Assessing Stability Challenges in Low-Inertia Power Systems: A Transmission System Operator Perspective

Core Concepts

The main stability constraint limiting the penetration of non-synchronous generation in the low-inertia All-Island power system of Ireland and Northern Ireland is related to frequency stability, particularly the limits on the rate of change of frequency (RoCoF).

Abstract

This paper discusses the stability assessment of low-inertia power systems using the real-world large-scale All-Island power system (AIPS) of Ireland and Northern Ireland as a case study. The AIPS currently accommodates world-record levels of system non-synchronous penetration at 75%, with plans to increase to 80% next year.
The paper presents one-month results obtained using the state-of-the-art stability tool called look-ahead security assessment (LSAT), which is implemented in the control centers of the transmission system operators (TSOs). The analysis evaluates rotor-angle, frequency, and voltage stability in the AIPS.
The results show that the main binding stability constraint in the AIPS is related to frequency stability, particularly the limits on the rate of change of frequency (RoCoF). The paper investigates the correlation between frequency insecurities and various system conditions, such as inertia, demand, and wind generation. It is found that low inertia, low demand, and high wind scenarios are more prone to RoCoF and over-frequency (Zenith) issues, while high demand and low wind scenarios are more prone to under-frequency (Nadir) issues.
The TSOs are working towards addressing these frequency stability challenges, such as procuring low-carbon inertia services and reviewing reserve products, as part of their Shaping Our Electricity Future Roadmap.

Stats

The AIPS currently accommodates world-record levels of system non-synchronous penetration at 75%, with plans to increase to 80% next year.
The TSOs have in place four operational constraints/limits: (i) an SNSP limit; (ii) a minimum number of conventional units online (MUON); (iii) a rate of change of frequency (RoCoF) limit; and (iv) a minimum inertia floor.
The total number of LSAT cases run for June 2023 is 8594, and out of these, only 418 cases (or approximately 4.86%) are reported as insecure.
Frequency stability, particularly RoCoF, is the main binding constraint, accounting for more than 45% of the total insecure cases.

Quotes

"The paper shows that, at the time of writing, the main binding stability constraint of the AIPS is related to the limits on the rate of change of frequency (RoCoF)."
"It appears that RoCoF is the main problem with 1.35% of total cases."
"Specifically, it appears that in the vast majority of cases low wind leads to RoCoF- and Nadir insecurities."

Key Insights Distilled From

Stability Assessment of Low-Inertia Power Systems

by Manuel Hurta... at arxiv.org 04-09-2024

https://arxiv.org/pdf/2404.04618.pdf

Deeper Inquiries

How can the TSOs further improve the stability assessment capabilities to address emerging stability phenomena, such as very-low frequency oscillations and sub-synchronous torsional interactions, in low-inertia power systems?

To enhance stability assessment capabilities for addressing emerging phenomena like very-low frequency oscillations and sub-synchronous torsional interactions in low-inertia power systems, TSOs can consider the following strategies:

Real-Time Monitoring: Implement advanced monitoring systems that can detect and analyze very-low frequency oscillations and sub-synchronous torsional interactions in real-time. This would require high-resolution data collection and sophisticated analytics tools.
Enhanced Modeling: Develop more accurate and detailed dynamic models of the power system components, including inverter-based resources, to better understand the interactions leading to these phenomena.
Advanced Simulation: Utilize advanced simulation tools that can simulate and predict the behavior of the system under various operating conditions, including scenarios that may trigger very-low frequency oscillations or sub-synchronous torsional interactions.
Training and Expertise: Provide specialized training to operators and engineers on identifying and mitigating these emerging stability issues, ensuring they have the knowledge and skills to respond effectively.
Collaboration and Research: Foster collaboration with research institutions and industry experts to stay updated on the latest developments in low-inertia system stability and leverage cutting-edge research to address these challenges effectively.

What are the potential market and regulatory mechanisms that could be implemented to incentivize the provision of low-carbon inertia services and other ancillary services required to maintain the stability of low-inertia power systems?

To incentivize the provision of low-carbon inertia services and other ancillary services essential for maintaining the stability of low-inertia power systems, the following market and regulatory mechanisms could be considered:

Capacity Markets: Implement capacity markets where providers of inertia services are compensated for their ability to provide grid stability services, including low-carbon inertia. This ensures that these services are valued and incentivized in the market.
Performance-Based Incentives: Introduce performance-based incentives that reward providers for delivering reliable and high-quality inertia services, encouraging them to invest in technologies that enhance system stability.
Regulatory Standards: Establish regulatory standards that mandate the provision of inertia services and other ancillary services as part of the grid operation requirements, ensuring that system stability is maintained at all times.
Market Flexibility: Create flexible market structures that allow for the participation of a diverse range of providers, including renewable energy developers, in offering inertia and ancillary services, promoting competition and innovation in the sector.
Long-Term Contracts: Offer long-term contracts or agreements to providers of inertia services, providing them with stability and predictability in revenue streams, which can incentivize investments in technologies that support grid stability.

How can the insights from the stability assessment of the AIPS be leveraged to develop more generic stability assessment frameworks for other low-inertia power systems around the world, considering their unique characteristics and operational challenges?

To leverage insights from the stability assessment of the AIPS and develop more generic stability assessment frameworks for other low-inertia power systems worldwide, the following steps can be taken:

Data Sharing and Collaboration: Encourage data sharing and collaboration among TSOs and power system operators globally to exchange knowledge and best practices in managing low-inertia systems.
Standardized Metrics: Develop standardized stability assessment metrics and criteria that can be applied universally across different low-inertia power systems, ensuring consistency in evaluating system stability.
Adaptability: Design the stability assessment frameworks to be adaptable to the unique characteristics and operational challenges of each low-inertia system, allowing for customization based on specific system requirements.
Benchmarking: Establish benchmarking processes that compare the performance of different low-inertia systems against common stability indicators, facilitating continuous improvement and knowledge sharing.
Continuous Learning: Foster a culture of continuous learning and improvement by regularly updating the stability assessment frameworks based on new insights, technological advancements, and operational experiences from diverse low-inertia systems worldwide.