The outputs of the project are primarily focussed on R&D that will provide the basis of a new ROCOF standard(s). This lead to the following outputs:

1. To evaluate the problem of ROCOF measurement in the context of actual use cases and the “wish list” from an end-user point of view. To develop a library of standard-test-waveforms representative of typical PQ events on electricity networks, including extreme events, in order to adequately test ROCOF algorithms and instrumentation containing these algorithms.

A table of use cases and an associated waveform library available online that are typical in normal and extreme operational conditions of the power grid. Each use case table entry will have an expected ROCOF accuracy and measurement latency (which will vary in accordance with the complexity of the use case). This table will be suitable for inclusion in an international standard. A virtual workshop was held to obtain information from the power industry and instrument manufactures on what they considered to be the required information. The consortium has circulated questionnaires, based on experience and information from the virtual worshop, on the impact of ROCOF on smart grids PQ stability and received feedback from industry and standards bodies. The responses have been tabulated and work is ongoing to define the worst case scenarios where ROCOF could interfere with PQ.

Three main uses cases have emerged which cover categories of particular electricity network scenarios.

  • “Loss of mains detection”, which protects the power system and personnel from so called island operation using ROCOF to detect island operation.
  • “Under frequency load shedding”, where selected customers supplies are progressively cut-off to protect the supply and demand balance which is measured using ROCOF.
  • “Frequency response requirement calculation” (synthetic Inertia), uses ROCOF to measure the possible reserve power available for injection to the grid on a short-term basis.

Each use case has different demands in terms of ROCOF accuracy and response time. Within each use case there exist particular examples of waveforms particular examples of ROCOF and events caused by transients and poor power quality which may give rise to spurious ROCOF readings.

An on-line waveform library is being developed which will make these reference waveforms available to researchers and instrument manufacturers who wish to develop and test algorithms.

This work will define is defining the terms of reference for future ROCOF measurements and will set expectations of users as to the accuracy of the ROCOF measurement verses its delay response before updating its readings.  This trade-off is governed by the need to reject spurious PQ events.

2. To review, develop and optimise algorithms to reliably and accurately measure ROCOF over the full range of network conditions, specifying any use cases where this is not achievable.

A set of simulated and lab tested algorithms with recommended configuration parameters (window length, filter type and window shape) matched to the use cases. These results will give-rise to a table of algorithms and configurations which will facilitate selection against given use cases.  The most appropriate algorithms have been selected and work is ongoing to configure them. The optimal windows to minimise ROCOF inaccuracy due to noise (from ADC resolution for example) has been investigated and implemented.

So far, an adaptive digital filtering algorithm has been selected for its particular properties in rejecting PQ events and its computationally efficient structure.  The commonly used IEEE algorithm is also being used for comparison.  Other algorithms will also be considered.

These algorithms are being testing in simulation, in the lab and in the field and the response of the algorithms to different test signals with various different setting of window lengths and various other technical parameters are being assessed.

3. To implement and test selected ROCOF algorithms utilising the standard waveform library via computer simulations as well as in instrument hardware that will be tested using precisely generated electrical waveforms in the laboratory. This will lead to compliance verification protocols for ROCOF instruments suitable for inclusion in a ROCOF standard (new or pre-existing).

Two ROCOF algorithms have been implemented in special instruments which digitise the measured grid waveforms.  The algorithms must run in real time and the detailed waveform data is captured near any event that exceeds a pre-set ROCOF threshold. This allows post-processing and replay of the events through different algorithms and/or configurations.

Six such instruments have been installed on Bornholm Green Island which contains a high penetration of renewable energy and often operates independently of the nearby Nordic Grid (see Loss of Mains use case above).  The new algorithms are being tested in this unique experiment and data from real and spurious ROCOF events is being captured to allow the optimisation of ROCOF algorithms.

A laboratory test-bed has been set up which can accurately synthesise use case waveforms (such as idealised versions of those captured on Bornholm).  This will form the basis of a recommended ROCOF lab testing set-up suitable for compliance testing of ROCOF instruments. This will include a test procedure and uncertainty budget and will be in a form suitable for inclusion in an international standard.

4. To specify a reference signal processing architecture for a ROCOF instrument suitable for inclusion in a ROCOF standard. To use sensitivity analysis to determine the uncertainty specification for each element of the measurement chain (this could include: transducers, analogue signal processing, filtering, analogue to digital convertors, digital signal processing, computational processing) required to manufacture an instrument to implement the selected algorithms and be capable of compliant accuracy measurements for each of the use cases.

A reference signal processing architecture for a ROCOF instrument which will be a block diagram of the measurement chain from transducers to processing the fundamental of this have emerged from the work in the previous objectives in particular producing the Bornholm instruments. Monte-Carlo simulations are being developed using this reference architecture and the results will provide overall predicted uncertainties for the measurement use cases.

5. To work closely with the European and International Standards Developing Organisations, in particular CENELEC TC8X and the working-group/technical committee responsible for IEEE/IEC 60255 118-1, and the users of the standards they develop, to ensure that the outputs of the project are aligned with their needs, communicated quickly to those developing the standards, and in a form that can be incorporated into current standards and used to develop a new internationally accepted standard at the earliest opportunity.

All of the above outputs will be submitted to an international standards committee for consideration on the inclusion in a future ROCOF standard. The project will engage in discussion with the standards committees and other stakeholders to ensure that the outputs align with the requirements and expectations. The consortium have been in regular discussions with the stakeholder community. To date the need for ROCOF standards has been discussed  with the following seven standard committees: IEC/IEEE TC95 / WG1 (60255-118-1), CENELEC TC8X WG7, BSI GEL/8, UK National Grid working group GC0087, ENSTO‑E, ISGAN and SIRFN.  The project is particularly engaged with the first two committees and is targeting this research to tangible contributions to ROCOF and grid frequency measurement standards under their control.