Electronic Voltage Transformer Research Articles

Error state prediction method for electronic voltage transformer based on empirical mode decomposition and auto-regressive moving average

Electronic voltage transformers have been used in the power system in conjunction with the development of power grid intelligence due to their good insulation structure, economy, volume, and other advantages. However, in its long-term operation, the phenomena of error overshooting and unstable operation will inevitably occur, and the existing periodic off-line testing methods require a high calibration cycle, which is difficult to achieve. To solve these problems, an error state prediction method based on empirical mode decomposition and autoregressive moving average model is proposed. Firstly, according to the physical correlation between the secondary output signal and the error, the output signal is quantified as a statistic Q by the method of principal component analysis, and then the statistic is used as the prediction object to establish a prediction model for predicting the operating state of the electronic voltage transformer. The simulation results show that the model can accurately predict the trend of the transformer error, which meets the prediction requirements.

Metrological support of digital electronic voltage transformers and low-power voltage sensors

Metrological support of digital electronic voltage transformers and low-power voltage sensors

Design of Electronic Voltage Transformer Error Pattern Recognition and Classification Algorithm Based on Data Mining

With the development of smart grids, electronic voltage transformer (EVT) has gradually entered the stage of large-scale applications. Accurately identifying errors in electronic voltage transformers is crucial for the stability of power systems. Strengthening the measurement accuracy of EVT is of great significance for the operation of power systems and measurement and protection devices. However, due to the limitations of traditional verification methods, there are still challenges. To better improve the accuracy of transformer identification, a data-driven method for enhancing transformer error evaluation and prediction was developed. Based on the low accuracy of traditional EVT error verification and the difficulty of monitoring, data mining technology is proposed for EVT error analysis and evaluation. Recursive principal component analysis is used to separate errors from EVT measurement data, and feature statistics are used to monitor its operating status. Then, regression analysis under support vector machines is added to predict errors for active error correction and better evaluation of its status. The evaluation of the transformer monitoring dataset shows that the classification accuracy of error detection of the proposed method exceeds 93%, and the deviation between the predicted error value and the actual error value is less than 0.05%. Compared with methods such as artificial neural networks and ARMA, the average error rate has been reduced by more than 18%. The accuracy and average accuracy of the algorithm proposed in the study exceeded 80%, with values of 96.23% and 85.12%, respectively. The average error of the ratio difference feature of the EVT is only 0.023, and the average error of the angle difference is less than 0.01, which is much smaller than the algorithm used for comparison. The application response time is less than 0.1 s and the evaluation threshold can better identify data anomalies, with high application accuracy. This method can effectively provide real-time evaluation tools for the operational status of electronic voltage transformers and more accurately and proactively identify transformer errors from conventional data. This study provides an important data-driven solution for improving power grid reliability.

Metrological support of digital electronic voltage transformers and low-power voltage transformers

Metrological support of digital electronic voltage transformers and low-power voltage transformers (sensors) is represented. The methods and reference measuring instruments of the State primary special standard of units of the ratio error and the phase displacement of AC electric voltage of power frequency in the range from to and units of electric capacitance and tangent of loss dissipation factor at AC voltage of power frequency in the range from 1 to 500 kV – GET 175-2023, used for metrological support of the measuring instruments mentioned above. The results of research of GET 175-2023 are presented. The expanded uncertainties of GET 175-2023 when reproducing the units of the ratio error and the phase displacement of AC electric voltage of power frequency for metrological support of analog low-power voltage transformers (sensors) include the budget of the uncertainties of the current comparator, low-voltage (reference) and high-voltage measuring measures, the high-voltage MVE-01 bridge (SA7400MA1 amplifi er) and are respectively 9.62·10–5 and The expanded uncertainties of GET 175-2023 when reproducing the units of the ratio error and the phase displacement of AC electric voltage of power frequency for metrological support of electronic digital voltage transformers and digital low-power voltage transformers (sensors) include the budget of uncertainties of the converter «high voltage – current», converter «current – low voltage», converter «low voltage – a digital copy of voltage», a digital comparison device and constitutes 10.8·10–5 and respectively. GET 175-2023 allows solving the problems of metrological support of electronic digital voltage transformers and digital low-power voltage transformers (sensors).

Analyses on an electronic voltage transformer's failure by its resonance with very fast transient overvoltage and suppression

AbstractAs voltage measuring devices are widely used in the high voltage power system with a primary‐secondary‐fusion structure, electronic voltage transformers are directly connected to the primary conductor and would face much more serious electromagnetic environments than general secondary equipment. As a result, they would still experience failures even when general protection measures are adopted to suppress overvoltages' amplitudes. To address this issue, an innovative method is proposed after analyses are conducted on the resonance between a transformer and an overvoltage. Within this method, an air‐cored coil is installed in a transformer to artificially shift its natural frequency and to dodge the high‐frequency dominant component of a transient overvoltage, avoiding the aforementioned resonance and suppressing the secondary overvoltage. In addition, simulations and laboratory tests are conducted to prove this method's validity.

