Power system resilience is an overarching concept covering the whole spectrum of the power system, from design and investment decisions to planning, operations, maintenance and asset management functions. Flexibility concerns the power system's ability to manage changes, with flexibility features able to improve the resilience characteristics of the system, provided that they are integrated into grid planning, in defence plans, and evaluated adequately in the energy market design. An analysis of ongoing worldwide initiatives provides relevant insight into ongoing worldwide initiatives. They provide relevant insight into how flexibility can support resilience, showing the prominence and potential values that can be unlocked, with potentially some low-hanging fruits to start. This paper introduces four innovative concepts: Alternative grid development, system integrity protection schemes, the next level of flexibility and LINK holistic approach to flexibility for resilience as solutions contributing to improving future power systems' resilience.

The transition to a clean energy future requires thorough understanding of increasingly complex interactions between conventional generation, network equipment, variable renewable generation technologies (centralised and distributed), and demand response. Secure and reliable operation under such complex interactions requires the use of more advanced power system modelling and simulation tools and techniques. Conventional tools and techniques are reaching their limits to support such paradigm shifts. This paper provides an overview of commonly used and emerging power system simulation tools and techniques. Applications of these tools ranging from real-time power system operation to long-term planning are also discussed. Various approaches to gain confidence in the accuracy and applicability of the simulation models are presented. The paper then discusses emerging trends in simulation tools and techniques primarily stemming from the transition to a power system with increased penetration of inverter-based resources as these are used in variable renewable energy technologies.

The focus of the work presented here is to raise awareness of how ancillary services within the NordPool area could be of value in supporting the future grid, and who could be the provider of these services. The ancillary services considered here are not limited to the current market, but also services for future market solutions as well as services for fulfilment of grid codes. The goal is to promote the development of existing and novel solutions to increase the utilisation and thus the value of equipment within the power system. The paper includes a techno-economical categorisation of ancillary services, from a provider's perspective, presenting opportunities and competition. Furthermore, procurers of services could utilise this kind of categorisation to identify possible providers or partners. The analysis of the categorisation shows a broad range of possible providers for each service and a broad range of possible services from each provider.

Power system security is defined as the ability of the power system to withstand the occurrence of

credible disturbances as defined by security criteria or standards. Stability control, which is one of the

pillars to system security and the subject of this technical brochure, aims at maintaining the security

of supply according to cost-effective criteria. It has always been a top priority in both industrial

practice and academic research to ensure the reliable operation of power systems. To this end,

extensive activities have already been undertaken by e.g. CIGRE in the field of power system stability

control and Dynamic Security Assessment (DSA).

Analysis from past blackouts and major system disturbances has pointed out some potential

deficiencies in current stability control techniques. These deficiencies are related to various aspects of

design and maintenance of control systems, being a direct result of the insufficient systematic design

and adaptability of, and coordination among, the conventional stability controls. According to a

questionnaire survey conducted by this JWG, the full benefits from a systematic framework approach

for power system stability were recognized by many of the respondents. All these key elements are

integrated in the framework proposed by this JWG and reflect the existing experience.

This TB proposes a framework consisting of the four established control types described below and

coordinating them to achieve enhanced performance. As fundamental requirement to achieve this

goal, the proposed framework associates these stability control types with their respective system

states. The first control type is named preventive control. It is activated in the normal or alert state,

and is carried out to maintain a sufficient stability margin. Once a predefined contingency occurs the

system could rapidly evolve towards an emergency state, where the second stability control type,

called event-based control, is triggered. The third stability control type, called response-based control,

is usually initiated following the violation of key variable limits in the emergency state. In cases where

the operation of all the previous controls proves insufficient, the system will degrade to a blackout

state. Restorative control, the fourth control type, is activated following a blackout or after an

emergency state and remains active over the whole restoration process.

This TB emphasises that these control types gain added value if they are adaptive and coordinated as

recommended in the proposed framework. When adaptive, they are able to adjust their control

decision set to the current operating condition and identify the contingencies. The coordination of

these adaptive controls yields a more cost-effective set of planned control decisions

This TB describes the functional structure of the proposed framework whose design shares the same

architecture of an online DSA system as well as the same configuration and hardware of existing

automatic control devices at substations.

