Proper Utilization of PMU Data: Towards Prevention of Wide Area Blackouts

Sep 25, 2018 | Blog, Utility Infrastructure Engineering and Analysis

Proper Utilization of PMU Data: Towards Prevention of Wide Area Blackouts

 

The North American Bulk Electric Systems (BES) comprises of Eastern and Western Interconnection and Electricity Reliability Council of Texas (ERCOT). These are the combination of several complicated rotating machines along with several pieces of equipment for communication, control and protection. The complexity of the North American power grid on one hand, provides very reliable power to the customers, however, on the other hand, there is an equal risk of initiating cascading outages following some major disturbances resulting in wide area blackouts. The cascading blackout of August 14, 2003 in the northeastern U.S. and southeastern Canada has influenced many studies and practices toward preventing similar events in the future.

In order to prevent the interconnected power systems from wide area blackouts, an understanding of situational awareness is important. The transmission system power flow conditions should be continuously monitored in real time in order to provide early detection of problems. System information comprising of phase angles, frequency, rate of change of angles, etc., provide very useful information about the health of the power systems. In order to enhance the monitoring of the dynamic behavior of the system, several utilities have led an effort to deploy a network of Phasor Measurement Units (PMUs) throughout the system.  PMUs on electric power systems have been compared with Magnetic Resonance Imaging (MRI) of a human body. PMUs do provide the information about system states at a sampling rate as high as 120 samples / second, able to capture oscillatory events following any severe disturbances. The technological capability of PMUs is well understood, but the industry is still working out the best ways to use these devices. An important function would be to provide early detection and protection of the power system from system disturbances.

EnerNex recently completed a Major Disturbance Mitigation Study (MDMS) project that provided appropriate ways to utilize the information relayed by PMUs with the use of an intelligent angle prediction algorithm which is able to initiate the protective actions before the system goes unstable. By assisting in the detection and actions necessary to bring the bulk system swinging oscillation centers back to the stable operating range, the algorithms in this project can be used to prevent wide area blackouts, and  also provides important functionality to PMU data.

Controlled Systems Separation (CSS) was one of the recommendations provided in the August 14, 2003 Blackout Final Report by the US-Canada Power System Outage Task Force in order to save the system from a cascading outage. During CSS, the lines, generators and loads in the system are intentionally taken out of service following some procedures in order to stop the unintentional breakup of the network due to cascading events. Then, the system is left in a more favorable state for restoration.

EnerNex completed the earlier project named Control Systems Separation Study (CSSS) in which the possibility of getting the power system back to the stable operating conditions after severe disturbances through controlled separation of large systems into two or more islands was proven in a large bulk power system network through PSS/e dynamic simulations. This MDMS project utilizes CSS along with Under Frequency Load Shedding (UFLS) and system wide generator tripping, if required, as the mitigation measure to save the system from possible instability.

This MDMS study has successfully developed an algorithm using PMU measurements that is capable of predicting evolving angular instability under extreme contingencies both internal and external to the any bulk power system. The algorithm developed during this project was based on two Kalman filters, guided by a measurement prediction algorithm based on the Taylor series expansion and finite difference method. This algorithm was validated in several stable and unstable disturbance scenarios to make sure that the algorithm is capable of providing correct predictions of impending instability for any kind of system disturbances, and also importantly that the algorithm does not give a false alarm during stable system conditions. It was shown from all the testing that the proposed algorithm has a very fast response time and is very accurate in the prediction of angular instability. The cases tested included heavy load cases with heavy transfer conditions. The two Kalman filter prediction algorithm is used to make a decision on the system instability and then initiate the mitigation measure. Mitigation actions could be controlled system separation, along with under frequency load shedding, out of step generator tripping, and then as a last resort, system wide generator tripping. The figure below shows a basic representation for overall strategy of properly utilizing PMU measurements of angular difference between two interfaces to bring the system back to stable system conditions following any severe disturbance.

