Projects

Started

Applied Research and Development

ENGINEERING AND TECHNOLOGY (Electrical and Electronic Engineering)

Not Cross-cutting

Project Contact
Northern Powergrid

Network Innovation Allowance

Ofgem

01 October 2025

31 July 2026

ENA months

£170,000

Power

Yorkshire & Humberside

NULL

Project Contact, Northern Powergrid

We are proposing that this work is used to conduct an in-depth fact-finding exercise whereby the problem statements are extracted through a literature review, a limited number of studies and gap analysis which will present the issues in a clear and concise manner to NPg, who will review the outputs and make a decision regarding further work.The allocation between Newcastle University and Blake Clough is provided within the commercial section. In general, Professor Vladimir Terzija will deliver the literature review and provide expert input into the modelling work, with Blake Clough carrying out the majority of the modelling and reporting of modelling findings.Core Aim of Project The project aims to investigate STVS issues on the DNO network, take these findings and provide recommendations for further work. This could include development and deployment of Open-Source tools for the use of NPg relating to the following:Understanding the phenomenon of STVS, its causes, correlation with the level of IBR integration and the type of converter (GFL, or GFM) used.Enhanced monitoring of STVS on the current network.Provide enhanced forecasting capabilities to gauge where voltage issues may arise on the network in planning timescales. The tool can also be used for long term planning.STVS tools for voltage stability assessment could also aid in more robust EREC P28 voltage calculations although P28 analysis is not a focus area of this project.This proposal covers Literature Review, exploratory power system studies and analysis. Further work will be initiated once NPg have reviewed the outputs from WP1, whereby NPg will assess the merits of the findings and whether further funding should be allocated to the project. This work focuses on identifying the critical phenomena that lead to STVS issues and is covered by the following three core scope items, which are discussed in this section:Literature reviewStakeholder engagementStudies and analysisThe project will deliver the following:Perform a comprehensive literature review to establish baseline methodologies, STVS metrics, refine scope, identify opportunities for further work, focusing on STVS analysis and related issues such as changes to fault levels and the networks dynamic performance.Engage stakeholders (e.g., NPg, OEMs, NGESO) to ensure alignment.Gather and prepare detailed RMS and EMT model data.Determine and agree on power system models to be used.Collect, build and validate steady-state and RMS models to be used in the analysis.Conduct RMS Simulation studies to identify STVS mechanisms in NPgs network.Perform fault level assessments, comparing steady-state and time domain calculation methods.Validate IBR performance using EMT simulations - Identify limitations of RMS modelling and assess the need for detailed EMT models to be used in additional (optional) studies.Prepare comprehensive reports and presentations to summarise findings and propose future research directions.Literature ReviewThis section involves a thorough review of existing research and methodologies related to STVS and its relation to the systems dynamic properties, such as fault levels. It aims to establish a baseline understanding and identify knowledge gaps. The project team already has an understanding of current STVS mechanisms and study methodologies; however, the literature review will be important to consolidate and decide which methodologies we should deploy and what stability metrics would be most useful for NPg.Stakeholder EngagementThe project will engage with NPg, OEMs and NESO to ensure alignment on the objective of the Work Package. The project will conduct an initial high-level engagement with NPg to determine the modelling practices, reviewing available models, discuss existing issues and problem areas with NPgs Engineers and modelling approaches such as treatment of critical components, such as load models.OEMs will be engaged with the intention of obtaining permissions to use vendor specific models for IBRs. Through stakeholder engagement, the project will seek permission from OEMs to utilise real dynamic models for various IBR types (with encrypted control blocks). In the event that OEM models are not allowed, the project will utilise industry standard models, tuned for G99 compliance, such as those from WECC/IEC.We also intend to engage NESO to raise awareness of the works, as well as keeping them informed of developments on the project. NESO could also provide inputs on their views on STVS and fault levels on the wider network and how DNO networks will impact this in the future.Power System Modelling & AnalysisThe main intentions of the power systems modelling exercises in this WP1 are to explore the STVS phenomena and the mechanisms that could lead to related unstable operating conditions in distribution networks.The studies intend to contribute towards answering the following questions, which are discussed further in the three subsections below:What are the main phenomena and mechanisms that trigger STVS in distribution networks.Under what system conditions and network topologies might STVS become a concern