Hence, it can cope with short circuit-, overload-, and inrush situations for an indefinite time without excessive dissipation. The disadvantage of the PWM switch resides in the larger volume and mass due to the needed in- and output filters. For reasons of miniaturization, all SSPCs must be built in modern hybrid technology. Hence, a lot of development effort is to be spent which again underlines the criticality of this area for COLUMBUS. With regard to the described features, PWM- and linear switches will be used in different locations of the distribution system. The PWM-switch will be applied as primary switching element for overall bus management. The linear switch is located close to the loads (so called secondary switch). However, when a load draws a very high inrush current (motor load), the PWM-switch may be used as a load-dedicated switch too. It is, furthermore, important to recognize that the SSPC is able to distinguish very accurately between normal operation and faulty overload conditions. This is due to its fast response time and the fact that the limitation current is exactly set. This feature of the SSPC is in the following referred to as ‘high selectivity'. In low voltage power systems applying mechanical switchgear (as e.g. EURECA), inrush current limits according to Fig. 5 have been adopted. These relative high limits have been introduced because a mechanical relay contact can easily cope with the shown overcurrents and the power source (regulator) is able to keep resulting voltage transients low. In medium voltage systems with solid state power controllers it does not make much sense to specify such general inrush current limits because the SSPC will automatically limit the current as shown in Fig. 5 (dashed line). The question arising now is, how the Limit I£ shall be fixed. In order to answer this question we have to recall that the SSPC provides excellent properties with respect to selectivity and that it is rather expensive. Both features exclude any overdesign which means that the limitation current shall be set as close as
RkJQdWJsaXNoZXIy MTU5NjU0Mg==