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Over time, there has been a continuous surge in the demand for electrical energy, necessitating the development of larger and more intricate electrical power networks. These extensive networks pose a significant challenge, primarily in the form of considerable loss of electrical energy, which, if not effectively addressed, may lead to persistent and imperceptible losses. In response to this challenge, this research proposes the application of quantum binary particle swarm optimization (QBPSO) for the coordinated management of on-load tap changers (OLTC) in loaded transformers within a distribution network, with a specific emphasis on reducing power losses. The experimental results demonstrate that the implementation of QBPSO results in a reduction of power loss from 21.756107 kW to 19.157321 kW and an increase in the average voltage from 19.00467941 kV to 19.93068 kV in a 20 kV 34-bus distribution network. This has the potential to significantly enhance overall system efficiency. [ABSTRACT FROM AUTHOR]

Reliability and long lifetime of on-load tap changers are very important issues for the power transformers. In this work, a novel model switch is developed to simulate the switching process of diverter switches and flexibly adjust the individual contact gap. Then, the contact voltage, contact current and mechanical vibration acceleration are measured simultaneously to reflect the switching characteristics. Further, the complete contact tap time sequences during switching process are obtained based on the joint electrical and mechanical vibration acceleration responses. In addition, the effects of arcing contact gap and transition contact gap on the contact tap time, main vibration frequency and power spectral density are investigated experimentally. The results could be used to discriminate the possible contact wear defects and associated electrical contact fault. [ABSTRACT FROM AUTHOR]

In order to solve the coordinated optimization problem of distributed generation (DG), on‐load tap changer (OLTC) and capacitor banks, a dynamic reactive power optimization (DRPO) method based on fuzzy time clustering is proposed. In the method, fuzzy time clustering algorithm is used to cluster the static optimal switching sequence of OLTC and capacitor banks. The time decoupling of control variables is realized and it meets the constraints of the maximum switching times. Next, the influencing factors of DG reactive power limit are analysed. Considering the control ability of OLTC, capacitor banks and DG in voltage and reactive power optimization, a coordinated optimization method is proposed. Since the adjustment of OLTC tap position directly affects the voltage and reactive power distribution of the whole line, the switching time and tap position of OLTC are determined based on the static optimization results of each time and fuzzy time clustering algorithm. Then, the switching time of capacitor banks is determined by fuzzy time clustering algorithm. At last, the switching capacity of capacitor banks and DG reactive power are jointly optimized to get the final control scheme. The proposed method demonstrated good performance in the modified IEEE33 node system and two actual power grid examples. [ABSTRACT FROM AUTHOR]

Voltage/VAR regulation (VVR) implemented by capacitor banks (CBs), on-load tap changers (OLTCs), and photovoltaic (PV)-associated inverters is effective to enhance voltage stability and reduce power loss. On the other hand, conservation voltage reduction (CVR) has been widely adopted in distribution networks to reduce load demand. Existing works mainly focus on each of them. This paper proposes a VVR method with CVR, forming a multi-objective optimisation problem which minimises (i) voltage collapse proximity indicator (VCPI), (ii) load demand, and (iii) power loss. Besides, PV power generation as uncertainty significantly impairs the VVR results. To deal with the uncertainty issue, this paper proposes a rollinghorizon framework to determine VVR and applies Taguchi's orthogonal array testing (TOAT) to model the uncertain PV power generation, achieving rolling-horizon-based multi-objective robust VVR. The proposed model is tested and demonstrated on the IEEE 33-bus and 69-bus systems, and simulation results verify that the proposed method can support robust solutions of the multi-objective VVR problem for decision-making. [ABSTRACT FROM AUTHOR]