Error Prediction Method of Electronic Voltage Transformer based on Improved Prophet Algorithm

Background: Electronic voltage transformer (EVT) is an essential metering device for future substation automation systems. One of the main drawbacks of EVT is its poor long-term stability, which affects its measurement accuracy. This will, in turn, adversely affect the entire protection and control systems it is employed for. Objective: Aiming at reducing the EVT measurement error over long-term operation, an EVT error prediction method combining Prophet, temporal convolutional network (TCN) and selfattention is proposed in this paper. Methods: The proposed method is based on building prophet and TCN error prediction models to estimate preliminary prediction values. On this basis, self-attention is introduced to further extract features and make full use of the useful information in historical data. Then the secondary prediction can be achieved, and the final predicted value can be reported as an output. Results: The proposed method is validated by applying the error data of an EVT in a substation to its historical operation. The results show that the model can effectively predict the error trend of EVT. Conclusion: The prediction results of this method are similar to the fluctuations of the actual values, indicating that it provides a new reliable method for error prediction of EVT.

Low Power Electronic Voltage Transformer Design and Construction

The use of advanced low-power sensing technologies instead of traditional solutions used in the distribution, measurement and control of the power grid has introduced core instrument transformers due to their physical limitations and other reasons. This situation has also brought about the design of low-power voltage transformers. As can be understood from here, analogue measurement and control systems used in power centres are approaching the end of their useful life. This substations need digital automation solutions and new technologies for more efficient performance. Since no iron core is used in the low-power electronic voltage transformer structure, it is robust against network disturbances such as ferroresonance and ferroresonance formation is not encountered. In this study, a low-power electronic voltage transformer is designed and performed experiments are presented. The most essential feature expected in a voltage sensor is that the conversion rate is precise and unchanging. For this reason, the temperature coefficient and leakage capacitance values of the voltage sensor have been designed to have the lowest margin of error. Performance tests were applied to the voltage sensor using mains frequency endurance, partial discharge, accuracy class, linearity and temperature distribution tests. The results of the performance tests show that it has been successfully applied for the design of a precision voltage sensor with an accuracy class conforming to the IEC 61689-11 standard.

Introduction on Current Application of Voltage Transformer

As an important equipment, voltage transformer is widely used in power grid to obtain voltage signal and protect the system. In this paper, the voltage transformers in power system are classified according to the working principle. The working principle and characteristics of potential transformer (PT), capacitor voltage transformer (CVT), electronic voltage transformer (EVT) and optical voltage transducer (OVT) are briefly analyzed. Besides, this paper also introduces the principle, category and characteristics of voltage transformer, as well as the application and development of voltage transformer in power system.

The traceability method of electronic transformer calibrators based on time series-weighted correlation degree extension integrating Hilbert phase-shift.

The traceability method directly affects the reliability and accuracy of the measurement of electronic transformers. The stability and unreliable traceability performance of analog devices would affect the traditional analog differential method. Thus, we propose a digital differential method combining a time series-weighted correlation degree extension integrating Hilbert phase-shift of four-term continuous third-derivative Nuttall window function, effectively suppressing the end effect problem and realizing the high-precision addition of the differential. Results of simulation experiments showed that the differential's deviation was <10-10, much less than that (1.32 × 10-4) due to the analog differential. The voltage and current ratio difference's combined standard uncertainty was 5.01 × 10-5 and 5.08 × 10-5, respectively, and 0.1718' in the phase error. Finally, an automatic traceability detection system was constructed. Compared with the traditional method, the accuracy and stability of the automatic system were better and could meet the traceability requirements for 0.05-accuracy electronic voltage transformer calibrator.

Construction and Evaluation of an Optical Medium Voltage Transducer Module Aimed at a 132 kV Optical Voltage Sensor for WAMPAC Systems.

This paper reports on the construction and characterization of an optical voltage transducer module for applications in the field of wide-area monitoring, protection, and control (WAMPAC). The optical medium voltage transducer (MVT) module was designed to be combined with a capacitive voltage divider (CVD) to form a voltage sensor intended for 132 kV high voltage (HV) networks. The MVT module comprises a combination of a piezoelectric transducer (PZT) and a fiber Bragg grating (FBG) as a core optical sensing element. Changes in the input voltage across the PZT translate into strain being detected by the FBG. The resultant FBG peak wavelength can be calibrated in terms of the input voltage to obtain a precise voltage measurement. The module was experimentally evaluated in the laboratory, and its performance was assessed based on the requirements specified by the IEC standards for electronic voltage transformers and low power voltage transformers. The results of accuracy tests demonstrate that the MVT module is free from hysteresis, within the experimental error, and is capable of simultaneously meeting the requirements for 0.1 metering and 1P protection classes specified by the IEC 60044-7 and IEC 61869-11 standards.

