Project Summary

As the share of inverter-based resources, including renewable generation, increases, lower system strength can lead to uncontrolled voltage changes which can escalate to instability and risk widescale customer disconnections. To secure the Net Zero grid, Network Owners urgently need to monitor system strength conditions to implement the most effective and economic mitigations. At present, neither the requirements for system strength monitoring nor the possible hardware and digital solutions are well defined. The SYSMET Project brings together leading experts to create the pathway for confident implementation of measurement-based tools that provide comprehensive visibility of system strength status for operational decision making.

Innovation Justification

Challenge Theme

The Project addresses Innovation Theme 2 “Leveraging disruptive computing technologies for improving system visibility, performance, and cyber-security.”.

Innovation

GB grid operators are increasingly concerned with power system strength because of the rapid growth of renewable resources connected to the grid by inverters, but at present have only limited or no capability for real-time system strength monitoring. The state-of-the-art of system strength assessment is summarised by a lack of standardisation. Various versions of the Short Circuit Ratio (SCR), defined fundamentally as the fault level divided by nominal active power, have been proposed. However, the results do not necessarily provide consistent conclusions for network operation.

Two UK distribution system operators (SPEN and UKPN) are trialling real-time fault level monitoring, but this has not yet been demonstrated at transmission voltage levels. Fault level monitoring is based on measurement of the impedance at the fundamental frequency which characterises the responsiveness between changes in voltage and current. Inverters have more complex responses that span across frequencies other than the fundamental, which can induce e.g., sub-synchronous oscillations. Therefore, new system strength metrics require as input the impedance across a range of frequencies.

The SYSMET Discovery Phase has engaged directly with network contacts from five relevant previous innovation Projects, including the Strength-to-Connect and DOME Projects. Building on their outputs, a clear user requirement for real-time frequency-dependent impedance determination was identified. The Alpha Phase will directly utilise the SYSMET Discovery Phase outputs including a list of potential vendors, report on candidate measurement and machine learning techniques as well as preliminary measurement specifications and data accessibility requirements.

The core innovation of the SYSMET Project is a pathway to verified implementation of frequency-dependent impedance measurement to enable real-time monitoring of system strength metrics in the GB Net Zero grid dominated by Inverter Based Resources (IBRs). The target approach is an active frequency scanning method, which requires suitable injection equipment to create small perturbations in the required frequency range and measurement systems capable of extracting the response under normal grid operation conditions. The measured voltage and current signals will be processed with advanced digital signal processing algorithms robust to noise effects to obtain impedance values and transform these into system strength metrics. The use of machine learning techniques will be explored to extend spatial coverage.

Three technical work packages will develop specifications for solutions that leverage novel computational algorithms to achieve system strength visibility which will improve the performance of an IBR-dominated Net Zero power system, thus aligning with the SIF innovation challenge and with the SIF Alpha Phase both in scale and technical risk. The Project will expand to integrated demonstration with grid operation and control systems in the Beta Phase.

System strength monitoring via frequency-dependent impedance identification is a novel capability that goes beyond incremental extension of existing monitoring infrastructure. There is no blueprint implementation in the UK to provide guidance. New equipment and software may need to be procured and installed, tested and integrated, requiring dedicated resources and expertise that cannot be met within business-as-usual activities.

We are aware of high CRL system strength tools available, but these have not been adapted/proven in the UK. These and other novel SYSMET solutions for different system strength indicators are at low CRL for the UK market. TRL progression planned:

Current: TRL2/3 relevant processes understood in other applications.

Alpha: TRL4 is targeted through proof-of-concept validation in a commercial simulation environment.

Beta: TRL7 achieved through prototype demonstration in the field.

Impacts and Benefits

Current Position

As the power system evolves to integrating more Renewable Energy Sources (RES), fossil-fuelled Synchronous Generators (SGs) are being displaced by Power-Electronics-Interfaced Devices (PEIDs) such as Inverter Based Resources (IBRs), which do not generally have the same inherent electromechanical properties as SGs such as large inertia capability.

 
The fundamental-frequency short-circuit level (SCL) and short-circuit ratio (SCR) have been traditionally used to define system strength in the SG-dominated power system. With the advent of RES and IBRs, one of the main assumptions that supported the use of SCL and SCR as system strength metrics, i.e. the dominance of SG-based electrical generation, no longer holds. Hence, a new way of measuring power system robustness for the electrical grid of the future is required.

Currently, there is no standardised approach to measuring system strength for the electrical grid of the future, where RES and IBRs will start to dominate electrical power generation and transmission. Furthermore, whilst there are monitoring tools and digital solutions available in the UK and internationally, they are immature and inadequate for IBRs.

Adopting a standardised approach to measuring system strength based on frequency-dependent impedance of grid-connected devices such as IBRs will ensure a stable transition to the RES-based electrical power grid of the future. This standard system strength measurement approach will enable manufacturers of grid monitoring systems to develop new and innovative devices that are fit-for-purpose and industrially relevant. It will also provide Network Owners with a set of requirements that can be issued to prospective monitoring tool providers who must demonstrate compliance with functionality and measurement accuracy requirements.

Reliable, widespread, and consistent monitoring of system strength indicators will enable Network Owners to address problems arising from lower system strength to ensure the availability of the power system. Furthermore, greater knowledge of real-time system stability will allow better decision-making when disturbances occur so mitigating actions minimise the overall cost and impact on customers.

Qualitative Benefits

High-level net benefits:

a) reducing constraints and costs for renewable generation customers. 
b) increasing system resilience due to improved system stability, thereby reducing the risk of severe disruption. 
c) optimising network operating costs and reducing consumer bills.

Quantitative Benefits

Benefits include reduced cost to the network’s balancing mechanism, Pathfinder 3 (addresses stability issues) plus a lower risk of outages; major or minor. The estimated cumulative discounted net benefits to consumers up to 2050, including SYSMET technology investment, is £220 million.

Financial - cost savings per annum on energy bills for consumers

Accurate quantification and measurement of the strength of the network allows efficient and targeted real-time deployment of stability services. Low system strength can cause issues with network stability and the default countermeasure is constraining generation and implementing stability services to increase the fault level or inertia of the system. These reactive actions can have high operational costs (£7 million per annum).

Environmental- carbon reduction - direct CO2 savings/annum against a business-as-usual counterfactual

Improvements in the management of grid stability build operational confidence in the stability of the network, allowing increased system capacity for renewable generation, and reducing CO2 emissions if it avoids the need to use of synchronous fossil fuel generation for system strength.

New to market– products

SYSMET defines a new way to measure system strength, measurement requirements, and test methods. Standardised requirements will enable focussed development and procurement of adequate hardware (injection equipment, instrument transformers and digital measurement devices) as well as software for evaluation and visualisation of system strength indices. Potential technology developers include Reactive Technologies and Outram Research Limited who have existing fault level monitoring products, as well companies that offer wide area monitoring solutions such as GE Digital.