Voltage/VAR regulation (VVR) implemented by capacitor banks (CBs), on‐load tap changers (OLTCs), and photovoltaic (PV)‐associated inverters is effective to enhance voltage stability and reduce power loss. On the other hand, conservation voltage reduction (CVR) has been widely adopted in distribution networks to reduce load demand. Existing works mainly focus on each of them. This paper proposes a VVR method with CVR, forming a multi‐objective optimisation problem which minimises (i) voltage collapse proximity indicator (VCPI), (ii) load demand, and (iii) power loss. Besides, PV power generation as uncertainty significantly impairs the VVR results. To deal with the uncertainty issue, this paper proposes a rolling‐horizon framework to determine VVR and applies Taguchi's orthogonal array testing (TOAT) to model the uncertain PV power generation, achieving rolling‐horizon‐based multi‐objective robust VVR. The proposed model is tested and demonstrated on the IEEE 33‐bus and 69‐bus systems, and simulation results verify that the proposed method can support robust solutions of the multi‐objective VVR problem for decision‐making. [ABSTRACT FROM AUTHOR]

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]

Highlights • A bi-level robust planning model for active management elements is proposed. • Variables in both investment level and operation level are associated together. • The planning model can be formulated as a mixed integer second order conic problem. • The renewable uncertainties in four seasons is addressed by a typical budget uncertainty set. • The two-stage robust mathematical model is solved by CCG algorithm. Abstract The distribution companies will face huge challenges in upgrading the existing network due to the uncertain integration of distributed renewable generations. In this paper, we propose a bi-level robust planning model for active management elements (AMEs) including on-load tap changer (OLTC), electrical storage system (ESS), capacitor bank (CB), and static VAR compensation (SVC) in order to accommodate uncertain development of wind power and photovoltaic power. The planning problem is constructed in two levels which are investment level and operation level. To overcome the poor convergence of the bi-level model, variables in both investment level and operation level are associated together. After equivalent transformation for non-linear terms the planning model can be formulated as a mixed integer second order conic programming (MISOCP) problem by some special means such as second order conic relaxation (SOCR) and big-M approach. We address the renewable uncertainties in four different seasons by a typical budget uncertainty set with adjustable budget. Then a two-stage robust mathematical model is proposed to decide a robust AME deployment scheme and solved by column and constraint generation (CCG) algorithm. [ABSTRACT FROM AUTHOR]

The growing penetration of low-carbon technologies in residential networks such as photovoltaic generation (PV) units and electric vehicles (EVs) may cause technical issues on the grid. Thus, operation planning of electrical distribution networks (EDNs) should consider the inclusion of these technologies in order to avoid operational limit breaches. This paper proposes a dynamic scheduling method for the optimal operation of PV units and EVs in unbalanced residential EDNs, considering energy storage systems (ESSs). The proposed method optimizes the joint operation of PV units and EVs, using ESSs to increase the local consumption of the renewable energy. A rolling multi-period strategy based on a mixed integer linear programming model is used to dynamically optimize a centralized decision making, determining control actions for on-load tap changers (OLTCs), ESSs, PV units, and EVs connected to the network. At each time interval, data for PV generation and EV demand is updated using actual information and historical profiles, generating an updated forecast for a one-day-ahead operation in order to properly cope with weather uncertainties and EV owner’s behavior without the need of multiple scenarios. The effectiveness and robustness of this approach are verified in different cases via a 107-node test EDN. [ABSTRACT FROM AUTHOR]

Vibro-acoustic measurement on a transformer's on-load tap changer (OLTC) can provide indications on its mechanical condition. Recently, a joint vibro-acoustic and arcing measurement system has been proposed, which can correlate the vibro-acoustic signal to mechanical events of OLTC's operation. However, there are still considerable difficulties in extracting useful information from both vibro-acoustic signal and arcing signal in a synchronized manner without any distortions in the extracted signals. In this paper, Savitzky–Golay filter is introduced to process the signals acquired from a joint vibro-acoustic and arcing measurement system installed on in-service OLTCs. It proves that the Savitzky–Golay filter can process both vibro-acoustic and arcing signals induced by OLTC, extract essential information without any time delay from both types of signals, and retrieve voltage phase information from the arcing signal. The methodologies developed in this paper can improve the visibility of OLTC's mechanical operation for an effective online condition monitoring. [ABSTRACT FROM PUBLISHER]