Important Contributions and Findings:

The major outcomes from this project are summarized below:

  • A new fast, online and accurate angular instability detection and prediction algorithm is proposed, developed and implemented with Python in PSS/e platform in a full stability model of the bulk system with more than 60,000 buses. The algorithm is based on two Kalman filters guided by the angle measurement prediction method based on Taylor series expansion and finite difference. This algorithm is capable of accurately predicting the angular difference between any two important interfaces in any large bulk transmission system.
  • The developed algorithm is capable of converging quickly enough to initiate mitigation measures in a timely fashion to stabilize the bulk system.
  • The testing included simulated noise on the PMU measurements that is thought to be significantly greater than what is existing with the present day technology.
  • The algorithm was tested under a wide range of stable situations as well and it did not falsely predict instability in any of those tested cases.
  • The two Kalman filter based angle prediction algorithm is capable of providing the information on impending instability 12 cycles ahead in time scale. Hence, any type of mitigation action can be initiated 12 cycles ahead in case the algorithm senses any type of system instability in future.
  • The delay of 4 cycles before initiating the CSS action was considered to account for breaker operation, teleprotection and communication delays. This is included to represent the practical scenario of the system under CSS.
  • This study reduces a large amount of offline simulations to find out the exact time when the CSS should start, because the two Kalman filter prediction algorithm is capable of finding the exact time at which the separation should begin and initiate the protection measures automatically. This adaptive capability is very important.
  • Mitigation measures included controlled separation of critical interfaces upon detection of instability across those interfaces. The mitigation measures required operation of the UFLS in places where the load/generation mismatches occurred after the controlled separation.
  • This project also recommends that the UFLS scheme needs to be adaptive and should be adjusted as needed from the settings following different criteria in order to separate the large system into several stable island systems based on the system conditions following any severe disturbance.
Smart Metering (SM) and Advanced Metering Infrastructure (AMI)

Smart Metering and AMI is a transformational process addressing multiple business and technical needs of the utility enterprise. This is more than just smart meters and communications networks; it includes all of the back end applications that can leverage the meter assets, such as outage notification, demand response, call center optimization, disputed billing process handling, pre-payment opportunities, and service connection management methods and procedures, to name a few.

Implementing SM and AMI faces the same business, engineering, and operational challenges as any other across-the-utility information technology endeavors – most notably risk associated with embracing proprietary technology, missing functionality and early obsolescence. Effective SM and AMI development, implementation, and operation relies on a marriage of electric power engineering with information technology expertise: a key component of EnerNex’s expertise and experience.

EnerNex provides an array of engineering and consulting services geared towards intelligent and effective implementation of SM and AMI. This covers all phases of project development, starting with capturing system requirements where our experts leverage a “Use Case” centric view of activities needed to be accomplished and their interaction with systems and other users. Subsequent project steps typically examine other critical areas, such as: modeling of business cases, building inter-department consensus, assembling and assessing system functional requirements and non-functional requirements, developing a system design, hardware and software specifications and standards, complete procurement services including RFI and RFQ process support, supplier rating system, response evaluation methodology, deployment management, and training of office and field personnel.

Demand Response (DR)

Demand response can be as simple as load interruption directed by the energy supplier in response to severe demand requirements, to complex customer defined load management in response to price signals. DR is one of the components of a “Non-Wires Alternative” that many utilities are effectively using to avoid expensive distribution fortification or upgrade.

 

Often the success and/or failure of demand response programs can be linked to program implementation challenges such as rate/tariff design rate structures communication (e.g. price signals) or ineffective incentives used by utilities to encourage customers to accept operational change. The issues of program design, rate structure and customer impact have a tremendous influence on the success or failure of load management initiatives. Demand response has traditionally been used as a tool of the energy industry to ensure system stability. However, the introduction of microelectronics, communications, home automation and the Internet of Things (IoT) has led to the development of cost effective solutions that have the capability to allow the consumer to take control of managing their energy load and ultimately, the price they pay for energy.

EnerNex has the experience and skills to turn your DR program into a successful operational asset and customer engagement process that can deliver value to all parties.

