Overvotages Protection in Electrical Devices and Transient Analysis by Duhamel's principle

The present work is further development of our previous publication about overvoltages protection of the electrical devices (usually electronic) in increasing the DC-power supply voltage. The main purpose of the both papers are to design a solution, realizing this protection. On this base a protective device, using the so-called “artificial” short circuit in the input of the network, have been synthesized. An additional inductance L, connected in series to the power supply, is used. It guaranties the necessary time for switching on the protection after increasing the power supply voltage. As a result of this forced short circuit, the switching off of the DC-power supply is realized by a standard protective circuit-breaker. The short circuit is performed by a fast-acting semi-conductor device (e. g. thyristor, triac etc.). The controlling signal is formed as a potential on the average node of two RC-circuits. The novelty in this publication consists in getting the analytical expression for this voltage, using a Duhamel's principle for transient analysis. By this expression the exact time of switching on the protection is determined. The analysis is confirmed with simulations by OrCAD PSpice under exactly values of the elements in the RC-circuits considered. Two cases of rapidly increasing of the power supply voltage are considered - positive jump and linear increasing. Both the advantages and disadvantages of the suggested protection is also discussed in the end of the work.