Voltage unbalance and magnitude violations under normal operating conditions have become main power quality problems in many low voltage (LV) distribution networks. Maintaining the voltage level in an LV network within the standard limits is the main constraining factor in increasing the network hosting ability for rooftop photovoltaic (PV). This study presents a new effective method for voltage management in unbalanced distribution networks through the implementation of optimal residential demand response (DR) and on-load tap changers (OLTCs). The proposed method minimises the compensation costs of voltage management (cost of DR and network loss), while prioritises the consumer consumption preferences for minimising their comfort level violations. A modified particle swarm optimisation algorithm (MPSO) is utilised to identify the optimal switching combination of household appliances and OLTC tap positions for the network voltage management. The proposed method is comprehensively examined on a real three-phase four-wire Australian LV network with considerable unbalanced and distributed generations. Several scenarios are investigated for improving the network voltage magnitude and unbalance considering individual and coordinated operations of DR and OLTCs (three phase tap control and independent phase tap control). Simulation results show that the coordinated approach of DR and OLTC, especially, DR integrated with OLTC independent phase tap control effectively improves the network voltage and increases the PV hosting capacity. [ABSTRACT FROM AUTHOR]

This paper presents a simultaneous network reconfiguration with DG sizing and tap changer adjustment to minimize power loss in a distribution system. Imperialist Competitive Algorithm is used to identify the best set combination of reconfiguration, DG size and tap changer. The performance of the proposed method has been tested on 33 bus distribution system at different load levels and different scenarios of DGs location. The test results indicated an improvement of power loss reduction as compared to existing method. Furthermore, the simultaneous approach is able to produce lowest power loss than any combination of two components simultaneously. At the same time, voltage also maintains within allowable limit. [ABSTRACT FROM AUTHOR]

The progression towards smarter grids, incorporating clean energy resources, has increased the integration of distributed generators (DGs) into power distribution networks. The DGs often cause a rise in voltage at their points of common coupling. Ordinary voltage regulation devices such as on-load tap changers (OLTCs) are not capable of addressing these issues adequately without careful coordination with DGs. In this paper, a new supervisory control and data acquisition-based two-stage voltage control scheme for the coordination of an OLTC transformer, capacitor banks (CBs) and the DGs is presented. The proposed scheme sets forth a new criterion for the selection of tap positions of an OLTC. In the first stage, tap positions of the OLTC are changed optimally using the micro genetic algorithm, whereas in the second stage, a recursive genetic algorithm is run to minimise the power losses in order to find the optimal reactive powers for the distribution network. Stochastic modelling of wind speed and solar irradiance data is also performed. The scheme is verified by studying it under four different test cases. An OLTC, CBs, photovoltaic panels, wind power DGs and dispatchable DGs are installed in the distribution network, and an IEEE 37-node test feeder is used for the verification of the proposed scheme. The simulation results show that the scheme achieves the objective of voltage regulation. [ABSTRACT FROM AUTHOR]

This study contemplates the possibility of estimating in near real-time the extreme voltages (minimum and maximum phase-to-neutral voltages) in a low voltage (LV) network using some, but as little as possible, advanced metering infrastructure (AMI) data. The main target application is to control an on-load tap changer at a secondary substation (medium voltage/LV substations) so as to maintain adequate voltage in the entire downstream LV network. The authors focus on the practical problem that consists in choosing the customers whose (AMI-based) voltage measurements will be used as inputs to the voltage control. They propose a method for the selection of customers that is based solely on statistical load profiles (without the need to resort to past AMI data) and they assess it using real-world data from 38 different French urban and semi-urban LV networks. The authors’ results show that working with simple load profiles instead of large amounts of past AMI data is acceptable, and that in most cases, choosing only a set of about ten customers at most is sufficient to guarantee an almost negligible level of error in the estimation of the minimum and maximum voltages in the LV network. [ABSTRACT FROM AUTHOR]