for DSOs in the future.What type of models, and which modelling domains, are expected to be required to accurately capture STVS phenomena.Models and AssumptionsThis section discusses the models to be used in the initial power systems analysis.Network Model:The WP1 assessment will be performed on a selected Extra High Voltage (EHV) Network model of one GSP area. The GSP area will be proposed by NPg to represent a part of the system that has high IBR penetration. It is expected that NPg will provide the network model(s) in DIgSILENT PowerFactory software for the partners to utilise and build upon.Upon provision of the GSP-EHV model, we will review the model, identify missing data, discuss and feedback to NPg and develop technical assumptions where required.In the event that the modelled GSP and study year does not present voltage instability challenges, the investigation will aim to alter the given network to provoke STVS issues. These tests will determine the limits of the given network with respect to STVS. Where, through thorough testing, no STVS issues are found, for example due to other constraints always being dominant, these results will be presented and analysed in the context of the given piece of network and recommendations will be made.Additional Option 2 Grid Forming Converters: Adding grid forming converters (GFM) can bring benefits to voltage performance due to their voltage source behaviour and less reliance on a PLL to synchronise compared to grid following technology. Studying the impacts of GFM to improve STVS challenges is identified as an optional additional cost for WP1, where the outcomes of the core scope can inform the need for this work.Dynamic Performance Considerations STVS is typically concerned with the dynamics of loads and generation in the short time period following a large disturbance (e.g. a fewseconds usually before the operation of transformer tapping).Key areas of dynamic performance to be considered subject to literature review outcomes are expected to include:The behaviour of new types of fast acting load components such as induction motors or power-electronic interfaced loads. The sensitivity to voltage; e.g., the effect of constant power loads, with a low voltage dependency, can draw more reactive power from the local voltage-regulating resources. The location of new loads not included in existing models will be selected in locations sensitive to STVS and will be informed by the literature review and initial discussions with NPg. Aggregation of load models is expected to be required, at the 11 kV bus.The behaviour of IBRs and their control modes: IBRs can be a valuable source of dynamic reactive power. However, increasing penetration of IBRs can lead to high power transfers affecting voltage stability. The fault ride through (FRT) capability of IBRs should be modelled to capture its influence on the voltage depression during a fault, as well as the post-fault recovery profile. All explicitly represented IBRs will have LVRT controls to give a system-wide response.The effects of dynamic resynchronisation issues during fault recovery (i.e., stability of phase-locked-loop controls, or PLL) will be considered. This study topic will be performed and validated using EMT simulations in PSCAD to properly capture the dynamics of the PLL in the post-fault period (see models Section 1.3.1). These EMT studies are performed at the individual device level and are used to validate the performance of the IBR RMS controller. Wider EMT network modelling can be performed at additional cost as noted in Section 2.1.3.1.For the avoidance of doubt, converter-driven control instabilities (often categorised as sub-synchronous oscillations or SSO) are not the focus of these studies. STVS and converter-driven stability are similar in that they can be related with maximum power transfer between the converter and the rest of the system over a relative weak high impedance path. However, the two mechanisms are different in that voltage instability is driven by power flows through the system and availability of reactive power support, while converter-driven instability is associated with interactions within the converter controllers. These differences will be clarified in the literature review outputs.Fault Level AssessmentsThis project will investigate the relationship between fault levels and STVS. The Fault Level (FL) at a given point in the network is related to STVS as it is a measure of the systems impedance at the fundamental frequency.In addition, the nature of fault levels in NPgs distribution network can be assessed. Fault level calculations for sizing of protection devices are typically calculated using industry standard methods that employ steady-state calculation techniques to estimate fault infeed from various sources. However, they can often over-estimate the fault current contributions and do not provide a full representation of fault current sources, potentially leading to over-investment and limiting new connections.In this WP1, fault level calculations performed by normal G74/IEC60909 methods will be compared with the more detailed fault current contributions derived from dynamic simulations using accurate representation of OEM models. This can identify issues with respect to rising fault levels in NPgs network and potentially offset investment in fault-level related network reinforcements.3-phase Fault Levels will be calculated at all major busbar