Electromagnetic Voltage Transformer Research Articles

Research on the mechanism and restraining measures of ferroresonance in distribution network based on ATP-EMTP

In order to monitor the three-phase voltage of the busbar to ground, the substation bus is usually connected to the electromagnetic voltage transformer by YN connection in the distribution network. Under certain conditions, the excitation characteristics are easy to saturate, and the inductance parameters match the system capacitance, excite ferromagnetic resonance, cause damage to fuses or voltage transformers, and seriously affect the safe and stable operation of the power system.By analyzing typical single-phase ground faults, this paper introduces the generation mechanism of ferromagnetic resonance and the main suppression measures at this stage. The electromagnetic transient analysis software ATP-EMTP is used to analyze the operation of a typical transformer, and the change of ferromagnetic resonance waveform after the neutral point of the voltage transformer is replaced by resonant eliminator and arc suppression coil grounding. The results show that when eliminating the single-phase ground fault, it is easy to cause the frequency division resonance of the system, and the use of these two measures can effectively suppress the ferromagnetic resonance of the system.

Monitoring in 6–35 kV power networks, location of single-phase ground fault and detection of fault feeder

To minimize the negative impact of arc overvoltage in three-phase electrical power system (ES) with the ungrounded or high impedance grounded neutral, it is proposed to monitor transient electromagnetic processes, which will allow evaluating the current condition of the insulation, and in addition, detecting the damaged feeder and a single-phase ground fault zone using telemetry systems. Detection of the damaged feeder (with a single-phase ground fault) using the parameters of the ground fault transient process can be incorrect due to low free oscillations frequencies of electromagnetic instrument voltage transformers (EMVT). The superposition of EMVT free oscillations on the ES oscillations leads to an incorrect determination of the power direction of the first high-frequency oscillations and, as a result, to incorrect detection of the damaged feeder. A more accurate detection of the damaged feeder can be done by the proposed method based on the processing the pre-breakdown voltage of power frequency in the damaged phase. It is shown that the method is suitable for networks with an isolated neutral, as well as grounded through an arc-suppression reactor (ASR) or a high-value resistor.

Research on the traceability method based on half symmetric superposition

In order to achieve high-accuracy self-calibration and traceability of electromagnetic standard voltage transformers, a measurement method that can be used for voltage ratio standard error voltage coefficients is proposed. Using two auxiliary standard voltage transformers, the error variation of the voltage transformer under different voltages can be obtained through three-step measurement. Compared with the traditional error voltage coefficient measurement method and international comparison, the feasibility of the method and the rationality of the uncertainty evaluation of the measurement results are verified. The self-calibration ratio difference measurement uncertainty of the 110 kV standard voltage transformer is better than 5 × 10−6, and the angular difference measurement uncertainty is better than 5 µrad. The method can be used to trace the source of standard devices up to 1000 kV power frequency voltage ratio, which have characteristics such as high accuracy and good stability.

Simulation Analysis of Ferro resonance of Generator-Transformer Group Shock Tripping

As a common self-excited oscillation in power systems, ferromagnetic resonance has a great threat to the insulation of electrical equipment due to overvoltage and overcurrent. The magnetizing inductance of electromagnetic voltage transformers has nonlinear characteristics, which tend to saturate the excitation and cause circuit resonance and generate resonance overvoltage. The ferromagnetic resonance overvoltage caused by the saturation of the transformer has greatly affected the safe and stable operation of the power grid. Therefore, it is very necessary to analyze, calculate and simulate the ferromagnetic resonance overvoltage, and to study the measures to eliminate resonance. Through theoretical calculation and simulation analysis of a hydroelectric power plant generator-transformer group reverse transmission impulse tripping fault, the cause of its ferromagnetic resonance was analysed, and relevant operation and maintenance suggestions were put forward to provide a basis for further research.