This functional structure is comprised of four high-levels modules:

Wide area data acquisition and information processing,

Real-time monitoring, online estimation and online stability analysis,

Adaptive and coordinated decision planning of stability control, and

Automatic activation of event-based and response-based controls.

The first and second high-level modules are already well established in the industry. However, the

third module is not yet at the same maturity level. To this end, this TB recommends the following

elements in order to design and develop software with required functionalities in the proposed

framework: Quantitative stability analysis, Determining in advance the optimal stability control decision for each relevant control type,

and

Coordinating the previously determined stability control decisions across all control types.

This framework and its underlying software strongly rely on its integration with online DSA and other

tools used at the control centre. Besides, these systems are fed with field data from measurement

devices (e.g. PMUs) whose number and location should be effectively selected. Data exchange

protocols between all these elements are critical for their integration into the framework. Bad data

detection is a prerequisite for online monitoring and analysis, and absolutely critical for the smooth

functioning of the framework so that proper stability control decisions are always taken.

This TB also provides some key considerations and recommendations in the design and

implementation of the proposed framework for 1) specification designers, 2) manufacturers and 3)

system operators.

Before implementing such a framework, the grid owner (and also the specification designer) should

conduct a cost benefit analysis to compare its effectiveness with alternatives.

After the grid owner decides to implement such framework, demonstration projects and trial

operations have to be conducted with a particular focus on validation of

control decision planning. It is

highly recommended to develop laboratory or field validation tests for key devices and systems. These

tests need to be conducted before as well as after commissioning. Especially for event-based and

response-based controls, which operate infrequently, post-commissioning testing remains important.

It has to be mentioned that there are still some remaining issues. One of these is the execution of the

optimisation process that is quite complex and consists of an iterative search based on simulations.

Currently this optimisation does not guarantee a global optimum or even convergence. This issue

should be the focus of research and development by both manufacturers and academia. Another

major issue to be tackled by specification designers relates to cyber security aspects, which have only

been briefly touched upon in this TB. Thirdly, the remote modification of control settings is not yet a

widely accepted practice, and the proper design of operator’s intervention and validation mechanisms

is still lacking. To address these issues more effort is needed mainly from the system operator’s perspectives.

The proposed framework is expected to overcome most of the deficiencies of the current stability

controls. Yet, some challenges do remain and the following suggestions for future work are provided.

Firstly, the applicability of the proposed framework in a multi-TSO environment with common grid

model, mainly in the emergency state, needs further investigation. Secondly, power oscillations that

occasionally occur and might cause the triggering of incorrect control decisions, should be fully

understood and have their adverse consequences mitigated. Further development would be directed

towards the improvement of control decision planning by combining system-wide response

measurements with pre-disturbance simulation results. Thirdly, the stability characteristics of modern

power systems are changing due to the increasing level of power electronics devices. Its impact on

stability control needs to be properly determined in order to ensure the correct operation of the proposed framework.

In this paper, we describe the results from an ongoing project to update the modelling strategies of load models used for planning purposes by the Nordic Transmission System Operators (TSOs) Svenska kraftnät, Fingrid & Statnett. The background to this project and a description of the development of this methodology was published as Part 1 of this set of papers, presented at the Cigré 2016 Session [1]. During 2016, the methodology has been through a verification phase which is partly presented in [2] and [3] with further details presented in this paper.

The load response to voltage and frequency changes may have a significant impact on the dynamic behaviour of the power system. In this sense, the selection of load model structures and load model parameterisation gain an increased interest as power systems are operated closer to their limits. Modelling of loads is however highly complex due to the vast number of load devices in a power system, making it unfeasible to model each device separately as well as making it unfeasible to model each possible loading scenario. Based on this, a methodology for development of load models has been presented in [1]. In the work with validating this methodology, several challenges as well as strengths of the method have been identified. For the voltage dependency of the active power part of the load, the validation successfully provided evidence of the validity of the method. For reactive power, only a partial validation could be performed due to limited level of reactive power in gathered measurements. The load model structure used in this project is identified as a limiting factor for the representation of the non-linear behaviour of this part of the load. Frequency dependency of load has only been addressed to a limited extent, with results illustrating the difficulties to assess this kind of behaviour from measurements gathered during this project.

