Tap Positions Research Articles

Bad data identification method considering the on-load tap changer model

With the connection and integration of renewable energy, the on-load tap-changer (OLTC) has become an important device for regulating voltage in distribution networks. However, due to non-smooth and non-linear characteristics of OLTC, traditional bad data identification and state estimation methods for transmission network are limited when applied to the distribution network. Therefore, the nonlinearity and droop control constraints of the OLTC model are considered in this paper. At the same time, the quadratic penalty function is introduced to realize the fast normalization of the tap position. It proposes a two-stage bad data identification method based on mixed-integer linear programming. In the first stage, suspicious measurements are identified using projection statistics and maximum normalized residual methods for preprocessing the measurement data. In the second stage, a linearization approach utilizing hyhrid data-physical driven is applied to handle nonlinear constraints, leading to the development of a bad data identification model based on mixed-integer linear programming. Finally, the proposed methodology is validated using a modified IEEE-33 node test feeder example, demonstrating the accuracy and efficiency of bad data identification.

Evaluation Method for Voltage Regulation Range of Medium-Voltage Substations Based on OLTC Pre-Dispatch

A new energy industry represented by photovoltaic and wind power has been developing rapidly in recent years, and its randomness and volatility will impact the stable operation of the power system. At present, it is proposed to enrich the regulation of the power grid by tapping the regulation potential of load-side resources. This paper evaluates the overall voltage regulation capability of substations under the premise of considering the impact on network voltage security and providing a theoretical basis for the participation of load-side resources of distribution networks in the regulation of the power grid. This paper proposes a Zbus linear power flow model based on Fixed-Point Power Iteration (FFPI) to enhance power flow analysis efficiency and resolve voltage sensitivity expression. Establishing the linear relationship between the voltages of PQ nodes, the voltage of the reference node, and the load power, this paper clarifies the impact of reactive power compensation devices and OLTC (on-load tap changer) tap changes on the voltages of various nodes along the feeder. It provides theoretical support for evaluating the voltage regulation range for substations. The day-ahead focus is on minimizing network losses by pre-optimizing OLTC tap positions, calculating the substation voltage regulation boundaries within the day, and simultaneously optimizing the total reactive power compensation across the entire network. By analyzing the calculated examples, it was found that a pre-scheduled OLTC (on-load tap changer) can effectively reduce network losses in the distribution grid. Compared with traditional methods, the voltage regulation range assessment method proposed in this paper can optimize the adjustment of reactive power compensation devices while ensuring the voltage safety of all nodes in the network.

A coordinated voltage control scheme based on linearized power flow functions for non-optimal and optimal problems

This paper proposes a coordinated voltage control scheme for transmission systems based on linearized power flow functions to determine the set points of local control voltage devices. The scheme considers models and interactions between different devices to attain the appropriate performance (non-optimal or optimal) of the whole power system. The sensitivity analysis is used to formulate a partly linearized model that relates the voltage variations of buses to the reactive power variation of synchronous machines, settings of static VAr compensators (SVCs), shunt capacitors susceptance, and tap position of load tap changers (LTCs) to determine the set of the settings of the voltage control devices. Two formulations are proposed by considering the susceptance of SVCs or the slope and reference voltage of characteristics of SVCs as control variables. The developed formulation based on the linearized power flow functions provides the possibility of the practical implementation of the coordinated voltage control scheme, especially the optimal one, by reducing the model complexity and solving time. The performance of the proposed formulations is investigated by some studies of voltage control and an optimally coordinated problem on the IEEE 30-bus and IEEE 118-bus test systems.

Optimal operation of paralleled power transformers

Parallel operation of power transformers is a common practice. Interest is placed on minimizing the reactive current circulation between transformers due to mismatching of electrical properties. Several control schemes have been applied over the years to ensure efficient operation of paralleled transformers with OLTC. These methods rely either on field measurements of circulating currents or on classic Master/Follower approach and usually assume that the paralleled transformers have matching impedances and OLTC positions. On the present work a generalized approach is implemented calculating the circulating current and minimizing losses directly at the System Operation Office and using the distribution system SCADA to control tap position of the paralleled transformers. This permits the determination of optimal tap matching between transformers and calculation of losses under emergency situations where coupling of transformers with slight impedance mismatch might be considered. In the proposed method a map of circulating current is calculated based on the transformer impedance, X/R ratio and OLTC positions, then the optimal tap positions (minimizing losses) under parallel operation are determined.

