Sept.3-5, 2013, China AORC-B-3-0002 CIGRE-AORC 2013 Wide Area Monitoring System Planning, Strategy and Implementation in Thailand s Power Grid W. PIMJAIPONG L.SURAPONGPUN Electricity Generating Authority of Thailand THAILAND SUMMARY Power system stability is the major concerned in Thailand s power grid. Nowadays, the monitoring of the system based in the steady state with the SCADA system which cannot display the dynamic phenomena of the power system. The system s behaviors are forecasted by using the off-line power system simulation tool which is uncertainty in accuracy parameters and the roughly approximation. In some cases, the system operators need to know the continuous and detailed dynamic data to make the decision to manage the system. With Phasors Measurement Unit (PMU) technology, the system can be monitoring and focus on the angles and phasors with the time interval in dynamic state. PMU will show the dynamic data of the individual buses in the system for the system operators. This information will be useful for responding on the system situation suitably. PMUs also can use as the system analyst tool on the operation of the equipment in the system such as the controller of the generator, FACTS devices. PMU is the one of the smart grid road map to provide the data for the system operator to managing the system as the wide area monitoring system. Wide area monitoring system is the observation system on the dynamic phenomena which can inform the operators to understand the whole system behavior. The wide area - 292 -
monitoring consists of PMU, the communication system and the data center to analyst and display the information. The wide area monitoring system started on the system study on the system's constraint and the stability problem to locate of PMU installation over the power system to investigate the system phenomena and stability. The concept of implementation the wide area monitoring will be focused on the detection and monitor the problem in the system for system operator. This paper represents the wide area monitoring system using the PMU technology in Thailand as planning, strategy and implementation including the experience on the dynamic behavior of Thailand's power system. The wide area monitoring project is not only benefit for the system operator for supervising the event in the system as the dynamic view s point, but also use to observe and analysis the dynamic behavior of Thailand s power grid in varied scenarios. The wide area monitoring system will be the improvement method for the system security, stability and reliability of Thailand power grid as a whole. KEYWORDS Wide Area Monitoring, PMU, System Operation, Smart Grid, Power Stability, Dynamics I. Introduction Electricity Generating Authority of Thailand (EGAT) is a state enterprise organization responsible on the electric generation and transmission for the whole country of Thailand. EGAT transmits the bulk electric energy directly to two distribution authorities, namely Metropolitan Electricity Authority (MEA) and Provincial Electricity Authority (PEA). The voltage level of the transmission system is range from 115 kv, 230 kv and 500 kv. The system peak demand reached 26,598.14 MW, as of May 2013. The more complex power system changes, the more complicated tasks in managing the power system with high security are. Therefore, it is a challenge for EGAT to operate the system maintaining the high security and reliability with the lowest costs of operation and investment. Normally, the basic online monitoring tools in the power system control center are SCADA/RTU which has the scanning time interval for seconds. The duration between the first and second scanning point is the blind spot for the system operator to understand and observe the dynamic behavior of the system. Phasor Measurement Unit (PMU) technology - 293 -
provides phasor information (both magnitude and phase angle) in real time to fulfill the gap of the blind spot interval. The PMU is like a traditional RTU equipped with a GPS receiver, synchronizing the measurements with a time stamp. PMU is operated with the time interval standard at 100 ms which is enough for investigating the system s dynamic behavior. PMU has the ability to perform on high precision, speed of response and time synchronization as needed. PMU is suitable for the wide area steady state and stability monitoring for system protection and control. Wide area monitoring systems (WAMS) are the system using the new data receiving technology of PMU and allow monitoring transmission system conditions on the wide areas in view of detecting and further counteracting grid instabilities. PMUs measure the current, voltage and frequency at selected locations in the power system and stored in a data center. The measured quantities include both magnitudes and phase angles, and synchronized with the global positioning system (GPS) receivers. From the WAMS data, not only the steady state, but also the dynamic state of critical location in transmission networks can be detected and indicated the problem in the system. This early warning system from WAMS contributes to increase the system reliability by avoiding the spreading of large area disturbances, and optimizing the use of assets. II. Wide Area Monitoring System (WAMS) Wide area monitoring system (WAMS) is the monitoring system collecting the information from the power system, analyze the data and interpreted the results as the warning for system operator or initiating the defense scheme as for the preventive action refraining the stability problem. WAMS consists of the 3 major components: Phasor Measurement Unit (PMU), Phasor Data Concentrator (PDC) and communication channel. PMU is the input equipment for WAMS measuring voltage, current, frequency and frequency change rate as C37.118 standard and send to PDC with the synchronous time on GPS. The analytic part of WAMS to process the input data, monitoring and analyst is called phasor data concentrator (PDC).The communication channel plays the important role as the media to transfer the data from PMU to PDC. Wide area monitoring system (WAMS) is the integration system of the above equipments. WAMS provides the visualized data and calculation result to the system operator to manage the system as designed. The implementation of WAMS has the varied propose depend on the designed as - 294 -