Energy Harvest System Research for High Precision Electronic Voltage Transformer based on Coupling Capacitance

Energy Harvest System Research for High Precision Electronic Voltage Transformer based on Coupling Capacitance

An improved distance relay based on electronic transformer by using instantaneous value after equal transfer processes

This paper analyses the formation mechanism of the transmission distortion of electronic voltage transformer, and points out that the integrator will magnify the transient transfer error and superimpose the dynamic additional component on the output signal, which may cause the transfer distortion of voltage signal in serious cases. To restrict the electronic transformer transient variable error effect on distance relay, a distance relay method using instantaneous value after equal transfer processes is proposed. It directly uses output differential signals of the capacitor voltage divider and Rogowski coil. The capacitor voltage divider and Rogowski coil are decomposed into several typical variable link in series. The virtual digital transfer link, which is constructed by the digital filter, is used to compensate for the difference parts of the transfer link, so that the voltage and current signals pass through the same transfer link. It can mitigate the influence of voltage and current signal transfer difference on the calculation accuracy of distance relay. The simulation results show that the proposed distance relay method has fast operation speed and is less affected by abnormal voltage and current signal transfer, and its performance is better than existing distance relay methods.

The Principle of Intelligent Switch Composition and Algorithm of the Built-In Electronic Voltage Transformer

With the rapid development of the social economy, people’s demand for energy is increasing. Global warming has made people pay more attention to the importance of energy saving and emission reduction. The power grid is the system responsible for the transmission and distribution of electric energy. Therefore, in the context of energy saving and emission reduction, there are higher requirements for substations in the power grid. For this reason, an intelligent switch with built-in electronic voltage transformer is designed. The concept and key technical characteristics of the electronic voltage transformer intelligent switch are introduced; the overall design scheme of the built-in electronic voltage transformer intelligent switch is expounded; the hardware and software system of the device is designed; the management and control strategy of the design device is such as transformer tangent control, voltage and reactive control; and the operating system is ported. Finally, the simulation test of the system proves that the system has high effectiveness and stability. The research can provide reference for the realization of efficient, economic, stable, safe, and environmentally friendly distribution of power in a power grid.

A quantitative research on the level of disturbance to secondary signal ports of electronic voltage transformers under the operation of gas‐insulated switchgear

The collectors of electronic transformers has the problem of electromagnetic incompatibility under the operation of disconnecting switches, which limits their wide application in smart grids. To evaluate the maximum level of disturbance that collectors are able to withstand in the stochastic process of switching operation, this work introduces a quantitative approach based on limited test measurements, which can quantify the level of disturbance in the signal acquisition ports of electronic voltage transformers (EVT) in different gas-insulated switchgears (GIS). Based on large numbers of experimental statistical data of the true type simulation experimental platform, the Spearman rank correlation coefficient is used to prove that the amplitude of the disturbance voltage pulse at the secondary side port and the breakdown voltage between the primary side fracture approximately satisfy a linear relationship. Subsequently, the quantile regression model is used to quantify and verify the maximum disturbance level of the secondary side port. Moreover, a solution is proposed to tackle the difficulty in obtaining the breakdown voltage at breaks in the GIS substation field applicatvion, under which the quantified maximum disturbance voltage deviation of secondary ports is only −4.34% by comparison. The research work can further explore the practical value of the measured data in a few tests under GIS substation field conditions and provide references for the subsequent revision of EVT-related standards.

Self-Detecting the Measurement Error of Electronic Voltage Transformer Based on Principal Component Analysis-Wavelet Packet Decomposition

The poor long-term stability of measurement error is the main problem in the operation of an electronic voltage transformer (EVT). Prevalent methods of error detection involve calibrating it regularly with a standard voltage transformer, but this is not conducive to the timely detection of the degradation in the error of the EVT. In light of this, this paper proposes a method to self-detect error based on principal component-wavelet packet decomposition. A standard of comparison for error detection is first established based on the characteristics of three-phase symmetrical operation. Principal component analysis is then applied to the measurement data of the three-phase EVTs, and their error is mapped to the online process monitoring of squared prediction error (SPE) statistics. Furthermore, the SPE statistics are decomposed by a three-level wavelet packet to eliminate the influence of the time-varying characteristics of node imbalance on the results of detection. The results of experiments show that the proposed method can detect the measurement error with an accuracy of 0.2 class without a standard.

