Real-time Digital Power System Research Articles

Modified Re-Iterated Kalman Filter for Handling Delayed and Lost Measurements in Power System State Estimation

State estimator (SE) is a critical tool in the power system control center (CC) and is used by the system operators for real-time control and monitoring. Traditional SE techniques (static and dynamic) work under the assumption that there is no delay in communicating the sensor measurements to the CC. But in actual scenario, measurements are often randomly delayed and are not immediately available for processing. When the observations arrive with a delay, the current estimate of the system state may not be evaluated correctly, since the missing measurement may be carrying relevant information for estimating the states. With the increased deployment of phasor measurement units (PMUs) as sensors in the grid, time-stamped synchronized measurements are readily available. Time-stamped measurements enable the delay to be exactly known at the estimator. In this paper, a modified re-iterated Kalman filter that can handle both lost and delayed measurements without having any knowledge of the delay statistics, is proposed. The proposed algorithm is tested and validated in real-time using Real Time Digital Power System Simulator (RTDS).

Real time digital power system simulator design considerations and relay performance evaluation

Environmental pressures, right of way problems for new transmission lines, large scale system interconnection and increasing power demand especially in developing countries call for new transmission technologies. Use of FACTS and HVDC is gaining momentum. Relaying problems in such systems require a sophisticated approach and numerical technology using high grade processors offers a promising solution. To establish the performance of such relays which are designed more as powerful schemes rather than as a conglomeration of individual relays, detailed testing is required using an elaborate real-time simulator model. These tests are not only necessary during design and development but also are required by the utilities as a part of their acceptance. Highlighting the requirements of a hybrid real-time simulator including the complete spectrum of power system dynamics, this report describes an analog cum digital model used for real-time assessment of system performance. SVCs, HVDC, ASC and CSC can be modelled fully digitally by computer simulation and transient real-time data injection as well as by an analog method using physical simulation with original converter controllers for performance evaluation of numerical relays under real system conditions. As an example of the use of this simulator, tests on a numerical EHV-line relay are described and the relay performance is analyzed.