Analyze the post-event phenomena in the power system. Combination of RTU/SCADA measured values with PMU measured values for EMS utilizes. Models Validation: Comparison of simulation data with measured values of the PMU. Identifying system response with an analysis of the corresponding system damping. Improving state estimation in the control center monitoring system. Utilizing the full transfer capacity of lines. Estimation of a system stability index. Using as the guidelines for blackout restoration. Figure 1: WAMS concepts and implementation in Thailand III. Planning, Strategy and Implementation on WAMS in Thailand s Power Grid The wide area monitoring system using phasor technologies have been introduced as the real time monitoring system in Thailand by EGAT since 2005. The purpose of the WAMS project is to monitor the bottlenecked constraint between the southern and the central region. In case of critical system conditions, the networks may encounter stability problems. The first stage, with the original standard of the synchrophasors IEEE C1344-1995, GPSsynchronized PMUs installed in substations in 230kV Bang Saphan (BSP) and 230kV Suratthani (SRT) will transmit their data to the system monitoring center located in the central office. System analysts are provided with the online information enabling them to monitor the power transfer and voltage phase angles. The frequency of oscillations is identified and - 295 -
determined, as well as its damping. This information enables the power system operators to swiftly take well-informed decisions and counteract potential instabilities. Figure 2: PMU and Wide Area Monitoring System in Thailand (First Phase) In 2010, the second phase of the wide area monitoring system is implemented in EGAT. The project has upgraded from the existing of Digital Fault Recorder (DFR), totally 6 sites and 14 PMUs installed. This is as the pilot project to test the function of PMU on DFR platform. Phasor Data Concentrator (PDC) and its software application have been installed in the PDC server and its display available at the operator console for visualization. This project has only used for monitoring purpose and observe the system in broader scale. In 2013, EGAT deployed the wide area monitoring system in the full scale and use and the monitoring equipment to monitor the system behavior. WAMS is planning to use in Thailand power grid with the WAMS implementation roadmap to use and monitor in the first stage. For the second stage, WAMS will use to help system operator to control some of the equipment which is not effect on the security of the system. The final stage, WAMS will be implemented as the wide area protection system in the future. WAMS will be used to monitor and calculate with the EMS/SCADA and send the control signal to trip the load or generation as required. For the PMU site selection, the system study is performed and consideration with the environmental criteria to appoint the PMUs. The base criteria preference of the alternative - 296 -
PMU site is considered on the large generation or the large load center with significant location in the system. The other criteria issues are focused on the system dilemma such as voltage stability, oscillation or transient stability. Not only the major junction and the bottlenecked of the system but also the wind generator and HVDC equipment are judged as the point to install the PMU. For PDC component, PDC has multiple CPU devices that allow for the collection, concentration and synchronization of phasor data from different PMUs. PDC works together with PMU. PDC should visualize and calculate the state of the system to alert the system operator for the system difficulty. Operators can thus avoid potential cascade tripping and system islanding. The algorithm for system monitoring is fed with selected voltage and current phasors. By processing these input phasors, it detects the various swing (power oscillation) modes or voltage stability. The algorithm quickly also identifies the frequency and the damping of swing modes. Figure 3: PMU site selection in Thailand s power grid IV. Challenge and Suggestion - 297 -
Wide are monitoring system (WAMS) is also has some challenges on the stability and reliability of WAMS due to the uncertainty in the past project. GPS issue is one of the major concerned for the WAMS. Generally, the time synchronization via GPS is referred as the backbone of the WAMS. In case of GPS is not detected the satellite signal, it will cause the error on WAMS and may lead to WAMS s misoperation. The communication issues are also the other concern. Not only PMU to PDC and PDC to PDC communication can jammed but also communication bandwidth of PMU can lead to the error of WAMS. The increasing number of the PMU and monitoring signal also suspect for the WAMS issues. The communication bandwidth needs to be tested and observed to ensure the WAMS reliability. For the standard protocol for PMU, C37.118 is the international standard and reference. All PMU manufacturers refer that PMU comply with C37.118 standard. However, from the examination, some PMU is not compatible with the main PDC which also refer on C37.118 standard. On account of the various PMU suppliers in Thailand, this issue is on the process to test and discuss with the manufacturers to solve this problem. Finally, PDC s performance and function on the PDC are various and still on the test process. The implementation on the PDC s software still question about the time calculation and performance to solve the stability problem in the real system. Figure 4: Voltage Profile and voltage response on the system disturbance via WAMS - 298 -
