Electronic Instrument Transformers Research Articles

Trends in Measuring Instrument Transformers for Gas-Insulated Switchgears: A Review

Voltage and current measurements in high-voltage substations are fundamental for stable operation. Conventional instrument transformers (ITs) face challenges in gas-insulated switchgears (GISs), such as size, weight, accuracy limitations, and behavioral instability at abnormal voltages and currents. Non-conventional instrument transformers (NCITs) have emerged to address these issues, complying with International Electrotechnical Commission (IEC) standards and providing millivolt-level signals, enabling downsizing of GIS bays. The transition to digital substations, as mandated by IEC 61850-9-2, requires a shift from the conventional 110 V/5 A outputs to levels ranging from millivolts to volts. Electronic instrument transformers (EITs), compliant with the IEC 60044-7 and 8 standards, offer alternatives to conventional ITs with smaller sizes and wider frequency ranges. However, issues remain with EITs, including limited adoption, the necessity of separate power sources, and susceptibility to electromagnetic interference. Recent standards, transitioning to IEC 61869, focus on low-power instrument transformers (LPITs). Low-power voltage transformers (LPVTs) and low-power current transformers (LPCTs), designed with passive components, present potential solutions by directly connecting to merging units (MUs) for digital signal transmission. This review outlines the current status of various IT standards, covering conventional ITs, EITs based on IEC 60044-7 and 8, and LPITs based on IEC 61869-10 and 11. Advancements in sensor technology relevant to these standards are also explored. The paper provides insights into the evolving landscape of instrument transformers, addressing challenges and offering potential pathways for future developments in digital substations.

Validation of a Simplified Method for Estimating the Harmonic Response of Rogowski Coils with the Monte Carlo Method.

The need to monitor the power network is leading to a significant increase in the number of measurement points. These points consist of intelligent electronic devices and instrument transformers (or more in general sensors). However, as the number of devices increases, so does the demand for their characterization and testing. To this end, the authors formulated a new characterization procedure that offers numerous benefits for manufacturers and system operators. These benefits include: (i) reducing testing time (thus lowering costs), (ii) simplifying the existing procedures, and (iii) increasing the number of tested devices. In this study, to complete the validation of the proposed characterization procedure, the authors performed a comprehensive uncertainty evaluation. This included the identification and analysis of the uncertainty sources, the implementation of the Monte Carlo method to obtain the statistical parameters of the quantities of interest, and the final method assessment according to the obtained results. Each step is described in detail, and the results allow one to (i) replicate the uncertainty analysis on other types of instrument transformers and (ii) implement the proposed harmonic characterization procedure with the confidence that the method is accurate, flexible, and scalable.

Многофакторное автоматизированное исследование методов определения места повреждения на модели воздушной линии электропередачи 500 кВ

Fault location is one of the main means of automation of electric power on overhead power lines. Well-timed elimination and organization of maintenance and repair work to put power lines into operation require high accuracy of fault location. Fault location methods based on the parameters of emergency mode using data of electronic (digital or optical) instrument transformers have been developed in Ivanovo State Power Engineering University (ISPU). The use of electronic transformers makes it possible to reduce the instrumental error of fault location due to accurate measurements of electrical quantities during short circuit, including the measurement of the derivative of the primary current. The aim of the study of fault location methods developed by the ISPU team is to evaluate the errors of these methods with a variation of many factors affecting the calculation of fault location in an automated mode using modern modeling tools. A multifactorial automated research of the fault location methods is carried out using a simulation model of an ultra-high voltage network in the Matlab + Simulink software package. One-sided and two-sided fault location methods based on the parameters of emergency mode developed in ISPU are chosen as the studied methods. In the research methodology presented in the article, the values of the factors affecting the measurement of fault location, including the parameters of the network element models, are changed using a program in the MATLAB language with parallel calculations performed on different processor cores. A technique for automated research of fault location methods has been developed including a model of an ultra-high voltage electrical network in Simulink and a simulation model control program in Matlab. More than 100,000 computational experiments have been carried out for each fault location method. According to the study, the influence of transient resistance is excluded, and the influence of the network frequency is practically absent in the two-sided method. The change in the parameters of power transmission lines and equivalent systems is less affected in comparison with the one-sided method. The Monte Carlo method of fault location algorithms has shown that the errors of one-sided method do not meet the requirements of PJSC «FGC UES» standards in less than 20% of cases, and the errors of the two-sided method under the same modeling conditions do not meet the requirements only in 1% of cases. The developed research methodology makes it possible to evaluate the accuracy of fault location methods when changing the set of factors influencing the measurement in an automated mode. The carried-out research of one-sided and two-sided fault location methods based on emergency mode parameters and data of electronic transformers has showed sufficient accuracy on the model of a 500 kV overhead power transmission line with changes in individual factors affecting the measurement of fault location and when randomly setting a set of parameters of the network model.

