Many sustainable technologies, such as LED lighting, photovoltaic cells and electrical vehicles (EVs), are fundamentally DC, which results in inefficient power conversion when they are connected to traditional AC grids. Thus, the shift towards more renewable and sustainable technologies has increased the attractiveness of DC grids. The applications of DC grids are very broad, ranging from residential and business buildings to hospitals, agriculture, lighting, electrified transportation, data centres and telecommunication.
Standardisation of DC grid control currently focusses on installations, wiring rules, safety for users (shock, burns), equipment (discharges), voltage levels, and the detection of faults. However, the metrology infrastructure required for DC grids is currently lacking. For traditional AC grids, the metering of electricity is well regulated and standardised, whereas for DC, standardisation is still in its infancy. This project is a direct response to the metrology needs expressed by CLC TC8X WG1 “Physical characteristics of electrical energy” and IEC TC13 WG11 “Electricity metering equipment”. The needs expressed by CLC TC8X WG1 and IEC TC13 WG11 are for the development of the metrological underpinning for voltage characteristics in DC grids and test waveforms for DC electricity meters, respectively.
Compared to traditional AC grids, DC grids should provide such benefits as longer cables and fewer substations, improved response to EV demand, reduced power conversion, reduced disturbing harmonics, improved voltage control in distribution networks, and more viable battery storage schemes. Therefore, several DC grid trials are currently in place to test these claims. These include an industrial site in the Netherlands, local DC grids in Denmark and Finland, and a smart grid in Spain. However, these trials need metrological support.
Whilst DC grids are theoretically beneficial, their implementation brings many challenges and unknowns which are predominantly measurement related. Among these measurement challenges are current and voltage ripple, inrush currents, voltage fluctuations, short circuit events, and other PQ issues. PQ is well established in traditional AC grids, however widely accepted and standardised methods for measuring PQ aspects for DC metering or PQ measurement methods for DC grids are not currently available. Therefore, the corresponding measurement techniques and traceability for DC grids urgently need to be developed.