Supporting industry through increased access to AC quantum voltage references
Accurate electrical measurements are essential for the development of smart electrical grids, which can better integrate sources of renewable energy and supply power with greater reliability and efficiency. Quantum effects underpin the realisation, or conversion, of electrical units of the SI from theoretical definitions into reality. The volt is currently ‘realised’ using a Josephson quantum voltage standard, a superconducting chip operating at cryogenic temperatures (4k or -296 C), which generates highly stable voltages. Realisation of the SI is performed by National Measurement Institutes (NMIs) but only a few European NMIs had the metrological infrastructure and level of knowledge to realise voltage using existing AC quantum voltage standards (ACQVS), which are complicated to construct and difficult to operate. This technological barrier prevented most NMIs developing their own AC quantum standards and consequently the ‘gap’ in measurement capability for the volt was increasing in Europe. As ACQVS are important in a range of areas, including smart grids, the European research capacity in AC quantum voltage metrology needed to be improved and the measurement gap between NMIs reduced.
This project brought together 13 partners from across Europe to transfer increased measurement capability between NMIs in this important field. To transfer expertise in quantum-based voltage measurements a workshop was held covering the types and applications of Josephson voltage standards and this material is now freely available for download. An easy to use ACQVS, designed to be accessible to all NMIs, was constructed based on a programmable Josephson voltage standard. Two comparison exercises were performed on this using a newly developed transportable system, established by project collaborator BIPM. These exercises, a main prerequisite for the use of ACQVS in accredited laboratories and industry, indicated the new standard can achieve measurement uncertainties at the 1 μV/V level, and will serve as a basis for future worldwide comparisons of quantum voltage standards. The project also produced a good practice guide, targeted at NMIs and industry which is freely available from the project website or Research Gate. This guide details the required instrumentation, cryogenics and configuration as well as how to use the different components. A common software tool which controls and drives a programmable Josephson array to synthesize DC and AC quantum-accurate voltages is also free to download.
Four of the project partners TÜBİTAK (Turkey), CMI (Czechoslovakia), CEM (Spain) and JV (Norway) have now established new Quantum Voltage Standards. Strategies for developing accreditation and calibration services in AC quantum voltage metrology have been prepared across the consortium and these services will generate new or expanded calibration measurement capabilities (CMCs) related to power measurement, important in the development of smart grids. This will lead to a decrease in the wasting of electrical power, which in turn will have direct economic and environmental impact. As well as strengthening the connections between scientists all over Europe in this field, project outputs will ensure the coordinated development of traceability for AC quantum voltage metrology in Europe.