Electronic Current Transformer Research Articles

Failure Analysis of Electronic Current Transformer Air Chamber Basin Insulator Cracking in a 330 kV Substation

In operation, the combined electrical appliances in the substation leak, and the insulation basin breaks when the old insulation basin is replaced. By using the methods of macroscopic inspection, penetration detection, material analysis, and scanning electron microscopy, the failure analysis of the broken basin insulator of the combined electric apparatus is complete, and the process of crack generation and expansion is analyzed. The analysis results show that the reason for the fracture of the basin-type insulator is uneven force during fastening or disassembling, subjected to shear and bending stress. The crack source starts at the stress concentration part, that is, the root of the groove of the inner ring seal ring, and continues to expand, resulting in the final fracture of the basin-type insulator. The next step is to strengthen the daily control of the transportation process and installation process of the basin insulator.

Field Test Method and Equivalence Analysis of Delay Characteristics of DC Electronic Current Transformer

DC electronic current transformer is the data source of the system control and protection device, so its measurement delay has always been concerned. In this paper, the DC current transformer is modelled equivalently and the key factors affecting the delay of shunt and the remote module are analyzed. A field test method for the delay characteristics of the DC electronic current transformer is proposed. Moreover, a complex multi-state large current generator and integrated test system are developed. On the basis of the IEC 60044-8 standard transmission protocol, the accuracy of standard signal acquisition with the shunt is better than 0.2%. The maximum output current of the established testing system is 600 A. Based on the field test in an actual HVDC project, transient step and various frequency signal components are applied for analyzing.

A comprehensive design method of an active electronic current transformer for stable energy harvesting from power lines

AbstractThe real‐time monitoring technology of power line is an important guarantee for the digitization and intelligence of the modern power system. Traditional current transformers cannot provide continuous and stable energy when the power line current fluctuates in a large range. This paper proposes a comprehensive design method of an active electronic current transformer (AECT) based on a single‐phase full‐bridge voltage‐type PWM rectifier (VSR), which can acquire continuous and stable energy from the power line with a minimum magnetic core. The control of the AECT is divided into four different operation modes to adapt the fluctuation of primary current. Maximum power point tracking (MPPT) mode and minimum loss (ML) mode is designed to harvest the maximum power with lower iron core loss when the primary current is relatively low. Excitation mode and demagnetization mode are designed to harvest stable power when the primary current is higher than a certain current. The specific mode operation principles and control strategies are analysed in detail. Besides, the calculation method of the primary current is also presented for the primary current measurement. Finally, simulations and experiments verify that the iron core can obtain power steadily (9.91 W/kg) when the current fluctuation between 50 and 600 A.

Error Model and Forecasting Method for Electronic Current Transformers Based on LSTM

Error Model and Forecasting Method for Electronic Current Transformers Based on LSTM

Study on harmonic metering characteristics of Rogowski coil current transformer

This paper introduces the harmonic requirements of a power system transformer and the principle of the Rogowski coil electronic current transformer, summarizes the simple and practical methods for harmonic measurement of the Rogowski coil electronic current transformer, and conducts harmonic measurement of the electronic current transformer through high-precision harmonic source and standard current transformer and transformer calibrator. The results show that this method has strong applicability and simple operation, which greatly enriches the harmonic measurement methods.

The Performance of Electronic Current Transformer Fault Diagnosis Model: Using an Improved Whale Optimization Algorithm and RBF Neural Network

