the applied method of grounding the generator neutral, the parameters of generator ... icant stresses for the wind turbine (WT) mechanical system and may also.
Pattern Recognition-A Technique for Induction Machines Rotor Broken Bar Detection Haji, M.; Toliyat, H.; Author Affiliation: Texas A&M University, College Station, TX Abstract: A pattern recognition technique based on the Bayes min-
imum error classifier is developed to detect broken rotor bar faults in induction motors at the steady state. The proposed algorithm uses only stator currents as input without the need for any other variables. First rotor speed is estimated from the stator currents, then appropriate features are extracted. The produced feature vector is normalized and fed to the trained classifier to see if the motor is healthy or has broken bar faults. Only a number of poles and rotor slots are needed as preknowledge information. Theoretical approach together with experimental results derived from a 3 hp ac induction motor show the strength of the proposed method. In order to cover many different motor load conditions data are obtained from 10% to 130% of the rated load for both a healthy induction motor and an induction motor with a rotor having four broken bars. Keywords: Fault diagnosis, broken bars fault, induction motor, statistical classifier, speed estimation. Preprint Order Number: PE-227EC (09-2001) Discussion Deadline: February 2002
Energy Development and Power Generation Ground-Fault Currents in UnitConnected Generators with Different Elements Grounding Neutral Fulczyk, M.; Bertsch, J. Author Affiliation: ABB Corporate Research, Cracow, Poland; ABB Power Automation, Baden, Switzerland Abstract: The results of the analysis of zero-sequence currents flowing in generator neutral and at ground-fault location during the generator normal operation and during ground faults in the stator windings are presented. The influence of different methods of grounding the generator neutral on these currents in the primary circuits for different parameters of generators, transformers, and additional capacitance to ground of the generator breakers was determined. This influence was analyzed for generators with ungrounded neutral, for generators with the resistance in neutral, and for generators with ground-fault neutralizer (GFN) grounding the generator neutral. The analysis has been done for real resistance of the breakdown channel during ground faults along the whole length of the generator stator winding. It has been found that the applied method of grounding the generator neutral, the parameters of generator and transformer, the additional capacitance to ground of the generator breakers, the level of fault resistance and ground-fault location have a substantial influence on currents flowing in the generator neutral and at ground-fault location in the breakdown channel in the main insulation of generator stator winding.
Keywords: Generators, grounding, protection, windings. Preprint Order Number: PE-070EC (09-2001) Discussion Deadline: February 2002
A Detection Algorithm for IslandingPrevention of Dispersed Consumer-Owned Storage and Generating Units Pai, F.S.; Huang, S.J. Author Affiliation: National Cheng Kung University, Taiwan, China Abstract: One of critical concerns in the operation of grid-connected dispersed generating units is the occurrence of islanding. Islanding may pose hazards to utility personnel and complicate the orderly reconnection of the grid. Hence, in this paper, a new algorithm IEEE Power Engineering Review, December 2001
based on the monitoring of the change in aflaPL to detect the islanding is proposed. By the proposed method, a detection index can be evaluated that serves as a useful reference to activate the protective relays. This approach has been applied to investigate different scenarios, including the loss of grid and the parallel operation. Effects of load change and power-quality disturbances to the detection performance are also examined. From these test results, they help solidify the feasibility and effectiveness of the approach for the applications considered. Keywords: Islanding, dispersed generating units. Preprint Order Number: PE-344EC (09-2001) Discussion Deadline: February 2002
Mechanical Stresses in Fixed-Speed Wind Turbines Due to Network Disturbances Papathanassiou, S.A.; Papadopoulous, M.P. Author Affiliation: Public Power Corporation; National Technical University of Athens, Greece Abstract: Electrical faults and other network disturbances generate transients of the generator electromagnetic torque, which result in significant stresses for the wind turbine (WT) mechanical system and may also have a detrimental effect on the fatigue life of important drive train components, such as the gearbox. In this paper the effect of faults and other disturbances, common in rural medium voltage (MV) distribution systems, is analyzed for a typical fixed speed WT, equipped with an induction generator. The resulting torque transients are evaluated and their propagation in the drive train is examined. Important conclusions are drawn with respect to the type of electrical faults to be considered in the design and certification of WTs according to the current IEC 61400-1 Standard. Although the emphasis is placed on the developed torque transients, the methodology presented is also suitable for analyzing electrical stresses in the generator, due to over-currents or over-voltages. Keywords: Wind turbines, distribution system faults, induction generators, unbalanced operation, mechanical stresses. Preprint Order Number: PE-1 17EC (09-2001) Discussion Deadline: February 2002
Reliability/Cost Implications of PV and Wind Energy Utilization in Small Isolated Power Systems Karki, R.; Billinton, R. Author Affiliation: University of Saskatchewan, Saskatoon, Saskatchewan, Canada Abstract: The application of renewable energy in electric power systems is growing rapidly due to enhanced public concerns for adverse environmental impacts and escalation in energy costs associated with the use of conventional energy sources. Photovoltaics and wind energy sources are being increasingly recognized as cost-effective generation sources in small isolated power systems primarily supplied by costly diesel fuel. The utilization of these energy sources can significantly reduce the system fuel costs but can also have considerable impact on the system reliability. A realistic cost/reliability analysis requires evaluation models that can recognize the highly erratic nature of these energy sources while maintaining the chronology and interdependence of the random variables inherent in them. This paper presents a simulation method that provides objective indicators to help system planners decide on appropriate installation sites, operating policies, and selection of energy types, sizes, and mixes in capacity expansion when utilizing PV and wind energy in small isolated systems. Preprint Order Number: PE-449EC (09-2001) Discussion Deadline: February 2002
Market Power in Electricity Supply David, A.K.; Wen, F. Author Affiliation: Hong Kong Polytechnic University, Kowloon, Hong Kong 67