Research on Self-Adaptive Algorithm of Transient Performance Analysis for DC Electronic Instrument Transformer Calibration

DC electronic instrument transformers (DCEIT) are widely used in the voltage source converter based high voltage direct current transmission (VSC-HVDC) system to measure the bus voltage or current, and should be of accurate and quick transient response. The transient performance of the DCEIT need to be calibrated using a calibrator. The existing schemes are difficult to recognize different transient step responses automatically, and usually require human intervention, which limits their flexibility and applicability. Besides, the accuracy of the calculated results is affected by human factors. A self-adaptive algorithm of transient performance analysis is proposed. It recognizes the characteristics of the transient step response based on wavelet analysis, and distinguishes the steady-state and step intervals automatically. Then it evaluates and finds the stable data segments in the steady-state intervals adaptively to calculate the high and low steady-state values. Finally, the data in the step interval are interpolated to search the feature points of the waveform, and then the transient response parameters are calculated according to the coordinates of feature points. In the validation stage, six kinds of step response waveforms are generated by MATLAB to test the performance of the proposed algorithm. Compared with the boundary window method, the proposed algorithm could recognize the characteristics of the tested waveforms automatically and achieve a more accurate analyses of transient performance. In addition, a calibrator prototype based on the proposed algorithm is developed, and some tests are carried out at the National Center for High Voltage Measurement (NCHVM) in China, whose results verify the feasibility of the algorithm.

Toward the Standardization of Limits to Offset and Noise in Electronic Instrument Transformers.

The scenario of instrument transformers has radically changed from the introduction of the Low-Power version, both passive and active. The latter type, typically referred to as Electronic Instrument Transformers (EITs), has no dedicated standard within the IEC 61869 series yet. To this purpose, in the authors’ opinion, it is worth understanding how the limits of typical disturbances affecting EITs should be standardized. In particular, after a brief review of the standards, the work presented a mathematical approach to determine the sources of signal disturbances influence, which affect the rms value, on the ratio error. From the results, we discussed that the emergence of disturbances generated within the EIT is a critical aspect to be studied with data of typical off-the-shelf devices. Therefore, to guarantee a correct operation of the devices, a proper standardization of the sources of disturbance should be provided.

A New Online Temperature Compensation Technique for Electronic Instrument Transformers

Electronic instrument transformers are expected to play a significant protection and control role in the future smart grids. This paper aims at improving the performance and accuracy of electronic instrument transformers that are replacing the conventional current and potential transformers in the future digital substations. One of the main issues associated with the electronic instrument transformer is its poor thermal stability that affects the accuracy of the measurements. In this paper, to overcome this issue, a new wireless temperature measurement and compensation technique is proposed. In this technique, the operating temperature of the electronic transformer is continuously monitored and its impact on the measurements is compensated in real-time. The experimental results reveal that the proposed technique can effectively improve the thermal stability and measurement accuracy of the electronic instrument transformers.

