Potential DC Applications for Low Voltage Switches

Abstract

In this thesis, the essential DC applications for low voltage switches, primarily solar photovoltaic energy systems, UPS systems and electrical railway traction, are individually reviewed and analysed from the DC switches’ perspective. Application specific conclusions are drawn regarding the electrical nature of typical system setups and the AC switch designs’ suitability for DC use in these systems. The general trends within each of these applications are also discussed.

The study is based on examining and reviewing literature, e.g., application specific publications, standards and norms, and on consulting with industry professionals.

Applicable DC use for switches is found particularly in solar photovoltaic energy systems where the electrical characteristics of the supplies are rather unchallenging, and also, with certain restrictions, in UPS systems and electrical traction applications. Generally, the DC use of switches is found to require non-inductive loads and voltage levels below 1 kV, as to allow successful current breaking. Inverters and electronic systems are seen as resistive loads rather than inductive. While most DC applications today are seen to be suitable for the use of switches regarding the reactivity of the load, voltage levels in some systems make the current breaking too demanding.