Power System Stability Analysis Using Wide Area Measurement System

Advances in wide area measurement systems have transformed power system operation from simple visualization, state estimation, and post-mortem analysis tools to real-time protection and control at the systems level. Transient disturbances (such as lightning strikes) exist only for a fraction of a second but create transient stability issues and often trigger cascading type failures. The most common practice to prevent instabilities is with local generator out-of-step protection. Unfortunately, out-of-step protection operation of generators may not be fast enough, and an instability may take down nearby generators and the rest of the system by the time the local generator relay operates. Hence, it is important to assess power system stability over transmission lines as soon as the transient instability is detected instead of relying on purely localized out-of-step protection in generators. This thesis proposes a synchrophasor-based out-of-step prediction methodology at the transmission line level using wide area measurements from optimal phasor measurement unit (PMU) locations in the interconnected system. Voltage and current measurements from wide area measurement systems (WAMS) are utilized to find the swing angles. The proposed scheme was used to predict the first swing out-of-step condition in a Western Systems Coordinating Council (WSCC) 9 bus power system. A coherency analysis was first performed in this multi-machine system to determine the two coherent groups of generators. The coherent generator groups were then represented with a two-machine equivalent system, and the synchrophasor-based out-of-step prediction algorithm then applied to the reduced equivalent system. The coherency among the group of generators was determined within 100 ms for the contingency scenarios tested. The proposed technique is able to predict the instability 141.66 to 408.33 ms before the system actually reaches out-of-step conditions. The power swing trajectory is either a steady-state trajectory, monotonically increasing type (when the system becomes unstable), or oscillatory type (under stable conditions). Un- der large disturbance conditions, the swing could also become non-stationary. The mean and variance of the signal is not constant when it is monotonically increasing or non-stationary. An autoregressive integrated (ARI) approach was developed in this thesis, with differentiation of two successive samples done to make the mean and variance constant and facilitate time series prediction of the swing curve. Electromagnetic transient simulations with a real-time digital simulator (RTDS) were used to test the accuracy of the proposed algorithm with respect to predicting transient in- stability conditions. The studies show that the proposed method is computationally efficient and accurate for larger power systems. The proposed technique was also compared with a conventional two blinder technique and swing center voltage method. The proposed method was also implemented with actual PMU measurements from a relay (General Electric (GE) N60 relay). The testing was carried out with an interface between the N60 relay and the RTDS. The WSCC 9 bus system was modeled in the simulator and the analog time signals from the optimal location in the network communicated to the N60 relay. The synchrophasor data from the PMUs in the N60 were used to back-calculate the rotor angles of the generators in the system. Once the coherency was established, the swing curves for the coherent group of generators were found from time series prediction (ARI model). The test results with the actual PMUs match quite well with the results obtained from virtual PMU-based testing in the RTDS. The calculation times for the time series prediction are also very small. This thesis also discusses a novel out-of-step detection technique that was investigated in the course of this work for an IEEE Power Systems Relaying Committee J-5 Working Group document using real-time measurements of generator accelerating power. Using the derivative or second derivative of a measurement variable significantly amplifies the noise term and has limited the actual application of some methods in the literature, such as local measurements of voltage or voltage deviations at generator terminals. Another problem with the voltage based methods is taking an average over a period; the intermediate values cancel out and, as a result, just the first and last sample values are used to find the speed. This effectively means that the sample values in between are not used. The first solution proposed to overcome this is a polynomial fitting of the points of the calculated derivative points (to calculate speed). The second solution is the integral of the accelerating power method (this eliminates taking a derivative altogether). This technique shows the direct relationship of electrical power deviation to rotor acceleration and the integral of accelerating power to generator speed deviation. The accelerating power changes are straightforward to measure and the values obtained are more stable during transient conditions. A single machine infinite bus (SMIB) system was used for the purpose of verifying the proposed local measurement based method

Software-Defined Virtual Synchronous Condenser

Synchronous condensers (SCs) play important roles in integrating wind energy into relatively weak power grids. However, the design of SCs usually depends on specific application requirements and may not be adaptive enough to the frequently-changing grid conditions caused by the transition from conventional to renewable power generation. This paper devises a software-defined virtual synchronous condenser (SDViSC) method to address the challenges. Our contributions are fourfold: 1) design of a virtual synchronous condenser (ViSC) to enable full converter wind turbines to provide built-in SC functionalities; 2) engineering SDViSCs to transfer hardware-based ViSC controllers into software services, where a Tustin transformation-based software-defined control algorithm guarantees accurate tracking of fast dynamics under limited communication bandwidth; 3) a software-defined networking-enhanced SDViSC communication scheme to allow enhanced communication reliability and reduced communication bandwidth occupation; and 4) Prototype of SDViSC on our real-time, cyber-in-the-loop digital twin of large-wind-farm in an RTDS environment. Extensive test results validate the excellent performance of SDViSC to support reliable and resilient operations of wind farms under various physical and cyber conditions

Advanced laboratory testing methods using real-time simulation and hardware-in-the-loop techniques : a survey of smart grid international research facility network activities

The integration of smart grid technologies in interconnected power system networks presents multiple challenges for the power industry and the scientific community. To address these challenges, researchers are creating new methods for the validation of: control, interoperability, reliability of Internet of Things systems, distributed energy resources, modern power equipment for applications covering power system stability, operation, control, and cybersecurity. Novel methods for laboratory testing of electrical power systems incorporate novel simulation techniques spanning real-time simulation, Power Hardware-in-the-Loop, Controller Hardware-in-the-Loop, Power System-in-the-Loop, and co-simulation technologies. These methods directly support the acceleration of electrical systems and power electronics component research by validating technological solutions in high-fidelity environments. In this paper, members of the Survey of Smart Grid International Research Facility Network task on Advanced Laboratory Testing Methods present a review of methods, test procedures, studies, and experiences employing advanced laboratory techniques for validation of range of research and development prototypes and novel power system solutions

