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Graphical abstract Highlights • An original OLTC model has been introduced that benefits from the arc modeling concepts of CB. • A new arcing power-based algorithm has been introduced for condition monitoring of OLTCs. • The proposed algorithm uses the power difference between terminals of transformer to calculate the arcing power of OLTC contacts. • The proposed algorithm determines the electrical wear of OLTC's contacts for estimating the maintenance schedule of OLTC contacts. Abstract An on-load tap-changer (OLTC) regulates the output voltage level of transformer by changing the winding voltage ratio without current interruption. It is one of the most expensive and vulnerable parts of power transformers. Therefore, modeling and condition monitoring (CM) of OLTCs are important for the power system operation. This paper presents a new modeling principle for OLTCs based on the circuit breaker (CB) arc models. There is a sequence of switching events with certain timings during each operation of OLTC. These switching operations are modeled individually and a full model of OLTC operation is derived. Computer simulation studies and the measurements captured from the real-time test studies of OLTC operation verify and validate the performance of the proposed OLTC model. On the other hand, the instantaneous differential power of tap-changing transformer measured from its input and output terminals is used to calculate the arcing power and energy associated with OLTC operation. The cumulative arcing energy is a good indication of the electrical wear of OLTC contacts. Therefore, it is used to propose a novel CM algorithm for OLTCs. The proposed method considers the effects of both arcing voltage and current signals to accurately estimate the arcing energy. The results obtained from computer simulation studies demonstrate that the proposed algorithm accurately evaluates the electrical wear of OLTC contacts and determines the inspection or maintenance schedules of OLTC contacts. [ABSTRACT FROM AUTHOR]

Owing to the increasing penetration of single-phase small generation units and electric vehicles connected to distribution grids, system operators are facing challenges related to local unbalanced voltage rise or drop issues, which may lead to a violation of the allowed voltage band. To address this problem, distribution transformers with on-load tapping capability are under development. This study presents model and experimental validation of a 35 kVA threephase power distribution transformer with independent on-load tap-changer control capability on each phase. With the purpose of investigating and evaluating its effectiveness under different operative conditions, appropriate scenarios are defined and tested considering both balanced and unbalanced situations, also in case of reverse power flow. The experimental setup is built starting from an analysis of a Danish distribution network, in order to reproduce the main feature of an unbalanced grid. The experimental activities are recreated in by carrying out dynamics simulation studies, aiming at validating the implemented models of both the transformer as well as the other grid components. Phase-neutral voltages' deviations are limited, proving the effectiveness of the phase-independent tap operations. Furthermore, minor deviations of the results from simulations and experiments confirm that all the system components have been properly modelled. [ABSTRACT FROM AUTHOR]

The static on-load tap changer is a better alternative than conventional on-load tap changers. The proposed solution involves the use of a compensation transformer and a bidirectional diode–insulated-gate bipolar transistor combination with appropriate switching techniques. Any required load voltage can be obtained with less injection of harmonics to load voltage waveform, and the response is practically instantaneous. The general structure of an electronic tap changer and the proposed modified model with voltage controller are presented. A gravitational search algorithm-based soft computing technique is used for the compensating voltage to optimize the switching angles for minimization of the output voltage harmonics. Various simulation and experimental results are presented to validate the proposed concept. [ABSTRACT FROM PUBLISHER]

Most of the faults on power Circuit Breakers (CBs) and On-Load Tap Changers (OLTCs) on high voltage transformers are of mechanical origin. Mechanical malfunction, mechanical wear and other types of abnormal behaviors can be detected as changes in the acoustic signatures. In this paper, an Expert System (ES) with the addition of a signal processor module and factual database module to the conventional ES has been proposed for the diagnosis of CBs and OLTCs. The feature extraction of the acoustic signatures has been done by decomposing them into voiced and silent portions in time domain and through FFT spectrum analysis in frequency domain. The OLTC's motor current has been decomposed into inrush, steady-state and extended currents to locate the cause of different anomalies in the OLTCs and acoustic-current pair has been used for the synchronization testing. Each extracted feature of the testing signal has been compared to the similar feature of a reference signal to not only identify the health of the testing device but also to locate the cause of each anomaly. Several test signals have been compared against the reference signature and the proposed expert system has proved to be a suitable, effective and reliable system for the acoustic diagnosis of OLTCs and CBs. [ABSTRACT FROM AUTHOR]

A distribution system was designed and operated by considering unidirectional power flow from a utility source to end-use loads. The large penetrations of distributed generation (DG) into the existing distribution system causes a variety of technical problems, such as frequent tap changing problems of the on-load tap changer (OLTC) transformer, local voltage rise, protection coordination, exceeding short-circuit capacity, and harmonic distortion. In view of voltage regulation, the intermittent fluctuation of the DG output power results in frequent tap changing operations of the OLTC transformer. Thus, many utilities limit the penetration level of DG and are eager to find the reasonable penetration limits of DG in the distribution system. To overcome this technical problem, utilities have developed a new voltage regulation method in the distribution system with a large DG penetration level. In this paper, the impact of DG on the OLTC operations controlled by the line drop compensation (LDC) method is analyzed. In addition, a generalized determination methodology for the DG penetration limits in a distribution substation transformer is proposed. The proposed DG penetration limits could be adopted for a simplified interconnection process in DG interconnection guidelines. [ABSTRACT FROM AUTHOR]

A portable system for the condition monitoring of on-load tap changer in on-line power transformers by non-invasive inspections was developed. The system was based on a virtual instrument for measuring signals of voltage, current and vibration that a tap change produces. The the diagnosis of the functioning condition was done using vibration analysis. Inspections on transformers of several substations were done to test the proposed portable system. From the results, it is concluded that the virtual instrument facilitates this kind of inspection. Besides, a study carried out on a sole on-load tap changer did not discard the possibility of estimating the operating condition of on-load tap changers from the measured vibration signals. However, in order to guarantee this it will be necessary to performed more tests. [ABSTRACT FROM AUTHOR]