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The issue of resilience in electrical distribution systems has been proposed increasingly with the frequent occurrence of natural disasters in recent years and the imposition of high costs due to widespread power outages. To date, various resilience indices have been proposed, some of which have been improved upon over time by extensive research, leading to more comprehensive indices. However, a standard index has not yet been approved and presented in this regard by international committees, despite the efforts made. The issue of resilience in electrical networks was examined by curve analysis index in more detail compared to other proposed indices, although it is not yet complete and should be investigated from various aspects and its shortcomings be eliminated. The present study aims to evaluate some fundamental obstacles in the "curve analysis" index and correct it in a new index called "Combining Investment and Reform" (CIR) index. Two issues of "costs in terms of investment and repairs imposed by the event" and "need to separate critical and non‐critical loads" are considered simultaneously in the proposed index. Finally, the capabilities of the proposed index are evaluated and compared in a sample electrical network in the face of events with different intensities. [ABSTRACT FROM AUTHOR]

Monitoring of partial discharge (PD) and its progress as the main cause of the insulation deterioration process in power transformers can encompass valuable information about the related insulation condition and reveals degradation mechanisms. In this study, some simple sensors, which are made from a few turns wrapped around the transformer core, are used to detect PD signals. Moreover, a feasibility study is done to identify defective phase/region based on the captured PD signals waveforms through these sensors. The idea is implemented on a 50 kVA, 20 kV/400 V three‐phase transformer by injecting artificial and quasi‐real PD signals to different sections of HV windings. Also, various transformer connections are considered in the experimental studies to find the effect of them on the waveforms of the captured signals (e.g. peak‐to‐peak value and signal energy). The obtained experimental results show that small PDs (as low as 10 pC) is detectable by the mentioned sensors and defective phase can be identified in all of transformer connection cases. Furthermore, considering failure to identify defective regions by broadband analysis, a limited‐band approach is proposed through obtaining |H(s)| for the sensors. The results show that exact defective phase/region identification is feasible by selecting a frequency band compatible with IEC60270 recommendation. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) is the most important factor in gradual insulation deterioration of high-voltage (HV) power equipment, and then PD trend monitoring is a great issue for their condition assessment. Impulsive high-frequency PD current/voltage signals can be detected by using electrical sensors, e.g. inductive/capacitive sensors. A comprehensive feasibility study is carried out to use the power frequency current transformers (CTs) that are already installed in medium voltage and HV electrical power systems instead of high-frequency CTs. To achieve this aim, frequency response of a sample protection CT is extracted experimentally and it is fitted to appropriate transfer functions to access the related frequency characteristics. Regarding improper CT frequency response and its extreme variations in different frequencies, reversed transfer function is obtained to apply to CT secondary signals for reconstructing CT input PD pulses. Two types of artificial PD pulses are examined to validate the proposed method and the experimental results show that power frequency CTs can be used for PD detection and measurement in some frequency bands. [ABSTRACT FROM AUTHOR]

Since the internal turn‐to‐turn faults (TTFs), as a common cause of the transformer failures, result in minor changes on terminal currents/voltages, they maybe undetected by the conventional protective relays. In this study, a simple, sensitive and robust linkage flux‐based technique is proposed to protect the power transformers against TTFs. In this approach, some separated multi‐turn windings as search coils (SCs) have to be wrapped around the transformer core legs to sense the related passing flux. Since passing equal flux through a transformer core leg in normal condition induces equal voltages in the related SCs, variation of the induced voltages indicates the fault occurrence in that phase. Against the traditional differential protection schemes, current transformer error and saturation, tap changer operation, energising inrush current, over‐fluxing etc. cannot impact the proposed technique performance. Therefore, it can be introduced as a comprehensive protection technique for power transformers.To confirm the proposed technique performance, it is tested on a real 50 kVA, 20 kV/400 V three‐phase distribution transformer, in various conditions, too. [ABSTRACT FROM AUTHOR]

Internal turn‐to‐turn faults (TTF) are considered as a common cause of transformer failures. Such defects (especially minor TTFs) may result in minor changes in terminal currents/voltages as these are undetectable by conventional current and/or voltage‐based methods. In this study, a simple, sensitive and robust method is proposed to identify the TTF locations in power transformers by using core flux based technique. In this approach, a few turns must be wrapped around the transformer core legs to sense and detect the related core flux. Passing asymmetrical flux through a transformer core leg (due to a TTF) induces different voltages in the related sensors, which are located at different places. Variation of the core flux in the corresponding sensors indicates the faulty phase and the TTF location on that phase as well. The proposed technique is verified by some simulations and experimental tests. The obtained results show that the proposed technique successfully (i) detects all the TTFs, (ii) identifies the faulty phase, and (iii) specifies the faulty region on the related phase. Although the proposed method requires a few search coils to be installed on the transformer core legs, installing these thin wires will not change the transformer design significantly. [ABSTRACT FROM AUTHOR]