An online correction system for electronic voltage transformers

As a vital piece of equipment, electronic voltage transformer is widely used in the power system measurements. The current calibration techniques of this asset class exhibit several issues including complex real time implementation. In contrary with existing calibration techniques, this paper proposes a new correction system for electronic voltage transformers, which can be conducted online without causing any interruption to the electricity grid. The new proposed correction system utilizes an SF6 cylinder capacitor and employs an advanced signal processing technique based on the improved Rife frequency shift algorithm. The improved Rife frequency shift algorithm is a combination of the Hanning self-convolution window and the conventional Rife algorithm, which features simple calculation and high accuracy. Results show that the accuracy of the proposed algorithm is higher than the conventional commonly used interpolation algorithms. Compared with the existing traditional calibration techniques, the proposed system features easy online implementation, simple calculation and high accuracy. The robustness of the proposed system is validated through simulation analysis and practical field measurements.

Online Evaluation for the Accuracy of Electronic Voltage Transformer Based on Recursive Principal Components Analysis

The electronic voltage transformer (EVT) has received much attention with the recent global trend to establish smart grids and digital substations. One of the main issues of the EVT is the deterioration of its performance with long-term operation which affects the control and protection systems it is employed for and hence the overall reliability of the power grids. This calls for the essential need for a reliable technique to regularly assess the accuracy of operating EVT in real-time. Unfortunately, traditional calibration methods cannot detect the incipient EVT performance change in real-time. As such, this paper presents a new online method to evaluate the accuracy of the EVT. In this regard, the Q-statistic is calculated based on the recursive principal components analysis (RPCA) using the output data of EVT to map up the changes of metering error on the electric–physics relationship. By employing the output data of the EVT along with the power grid characteristics, the performance of the EVT is evaluated without the need for a standard transformer, as per the current industry practice. Results show that the proposed method can assess the EVT with a 0.2 accuracy class.

Travelling wave fault location principle for hybrid multi-terminal LCC-MMC-HVDC transmission lines based on C-EVT

This paper considers the fault location problem of hybrid multi-terminal high-voltage direct-current (HVDC) transmission systems based on the line-commutated converter (LCC) and modular multi-level converter (MMC). Two issues are addressed in this study: (i) the travelling wave (TW)-based fault location principle and (ii) the method of capturing the high-frequency TW signals. Therefore, a novel TW fault location principle for the hybrid multi-terminal LCC-MMC-HVDC transmission lines is proposed based on the capacitance-divided electronic voltage transformer (C-EVT). Firstly, the TW transfer characteristic of the C-EVT is analyzed. Secondly, a novel TW fault location principle based on the secondary differential voltage TW (D-VTW) is proposed. Finally, a typical ± 400 kV hybrid three-terminal LCC-MMC-HVDC system is used for the case study to verify the high accuracy of the proposed method. Furthermore, its robustness against different fault locations, fault resistances and fault types is also investigated.

Design and Research of 10KV Electronic Transformer Live Performance Evaluation Platform

Design and research a test platform suitable for 10KV electronic voltage transformer and 10KV electronic current transformer for long-term charging performance evaluation. The 10KV electronic transformer live test platform includes a primary boost device, a primary current boost device, a reference voltage transformer, a reference current transformer, a standard voltage transformer and a standard current transformer. The test circuit is designed to be three-phase. Under the condition that the system input voltage is 380V / 220V and the total input capacity is not greater than 100KVA, the auxiliary transformer and other auxiliary equipment are used to achieve long-term live operation and performance evaluation of the 10KV electronic transformer.

Electronic transformer performance evaluation and its impact on PMU

The electronic transformer of smart substations, which transfers primary signals, is important for measurements and controls. In this study, the transformation characteristics of a Rogowski electronic current transformer (ECT) are analysed theoretically. Then, experimental platforms are established to verify the analysis and study the impact of the transformation characteristics of the ECT and an electronic voltage transformer (EVT) on a phasor measurement unit (PMU) using standard test signals. The analysis and the testing results show that this ECT can transfer the phasor well under both steady and dynamic conditions. However, the harmonics introduced by the ECT may lead to the measurement errors of frequency and the rate of the change of the frequency (ROCOF) from the PMU. Therefore, a phasor algorithm with powerful DC offset and harmonics immunity is suggested for PMUs connected to the output of this type of ECT. For the EVT, the ROCOF measurements are easily affected as well. The EVT was also shown to be more sensitive to temperature than the potential transformer (PT).