With the widely application of electronic transformers in smart grids, transformer faults have become a pressing problem. However, reliable fault diagnosis of electronic current transformers (ECT) is still an open problem due to the complexity and diversity of fault types. In order to solve this problem, this paper proposes an ECT fault diagnosis model based on radial basis function neural network (RBFNN) and optimizes the model parameters and the network size of RBFNN simultaneously via an improved whale optimization algorithm (WOA) to improve the classification accuracy and robustness of RBFNN. Since the classical WOA is easy to fall into a locally optimal performance, a hybrid multi-strategies WOA algorithm (CASAWOA) is proposed for further improvement in optimization performance. Firstly, we introduced the tent chaotic map strategy to improve the population diversity of WOA. Secondly, we introduced nonlinear convergence factor and adaptive inertia weight to enhance the exploitation ability of the WOA. Finally, on the premise of ensuring the convergence speed of the algorithm, we modified the simulated annealing mechanism in order to prevent premature convergence. The benchmark function tests show that the CASAWOA outperforms other state-of-the-art WOA algorithms in terms of convergence speed and exploration ability. Furthermore, to validate the performance of ECT fault diagnosis model based on CASAWOA-RBFNN, a comprehensive analysis of eight fault diagnosis methods is conducted based on the ECT fault samples collected from the detection circuit. The experimental results show that the CASAWOA-RBFNN achieves an accuracy of 97.77% in ECT fault diagnosis, which is 9.8% better than WOA-RBF and which shows promising engineering practicality.

A Novel Current Transformer Based on Virtual Air Gap and its Basic Measuring Characteristics

If current transformer (CT) is saturated in operation, it will lead to incorrect current measurements and may cause relay maloperation, which can greatly threaten the safety of power grid. This paper analyzed the basic measuring characteristics of the proposed novel current transformer based on virtual air gap. This method can successfully compensate the distorted secondary current and expand the measuring range. Based on the simplified magnetization curve model, its working state is divided into linear working state, partially saturated working state and saturated state. Furthermore, its basic measuring characteristics are deducted theoretically. The theory is verified by FEM simulation results and prototype experiments. The difference between this method and other methods is also discussed. Compared with CT, this method adopts partial-gapped magnetic core and magnetic field sensor (MFS) for current reconstruction. When it works in rated state, this method is like a normal CT. Once the primary current saturated the small section core, it will be like a virtual gap, making the whole core more difficult to saturate and allowing the measurement of leakage flux. It has the advantages of simple and compact structure and can be embedded into the electronic current transformer (ECT) system. In this sense, it can have a good application prospect. The main limitation is the requirement of high permeability material for accuracy performance.

Operation of the Electronic Current Transformer for Transformation of Distorted Current Higher Harmonics

This paper evaluates an electronic current transformer’s wideband accuracy in the transformation of distorted current harmonics. The tests were performed in the range of frequencies from 50 Hz to 5 kHz. The utmost importance was dedicated to the transformation of the low-order higher harmonics. The novelty of this paper involves the analysis of the self-generation of the third and fifth higher harmonics caused by the nonlinearity of magnetic core magnetization characteristics. Therefore, what is considered new in this investigation is that this phenomenon has a significant influence on values of current errors and phase displacements despite the presence of the operational amplifiers and the Hall sensors in the output circuits. Another important factor to consider is the influence of the RMS value of the primary current and output load of the ECT on wideband accuracy. To show the backgrounds of the performed laboratory studies, we also discuss the operation principles of the ECTs with closed and open feedback loops. The accuracy of the tested ECT deteriorated—as with the inductive CT—by the self-generation phenomenon. This resulted in rapid changes in the values of current errors and phase displacements determined for the low-order higher harmonics.

Research on the performance of a fiber optical current transformer for high voltage filtering capacitor unbalanced current measurement

Subject of study. A fiber-optic measurement scheme for the unbalanced current of a high-voltage filtering capacitor is proposed, where an all-fiber temperature sensor based on temperature birefringence is presented to realize the real-time correction of temperature errors. Method. Prototypes of an all-fiber filter unbalanced fiber optical current transformer type and a magneto-optical crystal type with a rated current of 1 A and a rated voltage of 258 kV have been developed and performance tested. Main results. After temperature correction, the accuracy of the all-fiber filter unbalanced fiber optical current transformer type in the range of −40∘C to 70°C meets the error limit requirements of class 0.2 specified in the Chinese Standard GB/T 20840.8-2007 (Instrument transformers—Part 8: Electronic current transformers standard), whose accuracy, integration, reliability, and anti-interference ability are better than the magneto-optical crystal type. The proposed scheme has the ability of small current (less than 20 mA) measurement in high voltage (more than 110 kV) scenarios.