The growing interest in distributed generation (DG) in recent years has led to a number of generators connected to a distribution system. The integration of DGs in a distribution system has resulted in a network known as active distribution network due to the existence of bidirectional power flow in the system. Voltage rise issue is one of the predominantly important technical issues to be addressed when DGs exist in an active distribution network. This paper presents the application of the backtracking search algorithm (BSA), which is relatively new optimisation technique to determine the optimal settings of coordinated voltage control in a distribution system. The coordinated voltage control considers power factor, on-load tap-changer and generation curtailment control to manage voltage rise issue. A multi-objective function is formulated to minimise total losses and voltage deviation in a distribution system. The proposed BSA is compared with that of particle swarm optimisation (PSO) so as to evaluate its effectiveness in determining the optimal settings of power factor, tap-changer and percentage active power generation to be curtailed. The load flow algorithm from MATPOWER is integrated in the MATLAB environment to solve the multi-objective optimisation problem. Both the BSA and PSO optimisation techniques have been tested on a radial 13-bus distribution system and the results show that the BSA performs better than PSO by providing better fitness value and convergence rate. [ABSTRACT FROM AUTHOR]

Considering the possible overvoltage caused by the high proportion of photovoltaic systems (PVs) accessing distribution networks in the future, traditional centralized control methods will be too complex to satisfy the control response time demands. To solve this problem this paper presents a two-level voltage control method. At the day-ahead level, based on the PV-output and load-demand forecast, a community detection algorithm using an improved modularity index is introduced to divide the distribution network into clusters; a day-ahead optimal scheduling is drawn up on the basis of the network partition, and the objective is to minimize the operation costs of the distribution networks. At the real-time level, under the day-ahead optimal scheduling and network partition of the upper level, a real-time optimal voltage control algorithm is proposed based on the real-time operation data of the distribution networks, and the objective is to correct the day-ahead optimal scheduling through modifications. Thus, the algorithm realizes the combination of day-ahead scheduling and real-time control and achieves complete zonal voltage control for future distribution networks with high proportion of PVs. The proposed method can not only optimize the tap operation of an on-load tap changer (OLTC), improving the PV hosting capacity of the distribution network for a high proportion of PVs, but can also reduce the number of control nodes and simplify the control process to reduce the optimization time. The proposed approach is applied to a real, practical, 10 kV, 62-node feeder in Zhejiang Province of China to verify its feasibility and effectiveness. [ABSTRACT FROM AUTHOR]

In order to improve the intelligent diagnosis level of an on-load tap-changer's (OLTC) mechanical condition, a feature extraction method based on variational mode decomposition (VMD) and weight divergence was proposed. The harmony search (HS) algorithm was used to optimize the parameter selection of the relevance vector machine (RVM). Firstly, the OLTC vibration signal was decomposed into a series of finite-bandwidth intrinsic mode function (IMF) by VMD under different working conditions. The weight divergence was extracted to characterize the complexity of the vibration signal. Then, weight divergence was used as training and test samples of the harmony search optimization-relevance vector machine (HS-RVM). The experimental results suggested that the proposed integrated model has high fault diagnosis accuracy. This model can accurately extract the characteristics of the mechanical condition, and provide a reference for the practical OLTC intelligent fault diagnosis. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage control method during service restoration in the distribution networks with photovoltaic (PV) generator systems. In the current distribution automation system (DAS) process in Japan, voltage dips and surges occur during service restoration because PVs are disconnected simultaneously after a fault and subsequently reconnected after service restoration. However, in the current DAS, voltage regulators such as an on-load tap changer (OLTC) and step voltage regulators (SVRs) are not controlled during service restoration. The proposed DAS estimates the voltage in a distribution network during service restoration, and it controls the tap position of OLTC and/or SVRs according to the predicted voltage. The numerical simulation results using a real-world distribution system model on a real map and PVoutput profiles derived by actual square kilometer solar radiation data will be shown. Those results indicate that the proposed DAS prevents voltage deviation that occurs as long as the current DAS is used. The results also show high spatial resolution PV output data are needed to prevent voltage deviation absolutely. [ABSTRACT FROM AUTHOR]