Distribution Automation Laboratory Assignments for Students in Tampere University of Technology

Distribution automation is a fundamental part of distribution network operation. In Finland, the goal is to increase the number of automated functions in a distribution network, because of the constantly tightening requirements for decreasing the duration of outages. For students, who study power engineering, it is beneficial to understand the possibilities of distribution automation. In Tampere University of Technology, the course Distribution Automation ensures the understanding of the fundamentals of distribution automation and network operation for students. The course includes lecture subjects, written exercises and laboratory assignments. The main objective of this thesis is to improve and update laboratory environments of distribution automation for the course Distribution Automation. The laboratory environments should help students understand distribution network protection, the role of DMS and SCADA system, and smart metering. This thesis examines previous laboratory implementations on the course and distribution automation in general. The laboratory environments and students’ feedback from previous laboratory implementations are presented in this thesis. The chapter on distribution automation displays information about distribution network protection, SCADA and DMS systems, AMI system and protocols. The distribution network protection section presents basic needs and regulations for distribution network protection. SCADA and DMS section introduces functionalities of these systems whereas smart metering section describes AMI system naming and structure. Protocols and standards section describes IEC 104, IEC 61850, OPC, DLMS/COSEM, object oriented information models and OSI model communication structures. As a result of this thesis, implementations from two different laboratory environments are introduced. The first laboratory implementation includes distribution network protection and IEDs. The second laboratory implementation includes a smart meter, DMS and SCADA systems, and remote communication between the control center, the substation and the smart meter

Protection Performance Study for Secondary Systems with IEC61850 Process Bus Architecture

Following the introduction of the microprocessor into the power system protection field, modern microprocessor based numeric relays have developed very rapidly in the last 20 years, and modern power system protection schemes are virtually all based on microcomputers technology. The International Electro-technical Commission (IEC) recently launched the standard IEC61850, “Communication Networks and System in Substation”, which is having a major impact on the structure of new protection systems and schemes. In itself it describes the concepts for sub-station communications covering protection, control and metering functions. However, although it is going to have a major impact on the power systems communications, it will also influence the design of future protection systems. There will also be a host of other opportunities and advantages that can be realised. These include easier upgrading, refurbishment and replacement of sub-station protection. They also provide for greater use of general purpose Intelligent Electronics Devices (IEDs), self-healing systems, and plug and play type facilities. The Ethernet based communication network for data transfer between process level switchyard equipment and bay level IEDs, the process bus, is defined in IEC61850 Section 9-2. This process bus facilitates the communication of two types of real-time, peer-to-peer communication messages. Generic object-oriented substation event messages, the GOOSE messages and the data sample values, SVs which include the measured currents and voltages. Although this standard describes the message structures and the timing requirements, it does not describe the process bus topology. This work describes different LAN topologies that can be used in the design of process bus for protection systems. It considers the implications of the different structures on the operation of the protection scheme and how these relate to the operational strategy of different operators. It provides an assessment of the data handling capabilities of the system and how the demands of the protection system can be met. Several potential problem areas are identified and analyzed. The probabilistic nature of these systems is discussed and the implications explained. It also provides an insight into the implementation of the alternative topologies and their performance when applied to a transmission line feeder protection and transformer protection. The digital substation and the implementation of IEC61850 are fundamental to the future of protection ‘relays’. There are many pointers to the potential directions that these systems will develop and the skills required for the protection engineers of the future. This project is seeking to overcome some of the ownership challenges presented by modern protection and control (P&C) devices, which have an inherent short life due to their dependence on modern electronics and software.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Smart metering and its use for distribution network control

Global energy demand is increasing, with the adoption of electric vehicles, in particular, representing a significant prospective demand on electricity distribution networks. The exploitation of renewable generation sources, driven by increased economic viability, technological maturity, and the need for environmental sustainability, is expected to play an increasingly important role in meeting this demand. However, the adoption of such low-carbon technologies necessitates a significant change in the way that distribution networks are monitored and controlled. This work examines the state of the art in the impact of low-carbon technologies on distribution networks, the technical strategies available to mitigate these impacts and their relative merits, and the architecture of the control systems used to effect such strategies. Smart metering and advanced metering infrastructure (AMI) are a fundamental component of these smart grid systems, providing widespread visibility of conditions at the very periphery of distribution networks which has not previously been feasible, but where the impact of low-carbon technologies is significant. This work describes the development of a hardware-in-the-loop test rig incorporating multiple, custom-built, hardware smart meter test beds, and the use of this test rig to demonstrate the implementation of real-time voltage control within a simulated low voltage (LV) distribution network. However, the adoption of smart metering and AMI inevitably incurs cyber security vulnerabilities which did not exist in the case of meters with no facility for remote communication. This work examines cyber security issues pertinent to smart grids and AMI in particular, and describes the analysis of the cyber security vulnerabilities of a commercially deployed smart electricity meter. The exploitation of these vulnerabilities in a manner which permits unauthorised electronic access to the device is also described. Finally, recommendations are made of revisions to the hardware, firmware and communications protocols used by the compromised meter which may mitigate the vulnerabilities identified