Determine the Backup Protection Value of Low Voltage Switchgear by Computational Calculation of the Limit Load

An upstream circuit breaker may protect a down-stream breaker (e. g. miniature circuit breaker, MCB) at high short circuit currents. This paper describes a method to derive the data more efficiently using a computational method. So far, the backup values for various combinations are determined by testing two different circuit breakers in one circuit. The aim of this investigation is to find the maximum prospective short circuit current without destroying the downstream breaker. The technique of this work avoids the combinatoric efforts for test samples and test time. Therefore, each breaker is described with an empiric model which gives a forecast of the short circuit behavior. However, it is possible to calculate limit load, which may destroy the downstream device, by its empiric fingerprint. It is based on observable and calculatable mechanisms of destruction. The detailed normative definition of test conditions was developed to enable a correct modeling and determination of the required parameters. The models were implemented with the tool Simulation X. Overall, the method allows the determination of backup values for various combinations within minutes.