Voltage regulation by means of coordinated voltage control is one of the challenging aspects in an active distribution system operation. Integration of distributed generation (DG), which can also be operated in Volt/VAr control mode, may introduce adverse effects including control interactions, operational conflicts, steady-state voltage variations, and oscillations. Therefore, examining and analyzing the phenomenon (both steady state and dynamic) of the control interactions among multiple Volt/VAr support DG units and voltage regulating devices such as tap changers and capacitor banks would be essential for effective voltage control in active distribution systems. In this paper, the interactions among DG units and voltage regulating devices are identified using their simultaneous and nonsimultaneous responses through time-domain simulations. For this task, an analytical technique is proposed and small signal modeling studies have been conducted. The proposed methodology could be beneficial to distribution network planners and operators to ensure seamless network operation from voltage control perspective with increasing penetration of DG units. [ABSTRACT FROM PUBLISHER]

This paper provides an example of the application of the acoustic emission (AE) method for the diagnosis of technical conditions of a three-phase on-load tap-changer (OLTC) GIII type. The measurements were performed for an amount of 10 items of OLTCs, installed in power transformers with a capacity of 250 MVA. The study was conducted in two different OLTC operating conditions during the tapping process: under load and free running conditions. The analysis of the measurement results was made in both time domain and time-frequency domain. The description of the AE signals generated by the OLTC in the time domain was performed using the analysis of waveforms and determined characteristic times. Within the time-frequency domain the measured signals were described by short-time Fourier transform spectrograms. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of doubly fed induction generators (DFIGs) operational limits on longterm voltage stability. DFIG operational limits are defined based on wind generator's capability curve in terms of the actual terminal voltage and wind speed. Also, the limitations of the converter, machine and wind turbine are considered in DFIG control schemes. The evolution of different variables is examined using two models for DFIG operational limits: fixed limits and variable limits. Time domain simulations have been performed in three different cases: constant wind speed, ramp up event, and ramp down event. This study also considers the dynamic models of over excitation limiter (OEL) and on-load tap changers (OLTC) combined with static and dynamic loads. Some important conclusions can be extracted from the simulation results, which can help in choosing the appropriate model to represent the DFIG operational limits in long-term voltage stability studies. [ABSTRACT FROM AUTHOR]

This paper investigates daily volt/var control in distribution networks using feeder capacitors as well as substation capacitors paired with on-load tap changers. A two-stage coordinated approach is proposed. Firstly, the feeder capacitor dispatch schedule is determined based on reactive power heuristics. Then, an optimisation model is applied to determine the dispatch schedule of the substation devices taking into account the control actions of the feeder capacitors. The reference voltage of the substation secondary bus and the tap position limits of transformers are modified such that the model adapts to varying load conditions. The optimisation model is solved with a modified particle swarm optimisation algorithm. The proposed method is compared with conventional volt/var control strategies using a 14-bus system and its effectiveness is further illustrated on a 69-bus system. It is demonstrated that the proposed approach performs better than the conventional strategies in terms of voltage deviation and energy loss minimisation. [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 suitable condition of an on-load tap-changer (OLTC) is essential for the operation of converter transformer due to its frequent switch for the voltage regulation of power system. This paper describes a methodology to obtain the OLTC vibration characteristics in time–frequency domain. Considering the possible aliasing effect in vibration signal processing, an improved empirical mode decomposition (EMD) is proposed with masking signals of multiple frequencies added, which has obvious superiority in aliasing reduction compared with conventional methods. Then, an effective fault-diagnosis strategy based on energy distributions variations of OLTC vibration signals according to Lorentz information measure is brought up. The calculated results under normal and typical fault conditions of model and real OLTC have shown that the energy spectrums of different conditions vary significantly so that the similarity index can measure the difference degree of energy distribution. Meanwhile, the index of contact looseness is higher than the insulated panel looseness which indicates that the contact looseness fault has greater influence on switch-over process of OLTC. [ABSTRACT FROM PUBLISHER]

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]

