Analysis of Angle Stability Problems A Transmission

Analysis of Angle Stability Problems A Transmission - 1024...

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1024 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 3, JULY 2004 Analysis of Angle Stability Problems: A Transmission Protection Systems Perspective S. A. Soman, Tony B. Nguyen , Student Member, IEEE ,M .A .Pai , Fellow, IEEE , and Rajani Vaidyanathan Abstract— Postfault rotor angle oscillations lead to power swings. Both unstable and stable swings can induce distance relay tripping. For unstable swings, a new computational procedure to locate all of the electrical centers is developed. It simplifies the work associated with visual screening of all the - ˆ plots. For stable swings, a generic three-tier hierarchy of stability-related norms defined by branch norm, fault norm, and system norm is proposed. Ranking by branch norm leads to ranking of power swings. Ranking by fault norm leads to ranking of faults or contin- gencies. Magnitude and rate of change of system norm can be used to detect an out-of-step condition. Results on a ten-machine system and a utility system with detailed models are also presented. Index Terms— Power system simulation, power system transient stability, power transmission protection, ranking. I. INTRODUCTION :POWER SWINGS AND RELAYING DECISION UNCERTAINTY P OWER system protection at the transmission system level is based on distance relaying. The apparent impedance seen by a distance relay (i.e., relay impedance) on a transmission line connecting nodes and , and having flow is given by (1) where all quantities refer to positive sequence values. Thus, the quadrant of depends only on the direction of and flows. When is large and/or is small, then is small and the relay may trip. Following a disturbance, the power swing observed by a dis- tance relay refers to the relay impedance trajectory mapped on the - plane. Distance relays can trip on a power swing. Tra- ditionally, if a swing trajectory enters zone-1, then it is consid- ered to be severe enough to cause system instability [1]. The distance relay will also trip if the swing stays inside the backup zone for a time more than the corresponding time dial setting (TDS). In a stressed system, this can trigger cascade tripping. Tripping on a stable swing compromises security of the power system. Power swing blocking can either be applied selectively or to all of the distance relays. Blocking reduces dependability Manuscript received December 22, 2002. This work was supported in part by NSF Grant ECS00-00474 and the Grainger Foundation. S. A. Soman and R. Vaidyanathan are with the Indian Institute of Technology, Bombay 400076, India. (e-mail: [email protected]; [email protected]). T. B. Nguyen and M. A. Pai are with the University of Illinois at Urbana
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This note was uploaded on 01/29/2011 for the course ENGR 52 taught by Professor Mcmillan during the Spring '10 term at Baylor Med.

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Analysis of Angle Stability Problems A Transmission - 1024...

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