Voltage Transformer Research Articles

Reconstructing Primary Voltage Across Inductive VTs—Part II: Validation, Application, and Analysis

This two-part paper presents an inverse method to reconstruct the primary voltage of a VT from the available distorted secondary signals. In this second part, the performance of the proposed inverse method is validated by simulation using a 10 kV inductive voltage transformer (VT). Additionally, four laboratory experiments are performed to show the potential applications of the proposed method. These experiments closely represent realistic field conditions. The simulation and experimental results verify the accuracy and reliability of the method. The robustness and parameter accessibility are discussed. The novel inverse method provides an effective solution for the accurate reproduction of high-frequency transients and low-frequency over-voltages measurements. Furthermore, the reconstructed primary voltage waveforms provide usable data for the study of voltages in power systems.

Research on Traveling Wave Detection Performance Based on Optical Voltage Transformer

Traditional transformers cannot effectively transmit high-frequency traveling wave signals, which leads to the fact that traditional voltage transformers cannot fully reflect the panoramic information of fault traveling waves and ensure fault location accuracy. This paper mainly analyzes the working principle of optical voltage transformers. The Jones matrix models the optical path system and its optical components, and the output model of the optical path system is obtained. The principle of photoelectric signal conversion is analyzed. The test principle, experimental method, and data results are studied and analyzed by power frequency, withstand voltage, lightning impulse, and arc tests. The transmission effect of fault traveling wave signal is verified, which provides the theoretical and experimental basis for the fault location of the distribution network.

Non Linear Modelling of a New Three-Phase High Voltage Transformer with Magnetic Shunts

Non Linear Modelling of a New Three-Phase High Voltage Transformer with Magnetic Shunts

A novel Ethernet based processing system for remote source harmonic detection

This work is carried out to objectively establish a new method to detect harmonics and measure the total harmonic distortion (THD) in a remote source, such as a high voltage transformer. The proposed approach utilized embedded design techniques to construct an embedded processor system with Ethernet intellectual property core to acquire data from a remote harmonics source. The designed system has several notable merits, namely, it is portable that can be applied in the work field, and it avoids workers from being subject to a hazard high voltage shock as well as its simplicity and high accuracy. The harmonics detection and analysis are achieved by inserting a microcontroller system near the high voltage transformer to acquire the necessary data and transmit it to a remote embedded processor system that is used to detect and analyze the harmonics. The microcontroller and the processor systems are connected by a wide-area network (WAN) through Ethernet and transmission control protocol/internet protocol (TCP/IP) protocols. The processor system is accommodated to perform 128 points fast Fourier transform for harmonics detection. Matlab simulations are used to validate the results. It is found that the results match very accurately the simulation results with an error of less than 0.02%.

Unlocking the Hidden Capacity of the Electrical Grid Through Smart Transformer and Smart Transmission

Power systems are experiencing a rapid and dramatic transformation driven by the massive integration of nondispatchable renewable energy sources, such as wind and solar, and highly variable loads, such as electric vehicles and air conditioning. This challenges existing grid assets, eventually leading to updating them, which, in turn, increases significantly the costs of sustainable technologies. Power electronics is a pivotal technology for electrical power processing for renewable energies and sustainable transportation. By means of “smart” functionalities, power electronics converters already embedded in such applications can also contribute to guaranteeing the overall system’s stable operation. Anyway, this cooperative contribution from distributed devices may be not enough leading to the need for the voltage transformation and power transmission of “system-level” power electronics solutions. In the case of large charging stations, a smart transformer (ST), while, in the case of large solar and wind parks, integration medium- or high-voltage direct current (HVdc) transmissions are system-level solutions. This article wants to review the potential of using such infrastructures to increase the capacity of existing grid assets, avoiding or deferring their upgrade and, hence, reducing the overall costs of renewables integration and the electrification of the transport sector. In fact, the power converters embedded in ST and HVdc can provide fast frequency and voltage response, and precise control of power flow acting at the system level much more effectively and feasibly for system operators as the distributed power converters embedded in several small sources and users. This article reviews, for the first time, these two key power electronics “system-level” solutions together—ST and HVdc—starting from their basic functionalities and showings how they can go beyond them, showing how, with grid-forming functionalities, they can offer new “smart grid” tools to enhance the capability of the existing electric grid infrastructures.