In this paper, we investigate secure device-to-device (D2D) communication in energy harvesting large-scale cognitive cellular networks. The energy constrained D2D transmitter harvests energy from multiantenna equipped power beacons (PBs), and communicates with the corresponding receiver using the spectrum of the primary base stations (BSs). We introduce a power transfer model and an information signal model to enable wireless energy harvesting and secure information transmission. In the power transfer model, three wireless power transfer (WPT) policies are proposed: 1) co-operative power beacons (CPB) power transfer, 2) best power beacon (BPB) power transfer, and 3) nearest power beacon (NPB) power transfer. To characterize the power transfer reliability of the proposed three policies, we derive new expressions for the exact power outage probability. Moreover, the analysis of the power outage probability is extended to the case when PBs are equipped with large antenna arrays. In the information signal model, we present a new comparative framework with two receiver selection schemes: 1) best receiver selection (BRS), where the receiver with the strongest channel is selected; and 2) nearest receiver selection (NRS), where the nearest receiver is selected. To assess the secrecy performance, we derive new analytical expressions for the secrecy outage probability and the secrecy throughput considering the two receiver selection schemes using the proposed WPT policies. We presented Monte carlo simulation results to corroborate our analysis and show: 1) secrecy performance improves with increasing densities of PBs and D2D receivers due to larger multiuser diversity gain; 2) CPB achieves better secrecy performance than BPB and NPB but consumes more power; and 3) BRS achieves better secrecy performance than NRS but demands more instantaneous feedback and overhead. A pivotal conclusion is reached that with increasing number of antennas at PBs, NPB offers a comparable secrecy performance to that of BPB but with a lower complexity. [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]

This paper proposes a vehicle-to-grid reactive power support (V2GQ) strategy for optimal coordinated voltage regulation in distribution networks with high distributed generation (DG) penetration. The proposed algorithm employs plug-in electric vehicles (PEVs), DG, and on-load tap changer (OLTC) to satisfy PEV charging demand and grid voltage requirements with relaxed tap operation, and minimum DG active power curtailment. The voltage regulation problem is formulated as a nonlinear programming and consists of three consecutive stages, in which successive stages apply the outputs of their preceding stages as constraints. The first stage aims to maximize the energy delivered to PEVs to assure PEV owner satisfactions. The second stage maximizes the DG extracted active power. Third stage minimizes the voltage deviation from its nominal value utilizing the available PEV and DG reactive powers. The main implicit objective of the third stage problem is relaxing the OLTC tap operation. In addition, the conventional OLTC control is replaced by a proposed centralized controller that utilizes the output of the third stage to set its tap position. Real-time simulations are developed to demonstrate the effectiveness of the proposed optimal coordinated algorithm on a typical distribution network using OPAL-RT real-time simulator (RTS) in a hardware-in-the-loop (HIL) application. [ABSTRACT FROM PUBLISHER]

• Two-timescale volt/var optimization that utilizes distributed energy resources. • Coordinating distributed energy resources along with utility-owned assets. • Engaging utility operator in the decision-making process. • Active distribution network with high distributed energy resources penetration. • Incorporate all resources and assets for enhanced network performance. The high penetrations of distributed energy resources of renewable energy sources, battery energy storage systems, and electric vehicles introduced several challenges to power networks. It can lead to high voltage variation, sudden over/under-power generation, high losses issues, and negatively impact distribution assets. Thus, there is a vital need for volt/var optimization schemes that integrate conventional volt/var devices with inverter-interfaced resources to overcome these challenges. This paper demonstrates a performance assessment of the volt/var optimization scheme utilizing different utility-owned assets and resources based on a two-timescale multi-objective algorithm. At the slow timescale, it utilizes capacitor banks and on-load tap changers to minimize system losses and maximize asset lifetime based on their conditions. The algorithm incorporates the utility operator's direct input for setting the conventional volt/var devices. The operation of these devices is optimized, in three steps, by limiting the number of switching operations based on the operator preferences. At the faster scale, it considers renewable energy sources, electric vehicle charging stations, and battery energy storage systems to be optimized to limit voltage variation and system losses further. The IEEE 33-bus distribution network is modified and used to demonstrate the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

