I. Introduction
The DC railway and metro systems supplied by unidirectional substations exhibit a notable energy inefficiency, primarily stemming from their incapacity to fully reclaim the energy generated during electric braking. Bidirectional substations and/or storage systems are expected to significantly improve energy efficiency, but IEC TC9, CENELEC SC9XC, and CENELEC TC14 raised concerns about the lack in this field of standard procedures for the determination of the actual performance of specific devices e.g. current measuring equipment, power transformers or converters and of efficiency of the overall system. In response to these concerns, the presented project [1] aims to tackle these issues by developing new methodologies for determining the electrical energy efficiency in DC transport systems.