Deep Neural Network-Based Autonomous Voltage Control for Power Distribution Networks with DGs and EVs

This paper makes use of machine learning as a tool for voltage regulation in distribution networks that contain electric vehicles and a large production from distributed generation. The methods of voltage regulation considered in this study are electronic on-load tap changers and line voltage regulators. The analyzed study-case represents a real-life feeder which operates at 10 kV. It has 9 photovoltaic systems with various peak installed powers, 2 electric vehicle charging stations, and 41 secondary substations, each with an equivalent load. Measurement data of loads and irradiation data of photovoltaic systems were collected hourly for two years. Those data are used as inputs in the feeder’s model in DigSilent PowerFactory where Quasi-Dynamic simulations are run. That will provide the correct tap positions as outputs. These inputs and outputs will then serve to train a Deep Neural Network which later will be used to predict the correct tap positions on input data it has not seen before. Results show that ML in general and DNN specifically show usefulness and robustness in predicting correct tap positions with very small computational requirements.

Allocation of PV Systems with Volt/Var Control Based on Automatic Voltage Regulators in Active Distribution Networks

This paper presents an optimal allocation methodology of photovoltaic distributed generations (PVDGs) with Volt/Var control based on Automatic Voltage Regulations (AVRs) in active distribution networks considering the non-dispatchable mode of PVDG operation. In the proposed methodology, an intelligent coordinated Var control is activated via controlling the AVR tap position and the Var injection of PV inverters to achieve a compromise between reducing active and reactive power losses and enhancing voltage quality in a distribution network. Also, the scheduled power factor mode of operation is investigated for the PV inverters. Added to that, the proposed allocation methodology is handled on the basis of hourly loading variation under simultaneous control modes of PV inverters and AVR. Moreover, the impacts of the specified number of PVDGs are assessed on the distribution system’s performance. A recent effective optimizer of the slim mold algorithm (SMA) is dedicated to solving the proposed optimization framework. The simulation implementations are executed on a practical distribution network of the Kafr Rabea area related to South Delta Electricity Company in Egypt. Also, the application is conducted for a large-scale distribution network from the metropolitan area of Caracas. The proposed methodology provides superior performance in minimizing the active and reactive power losses and improving the voltage profile.

A Fast Calibration Method for Pneumotachograph with a 3L Syringe.

The pneumotachograph (PNT), a commonly used flowmeter in pulmonary function diagnostic equipment, is the required frequency calibration to maintain high accuracy. Aiming to simplify calibration steps, we developed a fast calibration system with a commercially available 3L syringe to provide a real output flow waveform. The acquisition of the real output flow waveform is based on the reliable measurement of in-cylinder pressure and the real-time detection of plunger speed. To improve the calibration accuracy, the tapping position for measuring in-cylinder pressure was optimized by CFD dynamic-mesh updating technique. The plunger speed was obtained by tracking the handle of the plunger with a smart terminal. Then, the real output flow was corrected using a compensation model equation. The calibration system was verified by the pulmonary waveform generator that the accuracy satisfied the requirements for respiratory flow measurement according to ATS standardization. The experimental results suggest that the developed method promises the fast calibration of PNT.

A Broad Stopband and High Rejection HTS Lowpass Filter for Quantum Computers

This paper presents a novel approach for extending the upper stopband of lowpass filters. The proposed technique involves dividing the hairpin unit cells' coupled lines into multiple smaller components, which shifts the harmonics to higher frequencies while maintaining the cut-off frequency. Additionally, the stopband is further extended by modifying the tapping position to suppress the second harmonic. For demonstration, an improved dual-hairpin unit cell is devised, which is able to extend the stopband up to 11.3 times the cut-off frequency. Furthermore, a cascaded lowpass filter utilizing multiple improved dual-hairpin unit cells is also designed, which is divided into two sub-filters to suppress enclosure resonance. The cascaded filter is fabricated on an HTS (high-temperature superconducting) thin film deposited on a MgO substrate, demonstrating a cut-off frequency of 483 MHz, extending the stopband to 25.1 GHz (51.9 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_c</i> ), affording a rejection level exceeding 60 dB and insertion loss below 0.04 dB. Notably, the roll-off rate exceeds 569 dB/GHz, and the size measures only 0.144 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> × 0.030 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> .