Optimization design of electric field potential for high-speed EMU high voltage box

Establish the three-dimensional model of high-voltage box and its internal main electrical equipment of EMU. Under the lightning overvoltage condition, through modeling and analyzing the electric field potential distribution of high-voltage components of EMU, understand the insulation weak links of high-voltage components, optimize the insulation gap of high-voltage components, local structure of components and system layout, and systematically master the layout design of high-voltage equipment of EMU method. The research results show that under the lightning overvoltage condition, the areas with higher electric field strength are mainly concentrated in the inlet port of the cable and the outlet port of the circuit breaker, the maximum electric field intensity is concentrated near the electrode of the electromagnetic voltage transformer, and the maximum field strength in the high voltage box is 21.5kv/cm, which meets the air breakdown standard, has certain safety margin and meets the insulation requirements.

Study on Primary Harmonic Eliminator for Ferromagnetic Resonance in the Neutral Non-effective Grounding System

The ferromagnetic resonance overvoltage and overcurrent can often appear in the neutral non-effective grounding system, which is caused by the electromagnetic voltage transformer saturation under a certain condition. At present, two different types of primary harmonic eliminators are mainly used to solve the ferromagnetic resonance, which are voltage-sensitive resistor type and thermal resistor type. In this paper, the simulation model based on ATP-EMTP program is established and the results of different harmonic eliminators are compared. The results prove that the primary harmonic eliminator of thermal resistor type can more effectively suppress the ferromagnetic resonance.

Feature of Voltage Transformers Operation in the Direct Current Schemes of Ice Melting on Overhead Transmission Lines

It is well known that electromagnetic voltage transformers (VT), included in the direct current scheme of ice melting (SIM) on overhead transmission lines (OTL), must be switched off when the SIM is assembling and turned on during disassembling. This action increases the time of the power line output from work and reduces the reliability of the power system. It is noted that capacitance VTs used in the electrical networks of 110-500 kV are not subject to the dangerous influence of DC voltage. Three variants of capacitors installation for elec-tromagnetic VT protection from direct voltage at which it is not required to switch off VTs are considered. A conclusion was made on the conditions of applicability of each variant based on the analysis of basic SIM. The article includes the necessary for practical use equivalent circuits and the values of constant voltages on the VTs in the basic direct current schemes of ice melting on overhead transmission lines. The method and an exam-ple of parameters calculation of the capacitors' block and additional resistor, providing the required accuracy class of VT at its constant inclusion as in the normal scheme, and in the scheme of ice melting, are given.

Piezoelectric Disc Transformer Modeling Utilizing Extended Hamilton's Principle

Piezoelectric transformers (PTs) are resonant electromechanical voltage conversion devices used in a variety of applications including voltage boosting and galvanic isolation. They offer advantages over electromagnetic voltage transformers, including high energy density as well as the potential for monolithic fabrication, making them well suited to small-scale microelectromechanical applications. Among various PT topologies, circular discs lend themselves to microfabrication, and are considered here. In order to gain fundamental understanding of disc PT dynamics, this work applies the extended Hamilton's principle of variational calculus to the piezoelectric electric enthalpy, using cylindrical coordinates, in order to derive electromechanical constitutive equations for bulk disc transformers. The use of the Hamilton approach in this work supports the integration of mechanical tethers that physically support the disc, allowing the model to be applied to device designs that are compatible with monolithic microfabrication from sheets of bulk piezoelectric material. Using the integrated model, voltage gain (output voltage/input voltage) is predicted as a function of multiple variables including electrode area ratio, device size, tether stiffness, internal material damping, and output load impedance, and is compared against finite element numerical and experimental prototype results for verification. Prototype 4-mm diameter tethered disc PTs on the order of 0.002 cm3, two orders smaller than the bulk PT literature, were fabricated to validate the proposed model, and had peak voltage gains over 2.

