Power System Grid Operation Using Synchrophasor Technology

Synchrophasor measurements have been widely regarded as providing benefit to managing the electric power system. Various applications have been deployed, ranging from improved situational awareness to enhanced accuracy of dynamic models, enabled by improved measurements. This chapter will provide a brief introduction of the technology, how it evolved, and a summary of ongoing efforts by the US Department of Energy (DOE) to promote this technology for enhancing the reliability of the power system. It will serve as an introduction to other chapters of this book, which will delve into greater details about synchrophasor applications that are improving power system planning and operations.

Data quality is a term that can be broadly defined and used. Here, it is broken down into six categories: loss, corruption, inaccurate representation, lack of precision, incorrect measurement identification, and excessive latency. These are discussed along with their causes and impacts. The overall problem of assuring high data quality starts with the measurement system itself. High quality can be built into the measurement system starting with planning and carried through the installation. A good maintenance program coupled with an error detection system can keep the quality high. Some data quality problems affect all applications, like lost data, incorrect values, and misidentified quantities. Other problems, like excessive latency, may have an impact on operational uses, but not off-line analysis. High resolution is important for small-signal analysis, but not displays. These types of impairments and their impacts are analyzed for the principal categories of applications which are off-line (analysis), near real-time (operations), and real-time (controls). The use of an LSE is discussed for both measurement assurance and extension of the measurement set.

Synchrophasor-based monitoring and control applications are being integrated into power grid control centers or being explored in pilot phase projects to realize the vision of real-time monitoring and control of bulk power system.

Bonneville Power Administration (BPA) was among the first adopters of the synchrophasor technology in the early 1990s. Initial PMUs were installed as stand-alone disturbance recorders at four substations collecting data locally at a rate of 30 times each second. The value of the synchrophasor technology was evident when the synchronized dynamic data enabled detailed analysis of some of the events/outages that happened in 1996. Following the outages, BPA greatly expanded its PMU coverage to monitor large power plants, interties, and load centers. BPA also researched, developed, and prototyped several applications that use wide-area synchronized measurements for power system analysis. This chapter presents BPA’s efforts and contributions in using synchrophasor technology in managing the grid.

Since the first appearance of synchrophasor measurement technology, it has been playing a fundamental role for many advanced power system monitoring, analysis, and control applications around the world. Phasor measurement unit (PMU) and wide-area measurement system (WAMS) are becoming the critical measurement infrastructures for transmission and generation systems. In this chapter, firstly the recent development of PMU/WAMS, communication, and synchronization network in China is summarized briefly. Then, some basic applications, such as power system model parameter identification and validation, disturbance recognition and location, are introduced. Next, some major advanced applications utilizing synchrophasor measurement are emphasized and presented, including oscillation mode identification based on ambient PMU data, wide-area backup protection, wide-area damping control using HVDC modulation. Considering the operational problems caused by integration of large-scale renewable energy resources, such as cascading tripping and subsynchronous resonance phenomena, synchrophasor technology is expanded to meet the monitoring needs. Some pilot projects are utilized to illustrate the effectiveness of wide-area monitoring and control system.

One of the challenges brought about by the large wind portfolio in ERCOT is the presence of forced oscillations from wind generators driven by control systems with a bad setting. To address this, a study was undertaken to mine archived synchrophasor data from PMUs installed near wind farms for oscillations and identify location, frequency of oscillation, and minimum energy level for each mode. In this chapter, we present the results obtained from the study and the conclusions reached. The study utilized two metrics—Monthly Highest Energy (MHE) and Monthly Mode Occurrence (MMO)—to classify the identified oscillatory modes. The results of this study informed the configuration of real-time tools for monitoring of and alerting for these oscillations. The various modes were found to be associated with MW output and/or control system design and settings of wind farms. The results of the study also provided the needed information to validate models against specific oscillations events and determine plausible strategies for addressing these modes in real-time operations.