Equilibrium Optimizer Algorithm for Optimal Reactive Power Dispatch

Optimal Reactive Power Dispatch (ORPD) is a significant research area in terms of maintaining the reliability and safety of the power system and operating it more economically. ORPD problem can be formed from a variety of perspectives including the minimization of the active power losses and voltage deviation, and improving the voltage stability performance. The majority of methods so as to deal with ORPD problem is meta-heuristic techniques because of the complex, non-linear and non-convex nature of the problem. In this paper, a new physic-based meta-heuristic algorithm, Equilibrium Optimizer (EO), is proposed for ORPD problem to reach the optimal settings of control variables such as voltage magnitudes in PV buses, tap positions of transformers and reactive power support of shunt devices. The introduced algorithm is evaluated on IEEE 30-bus test system by using various objectives, and a comparison of the implemented method to other optimization techniques described in the literature is utilized to assess its efficacy. Simulation results and statistical indicators demonstrate that the EO algorithm validates its computational efficacy and robustness in handling the ORPD problem.

A Novel Co-phase Traction Power Supply System in Electrified Railway

The electrified railway has power quality problems such as three phases seriously unbalanced, large harmonics, and reactive power. In addition, the neutral section exists at each power supply section, which restricts the development of the high-speed and heavy-haul railway. This paper proposes a novel co-phase traction power supply system (TPSS) based on a YNvd balanced transformer, which can not only solve the above problems but also save one single-phase coupling step-down transformer, thus reducing the cost and space of the whole system. In addition, the voltage level of the converter switching device can be reduced by the rational design of the transformer tap position, which enhances the reliability and feasibility of the system. The compensation principle and control strategy of the co-phase TPSS based on the novel YNvd balanced transformer are analyzed in detail in this paper, and the compensation current detection and integrated power flow controller (IPFC) control methods are given. Simulation and analysis show that the proposed topology structure and control method are correct and feasible.

Automatic definition of topological corrective actions for post-contingency OPEX minimization

This paper presents a practical algorithm for the automatic definition of topological corrective actions (TCAs) to minimize the additional operating expenses required to mitigate the adverse effects of contingencies in the network. Contingency and sensitivity analyses are used to identify possible TCAs that comprise the disconnection of single branches, pre-defined switching actions on one or more circuit breakers (CB), and changing the tap position of phase-shifter transformers. A novel method is proposed for the identification of possible CB closing TCAs. For the TCAs that do not lead to uncontrolled cascade tripping, unit commitment (UC) calculations are eventually run to obtain the economically optimal amount of conventional generation redispatch, renewable energy curtailment and load shedding required to eliminate the residual overloadings after each possible TCA is applied. The proposed approach does not reformulate the UC optimal power flow problem but rather uses standard calculation functions available in industrial-grade software. The effectiveness of the proposed approach is shown for a reduced-order transmission system prepared to capture many post-contingency conditions found in practice.

A multi-objective decentralized optimization for voltage regulators and energy storage devices in active distribution systems

Centralized optimization methods have been widely used to manage the operation of distribution systems. However, these methods have some restrictions, such as the high computational cost, the reliance on a centralized computer system, and the lack of data privacy. To overcome these limitations, decentralized optimization methods have been proposed in recent years. Decentralized methods divide the control variables of the centralized optimization problem over several controllers, and each controller solves its own subproblem independently. This paper presents a multi-objective optimization framework for managing the operation of distribution systems. The primary objective of the proposed method is to optimize the tap positions of voltage regulators and charging and discharging powers for energy storage devices locally through a decentralized coordination process. The used objective functions take into account the voltage profile within the network, the lifetime of the devices, and the energy losses in the systems. Two decentralized methods, based on the Advanced Arithmetic Optimizer algorithm and the Profile Steering approach, are proposed to address the limitations of centralized optimization methods. The decentralized methods aim to improve the reliability and efficiency of the optimization process, while also minimizing communication and computational costs. The proposed methods are evaluated and compared to a centralized approach using the IEEE 33 and 69 bus systems. The results demonstrate that the proposed decentralized methods can effectively resolve voltage problems, minimize energy losses, and find high-quality solutions with improved computational efficiency compared to the centralized approach.