All in all, from the results of the validation it is found that the method is suitable to be employed on a larger scale with some differences in approach regarding the assessment of the voltage and frequency behaviour of the load. Furthermore, this work has provided valuable input for the understanding of the behaviour of the load.

In recent years, the impact of natural and man-made hazards on critical infrastructure has resulted in governments, regulators, utilities and other interested parties elevating requirements to enhance the ability of critical infrastructure. In this context, CIGRE C4 has established a technical working group (WG) to provide guidance in an attempt to standardise the approach to adopt resilience thinking in the utility environment. The first duty of the CIGRE C4.47 WG was to conduct an international survey to understand the existing trends of adoption and application of resilience concepts in the electricity sector. This reference paper will describe key observations and unpack the initial thoughts of the WG. Further insight into the survey observations and results can be obtained from the future CIGRE Technical Brochure.

System Integrity Protection Schemes (SIPS) are in use to increase secure power transfer in regions or cases where N-1 operation cannot be maintained. Utilization of PMU data in the development and deployment of solutions, enable SIPS to become response-based and thus providing increased security for a broader range of scenarios.

Power systems around the world are faced with a wide range of challenges in order to realize the objective to integrate an increased amount of renewable energy sources in the modern electricity grids. The consequences affect the daily operation and longterm planning of transmission and distribution systems, and the network owners and operator’s ability to ensure continuous, reliable and high quality of supply to the customers. The needs of each actor within the electrical supply chain provide drivers for revision of current practices and promotes future adaptions of functional components and systems, economic and regulatory areas. In this document, we describe the drivers for change regarding generation, demand, and grid, the resulting consequences this has on operation and planning of the power transmission and distribution systems, and finally the needs to ensure sustainability & security of supply from the technology, market and policy perspectives.

As cheap and affordable variable Renewable Energy Sources (vRES), such as wind farms and photovoltaics, are foreseen to dominate the future energy mix, the abundance of green electricity will allow the replacement of fossil fuels in sectors such as heating, cooling, industrial processes, and transport. The intermittency and/or low controllability of vRES implies the signi...

Developments of the power system are driven by the need to decrease the environmental footprint, to meet international climate goals, pushing for fossil‐free energy system. The transition towards clean energy will require power systems to adapt on a global scale with significant investments needed in fossil‐free electricity generation and transport. Renewable Energy Sources (RES) play an increasingly important role in the power system and may become the dominant sources of electricity. 

Significant RES are integrated in distribution grids globally, resulting in an increased need for distribution grids to perform new and complex tasks necessary for continued grid stability. The rapidity of small‐scale investments calls for agile, alternative grid development solutions. This agility is furthermore necessary to meet challenges arising from demand scenarios encompassing intermittent renewables along with electrification of transport and heat sectors. New technologies and markets are emerging to provide flexibility in consumption, generation, and power transfer capacity. 

Active Network Management (ANM) solutions provides alternative methods for planning and operation of the power system, through monitoring and control of multiple grid assets. This paper presents an overview of the ongoing project ANM4L, where a toolbox will be developed to support operation and planning of distribution grids.

The project ANM4L (Active network management for all - anm4l.eu), will develop and demonstrate innovative ANM solutions for increasing integration of distributed generation in electricity distribution systems. ANM solutions will consider management of active and reactive power to avoid overload situations and maintain voltage limits. The goal is to decrease the need of curtailment of renewable energy, theoretically enabling further integration of distributed generation potentially even above the current design limitations of the electricity network. 

Core research and development activities of the ANM4L project include development of: 

 ANM methods for local energy systems. 

 Economic considerations to provide decision support. 

 A toolbox to support the planning and operation. 

The toolbox, methods and business models for ANM will be demonstrated in real life distribution grids in both Sweden and Hungary. Furthermore, the project will consider the replicability and scalability necessary for these ANM solutions to be applied across the EU. 