Research and Experiment Verification of the Shielding Effect of a 1000 kV Equipotential Shielding Capacitor Voltage Transformer in Consideration of Surface Leakage Current

The non-uniform distribution of the surface contamination on insulation bushings of a traditional capacitor voltage transformer (Tra-CVT) will impact the electric potential distribution along the axis of the capacitor voltage divider (CVD), and causes variation of voltage dividing ratio of the CVT. An increased phase angel difference between primary and secondary voltage will be another consequence. The equipotential shielding CVT (EPS-CVT), with its unique double layer structure, is able to significantly reduce the additional measurement error (AME) caused by surface leakage current (SLC) flowing on the bushing surface. In this work the AME caused by SLC for both types of CVTs are evaluated by an implementation of newly developed equivalent simulation circuit models of both CVTs accounting SLC. A shielding effect evaluation test method is proposed and successfully demonstrated on an UHV EPS-CVT prototype to verify the effectiveness of the AME shielding function of an EPS-CVT.

Compact MV-Insulated MHz Transformer-Coupled Gate Driver With Staged Turn-Off Scheme for Series-Connected Power Devices in DC Circuit Breaker Applications

The short-circuit protection equipment of dc circuit breaker (DCCB) is important for the dc grid. Also, the series-connected power devices are usually employed in the solid-state circuit breaker (SSCB) or hybrid circuit breaker (HCB) to meet the clamping voltage requirement. A simple passive gate driver and power supply solution is a critical component to drive the circuit breakers more cost-effective and reliable. This article proposed a novel compact MV-insulated transformer-coupled gate driver method, which combines the auxiliary power and gate signal together. The proposed high-frequency-modulated multilevel transformer voltage enables both the simultaneous and the staged turn-off schemes. Besides, the cascade high- and low-voltage transformer structures simplify the insulation design and demonstrate better scalability. The common-mode current could be suppressed as well using this structure. The design example of a compact 2-MHz high-voltage planar transformer with >13-kV partial-discharge-free insulation capability is illustrated. Finally, the simulation and experimental results are also given to demonstrate the feasibility of the proposed gate driver method.

CONTROL SYSTEM OF PARAMETERS OF ELECTRICAL CURING OF CAST-IN-SITU REINFORCED CONCRETE STRUCTURES

At the moment in house-building industry cases of increase of efficiency of cast-in-situ concrete structures electrical curing are insufficiently studied. Development and implementation of control systems of parameters of electrical curing can be solve of current concerns. Development sequence of this control system included: collection of initial data; development of virtual model of considered structures, using ELCUT; analysis of rate of simulation parameters, depend on ambient conditions; fixation of values of simulation parameters; development of mathematical model of correlation between transformer voltage and temperatures of concrete, ambient air and time of electrical curing; development and description of circuit diagram of proposed control system.
 The control system, developed by the authors, can be the basis for creation of automated complex of electrical curing of cast-in-situ reinforced concrete structures. Application of this system will significantly allow to decrease electricity consumption and labor costs, connected with electrical curing of structures.

A Model for Determining the Optimal Decommissioning Interval of Energy Equipment Based on the Whole Life Cycle Cost

An appropriate technical overhaul strategy is very important for the development of enterprises. Most enterprises pay attention to the design life of the equipment, that is, the point when the equipment can no longer be used as stipulated by the manufacturer. However, in the later stage of the equipment, the operation and maintenance costs may be higher than the benefit of the equipment. Therefore, only the design life of the equipment may cause a waste of funds, so as to avoid the waste of funds, the enterprise’s strategy of technical reform and overhaul are optimized. This paper studies the optimal decommissioning life of the equipment (taking into account both the safety and economic life of the equipment), and selects the data of a 35 kV voltage transformer in a powerful enterprise. The enterprise may have problems with the data due to recording errors or loose classification. In order to analyze the decommissioning life of the equipment more accurately, it is necessary to first use t-distributed stochastic neighbor embedding (t-SNE) to reduce the data dimension and judge the data distribution. Then, density-based spatial clustering of applications with noise (DBSCAND) is used to screen the outliers of the data and mark the filtered abnormal data as a vacancy value. Then, random forest is used to fill the vacancy values of the data. Then, an Elman neural network is used for random simulation, and finally, the Fisher orderly segmentation is used to obtain the optimal retirement life interval of the equipment. The overall results show that the optimal decommissioning life range of the 35 kV voltage transformer of the enterprise is 31 to 41 years. In this paper, the decommissioning life range of equipment is scientifically calculated for enterprises, which makes up for the shortage of economic life. Moreover, considering the “economy” and “safety” of equipment comprehensively will be conducive to the formulation of technical reform and overhaul strategy.