Research on the Influence of Sampling Frequency on Energy Measurement Precision of Electronic Instrument Transformer

Digital metering system, the electronic energy meter analog-to-digital conversion sampling function moved to the electronic instrument transformer, and electronic instrument transformer sampling frequency compared with the electronic energy meter is low, the sampling frequency will be insufficient in the analog-to-digital conversion process Introduce quantization error. In this paper, the measurement error model of electronic instrument transformer based on analog-to-digital conversion sampling principle is established, and the influence of sampling frequency on energy measurement error is quantitatively analyzed. The analysis shows that the accuracy of electronic instrument transformer measurement is related to oversampling rate.

Development of Simulated Disturbing Source for Isolation Switch

In order to simulate the substation in the actual scene of the harsh electromagnetic environment, and then research on electromagnetic compatibility testing of electronic instrument transformer, On the basis of the original isolation switch as a harassment source of the electronic instrument transformer electromagnetic compatibility test system, an isolated switch simulation source system was developed, to promote the standardization of the original test. In this paper, the circuit breaker is used to control the opening and closing of the gap arc to simulate the operating of isolating switch, and the isolation switch simulation harassment source system is designed accordingly. Comparison with the actual test results of the isolating switch, it is proved that the system can meet the test requirements, and the simulation harassment source system has good stability and high reliability.

FPGA-based Adaptive Phase-shift Compensation Method for Electronic Instrument Transformers

Accurate and reliable instrument transformers play an important role in power system measurement and protection. This paper focuses on the phase accuracy of electronic instrument transformers and presents an adaptive phase-shift compensation method for measuring electronic current transformers. Different from the existing approaches in which the empirical evaluation and fixed phase-shift compensation are used, the proposed method measures the phase displacement in real-time and calibrates the corresponding phase error adaptively, with the aim of achieving high and reliable phase accuracy. In particular, several practical factors are considered in the design, such as the phase displacement composition, phase error uncertainty, synchronous mode diversity, and computational complexity and latency. The proposed method is developed in a field-programmable gate array platform with low-latency hardware implementation and further employed in a merging unit. Finally, the experimental results are provided to demonstrate the validity of the proposed method.

Transient Electromagnetic Disturbance Induced on the Ports of Intelligent Component of Electronic Instrument Transformer Due to Switching Operations in 500 kV GIS Substations

Switching operations in gas-insulated switchgear (GIS) substations generate transient electromagnetic fields in the GIS pipes. These fields leak out discontinuities of the GIS and induce electromagnetic disturbance voltages on the cables and ports of secondary circuits. In smart GIS substations, secondary devices especially, such as the intelligent component of electronic instrument transformer, are vulnerable to electromagnetic interference. In this paper, the disturbance voltages induced on the ports of intelligent component of electronic instrument transformer had been measured in three 500-kV GIS substations, respectively. The disturbance was generated either during disconnector (DS) switching operations or circuit breaker (CB) operations. Then, the time-domain and frequency-domain characteristics of the disturbance waveforms have been analyzed. The micro-pulses of disturbance voltages have been extracted from the raw data. The waveform parameters, including peak voltage, rise-time, dominated frequency, and duration, have been calculated by the statistical analysis. The comparison between disturbance during DS switching operations and that of CB operations has been made. Also, the differences and similarities of disturbances between the three GIS substations have been displayed. Furthermore, the differences between measured waveforms and the IEC 61000-4-18 immunity test standard waveform have been discussed.

