Changing systems inertia

Marcel Nedd saw the EPSRC Centre for Doctoral Training in Future Power Networks & Smart Grids as an opportunity to broaden his knowledge, skills and understanding of power systems and indeed the future of power systems. In addition, completing the programme would potentially lead to a more fruitful career, while availing him of the knowledge to understand how aspects of environmental sustainability and renewables impact the power system. In short, it is a chance to see more of the complete picture, as far as energy and sustainability are concerned. Furthermore, the programme is delivered by Strathclyde and Imperial College London, two highly reputable universities with strong industrial links.

After completing the training year, he began his PhD research project in October 2015. It is titled ‘Changing System Inertia’. Professor Keith Bell and Dr Campbell Booth are the project’s first supervisors, and Dr Andrew Roscoe is the second. ScottishPower Energy Networks (SPEN) is the project’s industrial partner with the contacts being Dr Cornel Brozio and Dr Colin Foote.

Research aims

As highlighted by, among others, National Grid in its ‘System Operability Framework’, replacement of large, fossil-fuelled generators by renewables is having a fundamental effect on the GB power system’s dynamic behaviour. One worry is its ability to survive fault outages of generators and still have a stable system frequency and a specific dimension of that is the coupling between the electrical and mechanical aspects of the system and a reduction in the inertia of operational generation.

The ‘Changing System Inertia’ research project addresses the following question: how much fast energy response does the GB power system need in the future and what are the options for delivering it? The project tasks include:

• development of a model that represents the GB transmission system
• investigating loss of in-feed events over a range of scenarios to determine minimum system inertia & minimum primary frequency response requirements, & maximum penetration of non-synchronous generation on the network, against different system limits, including frequency & rate of change of frequency (RoCoF)
• exploring options for delivering fast energy response & evaluating their performance
• identifying & quantifying the monetary & commercial value of inertia

Industry interaction & connections

There is significant industrial interest in this research project and the undertaking has received considerable support (meetings and continued correspondence) from SPEN and National Grid, who are both keenly interested in the next stages of the project. Meetings have also been conducted with Scottish Hydro Electric Transmission (SHET), the transmission subsidiary of Scottish and Southern Energy (SSE), who indicated an interest in the project. SPEN has recently requested a copy of the single bus model, to use as a basis of creating another simple model for other system studies. National Grid has indicated an interest in the current single bus model and operating scripts, as a tool for retrospectively investigating system conditions during a frequency event. Both transmission operators have indicated strong interests in the investigations concerning system limits, frequency and RoCoF, and the potential impacts to a future power system.

Similarly, both parties have indicated strong interest in this project’s research concerning system inertia and quantifying the economic value of the provision of the service, either as a sole service or as part of a bundle of services. The latter led to involvement in a Network Innovation Competition project recently approved by Ofgem, Phoenix.

The Phoenix project is a SPEN led project that sees them partnering with National Grid to investigate the implementation and impact of a synchronous compensator to the SPEN-owned transmission network. The student’s current research on changing system inertia, led to his involvement in the preparation of a bid document for the Phoenix project. His contribution included conducting preliminary system studies supported by two other research associates. These studies included an investigation of the potential impact of new synchronous compensation on frequency nadir and RoCoF, short circuit ratio, and voltage.

Similarly, informal discussions indicate the likely involvement of National Grid and SPEN on the topic of an economic basis for trading inertia. There have also been informal discussions with members of the National Grid Smart Frequency project and Scottish Power concerning regional inertia in the GB power system.

Research achievements to date

To date (15 months after the start of the research) the research project has produced a ‘single bus’ model of the GB transmission system, containing robust assumptions of system conditions, and incorporating different response options. Together with an graphic user interface and an algorithm for populating and driving the model to discover key system limits, the single bus package can be used to project and simulate a range of future transmission system scenarios. This allows the determination of the minimum inertia and energy response that the power system needs to survive loss of in-feed events across any future energy scenario.

This study is still in progress but has so far shown the need for faster response, and the role that loads play in primary frequency response. The results of the completed studies, the completed single bus model and operating scripts are currently being documented for submission to an academic journal.

The project will further add to the body of knowledge via an academic study on the implications of reduced RoCoF limits. This investigation will consider system inertia limits and the impact of high RoCoF on machines, as well as the required provision of primary response. Similarly, the research will address the possibility of reducing frequency limits in a future GB power system, while also assessing the implications of changes to frequency limits. The absolute limit of system inertia and RoCoF will be identified, such that low frequency demand disconnection services that have been put in place to prevent system failure are not compromised.

The project will also address regional inertia and the impact that applying remedial actions at given locations would have on the overall power system.

Lastly, the most suitable means and method of providing response in a future power system will be identified, alongside ascertaining the economic value of inertia.