One of important applications of Synchrophasor technology is Oscillation Detection. This chapter discusses the use of PMU data for oscillation detection in ERCOT System. It presents some examples demonstrating the use of PMU data for oscillation detection. As PMUs have been installed across the ERCOT grid, analyses using the incoming synchrophasor data have indicated that synchronized phasor measurements can greatly improve both ERCOT operations procedures and planning studies. This chapter covers in detail three oscillation events that were detected by Operations personnel as they were occurring on the system. The issues in all three situations were found to be incorrectly operating controllers and/or weak grid conditions (Chen et al, IEEE PES general meeting, 2012, [7]). The control systems in both cases were fixed and the behavior verified using PMU data in future operations.

Low-frequency oscillations (LFOs) are inherent to power system due to its nonlinear nature. These oscillations are non-observable and not of concern if their damping is high. However, with reduction in their damping, such LFOs become observable and can result in hunting in power plants leading to large-scale blackouts. So, it is essential to monitor such LFOs in order to enhance the small-signal stability of the power system. Earlier, these LFOs were not observable from the conventional SCADA system (Supervisory Control and Data Acquisition) due to its low scan rate and skewedness. However, with the advent of Synchrophasor technology, grid operators are now able to visualize such oscillations in real time. This chapter describes the several such cases of LFOs in the Indian power system observed through Synchrophasor measurement data and their analysis. Further, it also illustrates how the Synchrophasor has enabled the grid operator in taking various remedial actions for improving the damping of the LFO.

The use of synchrophasor technology in the Western Interconnection began with a collaborative project funded by the US Department of Energy. Various synchrophasor applications and tools were installed under this project. This chapter presents the details of the project and discusses the use of synchrophasor technology for oscillation detection and mitigation in grid operations at PEAK Reliability.

Installation of Phasor Measurement Unit (PMU) infrastructure in the ISO New England (ISO-NE) power system in 2012 has enabled monitoring of the actual dynamic behavior of the system. Multiple instances of oscillations in the frequency range from 0.05 to 2 Hz with significant MW magnitude and lasting from few seconds to hours have been observed. Majority of these oscillations can be classified as “forced oscillations” and caused mainly by the failure of equipment, failure or inappropriate settings of control systems or unplanned operating conditions. Forced oscillations represent the threat to the power system security and need to be mitigated. The critical step in the successful mitigation is finding the source of oscillations which is typically a specific generator or a power plant. The chapter describes the oscillations observed in the ISO-NE power system, forced oscillation mitigation, and the Oscillation Source Locating (OSL) application which is an online tool for the robust estimation of the source of sustained oscillations.

The phenomena, concerns, and possible solutions for monitoring, detecting, and controlling power system oscillations have been discussed in the power industry and academia around the world for decades. Recent advances in synchrophasor technology provided an opportunity to take a fresh look at possible solutions for monitoring, detecting and controlling these oscillations. Awareness of existence of certain frequency modes of oscillations in their electric grid due to Phasor technology provides an opportunity to monitor them which otherwise may get unnoticed. Awareness provides a further possibility of assessing the potential risk of such modes in their gird for their specific operating conditions. Wide-scale use of synchrophasor data with appropriate tools provides an opportunity to allow real-time monitoring of the frequency modes of oscillations. From the authors’ perspective, another important consideration in favor of using synchrophasor data is the market operation. Markets have put pressure on operators to operate the grid closer to the limits, warranting the need to monitor closely for stability concerns. PMUs provide an opportunity to closely monitor them providing an opportunity of economic benefits from markets perspective by operating closer to the limits, determined using synchrophasors once the confidence on the measurements and tools to monitor the limits is obtained. At CAISO, monitoring the oscillations is carried out and operating experience is being gained to identify alarms for the operators. Some of these monitoring experiences with specific examples at CAISO are shared.

