Technology for digital substations

The transition from conventional substations to digital substations requires the introduction of suitable references for the calibration of digital instruments. These include instrument transformers (ITs) with digital output and standalone merging units (SAMUs).

Coordinator: Jari Hällström


SAMUs can be employed to retrofit analogue ITs into digital ITs, removing the need to replace entire instruments, as mentioned above. However, the measurement accuracy of this hybrid solution must be guaranteed. EMPIR project ‘FutureGrid II’ is developing a reference SAMU for the calibration of other SAMUs. This reference instrument will be able to support the accurate assessment of sampling rates and the resolution of transmitted data. In order to calibrate already-installed SAMUs and other digital equipment, a suitable reference for on-site measurements is needed. For this purpose, project researchers are designing a high-accuracy, large-bandwidth portable reference digitiser. The digitiser will then be able to connect to a reference voltage transformer (VT), or to the reference open-core current transformer (CT) that has been produced by a previous EMRP project, 'Future Grid'.

The project ‘FutureGrid II’ is also working on techniques and algorithms for the synchronisation of samples to a common time reference, within and between substations. The project is additionally studying the impact of these algorithms on the final accuracy of power and energy measurements. As well as this, laboratory test signals aligned to a local time reference are being generated, using specifically-designed hardware that can create signals compatible with typical SAMU input levels (100/110 V and 1/5 A). Moreover, project researchers are trying to address the reliability and security of time synchronisation, tackling three key aspects - cryptographic security for NTP and PTP protocols, redundancy via different time synchronisation mechanisms, and self-assessment of the employed time synchronisation infrastructures via live-auditing and record-keeping.

The project consortium is also studying alternative methods for distributed measurements and for converting output from ITs or voltage dividers to the digital domain - including a novel photonic readout concept based on hybrid fibre Bragg grating (FBG) transducers, as developed in the preceeding project ‘FutureGrid’. This approach will allow the distributed ITs to be integrated with a single optical fibre from a single location. It will then be possible to convert optical analogue signals from the photonic sensors to digital signals, supporting seamless integration with digital substation equipment via the IEC 61850-9-2 protocol - thus forming an all-optical, FBG-based SAMU.

This work builds upon the achievements of project ‘FutureGrid’, extending the research by closing the traceability gap between measurements with conventional and non-conventional instrument transformers, and digital sample streams defined in IEC 61850-9-2LE and IEC 61869-9. The technologies being developed by this project will be able to support the European metrology community on a broader level, providing the means for traceable calibrations of any instrumentation with digital outputs.

For more information, see the project webpage >>