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Out-of-step Protection Using Energy Equilibrium Criterion in the Time Domain



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Disturbances in power systems are common and they result in electromechanical oscillations called power swing. The power swings could be severe and it may lead to loss of synchronism among the interconnected generators. This is referred to as out-of-step condition. The voltage and current swings during an out-of-step condition damage power system equipments and also cause unwanted operations of various protective devices. The protection systems require an effective algorithm for fast and accurate detection of out-of-step condition. This research is focused on the development of a simple and effective out-of-step relay capable of detecting out-of-step condition in a complex power system. To achieve this, the research has gone through four distinct stages: development of an algorithm, simulation, hardware implementation and its testing. An out-of-step algorithm is proposed based on equal area criterion in time domain. The equal area criterion in time domain is obtained by modifying the traditional equal area criterion in power angle domain. A single machine infinite bus system, a two machine infinite bus system and a three machine infinite bus system and a 17-bus multiple machines system are used as case studies and are modeled using simulation tool(PSCAD™). To test the effectiveness of the proposed algorithm, various out-of-step conditions are simulated by applying disturbances at various locations in the above chosen power system configurations. For hardware implementation and testing of the algorithm, a digital signal processing board (ADSP-BF533 from Analog Devices ™) is used. To test the performance of the developed digital relay in a closed loop, real time power system signals are necessary and therefore for this purpose, a Real Time Digital Simulator (RTDS™) available in the power research laboratory is used. The RTDS™ simulator mimics the actual power systems in real time. The signals required by the relays can be tapped from the RTDS™ and the signals coming from relay can be fed back into the RTDS™, which makes the closed loop testing of the digital relay possible. This research has yielded a simple out-of-step algorithm and unlike the other out-of-step detection techniques proposed in the literature does not need offline system studies to arrive at a solution.The developed digital out-of-step relay is capable of making decisions based only on the information available from its point of installation, thus it avoids the communication devices which is advantageous for the out-of-step protection of a complex power system. Finally, the simulation results show that the proposed algorithm can be applied to any power configurations and is faster compared to the conventional concentric rectangle schemes used in the literature.



Out-of-step, Equal area criterion, Relay, Power swing, Protection, RTDS ™



Master of Science (M.Sc.)


Electrical Engineering


Electrical Engineering


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