Power system flexibility relates to the ability of the power system to manage changes. Solutions providing advances in flexibility are of utmost importance for the future power system. Development and deployment of innovative technologies, communication and monitoring possibilities, as well as increased interaction and information exchange, are enablers to provide holistic flexibility solutions. Furthermore, development of new methods for market design and analysis, as well as methods and procedures related to system planning and operation, will be required to utilise available flexibility to provide most value to society. However, flexibility is not a unified term and is lacking a commonly accepted definition. The flexibility term is used as an umbrella covering various needs and aspects in the power system. This situation makes it highly complex to discuss flexibility in the power system and craves for differentiation to enhance clarity. In this report, the solution has been to differentiate the flexibility term on needs, and to categorise flexibility needs in four categories: Flexibility for Power, Flexibility for Energy, Flexibility for Transfer Capacity, and Flexibility for Voltage. Here, flexibility needs are considered from over-all system perspectives (stability, frequency and energy supply) and from more local perspectives (transfer capacities, voltage and power quality). With flexibility support considered for both operation and planning of the power system, it is required in a timescale from fractions of a second (e.g. stability and frequency support) to minutes and hours (e.g. thermal loadings and generation dispatch) to months and years (e.g. planning for seasonal adequacy and planning of new investments). The categorisation presented in this report supports an increased understanding of the flexibility needs, to be able to identify and select the most suitable flexibility solutions.

Power system flexibility relates to the ability of the power system to manage changes. Solutions providing advances in flexibility are of utmost importance for the future power system. Development and deployment of innovative technologies, communication and monitoring possibilities, as well as increased interaction and information exchange, are enablers to provide holistic flexibility solutions. Furthermore, development of new methods for market design and analysis, as well as methods and procedures related to system planning and operation, will be required to utilise available flexibility to provide most value to society. However, flexibility is not a unified term and is lacking a commonly accepted definition. Several definitions of flexibility have been suggested, some of which restrict the definition of flexibility to relate to changes in supply and demand while others do not put this limitation. The flexibility term is used as an umbrella covering various needs and aspects in the power system. This situation makes it highly complex to discuss flexibility in the power system and craves for differentiation to enhance clarity. In this report, the solution has been to differentiate the flexibility term on needs, and to categorise flexibility needs in four categories:

 Flexibility for Power: - Need Description: Short term equilibrium between power supply and power demand, a system wide requirement for maintaining the frequency stability. - Main Rationale: Increased amount of intermittent, weather dependent, power supply in the generation mix. - Activation Timescale: Fractions of a second up to an hour.

 Flexibility for Energy: - Need Description: Medium to long term equilibrium between energy supply and energy demand, a system wide requirement for demand scenarios over time. - Main Rationale: Decreased amount of fuel storage-based energy supply in the generation mix.  - Activation Timescale: Hours to several years.

 Flexibility for Transfer Capacity: - Need Description: Short to medium term ability to transfer power between supply and demand, where local or regional limitations may cause bottlenecks resulting in congestion costs. - Main Rationale: Increased utilisation levels, with increased peak demands and increased peak supply. - Activation Timescale: Minutes to several hours.

 Flexibility for Voltage: - Need Description: Short term ability to keep the bus voltages within predefined limits, a local and regional requirement. - Main Rationale: Increased amount of distributed power generation in the distribution systems, resulting in bi-directional power flows and increased variance of operating scenarios. - Activation Timescale: Seconds to tens of minutes.

Here, flexibility needs are considered from over-all system perspectives (stability, frequency and energy supply) and from more local perspectives (transfer capacities, voltage and power quality). With flexibility support considered for both operation and planning of the power system, it is required in a timescale from fractions of a second (e.g. stability and frequency support) to minutes and hours (e.g. thermal loadings and generation dispatch) to months and years (e.g. planning for seasonal adequacy and planning of new investments).

Overvoltage is becoming increasingly prevalent in distribution networks with high penetration of renewable distributed energy sources (DERs). Local control of converter-based resources is a flexible and scalable method to prevent this growing issue. Reactive power is used for voltage control in many local control schemes. However, the typical range of R/X ratios for distribution power lines indicates that mitigation of overvoltage often requires excessive amounts of reactive power. Complete reliance on reactive power thus limits the effectiveness of local control strategies. In this work we instead propose a method that combines enhanced power factor voltage control with upper voltage limit tracking using PI control. We develop a modelling framework and demonstrate the stability of the proposed method. We then simulate the nonlinear operation of two parallel PI controllers in a medium voltage test system. © 2022 The Authors

