Sharif Digital Repository

One of the most critical equipments in power grids are power transformers, which are vulnerable to damage due to the possibility of faults in its various components. A very common category of such faults is turn-to-turn fault in its winding. This fault initiates by the aging of the winding insulation with a short circuit of several adjacent loops to each other and if it is not detected quickly by the transformer protection, it will spread rapidly and can lead to irreparable failure in the transformer. Traditionally, turn-to-turn fault should be detected by mechanical pressure relays, however, due to the poor performance of these relays in the rapid detection of this type of fault, in the... 

Distribution companies typically use ADMD and coincidence factors to calculate aggregated loads. However, these factors have a significant impact on the selection of the optimal capacity of distribution network equipment; But so far, comprehensive studies at the level of single customers have not been implemented on the calculation of these factors. In this work, a comprehensive study has been conducted on residential customers in Tehran and the consumption data of 2121 residential customers, which were recorded during the summer of 2020, are used. The data were collected in two separate sets to investigate the effect of two factors: the type of cooling load and the welfare level of... 

One of the shortcomings of differential logic in power transformers is its inability to detect small percentage faults at the end of the winding. The occurrence of a phase-to-ground short circuit in the last few percent of the winding near the neutral causes a very large fault current to pass through the neutral and the faulted coils, while the changes in the current observed at the transformer terminal will be very small. To improve the performance of the power transformer protection system, a restricted earth fault (REF) protection is normally used in parallel with the differential protection. To implement REF protection, several solutions have been proposed in scientific and industrial... 

Power transformer is one of the most important equipment in the power system which plays a key role in the reliability and quality of power delivery. Among numerous failure modes of a typical power transformer, the turn-to-turn fault (TTF) is one of the most prominent reasons for its unplanned outage. A turn-to-turn fault quite often begins with the degradation of the winding insulation between two adjacent turns, then in a short time, this low-level fault can progress to a large number of turns and results in the transformer costly damages. Therefore, it is vital to detect TTF at an early stage and prevent its progression to a catastrophic disaster. The conventional percentage differential... 

The short-term expansion planning of the private utilities, as well as the emerging technologies such as photovoltaic panels (PVs), plug-in hybrid electric vehicles (PHEVs), cryptocurrency mining, and storage elements spread, make the long-term load estimation of distribution transformers (DTs) noticeably imprecise. In response, the number of overload and underload transformers is growing in recent years. The utilities normally analyze the loading of their DTs annually to determine the DTs, which should be replaced. The simplest, but expensive way is to substitute them with the newly purchased DTs. However, financial profit motivates the utilities to relocate in-service undersized and...