V. Future works on WAMS After the installation the WAMS project in 2013, the future plan to utilize WAMS for the smart grid and lead to the control in the future is blueprinted. The first priority platform is to integrate WAMS with the Energy Management System (EMS) and SCADA system in the system control center. The advantage of the EMS integration is for the system operator to receive the real time information to understand and manage the system effectively. WAMS is still ambiguous on the reliability and stability of the system for controlling and protecting the power system. Thus, for the introduction stage, mostly WAMS will be used as the tool for observation the system s dynamic behavior and response. Also after the collecting the dynamic data on the system response, the model validation for the off- line simulator can perform to improve the model as the same as the real system. The system study is also needed to accomplish to implement the WAMS for the defense scheme. The WAMS project needs to collect the data and information the system with adequate duration. As the proposal to use WAMS on the wide area control and wide area protection project in the future, reliability and stability of WAMS is necessary. VI. Conclusions EGAT has installed WAMS & PMU since 2005 and expanded to second phase in 2010 and full implementation in 2013 for the visualization of the power system in broader scale. The capabilities of PMU for high precision, speed of response and GPS time synchronization make PMU very appropriate for wide area monitoring for protection and control. An advanced early warning technology from WAMS helps operators to ensure grid reliability by detecting and counteracting the first signs of grid instability. Strategy for the PMU and WAMS employment in Thailand is to consider the whole project as the long term with the final goal using for the wide area control and protection. Each components PMU, PDC and communication channel need to be separately designed and considered for the integration efficiently. Communication bandwidth and GPS synchronization are also the important issues for WAMS. The future plans of the WAMS are also designed as the roadmap for the long run project. The first period will use WAMS as the monitoring tools to observe the system performance and model validation. The testing system and collecting data for the system - 299 -
reliability and stability are very significant before moving forward to the phase on the control and protection in the future. The implementation on the steady state related problem may use and prove that WAMS is accountable. WAMS and PMU are the future trend for the smart grid in Thailand s power system. The information of the system needs to pass through the system s operator. The analysis system with the suitable algorithm will help to filter the vital data and send to use as the trigger or alarm. WAMS technology will increase the Thailand s system stability and security as the whole. BIBLIOGRAPHY [1] Suphot Jitlikhit, Application of Phasor Measurement Units And Wide Area Monitoring System in Thailand, TSCON2011, Nonthaburi, Thailand [2] Tormit Junrussameevilai, Nitus Voraphonpiput, Characterization of Dynamic Phenomena on EGAT Tie Transmission Line Caused by Major Disturbance, CEPSI2006, Mumbi, INDIA [3] Rene Avila-Rosales, Jay Giri, WIDE-AREA MONITORING AND CONTROL FOR POWER SYSTEM GRID SECURITY,AREVA T&D Inc.Bellevue, WA, USA [4] Kenneth E. Martin, Phasor Measurements at the Bonneville Power Administration, Power Systems and Communication Infrastructure for the Future, Beijing, China September, 2002. [5] Robert E. Wilson, Carson W. Taylor, Using Dynamic Simulations to Design the Wide- Area Stability and Voltage Control System (WACS), paper 0-7803-8178-X IEEE PS General Meeting 2004. [6] C. Martinez, M. Parashar, J. Dyer, J. Coroas, Phasor Data Requirements for Real Time Wide Area Monitoring, Control and Protection Application, White Paper, CERTS/EPG, Jan 26, 2005 [7] IEEE Standard for Synchrophasors for power system, IEEE C37-118-2005, March 2006. [8] Larsson, M., ObjectStab an Educational Tool for Power System Stability Studies. IEEE Transactions of Power Systems, vol. 19, no. 1, p56.63, 2004. [9] Larsson, M., Rehtanz, C., and Bertsch, J., Real-time Voltage Stability Assessment for Transmission Corridors, Proceedings of IFAC Power Plants and Power Systems Control - 300 -
Conference, Seoul, Korea, 2003. [10] T. L. Baldwin, L. Mili, M. B. Boisen and R. Adapa, Power System Observability with Minimal Phasor Measurement Placement, IEEE Trans. Power Systems, Vol. 8, No. 8, May 1993 Short Bio-data of Main Author Witchaya Pimjaipong received his B.E. degree from Kasetsart University, Thailand in 1994 and M.Sc. degree from University of Southern California, Los Angeles, US. He is currently Head, Disturbance Recording and Analysis Section with EGAT (Electricity Generating Authority of Thailand). He has involved in various power system studies including load flow study, dynamic simulation and implementation on the special protection scheme. His areas of research interest are power system protection, power system simulation, especially system stability and wide area monitoring system - 301 -