Phase angle monitoring is carried out at CAISO considering two different purposes, one for validation of conflicting SE results between neighboring Utilities and another for making operating decision to reconnect a disconnected transmission equipment. Validation of State Estimator results in certain portions of the network providing conflicting results is done by model-independent phase angle measurements. Validation of SE results involves comparing calculated angle as the output of State Estimator and actual observed angle as measured by PMUs. State Estimator uses traditional SCADA measurements (such as bus kV, MW, MVAR) along with transmission topology model, whereas PMU-based measurement is “model-less”. Comparing the two values for a certain period of time provided a good network topology model validation as well. When a transmission line trips out of service or is taken out on a planned outage, the open phase angle difference between the two bus terminals increases. When the line needs to be reclosed, a large phase angle difference across the terminals of the line can lead to significant power swings and power system instability or damage to electrical equipment. Both State Estimator solution and PMU calculated angle pairs provide immediate feedback on whether it is safe to restore the transmission line or if further system re-dispatch is needed prior to reclosing the line. Knowing how large the open angle is, an operator will not waste time in attempting to reclose the transmission line if the phase angle difference is larger than what the synch-check relay in the station would allow. CAISO uses State Estimator calculated values and PMU calculated values to measure the open angle difference. The State Estimator calculated values are updated (every 30 s). PMU calculated values are updated much more frequently.

One of the important applications of synchrophasor technology is in state estimation. The purpose of this chapter is to illuminate several of the contemporary estimation techniques that are either in use or will be in use across the industry in the very near term. The role of state estimation techniques play in the analytics pipeline as well as an introduction to network observability and topology processing in the context of a completely synchrophasor based measurement set are presented. This is followed by a presentation of both a linear weighted least square (WLS) and a robust linear least absolute value (LAV) power system state estimator in both a positive sequence and a three-phase formulation. Following this, several applications that employ estimation techniques and/or estimation results were presented including dynamic load modeling, exciter failure detection, and symmetrical component calculation.

The power industry has been pushing forward the adoption of synchrophasor technology for wide-area monitoring and situational awareness. Many applications have been developed to take advantage of the GPS time-stamped synchrophasor data. Linear state estimator (LSE) is one of the recent developments in the synchrophasor industry that has been gradually accepted and adopted by several US utilities under pilot projects. This chapter first introduces the theory of LSE using Phasor Measurement Unit (PMU) data and then demonstrates the implementation of LSE toward a production-grade application for real-time operation at control center. The other major highlight of this chapter is to demonstrate the benefits and use cases of the LSE application based on firsthand implementation and successful deployment experience at utilities. The LSE can (1) validate and condition PMU data, (2) provide an independent non-iterative state estimator to complement the State Estimator (SE) in Energy Management System (EMS) for situational awareness, data analytics, and grid resiliency, and (3) expand synchrophasor measurement observability for downstream synchrophasor applications. Several use cases are demonstrated in real time by pilot projects deployed at Bonneville Power Administration (BPA), Duke Energy, and Southern California Edison (SCE). LSE application’s use cases and business values are presented to illustrate its successful deployment and operational experience in wide-area monitoring and situational awareness system.

This chapter presents experiences in the use of synchronised phasor measurement technology in the Electric Reliability Council of Texas (ERCOT) interconnection, USA. It discusses the details of post-event analysis performed based on PMU data. It also presents a case involving a compound event in the ERCOT system involving a fault, which, due to relay mis-operation, induced a loss of generation event. This paper presents the insights gained from studying the synchrophasor data and points out the various indicators that determine the characteristics of the event. The owners (also the operators) of the affected equipment corroborated the conclusions drawn from the post-event analysis. This paper demonstrates a new use case for synchrophasor technology that helps identify and correct possibly incorrect operation of the equipment.

System Protection Schemes (SPSs) or Remedial Action Schemes (RASs) are considered as an effective tool and way for enhancing the reliability and resiliency of the power system toward rare contingencies. The validation of SPS is difficult by using conventional Supervisory Control and Data Acquisition (SCADA) system data due to its inherent low scan rate and skewedness. Under such condition, Synchrophasors data has been found to be better suited for performance evaluation SPS and review of its design due to high scan rate and time synchronization. This chapter describes few case studies to explain the usage of Synchrophasors for evaluation and review of SPS in the Indian Grid. It also demonstrates how grid operator has utilized the Synchrophasor data in improving the system performance under various contingencies and laid down the foundation for effective utilization of WAMS for evaluating SPS operation, modifying SPS design, and designing a new SPS.