Resonant Overvoltage Mechanism of Electromagnetic Voltage Transformer in 6kV Non-Direct Grounding System

This paper expounds the principle and conditions of ferromagnetic resonance generation, and analyzes the ferromagnetic resonance accident of Hetan substation. The article explains the concept of “illusive grounding” caused by ferromagnetic resonance, combined with the Peterson curve. The conditions for the generation of ferromagnetic resonance are analyzed, and the common measures to eliminate ferromagnetic resonance are given.

Mechanism analysis of ferromagnetic resonance of electromagnetic voltage transformer in neutral ungrounded system

In the neutral point ungrounded power distribution system, due to the nonlinear characteristics of the electromagnetic voltage transformer (PT) excitation inductance, ferromagnetic resonance overvoltage is easily generated under certain conditions, which seriously affects the safe operation of the system. This paper takes the Yecheng substation 6 kV distribution network as the model, and uses ATP-EMPT electromagnetic transient calculation software to theoretically analyze the characteristics and mechanism of ferromagnetic resonance caused by electromagnetic voltage transformer, and points out the main problems of ferromagnetic resonance in PT operation. This article discussed the existing harmonic elimination measures, proposed some effective suppression schemes and demonstrated the effectiveness of some mainstream harmonic elimination methods. The author’s work can provide a good reference for the prevention and control of ferromagnetic resonance overvoltage, and it also has high practical value for improving the power supply safety and reliability of the distribution network.

Analysis and Countermeasure of Burnout of Electromagnetic Voltage Transformer of High Altitude Area in Western China

3 burning accidents of electromagnetic voltage transformer of Qinghai power grid in the southern high altitude area was introduced in this paper, and the cause of the accident was analyzed, which is due to a phase grounding line, then the other two phases voltage rising caused voltage transformer damaged; occurrence of Ferro resonance over-voltage, which resulting in serious core saturation, and the over-current caused voltage transformer damaged; due to open delta is short circuit, when the single-phase grounding fault occurred, because the voltage output of 100 V from open delta winding, a very large current is formatted, and a lot of heat is made, also led to the current in primary side very large, resulting in burning TV. In view of these three reasons, the corresponding prevention measures are put forward to ensure the normal operation of the power system.

Compact system for onsite calibration of 1000 kV voltage transformers

This study describes the development and evaluation of a compact system for onsite calibration of 1000 kV voltage transformers in ultra-high-voltage (UHV) AC power transmission projects. The proposed compact system consists of a 1000 kV electromagnetic voltage transformer as a standard, a high-voltage resonant power supply, and a voltage transformer test set, which are assembled and mounted on a calibration truck. The developed system accuracy is 0.05% in ratio and 0.058 mrad in phase angle, respectively. Also, the total basic uncertainty is about ±0.028% and ±0.03 mrad under field conditions. The compact system can be automatically set up and taken down quickly on site requiring no substation cranes or utility operating crews. It has successfully undergone complete field tests and calibrated 63 1000 kV voltage transformers in total at 5 UHV substations. The feasibility of an automatic and efficient approach to calibrating UHV voltage transformers on site has been demonstrated.

Suppressing ferroresonance in potential transformers using a model-free active-resistance controller

Ferroresonance, excited by saturated electromagnetic voltage transformers, can severely damage power systems because it produces long duration large overvoltages. In this paper, a method is developed to eliminate potential transformer (PT) ferroresonance through a model-free method. First, a structural diagram of the ferroresonance eliminating device is established based on a practical ferroresonant circuit. The effect of the adjustable parameters of the device is investigated, including resistance, pulse frequency, and pulse duty cycle. Then, Iterative control strategies are developed to adjust the gate signal duty cycle of the controller for limiting the ferroresonance to a normal status and then switching off the elimination device. Finally, simulations are conducted demonstrating that the method proposed was effective.

