficients the trip threshold may be much higher than the steady state load current. The result is a reduced detection capability of faulty overload conditions (low selectivity). 2. The SSPC as Switching Element After switch-on by the SSPC, i(t) and uft) will rise in the same manner as described in Chapter 1 (the on-resistance of the SSPC is assumed to be small in comparison to the load R). When the input current exceeds the limitation value IL of the SSPC, input filter and load will see a constant current source delivering IL. This new situation is characterized by: (2.2) establishes a relative simple relation between differentials of dependent and independent variables. The rate of energy dissipated by the SSPC in the constant current mode is given by:
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