Challenges of Accurate Measurement of Distorted Current and Voltage in the Power Grid by Conventional Instrument Transformers

Power grids are a combined system where the electrical energy produced by the power plants is transmitted to consumers. This forms a specific interdependence where the recipients have a significant impact on the power quality. Therefore, the nonlinear loads connected by households and industrial customers cause current and voltage distortion in the power networks. This creates the need for accurate measurement of nonsinusoidal voltage and current composed not only from the fundamental component but also containing higher harmonics, interharmonics, and subharmonics. In order to ensure high transformation accuracy of distorted current and voltage, the inductive instrument transformers have to be tested in these conditions. Many papers describe their behavior during the transformation of sinusoidal current or voltage. Nowadays, the scientific field in this scope is focused on the evaluation of their exploitation properties for distorted signals. The common problem of inductive instrument transformers is the self-generation of low-order higher harmonics to the secondary current or voltage. In the case of the inductive VTs, an additional problem results from the resonance caused by the parasitic capacitance of the primary winding. The proposed solutions to compensate for the values of current or voltage errors and phase displacement of inductive instrument transformers are also analyzed.

A High Frequency Multiphase Modular Hybrid Transformerless DC/DC Converter for High-Voltage-Gain High-Current Applications

In order to meet the demands of desirable efficiency, transformerless DC/DC equipment with great voltage step-down are inevitable needed. This research offers a unique type of high-frequency, high-voltage-gain DC/DC converter, which comprises a switched capacitor (SC) converter and a buck converter. Thanks to the transformation of a two-stage converter to a single-stage converter, it has a considerable ratio of step-down voltage transformation and a reasonable duty cycle. In addition, it can permit low voltage stress on the switches. The simple control method and easy driving circuit implementation makes it scalable for high-power-level devices. Low cost can be realized as fewer components are needed. Under all operational circumstances, total soft-charging and low equipment voltage stresses are accomplished. Compared to those classic high-voltage-gain converters, the proposed converter exhibits merits of higher efficiency, higher flexibility, lower ripples, and lower costs. A comprehensive analysis is carried out for the converter’s steady-state operations. With a 1 MHz switching frequency, a 900 W prototype of a 20-time converter is constructed, with a peak efficiency of 92.5%. Simulations and experiments verify the effectiveness of the theoretical investigation of the converter’s operation.

An asynchronous interrupt driven sampling technique for a practical monitoring system of power-line single-phase voltage and current signals

<span lang="EN-US">A practical monitoring system implementing an asynchronous interrupt driven sampling technique has been developed in this research. This system is intended to acquire power-line single-phase voltage and current signals as well as their related information such as RMS values and harmonic contents. The system uses a voltage transformer and a current transducer to acquire the signals of the voltage and current. A microcontroller is used in the system to perform acquisition processes, calculation, and wireless data transmission. The design activities include the development of hardware of the system and software in the microcontroller as well as monitoring software with Bluetooth technology that will run on portable devices. As part of the research, a new sampling technique was developed to provide constant and precise timings during the acquisition processes. In this technique, some peripherals related to the acquisition process were driven asynchronously using interrupt mechanisms. Some experimentation has been carried out, and the result showed that the system implementing this technique could successfully manage the timings for the synchronous acquisition sequences. Furthermore, the use of the Bluetooth interfaces in the system allowed practical monitoring process to be performed using portable devices.</span>

Research on Harmonic Transfer Characteristics of Capacitive Voltage Transformer and Design of Testing Device

