Hybrid switches in protective devices for low-voltage DC grids at commercial used buildings

The joint undertaking "Direct Current Components and Grid" (DCC+G) takes on the strategic challenge to reduce energy consumption and thus the reduction of CO2 emission caused by commercially used buildings. This is proposed by using low voltage Direct Current (DC) grids at a voltage level of +/- 380 V. The major energy consumers in these buildings (LED lighting systems, heat pumps, ventilation systems, air conditioning units, cooling units and information technology), ready for the "net-zero-energy" goal of the European Union, are in the most energy efficient versions executed with a rectifier system as interface to the alternating current (AC) grid. Furthermore these buildings get local producers of electrical energy (photovoltaic, wind energy) as well as energy storage systems that operate with DC. Avoiding the repeated conversion from DC to AC and vice versa reduces conversion losses and will save energy. Another effect is the transition from many small rectifiers to a small amount of very high efficient central rectifiers. Nowadays the established 400V/230V, 50 Hz, 3-phase AC power distribution systems in commercial buildings could be substituted by a direct current distribution and give a contribution to CO2-reduction. Fuses, mechanical and electronic safety switches and their combinations must, like in the AC grid, detect electric faults and switch off and if needed isolate electrical equipment just in time to protect it. Nominal currents in the distribution of a 380 V DC grid should be typical not exceeding 50 A. Plugs and sockets for DC grids in data centre are already available with nominal currents of 20 A offering already higher power levels than todays standard 230 V, 16 A sockets of 1-phase AC grids. Controlled power converters offer well defined DC short circuit currents. Beside the possibilities to switch DC-currents on various ways with an arc system, DC grids can make use of electronic switches. To reduce transmission losses in semiconductors during standard operation mode the focus is more on the hybrid switches. Basic investigations on a close to production prototype of a hybrid switch are realised and its limitations and performances are highlighted.