The robust curve-fitting based method for coordinated voltage regulation with distributed generator and OLTC in distribution network

The voltage violation in distribution networks may occur frequently due to the rising integration of flexible demands and supplies. In this paper, the reactive power of the inverter-based distributed generator (DG) and OLTC tap position are adjusted for voltage regulation in coordinated manner. Firstly, the reactive power adjustment for the voltage regulation has been carried out by use of the DG reactive power capacity. Afterwards, the tap position of the OLTC has been changed to regulate the bus voltage that has a voltage violation problem in the case of insufficient reactive power capacity of the DG inverter. The value of the distributed generator reactive power output that regulates the voltage on the bus that has a voltage violation is found with proposed curve-fitting method and tested with the Grid Search, Artificial Bee Colony methods. The proposed method derives mathematical expressions between DG reactive power output and bus voltages as quadratic equations by curve-fitting technique. Moreover, addition to inherent upper and lower reactive power limits of the DG inverter, they are determined by the proposed curve-fitting based technique while considering voltage constraints on all buses. Proposed method is much faster than other two methods because of its plain structure and gives adequate accurate results.

Implementation Strategy of Test Facility Based on Auto-Transformer for LVRT/HVRT Evaluation of Large-Scale Wind Turbine

In accordance with South Korea’s recent 2030 Carbon Neutral Plan, an 8GW offshore wind farm is planned for construction in the South-west Sea. Therefore, it is expected that large-scale wind turbines will be installed, and these turbines must operate stably, even when there are instantaneous voltage fluctuations in the power system. The grid code is described for the low-voltage-ride-through (LVRT) and high-voltage-ride-through (HVRT) functions, and a test facility that can perform both LVRT and HVRT tests is essential. In the case of LVRT/HVRT test facilities developed by the existing RLC (impedance component) method, it may be difficult to test large-scale wind turbines due to problems such as power quality, frequent failures and narrow short-circuit capacity ranges. Therefore, to solve such problems, this paper proposes an LVRT/HVRT test facility of the autotransformer type, which is capable of outputting the desired voltage range by changing the wiring method and tap position. Specifically, in order to implement the test facility of the autotransformer type, which is able to output the desired voltage range by changing the wiring method and tap according to the LVRT/HVRT test status, this paper presents an impedance determination algorithm (two-step layer impedance determination algorithm) of auto-transformer based on the fault-current analysis and operation strategy at a real LVRT/HVRT testing evaluation facility.

Voltage Regulation Planning Based on Optimal Grid-Connected Renewable Energy Allocation Using Nature-Inspired Algorithms to Reduce Switching Cycles of On-Load Tap Changing Transformer

Due to the non-deterministic and probabilistic qualities of renewable energy resources (RER), integrating these resources has posed a challenge for energy companies and government policy planners. Hybrid power systems require frequent voltage regulation to address the changes in renewable generation and facilitate voltage management. This leads to an increment in the operating time of the tap changer in the power transformer, thus resulting in accelerated degradation of the on-load tap changer (OLTC) device. The primary focus of this paper is to optimally manage the penetration level of renewable generation while maintaining the minimum time for proper operation of voltage regulation devices. Accordingly, the major contribution of this paper is to address the switching cycle issues of the on-load tap-changing transformer. Initially, a framework is proposed to optimize the location and size of renewable power generation using a multi-objective cuckoo search optimization algorithm. The main goal here is to reduce power losses and tap changer operations while improving the system voltage profile under different levels of renewable energy penetration. The optimization problem takes into consideration the fluctuating nature of wind speed and solar irradiance for sunny and cloudy days over 24 h. The framework has been applied to the IEEE 57-bus and 118-bus systems with different load levels. The performance of the proposed approach has been benchmarked by comparing it with the genetic optimization algorithm to identify the higher potential buses for renewable generation allocation. The cuckoo search algorithm (CSA) shows outstanding results in reducing the number of switching cycles to about (37 – 43) % whereas the genetic algorithm (GA) only (17 – 18). In this sense, the number of changes in tap position when using the CSA is 1956 for sunny days and 1763 for cloudy days compared to GA 2558 for sunny days and 2547 for cloudy days. The voltage profiles for both algorithms are maintained in the range of (1.06 and 0.94) per unit. The results affirm the effectiveness of the proposed approach in determining the optimal placement and size of RER with voltage profile improvement and reduction in the switching cycles of OLTC.

