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The development of modern protection functions is a challenge in the emerging environment of smart grids because the current protection system technology still has several limitations, such as the reliable high impedance fault (HIF) detection in multi-grounded distribution networks, which poses a danger to the public when the protection system fails. This paper presents the wavelet coefficient energy with border distortions of a onecycle sliding window designed for the real-time detection of transients induced by HIFs. By using the border distortions, the proposed wavelet-based methodology presents a reliable detection of transients generated by HIFs with no time delay and energy peaks scarcely affected by the choice of the mother wavelet. The signature of different HIFs are presented in both time and wavelet domains. The performance of the proposed wavelet-based method was assessed with compact and long mother wavelets by using data from staged HIFs on an actual energized power system taking into account different fault surfaces as well as simulated HIFs. The proposed method presented a more reliable and accurate performance than other evaluated wavelet-based algorithms.Index Terms-High impedance faults, power system protection, wavelet transform. 0093-9994 (c)

The high-speed detection of fault-induced transients of an overhead three-phase transmission line is important to detect the fault, determine whether the fault is internal or external, and locate the fault. In this reported work, the wavelet coefficients of the maximal overlap discrete wavelet transform were used for real-time detection of fault-induced transients by means of the real-time digital simulator.Introduction: With the increasing power demand and complexity of modern transmission systems, protective systems with high-speed fault clearance have become vital in order to minimise the harmful effects of faults and improve system stability. As an alternative to conventional protection algorithms, the high-frequency components generated by faults can be used for high-speed fault detection and location.Fault currents at fault-clearing time in most transmission and distribution networks may be adequately represented by a power-frequency component, some harmonic components, an exponentially decaying DC component, fault-induced transients, and noises [1]. The faultinduced transients are non-stationary in both time and frequency domains with a typical frequency spectrum from a few hundred Hz to various kHz [2, 3], which can be extracted using the wavelet transform.The wavelet transform is a well-known powerful tool to detect transients in power system disturbances, such as faults and voltage sags [4,5]. Notwithstanding, the published number of papers regarding real-time diagnostic methods based on wavelet transforms is small. Real-time analysis of wavelet coefficients might be vital for developing a worthy diagnostic method to yield results in satisfactory agreement with real applications.This Letter addresses high-speed detection of fault-induced transients at two ends of an overhead three-phase transmission line based on realtime wavelet analysis by means of a real-time digital simulator (RTDS). This task is vital in order to design reliable fault detection and location methods for high-speed fault clearance purposes in protection systems.

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The analysis of fault-induced transients in three-phase overhead transmission lines can provide extensive information about the fault type, detection, location, direction and sustained time in satisfactory agreement with real application in protective relays. These transients depend on the system topology, load condition and the fault parameters, such as the fault type, resistance, inception angle and location. This study addresses the fault inception angle effects in the energies of the fault-induced transients in both voltages and currents by means of the wavelet coefficient energy analysis at the first three wavelet scales, in which a generic energy equation regarding the fault-induced transients as a function of the fault inception angle in all kinds of faults was established.

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