数字式检测装置相位误差量值溯源方法研究

当前智能变电站中大量使用电子式互感器与合并单元等智能设备，用于检测这些智能设备的主要有电子式互感器校验仪以及合并单元测试仪等。这些设备的准确度特性可使用电子式互感器校验仪整体检测装置对其进行检测，但该检测装置的准确度，特别是相位准确度尚无有效的方法溯源到现有的标准量值，导致现场运行的智能二次设备的量值溯源体系不完整，无法应用于电量的贸易结算。针对此情况，本文提出了一种用于校准数字式检测装置相位准确度的方法，该方法与现有基于数字微差源的方法相比，具有简便可行并可溯源的特点。该方法可将智能设备的相位准确度最终溯源到时间标准，完善了量值溯源体系，为智能设备科学准确的用于电能贸易结算提供技术依据值。 Electronic instrument transformers (EIT) and merging units (MU) are widely utilized in the smart substations, and EIT testers and MU testers are used to test the accuracy of EITs and MUs. The EIT tester calibrator can calibrate the accuracy of the equipment. However, the accuracy of calibrator, especially the phase accuracy, cannot be traced to the existing standards due to the lack of appropriate method, thus causing the incompleteness of the accuracy tracing system. Therefore, the EITs and MUs running in the smart substations cannot be used as electric power measurement equipment. In order to solve this problem, a method to calibrate the phase accuracy of the digital equipment is proposed in this paper. Compared to the currently used method based on digital micro-difference source, this method can trace the phase accuracy of EITs and MUs to a precise time standard. This method provides the technical basis for the smart equipment’s utilization as metrological devices.

The Research of Electronic Transformer Data Synchronization Method Based on Newton Interpolation

Data synchronization of electronic instrument transformer is introduced. Synchronization method commonly used are analyzed in aspects of their advantages and disadvantages, such as interpolation synchronization, impulsive synchronization method; Then, a new approach based on Newton interpolation is presented, and the simulation and error analysis are given. The theoretical analysis results show that this method can reach to the same precision with Lagrange interpolation which is accurate in synchronization of harmonic components and obtain the synchronized data fast. Finally this paper sets equal interval sampling and non-equal interval sampling data, and then calculates maximum error in the case of the steady state and transient state respectively by using Matlab. The simulation results proved the feasibility of this method and its engineering practical value.

Hierarchical protection control system of smart substations

This paper analyzes the problems of the relay protections and secondary circuits of traditional substations, and introduces the hierarchical protection and control system of smart substations based on the technologies like IEC 61850 Standard, electronic instrument transformer, process level network, and wide area optical fiber communication network, etc. The hierarchical protection and control system includes three levels: local area protection, substation area protection and control, and wide area protection and control. These three levels are combined to solve the problems of the relay protections in traditional substations, thus improving protection performance and control capability of the system.

A Method for Measurement Traceability of Calibrator for Electronic Instrument Transformer Tester

The bottleneck of the measurement traceability system of electronic instrument transformer is the calibrator, which is based on the digital micro-differential source principle and plays the role as intermediate between digital values in data frames and the analog output of the existing standard current transformer (CT) or voltage transformer (VT). A kind of working mechanism of the calibrator for electronic instrument transformer tester and related calibration method are proposed in this paper. The ratio accuracy can be calibrated by the high-precision multimeter and the phase accuracy can be calibrated by the high-speed oscilloscope, which records the waveforms of analog output and the synchronization signal, and the time offset between them can be traced to the time standard. A calibrator is designed and manufactured according to the mechanism and related experiments are conducted to verify the feasibility of the calibration method.

An On-Site Calibration System for Electronic Instrument Transformers Based on Labview

Abstract Electronic voltage transformers (EVT) and electronic current transformers (ECT) are important instruments in a digital substation. For simple, rapid and convenient development, the paper proposed an on-site calibration system for electronic instrument transformers based on LabVIEW. In the system, analog signal sampling precision and dynamic range are guaranteed by the Agilent 3458A digital multimeter, and data synchronization is also achieved based on a self-developed PCI synchronization card. To improve the measurement accuracy, an error correction algorithm based on the Hanning window interpolation FFT has good suppression of frequency fluctuation and inter-harmonics interference. The human-computer interface and analysis algorithm are designed based on LabVIEW, and the adaptive communication technology is designed based on IEC61850 9-1/2. The calibration system can take into account pairs of digital output and analog output of the electronic voltage/current transformer calibration. The results of system tests show that the calibration system can meet the requirements of 0.2 class calibration accuracy, and the actual type test and on-site calibration also show that the system is easy to operate with convenience and satisfactory stability.

