This paper presents a novel methodology for detecting fault conditions in the secondary side of electric arc furnace (EAF) transformer. The major focus of this study is to design a digital algorithm which uses solely the primary side current. Therefore, in this new methodology, only the primary side current is measured, and the fault presence in the secondary side is investigated. Here, there are two main objectives. The first objective is minimizing the fail-to-trip functioning probability, and the second one is minimizing the Mal-Trip operation probability. The fault characteristics are extracted using accurate simulation of EAFs installed in the Mobarakeh Steel Company (MSC) in Isfahan, Iran to fulfill the first objective. Three-phase field data of instantaneous current from the primary side of eight EAF transformers of MSC is also provided to evaluate performance of the proposed algorithm in the normal conditions and to achieve the second objective. The proposed algorithm is based on the sudden reduction of current harmonics in the fault conditions which is evaluated by a proposed special index which is called "the difference function" in this paper. Overall reliability assessment (dependability and security) of the proposed protective scheme demonstrates that even in this highly varying and unpredictable environment, the proposed algorithm is so precise and fast in fault detection. Figure 14. Harmonic components of one of the measured records in the normal conditions. a) Fundamental. b) Second. c) Third. d) Fourth.
A pilot protection method that uses the forward and backward voltage travelling waves to identify DC line faults is proposed in this paper. This method is based on the idea that under internal faults forward and backward travelling waves are observed at both sides of the line within a specific time period. However, under external faults and depending on their direction, backward voltage travelling wave is not observed at one of the terminals. Therefore, a transient-based criterion based on simultaneous existence of line-mode forward and backward voltage travelling waves is proposed. It is shown that the proposed protection method is able to identify internal faults at any location along the line with fault resistance up to 1000 𝛀 with fast response and high sensitivity and selectivity. Performance evaluations of the proposed protection method is performed using a bipolar MMC-HVDC transmission line, simulated in PSCAD/EMTDC. Index terms-Forward and backward travelling waves, HVDC protection, pilot protection, travelling wave protection.
Transient behaviour of high‐voltage direct current transmission lines under direct current faults can be easily affected by many factors, namely, fault location, fault resistance and transmission line length. In order to design a suitable protective scheme, the impact of these factors should be thoroughly investigated. An impedance‐based analysis is more suitable in evaluating high‐voltage direct current system behaviour during direct current line faults, and consequently, in comparison to similar harmonic current or voltage‐based schemes, a characteristic harmonic impedance‐based protection is more capable in fault detection. Therefore, this paper presents a novel pilot protection method for line‐commutated converter based high‐voltage direct current transmission lines, which relies on continuous monitoring of characteristic harmonic impedances. The proposed method can accurately calculate location of faults along the line, and estimate additional valuable information, such as fault resistance. The validity of the proposed method is evaluated by a wide range of fault scenarios using the CIGRE high‐voltage direct current benchmark model, simulated in PSCAD/EMTDC and codes written in MATLAB software environments. It will be shown that the proposed protection method sounds promising, and can serve as an excellent backup option in the case of primary protection malfunction.
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