HFR-Video-Based Fingertip Velocimeter for Multifinger Tapping Detection

In this study, we propose a novel concept of a software-based fingertip velocimeter using high-frame-rate (HFR) video processing that can simultaneously estimate when and where an operator taps with his/her finger by detecting the high-frequency component that develops when the fingertip actively contacts something. Our software-based fingertip velocimeter can precisely estimate the velocities of multiple fingers through HFR video processing in real time. Digital image correlation (DIC) operating at every frame for sub-pixel-precision velocity estimation is hybridized with CNN-based object detection operating at intervals of dozens of frames to robustly update the fingertip ROI regions during the frame-by-frame DIC operation. We developed a real-time multi-finger tapping detection system that can execute DIC operation on 720×540 resolution images at 500 fps with CNN-based fingertip detection at 30 fps. By presenting several experimental results for finger tapping detection, including virtual keyboard interaction with a ten-finger keyboard input, the effectiveness of our fingertip velocimeter as a finger tapping interface was demonstrated, which can simultaneously estimate the tapping positions and moments of multiple fingers when finger tapping is performed 10 times or more in a second.

Coordinated voltage control of three-phase step voltage regulators and smart inverters to improve voltage profile and energy efficiency in unbalanced distribution networks

This paper proposes a coordinated voltage control by three-phase step voltage regulators (3ϕSVRs) and photovoltaic (PV) units with smart inverters. An optimization problem is formulated to improve the voltage profile of distribution networks and reduce the active power curtailment of PVs. The tap positions of 3ϕSVRs and the active and reactive power output of PVs are coordinated by whale optimization algorithm. The effectiveness of the proposed approach is verified by case studies on the IEEE 123 node test feeder. The results show that the proposed approach achieves lower voltage unbalance while avoiding excessive PV curtailment, improving utility, consumer, and environmental benefits.

Optimal reactive power pricing with transformer variable taps using genetic algorithm

&lt;span lang="EN-US"&gt;Ancillary services in interconnected networks are crucial to secure real power transfers, maintaining network reliability, improving power quality as well as network stability. Reactive power has always been of special importance as one of the most substantial ancillary services required to control the voltage in power grid. This paper presents a fresh reactive power pricing approach by embedding variable transformer taps into voltage ampere reactive (var) pricing method. To carry out the resultant optimization problem with a set of complicating constraints, the genetic algorithm takes part and guarantees the global optimal solution. The simulation results show that when transformer tap works as a control variable, the total cost of reactive power can be decreased. However, the incorporation of transformer taps in the pricing model can slightly complicates voltage profiles as the sensitivity of bus voltages to the reactive power variations in the system is increased. Further, the findings reiterate that by optimal position of transformer taps, technically, the security index of the system can be enhanced while the var price for end-users (lowest purchase cost for independent system operator) being more reasonable. To simulate the proposed reactive pricing method, the standard IEEE 30-bus system is employed to analyze the proposed method.&lt;/span&gt;

Optimization and analysis of tapping position on leakage reactance of a two winding transformer

To ensure a reliable and stable power supply, optimal design and proper installation of the transformer are essential for the power suppliers and distributors. Short-circuit current is the main parameter of the transformer and causes the failure in the transformers. Accurate calculation and optimization of the leakage reactance help the transformer designers to mitigate against failure during the short circuit conditions. Transformer designers use different tapping positions for the manufacturing of the two-winding tap transformers. This study analysis and optimizes the leakage reactance of the two-winding tap transformer. Leakage reactance behavioral characteristics of the six different tappings are evaluated and examined in this study, including (1) without tapping, (2) upper tapping, (3) lower tapping, (4) middle tapping, (5) lower–upper tapping, (6) side tapping of the low voltage winding using finite element method. The results show that the side tapping has the least impact on the leakage reactance. The results also show that upper tapping and lower tapping have a significant effect on the leakage reactance. The comparison between the finite element method and experimental short-circuit test results for the optimized design also suggests that the finite element models can accurately evaluate the leakage reactance in the two-winding tap transformers.

Optimal Power Flow Analysis for Power Loss Reduction using Jaya Algorithm

This paper is engrossed in the usage of metaheuristic optimization methods named the JAYA algorithm and the teacher learning based optimization (TLBO) algorithm, which deal with the objective function of the optimal power flow (OPF) problem. TLBO and Jaya are parameter-free algorithms, which reduce the complexity of algorithms. The objective function of this paper is to reduce the real power losses and maintain the voltages and tap positions within their limits. IEEE-39 bus system data is considered for the practice of the algorithms. The results obtained by using the JAYA algorithm show better progress in objective function reduction. This entire work is done in a MATLAB environment.