locations using G74 steady state methods at peak demand with all generating units online. RMS simulations for comparison will be limited to five selected critical locations.Another potential benefit from assessing fault levels within the STVS is the development of fault level and STVS monitoring tools as part of later Work Packages.Specific Outcomes of the Power System Modelling WorkThis modelling work covering STVS and fault level assessments is expected to provide a wide range of related useful outcomes for NPg.Regarding STVS, the envisaged benefits are:A better understanding of STVS phenomena. Via the literature review and the modelling work, future system operational challenges will be better understood.Provision of a dynamic EHV model. This work will provide a fully dynamic EHV model suitable for RMS simulations. The dynamic behaviour of all major IBRs and loads will be represented. The model will provide the basis for the power system analysis, but also serves a tool for future work. The models will represent IBRs as close to reality as possible, providing a realistic response.Informed view on the risk of short-term-voltage-stability in NPgs network. A key outcome of the modelling work will be determination of the level of risk that NPg is exposed to in the future due to STVS challenges.Contribution to Enhanced Assessment Techniques. The work will inform the required assessment techniques to determine and study STVS issues. It will reveal operational scenarios fault conditions and system configurations of concern.Inform future work to develop Decision-Support Frameworks: the work will inform in the development of policy and tools that assist in managing the uncertainty and risks associated with IBR impacts on voltage stability, promoting the adoption of effective mitigation strategies (to be undertaken in future work packages).Regarding the fault level assessments, the envisaged benefits are:Review of accuracy of fault levels calculation assumptions. The comparison between steady-state and RMS fault level calculation techniques will inform on the accuracy of current approaches and the risk of over-investment due to assumed fault level rise.Understanding the relationship between fault level and STVS. Understanding this correlation will inform the co-benefits of active fault level monitoring and mitigation of STVS issues.Deliverables: Reporting and Presentation:An interim report will be provided detailing the outcomes of the literature review (end of month 2).The final WP1 report will cover all findings and modelling methodologies, including detailed analyses, recommendations, and proposed areas of further work.During the project, we will hold monthly progress meetings with NPg and project team. Additional meetings, for example to discuss and confirm power system models, may also be required and will be arranged on an ad-hoc basis. At the end of WP1, we will hold a presentation / workshop summarising the findings and content of the report, covering:Key risks and challenges.Practical recommendations for NPg and stakeholders.Long-term research directions and industry implications - Roadmap for WP1 leading into future Work PackagesThe power system model will also be provided as a project output. The objective of this piece of work is to prove or disprove the following hypothesis. Our hypothesis is that the dynamic behaviour of distribution networks is changing and Short Term Voltage Stability mechanisms are not well known or understood.We are keen to understand the fundamental causes of the STVS which could also result due to specific network configurations, complex control interaction between IBR control loops with the network, or the nature of the demand.This project will model in detail the existing networks to understand any existing issues and understand likely future issues as more IBRs connect. Where possible, we will use real inverter models obtained via engagement with OEMs to ensure that modelling is accurate. The modelling will include both GFL and GFM, including understanding the benefits that GFM can provide to the system.The project aims to conduct a series of fact-finding exercises within Work Package 1 and to present the key findings to NPg in order to progress the studies and creation of the forecasting tools pertaining to STVS and Fault levels for the DNO.

The aim of this project is to investigate and quantify the impact of increasing penetration of Renewable EnergySources (RES) on short-term voltage stability (STVS) and fault levels within Northern Powergrids future ED3network. As the scale and materiality of these impacts are currently uncertain, the project will deliver strategicinsights to inform investment decisions and support the development of NPgs Distribution System OperabilityFramework (DSOF).Through dynamic modelling, RMS and EMT simulations, and stakeholder engagement, the project will:Identify critical system conditions that may lead to voltage instability.Assess the influence of inverter-based resources (IBRs), including Grid Following and Grid Forming converters.Develop open-source tools for forecasting fault levels and STVS risks.Provide recommendations for future mitigation strategies and integration into business-as-usual planning.This initial phase (WP1) will focus on literature review, exploratory modelling, and analysis. Further developmentwill be considered based on the findings and their value to NPgs strategic planning

24/04/26