The Indian power system involves integrated operation of AC and DC transmission system in one synchronous system. Earlier HVDC back-to-back stations were used to transfer power between regional grids when the five regions in Indian grid were not synchronized. EHVAC and HVDC-based high power corridors helped regions deficit in power to obtain power from regions with surplus generation. The skewed distribution of natural resources like coal, hydro, and customer load gave an impetus for better connectivity across the grid. Now Indian power system also has international power transfer with Bhutan, Bangladesh, and Nepal in a step forward toward SAARC grid. The interconnection of the grids is basically an amalgamation of HVDC links (500 and 800 kV) and EHVAC (400 and 765 kV) lines for both inter-regional/national as well as intra-regional power transfer. Synchrophasors at transmission level were first introduced in India in the year 2010 in northern region quickly followed by other regions as well as wide area visibility at the National control centre. By the year 2017, the number of PMUs had ramped up to 77 and with the better visualization tools, and the usage of Synchrophasors for real-time operation by the system operator has increased. The enhanced visibility in grid operation with the use of synchrophasors has helped operator in identifying various aspects of integrated operation and take actions in real time. This chapter discusses the utilization of synchrophasors in control room application for both real-time despatch and post-despatch analysis. Various case scenarios have been discussed whereby one or the other parameter at nearby AC bus gave an indication of some HVDC-related phenomenon. As HVDC system is embedded in existing large-scale HVAC network, any phenomenon happening at HVDC station impacts the power flow of network as a whole. Apart from easily identifying HVDC restarts, reduced voltage operation (RVO) mode, HVDC islanding the synchrophasors helped in understanding voltage changes associated with filter bank switching. Several mathematical functionalities related to optimized power order across all HVDCs are under nascent stage.

Validation of power system models used for planning and operations of power systems is critical for the reliable operations of the power systems. Use of unrealistic power system models can lead to unreliable study results and can even cause widespread blackouts such as August 1996 blackout. Recent regulatory requirements in North America such as NERC MOD-027, MOD-027, MOD-033 require that power system models be validated periodically using field measurements. The installed base of PMUs is growing throughout North America as well as the World. This makes it possible to use Sychrophasor technology to aid model validation and improve accuracy of models. This chapter describes how to use Syncrophasor measurements for validation of power system models used for power systems planning and operations.

A software suite—named Grid Stability Awareness System (GSAS)—has been developed to monitor and analyze power grid stability in real time using wide-area synchrophasor measurements. GSAS consists of five analytical and monitoring tools including an Oscillation Monitoring Tool, a Voltage Stability Monitoring Tool, a Transient Instability Monitoring Tool, an Angle Difference Monitoring Tool, and an Event Detection Tool. System architecture and functionalities of the tools are described. The alarming mechanisms implemented in GSAS are also presented. In addition, a series of off-line simulations were developed to test, evaluate, and validate the immediate suitability of the tools for use in an operational environment of a North American utility, and to identify and support potential improvements in the tools. The testing methodology and the procedures to create the simulation cases are also presented. Findings and conclusions are provided at the end of the chapter.

The deployment of Phasor Measurement Units (PMUs) could support a new generation of wide area monitoring and situational awareness systems, but this has not yet occurred. Instead, PMU data exchange occurs through bilateral agreements, each reflecting substantial human involvement. Our work proposes a new model for PMU data sharing, based upon today’s cloud computing technology base. Cloud-based data capture, archiving, analysis and sharing represents a new paradigm, and provides access to flexible resources well-suited to intermittent bursts of heavy computational work. In addition, collaboration among entities could be greatly facilitated by hosting common applications in the cloud, with the further assurance when different operators examine the same data, they will see consistent information. Accordingly, we created GridCloud, a new cloud-hosted synchrophasor data sharing platform. GridCloud, which overcomes some apparent limitations of commercial cloud offerings, was developed and tested here to demonstrate the security, scalability, low latency and cost-effectiveness. The system scales well enough to support nationwide deployment.