Energy Assurance Planning

Natural and man-made disasters cause an estimated $57B in average annual costs for all parties; large single events have resulted in losses of $100B or more. Events, such as the World Trade Center disaster, Hurricane Katrina, and most recently Hurricane Helene, have demonstrated an acute need to revisit, revise and implement an effective energy assurance plan. Energy assurance plans assess the functionality and interdependencies of buildings and infrastructure systems and the role they play in sustaining service and rapidly restoring critical services to a community following a hazard event.

 

EnerNex assists our clients in developing comprehensive energy assurance plans that mitigate and minimize the impact of energy disruptions. Our experts assess critical infrastructure risks and evaluate appropriate mitigation strategies and can help in developing an effective business continuity/disaster recovery (BC/DR) plan for utilities and your customers.

Microgrid Development

As the electric grid becomes more distributed and interactive, microgrids are playing an increasingly important role in our energy future. Decision makers at military bases, corporate and institutional campuses, residential communities and critical facilities across the world are exploring and implementing microgrids to meet economic, resiliency and environmental goals. Utility-grade microgrids are being deployed to meet transmission constraints, reliability requirements and safe-havens in the event of a significant storm event.

Microgrid_development Graphic steps to support grid modernization

Bringing together a portfolio of distributed energy resources into a controllable, islandable microgrid comes with its own set of challenges. The key to solving these challenges is in architecting a system to support information exchanges between components across well-defined points of interoperability (interfaces) in a technology independent manner. This interoperability ensures that the system is resilient to technology change. Modern systems engineering techniques must be employed to ensure that individual sub‐systems are clearly identified, their functions enumerated, their data requirements known, and the points of interoperability clearly specified, along with the commensurate monitoring, command and control that is needed to ensure grid stability. With such architecture, we can apply best of breed technology available today to support those information exchanges at interface boundaries but be free to upgrade / change the implementation technology later without causing a ripple effect throughout the system.

Enterprise Architecture

Enterprise Architecture focuses on aligning an organization’s business strategies with its anticipated, desired and planned technology enhancements. Enterprise Architecture provides a framework to cost-effectively transition from a current “as-is” technology to future enterprise-wide technological solutions. An effective Enterprise Architecture program aligns business investments with long-term business strategies while minimizing risk and providing superior technological solutions. EnerNex’s key asset is its highly skilled and experienced staff who are closely connected to both the smart grid and EA standards and practices. We provide clients with the insight necessary to operate a fully functioning smart grid, which is flexible, scalable, and vendor independent.

Grid Modernization Roadmap

Utility companies across the globe are continually modernizing their grid. Each company often has different rationales, objectives and priorities. Frequently, smart grid plans are developed for individual, incremental initiatives, rather than as a part of a whole, intelligent and interoperable infrastructure. Planning may be developed around technology choices rather than business and technical requirements. The result of incremental and flawed planning leads to increased cost and risk, lost opportunities, disconnected expectations and dead ends.

 

EnerNex’s approach to grid modernization roadmap development follows a proven, industry-standard approach to grid modernization planning by collaboratively working with the utility to develop a set of prioritized and time-phased grid modernization initiatives unique to its business strategy and objectives. The roadmap developed is holistic, requirements-based, business value driven and actionable. It often builds on and leverages existing applications and infrastructure, and incorporates industry standards to ensure interoperability, flexibility and reduced cost and risk.

Utility Communications

Utility communication and control systems are increasingly interconnected to each other and to public networks and as a result, they are becoming increasingly more susceptible to disruptions and cyber attacks. EnerNex has experience with the various issues relating to development, implementation and optimization including feasibility analysis, design, software development and customization, project management and acceptance. Our expertise extends from being involved in the development of the fundamental standards that support utility communication and automation, through deployment and securing of those resources. EnerNex personnel were heavily involved in development of such standards and protocols as IEC 61850, IEC 60870-5 and DNp3. Our staff played a key role in the EPRI Utility Communication Architecture (UCA) project and the IntelliGrid Architecture effort.

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