High penetration of distributed generation (DG) has led to frequent voltage fluctuations in the distribution network. This paper describes the design of a partially rated, power-electronic-assisted onload tap-changing (OLTC) autotransformer. Positive and negative compensation of the grid voltage can be achieved on feeders that have high distributed generation and/or loading. A novel design of taps comprised of several no-load switches and a single semiconductor-mechanical hybrid switch have been proposed, that requires reduced voltage rating and a number of switches. In steady state, the mechanical switch in the hybrid switch conducts the load current resulting in low steady-state losses. During the tap change process, the OLTC uses semiconductor switches, namely insulated-gate bipolar transistor /metal–oxide semiconductor field-effect transistor, thus achieving arc-free tap change and long lifetime of switches. The OLTC system has been customized for both low-voltage and medium-voltage three-phase distribution networks. An open-delta configuration for the medium-voltage application has been proposed that requires only two OLTC units to control all three line voltages. Simulations are carried out to verify the steady-state and transient operation of the proposed OLTC. [ABSTRACT FROM AUTHOR]

This paper presents the impacts caused by the integration of variable speed wind turbines on long-term voltage stability. The technologies used are fully rated converter (FRC) and doubly fed induction generator (DFIG) with two control strategies: grid-side converter (GSC) at unity power factor, which is usually adopted, and GSC controlling reactive power. Also, this paper considers wind turbines capability curves and its variable limits, since they are subject to several limitations that changes with the operating point and wind speed. This study also considers the dynamic models of over excitation limiter (OEL) and on-load tap changers (OLTC) combined with static and dynamic loads using time domain simulations. Different penetration levels of wind generation are analyzed. The results show that long-term voltage stability can be improved when GSC of DFIG is controlling reactive power. Moreover, the capability curve plays an important role in this analysis since reactive power is a key requirement to maintain voltage stability. [ABSTRACT FROM PUBLISHER]

This paper presents a risk-based advanced distribution network management system (NMS) aimed at maximizing wind energy harvesting while simultaneously managing congestion and voltages. The NMS allows the adoption of multi-minute control cycles so the volume of actions from on-load tap changers (OLTCs) and distributed generation (DG) plants can be reduced while effectively catering for the effects of wind power uncertainties. This work presents the quantification of benefits and impacts from adopting different control cycles as well a comparison with a deterministic approach. The risk-based approach is implemented by adapting and expanding an AC optimal power flow. A risk level is used to determine the extent to which congestion and voltage rise could exist during a control cycle. The proposed NMS is applied to a real-life U.K. MV network from the North West of England to assess its effectiveness in managing high penetration of wind power considering minute-by-minute simulations for one week. The results show that the risk-based approach can effectively manage network constraints better than the deterministic approach, particularly for multi-minute control cycles, reducing also the number of control actions but at the expense of higher levels of curtailment. [ABSTRACT FROM PUBLISHER]

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]

Skewing is one of the most widely used methods to reduce the torque ripples. However, it was reported that the on-load torque ripple was not always reduced by the conventional skewing, in which the skewing angle is one period of torque ripple. This paper proposes the way of improving the skewing to reduce the torque ripple when the conventional skewing fails. It is found that by optimizing the skewing angle and current phase advance angle together, the improved skewing is able to meet the stringent torque ripple requirement over the whole load range. [ABSTRACT FROM AUTHOR]

Abstract: Management of reactive power resources is vital for stable and secure operation of power systems in the view point of voltage stability. This paper deals with the management of on-load tap changers (OLTCs) and dynamic VAR sources (including synchronous generators, synchronous condensers, and shunt reactive power compensators) to improve voltage stability margin (VSM) of power systems. This problem is usually called optimal reactive power dispatch (ORD) in the literature. The main contribution of the paper is to introduce a new objective function for the ORD problem. The proposed objective function is derived based on a local voltage stability index, called DSY, and has a strong correlation with VSM. This strong correlation makes the objective function effective for improving VSM, which is the main purpose of ORD. The proposed objective function is tested on the New England 39-bus test system and its performance is compared with some of the most common objective functions used in ORD. The obtained results show that solving ORD problem using the proposed objective function yields considerable increase in VSM. [Copyright &y& Elsevier]

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]