Electronic Current Transformer Defects Statistical Analysis of Intelligent Substation

In order to master operation status of the electronic current transformer(ECT), application investigation and defects statistical analysis were conducted on ECT of 110(66)kV~1000kV applied in smart substation of the State Grid Corporation of China(SGCC). The defect location, defect cause and defect type of ECT with different principles are analyzed. The results indicate that the defects of ECT are mainly concentrated in the acquisition unit, the defect rate is closely related to the reliability of electronic components, the technical level, production process and quality control of the manufacturer. In view of the typical defect analysis, the corresponding solution measures are put forward to provide reference for the subsequent research and application of ECT.

A Study to Resist Conduced Interference from GIS Bus-Charging Currents Switching for Electronic Current Transformer

In this paper, we study the conducted interference to an electronic current transformer introduced in the process of bus-charging currents which are caused by switching a gas insulated switchgear (GIS) disconnector. To cope with these issues, the EMTP-ATP and Matlab/Simulink software are used to carry out equivalent modeling simulations and experimental research, respectively. More specifically, the very fast transient current generated by disconnector switching (DS) is used as the input source of the equivalent simulation model of the Rogowski coil, and the characteristics of conducted interference waveforms of the Rogowski coil, the active integrator and filter outputs under single and multiple breakdowns are analyzed step by step. Moreover, several anti-interference methods are proposed to improve the resistance to the high-voltage and high-frequency conducted interference for the Rogowski coil, such as reducing the Rogowski cut-off frequency, increasing the transient voltage suppressor (TVS), active filter, and Cy capacitor. Besides, the study also reveals that the residual charge of the integral capacitor will discharge with a time constant τ = 1 s after arc quenching with the first-order discharge circuit, which is composed of the feedback resistance and the integral capacitor C. Lastly, the experimental results demonstrate the correctness of the modeling method proposed in this paper and the effectiveness of anti-interference measures.

Analysis of ECT effect on accuracy of measurement and protection

Electronic current transformer (ECT) is responsible for collecting and transmitting measurement, protection, and control signals of substations, which is regarded as a critical device for the connection of primary and secondary equipment in an intelligent substation. Naturally, a well-designed ECT is essential to ensure a safe and stable operation of power systems. This paper attempts to provide a detailed discussion and analysis of the principle, structure and characteristic of ECT, which mainly focuses on the following three aspects, i.e., steady-state accuracy, frequency response test and transient spread characteristics test. For a comprehensive performance test, a laboratory test platform is established in intelligent substations to simulate actual operation condition of ECT and further implement error accuracy analysis, frequency response test, transient response test and long-term test. Simulation results show the influence of ECT on measurement and protection accuracy, which can provide theoretical basis and evaluation criteria for further improvement of digital measurement performance and large-scale application in intelligent substations.

Mitigation of current transformer saturation on medium voltage switchgears in APR1400 of Nuclear power plants

Selection of current transformers (CTs) must be done carefully to ensure protection, control, and measuring systems function correctly. Some of the conventional CTs on medium voltage (MV) switchgear in nuclear power plants (NPPs) perform poorly due to accuracy errors and saturation. This paper suggests the use of electronic current transformers (ECTs) as a solution. Simulations were done on a 13.8 kV switchgear using electromagnetic transient program restructured version (EMTP‐RV) software to compare the performance of conventional CTs and ECTs under high fault currents. It was found that ECTs show significant improvement in performance with the secondary current output of 97.37% and eliminate saturation even in systems with high symmetrical and asymmetrical short‐circuit currents. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Electromagnetic Disturbed Mechanism of Electronic Current Transformer Acquisition Card under High Frequency Electromagnetic Interference