Capacitive voltage transformers (CVTs), as the main voltage detection devices in the power grid, can accurately measure power frequency voltage, but CVT’s measurement of harmonic voltage will pass errors, resulting in CVT cannot accurately monitor the harmonic voltage in the power grid. Based on the current status of CVT, this paper studies the structure of CVT and the harmonic voltage transfer characteristics of CVT, and analyzes the frequency characteristic curve of CVT by using MATLAB simulation. Based on the study of the CVT frequency characteristic curve, this paper proposes a method of series voltage divider capacitor C3 at the ground terminal of CVT low voltage capacitance to indirectly measure the harmonic voltage on the primary side of CVT and verifies the accuracy of this method. Finally, this paper presents a preliminary design scheme for the series capacitor voltage division method.

Acceleration of distance protection second zone: A non-pilot method based on the healthy phases data

Nowadays, power systems are operated closer to their stability margins and therefore, the need for faster protection algorithms is escalated. The second zone of distance protection is conventionally set to operate with some lengthy delay, which increases the fault clearing time for the end part of the protected line. Therefore, the acceleration of zone-2 for internal faults can remarkably increase the speed of line protection. This practice is traditionally performed by pilot protection systems, which rely on communication channels. This paper proposes a new non-pilot solution to this challenge using only local measurements. A phasor-based algorithm is proposed to detect the remote circuit breaker operation (RCBO) using the healthy phases data. The proposed method has been developed for both single- and three-pole circuit breaker (CB) mechanisms, which makes it practical for transmission and sub-transmission lines. Thanks to using the healthy phases data, the proposed method is immune to the current transformer saturation and capacitor voltage transformer transients. The performance of the proposed method is simulated and investigated in various critical situations besides some experimental tests. The obtained results approve the efficiency and robustness of the proposed method for different scenarios, e.g. noisy conditions, evolving faults, and parallel lines.

Voltage to Calcium Transformation Enhances Direction Selectivity in Drosophila T4 Neurons.

An important step in neural information processing is the transformation of membrane voltage into calcium signals leading to transmitter release. However, the effect of voltage to calcium transformation on neural responses to different sensory stimuli is not well understood. Here, we use in vivo two-photon imaging of genetically encoded voltage and calcium indicators, ArcLight and GCaMP6f, respectively, to measure responses in direction-selective T4 neurons of female Drosophila Comparison between ArcLight and GCaMP6f signals reveals calcium signals to have a significantly higher direction selectivity compared with voltage signals. Using these recordings, we build a model which transforms T4 voltage responses into calcium responses. Using a cascade of thresholding, temporal filtering and a stationary nonlinearity, the model reproduces experimentally measured calcium responses across different visual stimuli. These findings provide a mechanistic underpinning of the voltage to calcium transformation and show how this processing step, in addition to synaptic mechanisms on the dendrites of T4 cells, enhances direction selectivity in the output signal of T4 neurons. Measuring the directional tuning of postsynaptic vertical system (VS)-cells with inputs from other cells blocked, we found that, indeed, it matches the one of the calcium signal in presynaptic T4 cells.SIGNIFICANCE STATEMENT The transformation of voltage to calcium influx is an important step in the signaling cascade within a nerve cell. While this process has been intensely studied in the context of transmitter release mechanism, its consequences for information transmission and neural computation are unclear. Here, we measured both membrane voltage and cytosolic calcium levels in direction-selective cells of Drosophila in response to a large set of visual stimuli. We found direction selectivity in the calcium signal to be significantly enhanced compared with membrane voltage through a nonlinear transformation of voltage to calcium. Our findings highlight the importance of an additional step in the signaling cascade for information processing within single nerve cells.

Hardware-in-the-Loop Implementation of ROMAtrix, a Smart Transformer for Future Power Grids

The evolution of power generation brings about extensive changes in other parts of the grid, especially in the transmission and distribution components. Within the scope of the Internet of Energy (IoE), electric power flows more flexibly between different parts of the grid. DC power will play an essential role in IoE. Decentralized photovoltaic panels, energy storage, electric vehicle charging stations, and data centers are some of the significant components of future grids dealing with DC power. As a result, power transformers must be appropriately modified to manage power among the different parts of the grid. A power electronic transformer (PET), also known as a solid-state transformer (SST) or smart transformer (ST), is a solution enabling a power grid to deal with this growing complexity. ROMAtrix, as a matrix-converter-based ST, is a developing project targeting future power grids. ROMAtrix realizes the application of a medium voltage (MV) transformer using commercially available power electronic semiconductors. Due to the distinctive features of ROMAtrix and a high number of switches, the implementation of the control system using a single control board is highly demanding. This paper aims to illustrate the implementation, on a field-programmable gate array (FPGA), of pulse width modulation (SVMPWM) applied to the ROMAtrix, considering specific switching patterns. The proposed switching procedure was simulated with PLECS and validated with the hardware-in-the-loop using the OPAL-RT solver.