Congestion is a major limiting factor preventing expansion of renewable energy production in distribution networks. However, with large shares of connected power electronic-interfaced generators in combination with new types of controllable loads, such as electric vehicles (EVs), there is a potential to greatly increase network operation flexibility. Utilising these available flexible resources effectively is crucial to boost network capacity in a cost-effective manner and allow for safe integration of additional renewable energy sources (RESs). In parallel, the reactive power flows in distribution networks are changing. This can be attributed to the increased RES production and increased charging currents due to expanding cable networks. Also contributing to the changing flows is the rising number of new household appliances and consumer electronics with non-linear load characteristics. This makes systemwide coordination of resources an even more pressing issue. For distribution system operators (DSOs), minimising undesired reactive power flows at the connection to the transmission system is key to meet inter-network requirements. In this paper we propose a centralised near real-time control algorithm for combined congestion management and reactive power control in distribution networks. Through updated communication and measurement protocols, together with more extensive use of the active and reactive power control capabilities of local flexibility resources – such as wind power plants (WPPs), photovoltaic (PV) units, and flexible loads – bottlenecks can be detected and eliminated. Flexibility is offered by local resources and dispatched by the DSO through a common platform, which is independent of any specific financial arrangement for the participating flexibility providers. Thus, market solutions and individual contractual agreements are not mutually exclusive and can be implemented in parallel. The inclusion of reactive power simplifies the DSO’s coordination of intra-network and inter-network operational requirements. We demonstrate selected algorithm features through simulations of a congestion scenario in a medium voltage benchmark network. Aspects of deploying the solution in actual distribution network operation are also outlined.

This paper will provide insights regarding the financial implications of non-conventional grid development solutions, which are intended to provide agile, flexible and supportive solutions and thereby enable a sustainable development of the power system. As complements to traditional grid expansion developments, Active Network Management (ANM) solutions provide new methods to plan and operate the power system. In the case of long-term investment planning, different grid development solutions are weighed against each other based on e.g., their resilience, cost, environmental impact, and time to operation. The results presented in this paper originate from the ongoing European research project ANM4L [1]. While the developments in the ANM4L project are based on three pillars (ANM control solutions, Business solutions, & ICT solutions), the activity in focus of this paper is on the discussion on necessary investment decisions by the DSO and whether to continue traditional operations or to apply ANM solutions. The pillars of the ANM4L project are collectively resulting in a toolbox developed to support the operation and planning of distribution grids, which functionality and replicability will be tested and demonstrated within the ANM4L project. The activity in focus of this paper lies within the second pillar and is on the discussion on necessary investment decisions by the DSO and whether to continue traditional operations or to apply ANM solutions.

As zero operational-cost variable Renewable Energy Sources are foreseen to dominate the future energy mix, the abundance of green electricity will allow the replacement of fossil fuels in sectors such as heating, cooling, industrial processes, and transport. The intermittency of such energy resources implies significant systemic requirements for flexible solutions; thus, developments of the energy sector in general, and the power system in particular, instigate significant innovation activities in the fields of power system flexibility. Concurrently, complexities and interdependencies of system components and multitude of actors increase the risks of service failures and the complexity of production and grid planning, raising the demand for stronger and more agile resilience means and countermeasures. In this white paper we discuss the item “How can flexibility support resilience?”, considering the increased societal needs of a secure electricity supply. Power system resilience reflects the impact of severe events and is an overarching concept, covering the whole spectrum of the power system from design and investment decisions to planning, operations, maintenance and asset management functions. As such, the concept of power system resilience applies to the planning time frame that looks to build resilience into the future network, as well as the operational time frame, in which security is managed by optimizing the inherent resilience of the existing power system. Flexibility concerns the power systems ability to manage changes, with flexibility features able to improve the resilience characteristics of the broader view system of systems, provided that they are integrated in grid planning, in defence plans, and properly evaluated in the energy market design. Flexibility capabilities need to be considered from the planning stage, using a holistic approach aimed at grids to be flexible and resilient by design. Flexibility resources can also facilitate the restoration process by exploiting distributed black start capabilities including sector-coupling, which adds a new dimension to the necessary interactions pattern between electrical TSOs and DSOs, with utilities from other sectors. Power system planning for the future grid must embrace a wide range of network and non-network options to create operational flexibility options, including more active demand management techniques and customer-sensitive smart load shedding procedures. The next level of flexibility is seen as being fully deployed and utilized for operation and planning of the power system, being integrated in procedures for long-term planning as well as in tools for stability support. The integrated dependency of flexibility directly impacts the resiliency of the power system, thus flexibility solutions intended to provide resilience support must be reliable and secure to provide the trust required for operation and planning. Many of the worldwide ongoing initiatives can provide highly relevant knowledge to the question of How can flexibility support resilience? Indeed, they show the relevance and the potential values to be unlocked, with potentially some low hanging fruits to start with. Some of the examined areas include: • System Integrity Protection Schemes • System Technical Performance • Alternative Grid Development The economic value provided by large scale flexibility solutions can increase the benefit of maintaining high levels of resilience and thus provide incentives for resilience-enhancing investments. Additionally, cyber security is an area with increased focus as part of the power system digitalisation. Finally, standardisation of solutions is important to increase the reliability & acceptance in order for large scale deployment of flexibility.

