Algorithms and Testbed for Synchronous Generator Parameter Estimation
Challa, Kiran Kumar
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The development of dynamic power system component models became increasingly important in the modern grids dominated by high penetration of renewables because of the increased dependency of planning and operational decisions on dynamic simulation studies. The parameters of synchronous machines and associated control models play significant role in the overall model of the grid, which need to be updated regularly by the utilities. So, the parameters of the power plants are calibrated/estimated either using off-line testing or online measurements from phasor measurement units (PMU) or digital fault recorders (DFR). Development of individual generator models is feasible only if the PMU/DFR data is available for each generator in a power plant. Otherwise, they can provide only aggregate model of a generating plant as PMU/DFRs are usually placed in substations. Digital protective relay (DPR) records are available for individual generators in any generating plant. This thesis explores the possibilities of utilizing DPR records of individual generators for parameter estimation. About 36 relay records have been collected from a 247 MVA, 15.75 kV generator of a thermal plant in Karnataka. It is found that most of the records contain at the most 3 seconds data. The relay records should contain prefault data, during fault data and some post-fault data for accurate estimation. However, from the collected records only a small percentage of the records are found to be useful. Existing methods of parameter estimation using PMU/DFR data failed to work with the short duration records. There is no prior work reported in the literature which uses short relay records for parameter estimation of the synchronous generators. Constrained iterated unscented Kalman filter (CIUKF) and enhanced scattered search (eSS) algorithms are proposed for the parameter estimation using DPR records in this thesis. Parameters of the turbo alternator and its excitation system are estimated from the relay records collected using the proposed algorithms and the results are found be accurate. For the holistic validation of the developed algorithms and faster adaptation by GENCOs, realistic testbeds are needed. A scaled-down generalized substation model for translational research in smart grids is developed, which can be configured to operate in 7 widely used substation bus bar schemes with prevalent current transformer (CT) configurations. All the potential transformers (PT) and CT measurements, circuit breaker (CB), isolator and earth switch status signals are made available to configure any protection strategy like bus-bar protection, unit protection schemes, etc. precisely the same way they get implemented in the field. For studying the control interactions between renewable and conventional sources, frequency dependent (FD) transmission line models need to be physically realized. A new algorithm is proposed to fit a reduced-order R-L equivalent circuit to the frequency response of the modal impedances of a transmission lines. A close enough fitting is achieved with lesser number of passive elements using the proposed method compared to the widely used vector fitting algorithm. A scaled-down model of WECC 3-machine 9-bus system is developed with frequency dependent lines by selecting suitable tower and conductor configurations. Reduced order lumped parameter FD (LPFD) line models are derived for the 230 kV transmission lines in WECC system using the proposed fitting algorithm. A systematic procedure to scale down the 230 kV LPFD line models to 220 V laboratory model is presented. An experimental prototype of the scaled-down LPFD line is developed. Clarke and inverse Clarke transformations are implemented using specially designed 1-φ transformers. The inductances of the scaled-down model are realized using amorphous cores. Based on the prototype testing results, the six lines of WECC system are fabricated considering manufacturing tolerances. Parameter estimation using practical DPR records, development of substation model including detailed station configurations and CT arrangements, and physical realization of a frequency dependent power transmission line model in the laboratory are first of its kind efforts in the literature to the best of our knowledge.