Rujiroj Leelaruji

SmarTS Lab — A laboratory for developing applications for WAMPAC Systems

At the core of the development of “Smart Transmission Grids” is the design, implementation, and testing of synchronized phasor measurement data applications that can supplement Wide-Area Monitoring, Protection, and Control Systems (WAMPAC). Nevertheless, the development of new PMU data-based WAMPAC applications has been relatively slow. The great potential of WAMPAC systems is being limited by this, and efforts are needed so that new applications can be developed. The slow rate of development of these applications is strongly related to, among other factors, the application development approach used. This article starts by discussing the needs and approaches for developing WAMPAC applications that exploit synchronized phasor measurements, and illustrates how one of these approaches has been achieved. A preliminary work carried out to develop and implement a Smart Transmission System Laboratory (SmarTS Lab), a hardware and software-based system for developing and analyzing “Smart Transmission Grids” paradigms and applications for WAMPAC systems, are described. The laboratorys conceptual architecture and hardware and software implementation are presented, and some of its components are described. Finally, the article illustrates proof-of-concept examples of how PMU data-based applications can be developed.

Over-current relay model implementation for real time simulation & Hardware-in-the-Loop (HIL) validation

Digital microprocessor based relays are currently being utilized for safe, reliable and efficient operation of power systems. The overcurrent protection relay is the most extensively used component to safeguard power systems from the detrimental effects of faults. Wrong settings in overcurrent relay parameters can lead to false tripping or even bypassing fault conditions which can lead to a catastrophe. Therefore it is important to validate the settings of power protection equipment and to confirm its performance when subject to different fault conditions. This paper presents the modeling of an overcurrent relay in SimPowerSystems (MATLAB/Simulink). The overcurrent relay has the features of instantaneous, time definite and inverse definite minimum time (IDMT) characteristics. A power system is modeled in SimPowerSystems and this overcurrent relay model is incorporated in the test case. The overall model is then simulated in real-time using Opal-RTs eMEGAsim real-time simulator to analyze the relays performance when subjected to faults and with different characteristic settings in the relay model. Finally Hardware-in-the-Loop validation of the model is done by using the overcurrent protection feature in Schweitzer Engineering Laboratories Relay SEL-487E. The event reports generated by the SEL relays during Hardware-in-the-Loop testing are compared with the results obtained from the standalone testing and software model to validate the model.

Virtualization of synchronized phasor measurement units within real-time simulators for smart grid applications

Synchronized phasor measurement units (PMUs) provide GPS-time tagged, high-sampling rate, positive-sequence voltage and current phasors. When placed in high-voltage substations in power networks, PMUs can provide real-time information that is necessary for the development of Smart Transmission Grids software applications whose main objective is to improve the power systems monitoring, control and protection. The development of these applications, particularly for use within control centers for on-line purposes, is limited by the availability of and access to real-time PMU data and other information. One attractive approach for application development is the use of real-time simulators to which PMUs can be interfaced as hardware-in-the-loop (HIL) devices to harvest PMU data. However, this approach has technical and economical limitations, which can be tackled by the virtualization of PMU devices. This article describes the development of an entirely software-based synchronized phasor measurement unit for use within real-time simulators to emulate a large number of real-life PMUs, which in turn can be used for creating new phasor-based applications.

Voltage stability monitoring using sensitivities computed from synchronized phasor measurement data

Wide-area early warning systems are dependent on synchrophasor data-based applications for providing timely information to operators so that preventive actions can be taken. This article proposes the use of voltage sensitivities computed from syncrhophasor data for voltage stability monitoring, and a visualization approach that can be implemented in wide-area early warning systems. In order to provide reliable information, synchrophasor data must be pre-processed to extract only the useful features embedded in measurements and correct for errors. Hence, this article also addresses the issue of data filtering and correction, and proposes a filtering methodology for robust voltage sensitivity computation. The methodology is developed considering both positive-sequence simulations for methodology development purposes, and real phasor measurement data from a real-time (RT) hardware-in-the-loop (HIL) laboratory for testing the robustness of the developed approach for use in the control room. The results from both approaches are contrasted against each other, the limitations of the positive-sequence simulation approach for developing PMU-data applications are highlighted and the challenges of working with the RT HIL lab are recognized.

Coordination of protection and VSC-HVDC systems for mitigating cascading failures

This paper proposes a methodology to coordinate protection relays with a VSC-HVDC link for mitigating the occurrence of cascading failures in stressed power systems. The methodology uses a signal created from an evaluation of the relays status and simplifications of certain system parameters. This signal is sent to a Central Control Unit (CCU) which determines corrective action in order to reduce the risk of cascading failures.

Mitigating system's voltage instability through wide-area early warning signals and real-time HVDC control

Two sequential approaches to prevent voltage instability are proposed in this article. The first approach utilizes synchrophasors in order to establish when the system is leading to a voltage instability and also to trigger the operation of HVDCs to relieve the systems stress. The second approach is used to ensure that HVDCs will operate securely when their transfer is pushed towards the maximum transferable power level.

PMU-based voltage instability detection through linear regression

This paper proposes a linear regression method using synchrophasor measurement for voltage stability monitoring. The method preprocesses synchrophasor measurements in order to eliminate inconsistencies and errors that embedded in them. This data is then used in the computation of sensitivities suitable for voltage stability monitoring. Some important electrical components such as Over Excitation limiter and On-Load Tap Changer which create discrete changes affecting in voltage instability have been included to assess the methods performance. Moreover, both process and measurement noises, obtained from real-time hardware-in-the-loop simulation and real PMU measurements from the Norwegian network, respectively, have been applied to validate robustness of the proposed methodology.

Real-time implementation of an Automatic Voltage Stabilizer for HVDC Control

Classic HVDC systems are prone to voltage instability when operating on weak AC grids. This paper describes the implementation of a newly developed Automatic Voltage Stabilizer (AVS) in an existing CIGRÉ Benchmark Model for HVDC Controls and compares its performance with the Voltage Dependent Current Order Limitation (VDCOL) method. The tools used for the study are the eMegaSim OPAL-RT real-time simulator and the PSCAD/EMTDC digital simulator. With AVS, the power transfer can be optimized and kept at or close to the steady state stability limit thereby compensating for deficiencies of VDCOL. Using two different simulation environments provides important information on their capabilities to develop and improve future power system controls.

Prony-based on-line oscillation detection with real PMU information

Wide-area monitoring systems are a requirement in the current power systems in order to provide an appropriate monitoring, supervision and protection from undesired events. Electromechanical oscillations can provoke critical situations and affect the power transmission capability. This paper applies the Multi-Prony Analysis (MPA) to estimate the critical modes by using the tie-lines power measurements from Phasor Measuerement Unit (PMU)-data. The modes observation including an online sliding window give the frequency and damping variation allowing to detect and classify the range of the oscillation.