The Joint Working Group C4/C2.58/IEEE was established to review voltage stability of power systems in the context of increased penetration of Inverter Based Resources (IBR) in electric power grids. The focus was to evaluate the adequacy of existing methods of voltage stability assessment in the present-day context. The developed technical brochure reviewed the definition of voltage stability and explained the role of voltage stability assessment within the voltage security assessment task of near real time power system operation. The overall conclusion is that the controllers implemented on IBRs makes a significant influence on short-term, but also long-term voltage stability. The presence of IBRs at distribution voltage levels contribute to the dynamic behavior of the power grid. Voltage stability assessment must incorporate these facts to ensure that the methods and tools accurately capture voltage stability limits.

This Technical Brochure explores the integration of Wide Area Monitoring (WAM) and Wide Area Monitoring, Protection, and Control (WAMPAC) systems into decision support tools for control room processes of modern power systems. It highlights the need for synchronised measurement technologies as provided by Phasor Measurement Units (PMU) to observe and control the electrical grid effectively. The brochure discusses various applications and timeframes for decision-making processes using synchrophasor measurements, ranging from real-time control to post-event analysis. By sharing practical experience, it emphasizes the challenges and benefits associated with deploying WAM and WAMPAC systems into standard control room procedures and provides recommendations for areas of further research and development.

The energy transition is placing increased strain on power systems and making it challenging for Transmission System Operators (TSOs) to securely operate power systems. System Integrity Protection Schemes (SIPSs) are one of the solutions to address these challenges. SIPSs are a type of over-arching power system control; their goals are to increase the secure utilization of power system assets and to limit the impact of large disturbances on the system. Due to societal developments, the interest in utilizing SIPSs is increasing internationally, highlighting the importance of the standardization of terms and definitions to support collaboration between internationally interconnected power systems. This paper addresses the issue of increasing SIPS literature and the efficient exchange of knowledge about SIPSs by providing a new, up-to-date literature review and proposal for the standardization of SIPS terminology. The need for standardized terminology is highlighted by gathering various terms used to describe SIPSs and proposing a standardization of definitions, terms, and SIPS operational execution steps. The goal of the proposed standardization is to provide clarity and to decrease the sources of misinterpretation in an international collaborative environment. The analyzed literature is further classified according to the SIPS features it addresses, and conclusions about well-established and interesting future research areas are drawn. For example, it has been observed that the most commonly considered SIPS action is load shedding, while more sophisticated actions, e.g., using HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission System) installations, controlled together with var rescheduling, are more in the realm of future research that may provide additional benefits to TSOs.

To collate best praxis and ideas on local electricity markets, this paper surveyed a number of pioneering initiatives in local market design and implementation. The survey focused on the definition of the market itself and the roles and responsibilities of actors within, the distribution of the value of local markets, as well as challenges and current barriers. The results indicate that the main value of a local market is related to the benefits for society as a whole and to a lesser extent individual actors. The main benefits are expected to derive from deferred network investments and reduced network costs. Moreover, local markets are expected to allow for higher shares of clean energy integration and generate positive environmental impacts. Nonetheless, a number of regulatory, economic, stakeholder-related, and other barriers risk obstructing the operation of local markets in the short term and inhibit their adoption in the long run.