IS International Services LLC

Atlanta, GA, United States

IS International Services LLC

Atlanta, GA, United States

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Rahmati A.,IS International Services LLC | Dimassi M.A.,IS International Services LLC | Adhami R.,University of Alabama in Huntsville | Bumblauskas D.,University of Northern Iowa
IEEE Transactions on Industry Applications | Year: 2014

Power grid overcurrent relays are used to protect the interphase faults as well as single-phase-to-ground faults. However, these relays do not guarantee protection due to the rapidly increasing short circuits which may be the consequence of demanding more and more power usage by the commercial and residential users. In this paper, a method is presented to improve the functionality of the overcurrent relay. This method is based on locally accessible measurements. It does not require any online-information and communication facilities regarding varying short-circuit levels caused by distributed energy resource infeeds. This method is adaptive and uses a least square algorithm to determine the Thevenin circuit equivalent using local measurements. The proposed method is evaluated, and the results indicate that the Thevenin-equivalent-based method provides an improvement to the relay tripping time. © 1972-2012 IEEE.


Rahmati A.,University of Alabama in Huntsville | Rahmati A.,IS International Services LLC | Adhami R.,University of Alabama in Huntsville
IEEE Transactions on Industry Applications | Year: 2014

This paper presents a fault classification technique for transmission lines based on the fault sequence components, for fast and reliable operation of protective relays. First, symmetrical components of fault current and voltage signals are extracted. Next, the fault type is classified using the zero and negative sequences. To realize the faulted phases in ground faults, a criterion index based on the zero and negative sequences is defined. The imaginary part of the defined criterion index is used. This index is maximum in the faulted phase in single-phase-to-ground faults, and it is minimum in one of the faulted phases in phase-to-phase-to-ground faults. In addition, to identify ungrounded faults, a different criterion index using the positive and negative sequences is defined. The results show that the scheme provides a fast fault classification, without the need for a threshold to operate. © 1972-2012 IEEE.

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