Performance Analysis of IEC 61850 Sampled Value Process Bus Networks

Process bus networks are the next stage in the evolution of substation design, bringing digital technology to the high-voltage switchyard. Benefits of process buses include facilitating the use of nonconventional instrument transformers, improved disturbance recording and phasor measurement, and the removal of costly, and potentially hazardous, copper cabling from substation switchyards and control rooms. This paper examines the role a process bus plays in an IEC 61850-based substation automation system. Measurements taken from a process bus substation are used to develop an understanding of the network characteristics of “whole of substation” process buses. The concept of “coherent transmission” is presented, and the impact of this on Ethernet switches is examined. Experiments based on substation observations are used to investigate in detail the behavior of Ethernet switches with sampled value traffic. Test methods that can be used to assess the adequacy of a network are proposed, and examples of the application and interpretation of these tests are provided. Once sampled value frames are queued by an Ethernet switch, the additional delay incurred by subsequent switches is minimal, and this allows their use in switchyards to further reduce communications cabling, without significantly impacting operation. The performance and reliability of a process bus network operating close to the theoretical maximum number of digital sampling units (merging units or electronic instrument transformers) was investigated with networking equipment from several vendors and has been demonstrated to be acceptable.

Analysis of Key Factors Affecting Electronic Transformer Calibration System Error

Recently, electronic instrument transformers (EIT) meet some problems such as high error and instability in practical application, and some new EITs and the calibration system of electronic instrument transformers (CSEIT) are attracting wide concern. In this paper, some key factors affecting CSEIT error, including sampling synchronization, digital signals processing and error estimation of the calibration system itself, are analysed, and the corresponding solutions are also offered. Sampling synchronization is realized by outputting second pulse and trigger pulse at the same time, and the length of pulses response has been controlled in a short period. Digital signal processing synthesizes some special design such as FIR digital filter, industrial frequency measurement and zero-phase filter to overcome the effects of harmonics and noise, and uses FFT interpolated algorithm based on Hanning window to eliminate the calculation error when fundamental frequency spectrum leakage happens. A novel error estimation scheme of CSEIT is proposed based on the instruments with lower measuring error. Results of the error estimation of the CSEIT itself show that the system can reach the error of 0.01 % in magnitude and 30 second in phase at rated operation state.DOI: http://dx.doi.org/10.5755/j01.eee.19.5.1674

Analysis and Application of Electronic Instrument Transformer in Digital Substation

Electronic transformer Manager nature is a will simulation volume transformation for digital volume of device, they will simulation of current and the voltage signal in as possible near signal source of local used most has price of reliable way will its transformation for digital volume, electronic type transformer Manager and merged unit as digital substation of component, and traditional transformer Manager compared to has insulated simple, and dynamic range wide, and anti-saturated performance strong, and Advantages of data output. combined digital substation with IEC61850 in the text, examined issues such as data synchronization of electronic instrument transformers, made recommendations on engineering practice.

Research of Phase Compensation Technology in Electronic Instrument Transformer

Introduces the analog phase compensation technology used in electronic instrument transformer, put forward a method of digital phase compensation in electronic transformer and carries out in the 220KV electronic instrument transformer measurement system, the resolution ratio of the phase compensation is 1 second and the maximum range of the phase compensation is 270 second, which can meet the phase adjustment of electronic instrument transformer; compares the analog compensation technology and digital phase compensation technology, analyzes their characteristics and different applications.

Electronic Voltage and Current Transformers Testing Device

A method for testing electronic instrument transformers is described, including electronic voltage and current transformers (EVTs, ECTs) with both analog and digital outputs. A testing device prototype is developed. It is based on digital signal processing of the signals that are measured at the secondary outputs of the tested transformer and the reference transformer when the same excitation signal is fed to their primaries. The test that estimates the performance of the prototype has been carried out at the National Centre for High Voltage Measurement and the prototype is approved for testing transformers with precision class up to 0.2 at the industrial frequency (50 Hz or 60 Hz). The device is suitable for on-site testing due to its high accuracy, simple structure and low-cost hardware.