⚡Power System Stability and Control Unit 17 – Power System Restoration & Black Start

Key Concepts and Definitions

• Power system restoration process of restarting and reconnecting power system components after a partial or complete blackout
• Blackout widespread loss of electrical power across a large area, can be caused by various factors such as equipment failures, natural disasters, or cyber attacks
• Black start capability of a generating unit to start up independently without relying on an external power source
• Cranking path sequence in which generating units and transmission lines are energized during the restoration process
• Isochronous mode operation of a generator to maintain a constant frequency without relying on an external reference
• Load rejection ability of a generating unit to quickly disconnect from the grid and maintain stability during a disturbance
• Cold load pickup phenomenon of increased inrush current when restoring power to loads that have been without power for an extended period

Causes of Blackouts

• Equipment failures such as transformer breakdowns, transmission line faults, or generator malfunctions can trigger a cascade of events leading to a blackout
• Natural disasters like hurricanes, earthquakes, or ice storms can damage power system infrastructure and cause widespread outages
• Cyber attacks targeting power system control systems or communication networks can disrupt operations and lead to blackouts
• Human errors during maintenance, operation, or planning can inadvertently cause power system disturbances or exacerbate existing issues
• Inadequate generation capacity or reserve margins can result in insufficient power supply to meet demand, potentially leading to load shedding or blackouts
• Transmission system congestion or bottlenecks can limit the ability to transfer power between regions, increasing the risk of localized blackouts
• Lack of coordination or communication between power system operators and utilities can hinder effective response to emergencies and prolong outages

Power System Restoration Process

• Assessment of the extent of the blackout and the status of power system components is the initial step in the restoration process
• Prioritization of critical loads such as hospitals, emergency services, and communication infrastructure is essential to ensure public safety and facilitate restoration efforts
• Establishment of stable islands involves isolating portions of the power system that have maintained generation and load balance, which serve as building blocks for the restoration process
• Synchronization of islands requires carefully matching the frequency, voltage, and phase angle of adjacent islands before connecting them to avoid further disturbances
• Gradual load pickup is necessary to avoid overloading generators and transmission lines during the restoration process, as cold load pickup can cause significant inrush currents
• Continuous monitoring and adjustment of system parameters such as frequency, voltage, and power flows are crucial to maintain stability throughout the restoration process
• Coordination and communication among power system operators, utilities, and government agencies are essential for effective decision-making and resource allocation during the restoration process

Black Start Capabilities and Resources

• Diesel generators are commonly used as black start resources due to their ability to start up quickly and operate independently of the grid
• Hydroelectric units with self-starting capabilities can serve as black start resources, especially in regions with abundant hydro resources
• Gas turbines equipped with battery or compressed air starting systems can provide black start capabilities in areas with access to natural gas infrastructure
• Pumped storage hydroelectric plants can act as black start resources by using the stored potential energy in the upper reservoir to start up and generate power
• Distributed energy resources such as microgrids and renewable energy systems with energy storage can provide localized black start capabilities and support restoration efforts
• Redundancy and geographic diversity of black start resources are important to ensure resilience and flexibility in the face of various contingencies
• Regular testing and maintenance of black start resources are necessary to ensure their readiness and reliability when called upon during a blackout

Restoration Strategies and Techniques

• Build-up strategy involves starting with a small stable island and gradually expanding it by adding generating units and loads in a controlled manner
• Build-down strategy starts with a larger island and progressively splits it into smaller, more manageable islands as the restoration process progresses
• Parallel restoration allows multiple islands to be restored simultaneously, which can accelerate the overall restoration process but requires careful coordination
• Load shedding and load rejection are techniques used to maintain the balance between generation and load during the restoration process, preventing system instability
• Soft energization of transformers and transmission lines using reduced voltage can minimize inrush currents and prevent damage to equipment during the restoration process
• Reactive power management is critical during restoration to maintain voltage stability and prevent voltage collapse, which can be achieved through the use of shunt capacitors, static VAR compensators, or synchronous condensers
• Optimal power flow techniques can be employed to determine the most efficient and stable path for restoring the power system while considering various constraints and objectives

Challenges and Considerations

• Cold load pickup can cause significant inrush currents when restoring power to loads that have been without power for an extended period, potentially leading to system instability or equipment damage
• Coordination of multiple entities involved in the restoration process, such as power system operators, utilities, and government agencies, can be challenging due to different priorities, communication protocols, and decision-making processes
• Availability and readiness of black start resources can be a limiting factor in the restoration process, especially if they are damaged, unavailable, or unable to perform as expected
• Restoration of critical loads and infrastructure such as hospitals, emergency services, and communication systems must be prioritized to ensure public safety and facilitate the overall restoration process
• Cybersecurity concerns can arise during the restoration process, as the power system may be more vulnerable to attacks or intrusions when operating in a degraded state
• Dependence on communication and control systems can hinder the restoration process if these systems are damaged or unavailable, requiring alternative means of coordination and monitoring
• Balancing speed and stability is a delicate task during restoration, as rushing the process can lead to further disturbances or setbacks, while proceeding too slowly can prolong the outage and its impacts

Tools and Technologies

• Energy Management Systems (EMS) provide real-time monitoring, control, and optimization of the power system, facilitating the restoration process by offering situational awareness and decision support
• Supervisory Control and Data Acquisition (SCADA) systems enable remote monitoring and control of power system components, allowing operators to assess the status of the system and take necessary actions during restoration
• Wide Area Measurement Systems (WAMS) using Phasor Measurement Units (PMUs) provide high-resolution, time-synchronized data on power system parameters, enhancing situational awareness and assisting in the coordination of restoration efforts
• Advanced metering infrastructure (AMI) and smart grid technologies can help identify and isolate faults, manage load restoration, and facilitate communication between utilities and customers during the restoration process
• Power system simulation and modeling tools can be used to plan and validate restoration strategies, assess the impact of different scenarios, and optimize the restoration process
• Decision support systems and artificial intelligence techniques can assist operators in making informed decisions during the restoration process by analyzing large amounts of data and providing recommendations based on predefined criteria
• Resilient communication networks and backup systems are essential to ensure reliable information exchange and coordination among stakeholders during the restoration process, even in the face of disruptions or damage to primary communication channels

Case Studies and Real-World Examples

• 2003 Northeast Blackout affected 55 million people in the United States and Canada, highlighting the importance of coordination, communication, and the need for robust restoration plans
• 2011 Japan Earthquake and Tsunami caused widespread blackouts and damage to the power system, demonstrating the challenges of restoration in the face of natural disasters and the role of black start resources in the recovery process
• 2012 India Blackout impacted over 600 million people, emphasizing the importance of adequate generation capacity, transmission infrastructure, and the need for better coordination among regional power systems
• 2019 California Public Safety Power Shutoffs were implemented to prevent wildfires during high-risk weather conditions, showcasing the use of targeted load shedding and the importance of customer communication and preparedness
• 2021 Texas Power Crisis caused by extreme cold weather and inadequate winterization of power system components, underscoring the need for resilient infrastructure and the challenges of restoration in the face of fuel supply disruptions and equipment failures
• Successful black start exercises conducted by various utilities and system operators demonstrate the importance of regular testing, training, and validation of restoration plans and procedures
• International collaboration and knowledge sharing initiatives, such as the CIGRE Working Groups on Power System Restoration, promote best practices, research, and innovation in the field of power system restoration and black start capabilities