Black Start from Non‑Traditional Generation Technologies Network Innovation Allowance June 2019 Power Island Strength and Stability in support of Black Start In partnership with: National Grid ESO | June 2019 Power Island Strength and Stability in support of Black Start Contents Executive summary 02 1 Introduction 04 2 Microgrids – A technical overview 05 2.1 Microgrid definition and application 05 2.2 Microgrid components and topology 06 2.3 High-level technical requirements 08 2.4 Planning and design of Microgrids 11 2.5 Microgrid demarcation 11 2.6 Islanding use case 11 2.7 Power Island progression for Black Start 12 2.8 Clustering of microgrids 16 3 Microgrid operating challenges 15 3.1 Microgrid characteristics 15 3.2 System consequences 16 3.3 Operational and stability challenges 18 3.4 Improving microgrid strength and stability 22 4 Microgrid case studies 28 4.1 Flores Island, Azores Archipelago, Portugal 29 4.2 Island of St. Eustatius, Netherlands, Caribbean 36 4.3 Portability towards a distribution grid 42 5 Conclusions 43 5.1 Microgrid specifications 43 5.2 Main operational challenges 43 5.3 Strategies to overcome challenges 43 5.4 Learning points from case studies 43 References 44 Abbreviations 46 01 National Grid ESO | June 2019 Power Island Strength and Stability in support of Black Start National Grid ESO | June 2019 Power Island Strength and Stability in support of Black Start Executive summary TNEI Services Ltd (TNEI) was commissioned by National Grid ESO These technical attributes result in a number of operational The learning points from these case studies include: challenges including voltage and frequency stability, • 100% inverter-based grids can be operated at to investigate the capability of non‑traditional technologies in the converter stability, protection reliability, fault ride through megawatt-scale capability and electrical safety. restoration of the GB power system in the event of a partial or total • grid forming or voltage-control-mode inverters, used in system shutdown. The project is a Network Innovation Allowance This report summarises the learnings from a number conjunction with battery energy storage systems (BESS) of research papers and case studies to show how can be used successfully to establish and maintain the (NIA) project initiated by National Grid ESO, with support from SP the above-mentioned operational challenges could voltage and frequency on a microgrid without the support be addressed using a number of different techniques of synchronous machines Energy Networks. The overall aim of the NIA project was to provide to ensure the stable and reliable operation of microgrids. • system frequency stability can be improved by insight into the capability of several prevalent non‑traditional Solutions include: introducing energy storage systems which can provide technologies: wind, solar, storage, demand side response (DSR) • increasing system inertia using synchronous a fast frequency response to arrest frequency drops and compensators, exchanging kinetic energy from wind oscillations during network disturbances and electric vehicles (EV), to provide ancillary services to National farms, or using the synthetic inertia capability of energy • inverters can provide sufficiently high current during faults Grid ESO in the event that the GB network requires a Black Start. storage systems. to trigger the protection devices on the MV system • adaptive tuning of the convertor responses based on • microgrid controllers can dynamically control all the the mode of microgrid operation. generation and demand in a microgrid system. Responding to the significant changes in the energy Power islands, also known as non-isolated microgrids, • adding energy storage systems, wind-turbine de-loading landscape in the past decade, National Grid ESO are can improve the supply security and reliability of parts and/or demand response for low frequency support. The report concludes that the operational challenges seeking to understand how renewable generation and of the distribution network. The upfront planning and traditionally associated with MV microgrids can be • changes to protection relay settings to ensure faults can successfully mitigated through the application of distributed energy resources (DER) could facilitate the design of microgrids need to consider not only the be correctly detected in low short circuit level scenarios. restoration of the GB power system with the decline and main components (such as microgrid controller, modern-day microgrid controllers, energy storage systems, decommissioning of traditional Black Start providers distributed energy resources (DERs), controllable load, • installation of dedicated earthing. and the adaptive adjustment and finetuning of convertors (larger, synchronous power stations). The creation of and a communication system), electrical boundaries and protection systems. This suggests that microgrids/ smaller, distributed power islands is of particular interest and Point of Connection (POC), but also a range of The report examines the practical application of some power islands can be operated reliably, and have sufficient as a result, whereby these would be initiated on distribution technical requirements which include DER and storage, of these solutions through two microgrid case studies – strength and stability to play an important role in supporting networks and grow to energise the transmission network. voltage and frequency response, mode transfer and one located in the Azores and the other in the Caribbean. Black Start of the distribution and transmission power grid. This project has considered the technical capability of the stability, protection systems and settings, power quality, Both MV microgrids have a peak load of just over 2MW and technologies, the challenges of creating and maintaining earthing, control and communications. These and other contain traditional synchronous generators, high shares of small power islands with high penetrations of renewables requirements are addressed in IEC 62898-1:2017. renewable energy resources and energy storage systems. and DER, and how to better predict the reliability and availability of renewable generation in such a scenario. National Grid ESO’s Black Start System Operability Framework (SOF) envisages the application of non-isolated The project has three distinct deliverables. microgrids for Black Start restoration services by means • Report 1: Overview of the capability of non-traditional of a number of progression steps. Growing a microgrid technologies to provide Black Start and restoration or power island to energise larger parts of the distribution services; network could be achieved through the clustering of different microgrids, provided robust communication • Report 2: Investigation of the challenges around and control systems are in place to co-ordinate the power system strength and stability specifically interaction between the different microgrids. in relation to power islands with high penetrations of renewables and converter-based technology; and Due to their size microgrids have different electrical • Report 3: A sophisticated planning tool specifically characteristics compared to the larger power grid. designed to simulate distributions for the reliable output Furthermore, they tend to have a much higher share of wind over periods of hours to days, and how these of renewable and converter connected resources. distributions vary on timescales of months and years. This results in distinct technical characteristics which directly impact the strength and stability This report is Report 2, one of the three deliverables from of microgrids, namely: the “Black Start from Non-Traditional Technologies” project. • high variability of load and generation; • low system inertia; • low short circuit level; • greater voltage-frequency coupling; and • a loss of earth reference. 02 03 National Grid ESO | June 2019 Power Island Strength and Stability in support of Black Start National Grid ESO | June 2019 Power Island Strength and Stability in support of Black Start 1 Introduction 2 Microgrids – A technical overview The “Black Start from Distributed Sources” System Operability 2.1 Microgrid definition and application Framework (SOF) [1] proposes two possible methods of Black Starting the power grid using DER technologies. The IEC 62898‑1:2017 guidelines for microgrid project planning and The first method proposes the use of large embedded specification [2] defines a microgrid as a “group of interconnected generation, typically connected on the 132kV distribution loads and distributed energy resources with defined electrical network, that is able to self‑start and re‑energise the boundaries that acts as single controllable entity and is able transmission network. The second involves the establishment to operate in both grid‑connected and island mode”. and operation of small self‑contained distribution‑level A power island is defined as “part of an electric Microgrids can have many different applications microgrids or power islands at medium voltage (MV) levels. power system, that is disconnected from the remainder which include: of the interconnected system, but remains energised”. • improving supply reliability and securing supply Microgrids can exist at any voltage level between LV for all or part of their loads which could include In the context of this report a microgrid and power island Firstly, an overview is provided of microgrids looking and HV, but the “Distributed ReStart” NIC project will the distribution