The electronic current transformer (ECT) acquisition card is widely used in smart grids with many advantages. However, with the continuous improvement of the power grid and localized intelligent electronic devices, the electromagnetic environment under the operating conditions of gas insulated switchgear (GIS) substations is becoming more complicated. The reliability and safety of the ECT acquisition card will be endangered due to the complicated electromagnetic environment. In order to solve these problems, this paper investigates the electromagnetic disturbed mechanism of the ECT acquisition card. The effects of different grounding methods on the electromagnetic interference of the ECT acquisition card were studied. A platform based on IEC 61000-4-4 was built, and the electromagnetic interference (EMI) of the ECT acquisition card with different grounding methods was measured. The results show that the lower grounding impedance of the ECT acquisition system increased the internal EMI. Further, the high frequency electrical fast transient/burst coupling mechanism was analyzed. The parasitic parameters of the acquisition card were extracted based on the critical circuit by using the finite element method. Then, the high-frequency EMI coupling model of the ECT acquisition card was established.

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.

Electromagnetic Immunity Performance of Intelligent Electronic Equipment in Smart Substation’s Electromagnetic Environment

With the gradual increasing of the transmission voltage level, the situation of interference on secondary side equipment in smart substations is becoming more serious. The authors tested the interference waveforms caused by the circuit breaker’s operation at the smart substation, which showed the severity of the electromagnetic (EM) environment. This paper takes the electronic current transformer acquisition card as an example. The influence of EM interference sources on the reliability of the acquisition card is analyzed. Then, standardized electromagnetic compatibility (EMC) immunity tests of the international electrotechnical commission (IEC) for different interferences are implemented. Typical output characteristics of acquisition cards for different tests are analyzed. Innovatively, this paper proposes a quantitative evaluation method of output waveform disturbance to evaluate the acquisition card’s performance. This disturbance distortion is of great significance to the EM environment estimation of the acquisition card.

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).

Travelling wave fault location principle for hybrid multi-terminal LCC-VSC-HVDC transmission line based on R-ECT

This paper investigates the fault location issue of hybrid multi-terminal high voltage direct current (HVDC) overhead transmission line based on the line commutated converter (LCC) and voltage source converter (VSC). There exists two issues that should be addressed: (i) the travelling wave (TW) fault location principle’s adaptability to multi-terminal network topology and converter structures; (ii) the transfer method of high frequency TW signal. Therefore, a novel TW fault location principle for the hybrid multi-terminal LCC-MMC-HVDC transmission line is proposed based on the Rogowski coli based electronic current transformer (R-ECT). Firstly, the high frequency TW transfer capability of the R-ECT is studied. Secondly, a novel TW fault location principle based on the secondary differential current travelling wave (D-CTW) is proposed. Eventually, in order to verify the high accuracy of the proposed principle, a typical ±400 kV hybrid three-terminal LCC-VSC-HVDC transmission system is used for the case study based on PSCAD/EMTDC. Furthermore, its robustness against different fault locations, different fault resistances and different fault types is also investigated.

Impact of Coreless Current Transformer Position on Current Measurement

Magnetic sensors have been widely used for current measurements in diverse industries. In order to achieve a large current measurement without an iron core structure, magnetic sensors are often arranged to be a circular array for designing a new electronic current transformer (ECT). However, this ECT with a circular array of magnetic sensors usually suffers from tradeoffs between the number of sensors and the measurement accuracy. This paper visualizes this tradeoff and proposes a 3-D magnetic-field model to analyze the impact of the magnetic sensor circular array position on current measurements. We develop an analytical expression of the current measurement errors to estimate the minimum number of required magnetic sensors and point out the acceptable deviations of the ECT position under various accuracy classes. Based on the estimation results, we design a new circular array with eight magnetic sensors and build a three-phase current measurement system. The test results demonstrate the efficiency and the robustness of the designed class-1.0 ECT, which successfully maintains accuracy class 1.0 under various position deviations in balanced or unbalanced three-phase power delivery systems.

A Smart Substation Training Platform based on Primary Equipment Simulator

A training scheme based on combination of virtual substation primary equipment real secondary devices is proposed for smart substation accident management. The primary equipment simulator is implemented through communication between 3D cartoon server and simulated switch controller. Electronic current and voltage transformer is simulated by EMTDC transient model and FPGA+DSP terminal controller. A smart substation on-site training environment is established for the substation O&M personnel.