This paper presents a new approach to real-time fault classification in power transmission systems using fuzzy-logic-based multicriteria approach Only the three line currents are utilized to detect fault types such as LG, LL, and LLG, and then to define the faulty line An online wavelet-based preprocessor stage is used with data window of ten samples (based on 45-kHz sampling rate and 50-Hz power frequency) The multicriteria algorithm is developed based on fuzzy sets for the decision-making part of the scheme Computer simulation has been conducted using EMTP programs Results are shown and they indicate that this approach can be used as an effective tool for high-speed digital relaying, as the correct detection is achieved in less than half a cycle and that computational burden is much simpler than the recently postulated fault classification techniques

Combined fuzzy-logic wavelet-based fault classification technique for power system relaying

Inverter-Based Resources (IBRs), including Wind turbine generators (WTGs), exhibit substantially different negative-sequence fault current characteristics compared to synchronous generators (SGs). These differences may cause misoperation of customary negative-sequence-based protective elements set under the assumption of a conventional SG dominated power system. The amplitude of the negative-sequence fault current of a WTG is smaller than that of an SG. This may lead to misoperation of the negative-sequence overcurrent elements 50Q/51Q. Moreover, the angular relation of the negative-sequence current and voltage is different under WTGs, which may result in the misoperation of directional negative-sequence overcurrent element 67Q. This paper first studies the key differences between the WTGs and SG by comparing their equivalent negative-sequence impedances with SG's. Then, simulation case studies are presented showing the misoperation of 50Q and 67Q due to wind generation and the corresponding impact on communication-assisted protection and fault identification scheme (FID). The impact on directional element is also experimentally validated in a hardware-in-the-loop real-time simulation set up using a physical relay. Finally, the paper studies the impact of various factors such as WTG type (Type-III/Type-IV) and Type-IV WTG control scheme (coupled/decoupled sequence) to determine the key features that need to be considered in practical protection studies. The objective is to show potential protection misoperation issues, identify the cause, and propose potential solutions.

Impact of Inverter-Based Resources on Negative Sequence Quantities-Based Protection Elements

A novel fuzzy-logic-based phase selection technique for power system relaying

A static reactive power (VAr) compensator (SVC), constructed by fixed capacitors (FC) snd thyristor controlled reactors (TCRs), is designed and implemented to improve the damping of the synchronous generator. A digital propotional-integral (PI) controller is synthesised by the Motorola M68HC11 single chip microprocessor board to modify the reactive power compensation of the SVC from adjusting the conduction angle of the thyristors. The SVC is placed at the generator bus terminal with the speed deviation (Δω) as the feedback signal for the PI controller. The pole assignment method is used to determine the gains of the PI controller. Results from digital simulation and the implementation test show that the SVC with the PI controller can greatly enhance the damping of the system oscillation caused by disturbances. Although the PI controller is designed at a special operation point, it can also provide a good damping effect at other operation conditions. The voltage profile of the generator is also improved by the SVC.

Damping of synchronous generator by static reactive power compensator with digital controller

Abstract High penetration of renewable energy sources (RES) leads to new challenges for protection devices. Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources, while the RES dynamic response, mainly governed by inverters, is not considered. Consequently, some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle comparison, amount of negative-sequence, and short-circuit current level are affected by the RES. Therefore, an in-depth study of this issue is necessary, one which considers the main causes and new methodological criteria solutions. This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters. Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions. In addition, this work identifies the main protection functions affected and describes the new protection schemes that consider RES. Finally, an analysis and discussion of the selected bibliography are presented. 

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Transmission line protection challenges influenced by inverter-based resources: a review

The configuration and performance of a recently developed digital distance relay using negative sequence current for remote backup protection are described. Since relays for remote backup protection are designed for remote faults, the fault current that is input to the relay is small due to the influence of current distribution factors. This in turn makes the relay sensitive to the effects of load current. In order to resolve this problem, a distance relay using negative-sequence current has been developed and put into use. The characteristics of this relay are: (1) the effects of load current are reduced, so the relay rarely maloperated due to load current during a fault; and (2) the hardware configuration of a digital relay that performs calculation on a negative component is simple and thus relatively error-free. >

Y. Ohura

Papers

A digital distance relay using negative sequence current