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Title:Switch-on-to-fault scheme for transmission line protection
Author(s):Dasgupta, Sujay
Advisor(s):Sauer, Peter
Department / Program:Electrical & Computer Eng
Discipline:Electrical & Computer Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Overcurrent element (50)
Undervoltage element (27)
line relays
transmission line protection
Abstract:Switch-on-to-fault (SOTF) schemes are used to maintain dependability and speed when closing a transmission line breaker onto a faulted line. This is accomplished by enabling overreaching directional and nondirectional protection elements for a short window of time shortly after the transmission line breaker closes. When line potential transformers (PTs) are used to polarize directional distance relays, there is no benefit to using memory voltage during an SOTF condition and the polarizing signal used is directly related to the amount of fault voltage available. Depending on the magnitude of fault voltage available, the speed of a directional distance element can be quite slow, even for faults away from the PT location. To mitigate this dependability and speed issue, a nondirectional instantaneous overcurrent (50) element is typically used, sometimes with undervoltage (27) supervision to balance security. This thesis uses a case study to illustrate the speed sacrifices made when a directional distance element, rather than an instantaneous overcurrent element, must trip during an SOTF condition. Results are provided from testing various directional distance elements to determine the minimum voltage required for fast operation of these elements. This information, is used to determine the lowest value to use for undervoltage supervision of the instantaneous overcurrent element to ensure a voltage-supervised 50 element has adequate reach for fast SOTF operation. The benefits of using a nondirectional distance element for SOTF protection are discussed. This element is significantly easier to set than an undervoltage-supervised instantaneous overcurrent element, which helps to maintain dependability, security, and speed during SOTF conditions. To illustrate, we provide formulas to plot the reach of the 50 and 27 elements in the impedance plane so that we can directly compare to the nondirectional characteristic. A guidance formula on how to set 50 element to maintain dependability under single-contingency conditions is provided. For the 27 element, further setting optimization to maintain security during tapped loads and line charging current scenarios is illustrated. Additional considerations, including the SOTF duration timer window, security concerns for a sensitively set ground overcurrent element, resetting SOTF with healthy line voltage, SOTF benefits during the use of bus PTs, and high-speed reclosing are also discussed.
Issue Date:2020-07-24
Rights Information:Copyright 2020 Sujay Dasgupta
Date Available in IDEALS:2020-10-07
Date Deposited:2020-08

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