Technology for digital substations

The transition from conventional substations equipped with analogue instrument transformers (ITs) to digital substations requires the introduction of suitable references for calibration of digital instruments.

Coordinator: Jari Hällström

 

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

SAMUs are used to retrofit analogue ITs into digital ITs, avoiding the high cost of replacing the entire instrument. However, the measurement accuracy of this hybrid solutions must be guaranteed. In this project, a reference SAMU is developed for the calibration of other SAMUs, enabling the accurate assessment of sampling rates and 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, a high-accuracy large-bandwidth portable reference digitiser is designed. This digitiser connects to a reference voltage transformer (VT) or to the reference open-core current transformer (CT) developed in the ENG61   FutureGrid project.

Techniques and algorithms for synchronisation of sampling to a common time reference within and between substations are also developed, studying their impact on the final accuracy of power and energy measurements. Laboratory test signals aligned to a local time reference are generated using specifically-designed hardware that creates signals compatible with typical SAMU input levels (100/110 V and 1/5 A). Moreover, the reliability and security of time synchronisation is addressed, tackling three different 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.

Alternative methods for distributed measurements and for converting output from ITs or voltage dividers to the digital domain are studied, including a novel photonic readout concept based on hybrid fibre Bragg grating (FBG) transducers, developed in the ENG61 FutureGrid project. This approach allows the distributed ITs to be interrogated with a single optical fibre from a single location. The optical analogue signals from the photonic sensors will be converted to digital signals enabling seamless integration with digital substation equipment via the IEC 61850-9-2 protocol, and thus forming an all-optical FBG-based SAMU.

This work builds upon the work done in ENG61 FutureGrid project and extends it 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. European metrology community can therefore support the development of these technologies with traceable calibrations of all instrumentation with digital outputs.

For more information, see the project webpage >>