Transmission Line Voltage Calibration-Free Measurement Method

Voltage sensing technology is crucial in realizing distributed voltage sensing at critical nodes of the power grid and providing key state variables to provide information support for control decisions. Among the existing voltage measurement methods, voltage transformers have problems such as high insulation performance requirements and limited installation locations. However, non-contact voltage sensors designed based on the electric field coupling principle have sensor accuracy problems due to the instability of the coupling capacitance. Based on the above problems, this paper first proposes a floating ground measurement system based on an equipotential and differential structure. It also proposes a dual capacitance equivalent model for AC voltage measurement on transmission lines. Based on this method, a calibration method for the amplitude and phase of the sensor is built. Under the voltage test at 50 Hz operating frequency in the voltage range (100–300 V), the maximum relative error of the voltage amplitude is 0.89%, and the maximum relative error of the voltage phase is 0.68°. The maximum relative error of voltage amplitude under a 50 Hz operating frequency voltage test in the voltage range (600 V–10 kV) is 4.48%. In the final scenario adaptation analysis, the method’s specific height amplitude accuracy error was experimentally verified to be 0.88%, with a maximum difference of 0.52% for multi-type conductor testing.

Research on Suppression of Fuses of Potential Transformer Fuse

In this paper, through the analysis of an electromagnetic Potential Transformer (PT) fuse fault in the distribution network, it is found that the cause of this type of fault is the low-frequency oscillation and inrush current of the voltage transformer caused by the disturbance, and its occurrence mechanism is studied and explained. After analyzing the advantages and disadvantages of the common PT fuse-blowing fault control measures, this paper proposes a treatment plan for the PT neutral point to suppress the fuse blowing through a nonlinear flow-sensitive harmonic elimination device. The harmonic device has a remarkable suppression effect on the PT fuse blown fault.

A CVT Parameter Identification Method Based on Improved Grey Wolf Optimizer

Aiming at the problem that harmonic simulation model parameters of capacitive voltage transformer (CVT) are difficult to determine, an identification method of equivalent circuit parameters of CVT is proposed. By studying the frequency response, a nonlinear equation about the equivalent circuit parameters of CVT is established. By analyzing the characteristics of the equation and combining with the actual use, an improved grey wolf optimizer is applied to achieve the accurate identification of the key parameters of CVT. On the basis of grey wolf optimizer, the algorithm introduced a good point set and comprehensive dimension learning strategy to prevent the algorithm from falling into local optimum, and modified the convergence factor according to the actual needs to improve the convergence accuracy. Finally, three numerical examples are simulated by MATLAB/Simulink software, which proves the feasibility and superiority of the proposed method in CVT application.

Design and key technology of the energy consumption management system for the liquid cooling data center

AbstractIn view of the serious problem of energy consumption waste in the application process of liquid cooling data center, a new energy consumption management system of liquid cooling data center is constructed in this research. Energy consumption predictor, resource controller and resource configurator are used to monitor and manage energy consumption and optimize resource allocation of liquid cooling data center. The S3C2440A microprocessor with the internal core of ARM920T is adopted as the core controller of the energy consumption data collection system, and the energy consumption sampling circuit is designed with the voltage transformer and the current transformer, and attenuation network is adopted to prevent frequency aliasing in data sampling. Particle swarm optimization algorithm is used to identify the parameters in the model estimator, and the resource coordinator is used to solve the power consumption and the performance models. When using multiple physical servers to simulate the data center environment, the experimental structure shows that the system in the research can control the overall energy consumption of the server within 260 W, and the prediction error of the model estimator is kept lower than 2.4%.