Dual LiNbO3 Crystal-Based Batteryless and Contactless Optical Transient Overvoltage Sensor for Overhead Transmission Line and Substation Applications

Advanced high-voltage and overvoltage measurement techniques are required for smart grid construction. The existing overvoltage measurement methods that are currently used for power system measurements are mostly based on the use of electromagnetic voltage transformers and capacitive voltage transformers, which have contradiction in measuring accuracy, measuring distance, antijamming, and system compatibility. A batteryless sensor for contactless measurement of the overvoltage on overhead transmission lines based on a combination of the electrooptic effect in LiNbO3 with stray capacitance in the air is designed in this work. On the basis of this design, a dual-crystal structure-based electrooptic conversion unit is presented that eliminates the natural birefringence and improves the operating stability of the sensor. Testing platforms were set up to measure the characteristics of the sensor in thermal stability. In combination with a data acquisition device, the newly designed sensor was applied to online monitoring of the overvoltage in the ac bus and the overhead transmission lines of a 500-kV transformer station and a ±500-kV convertor station in the China Southern Power Grid.

Novel Detection Method of High Voltage Power Metering Circuit Fault based on Electric Energy Meter Phase and Voltage Transformer

The basic structure of the electromagnetic induction type voltage transformer is the core and primary, secondary winding. Characteristics of capacity are small and relatively constant. This paper introduces the application of electric energy meter, including two kinds of three-phase electric energy meter (three-phase two elements and three element phase) and non reactive energy meter. In this paper, the high voltage electric energy metering system of fault conditions is analyzed. The paper presents novel method of high voltage power metering circuit fault detection based on Electric energy meter phase and voltage transformer. The voltage circuit fault that electric energy meter pressure loss, less pressure fault detection method is analyzed.

English

Instrument transformers are the integral components of power system protection and metering. The objective of instrument transformers is to provide scaled down replicas of high voltages and currents of the power system. In case of high voltage transmission network (≥132KV), capacitive voltage transformers are widely used as an alternative to electromagnetic voltage transformers due to their techno economic advantages. They transform higher voltages to lower values which are easily measurable and can be directly used for metering, protection and control applications. During the system transient conditions, there is a deviation in the scaled down secondary voltage signal from the actual signal which comprises of wide range of frequencies, due to energy storing elements of capacitive voltage transformer. There are several practices in the industry to mitigate the deviation in the secondary voltage signal of capacitive voltage transformer. For satisfactory operation of capacitive voltage transformer, better frequency response is desirable. The simulation study to determine the effect of various factors influencing the frequency response of capacitive voltage transformer are presented in this paper.

Research on Harm of Harmonics on Electrical Equipment

Through the analysis of harmonics caused by transformer, capacitor, electromagnetic voltage transformer and other accident, harmonics is an important indicator of power quality, which has been included in the “pollution" of power grid is found. In order to understand the harmonic, this paper from the concept of quality of electric energy, and then gradually extended to the field of harmonics. This paper firstly introduces the various reasons and equipment may produce harmonic, Secondly, illustrate harm of harmonic to operation of transformers, capacitors, electromagnetic voltage transformers and other electrical equipment, let more people know and understand the relevant knowledge of the harmonic, In order to save technical force and provide scientific basis for future effective harmonic.

Measuring Method and Error Compensation for Amplitude-Frequency Characteristics of Electromagnetic Voltage Transformer

The amplitude-frequency characteristics of voltage transformer need to be measured accurately when the electrical parameters of inverter module are detected. Using frequency method to measure one electromagnetic voltage transformer entirely, the amplitude-frequency characteristics with waveform distortion and phase delay were tested and analyzed by FFT on some typical frequencies. Amplitude-frequency transfer errors were compensated by nonlinear fitting method mainly on 50Hz, 15kHz , 20kHz segment. One order and two order curve fitting of the least squares function called lsqcurvefit were simulated in the environment of MATLAB, the results proved that the two order curve fitting function has a better compensation effect.

Research on Optimization Technology of Electromagnetic Transformer

Taking the typical electromagnetic voltage transformer JDCF-110 as the research object, according to the performance characteristics, the optimization mathematical model is set up. Ant colony algorithm is selected as optimization algorithm. With the cost as objective function, the settings of key parameters are studied on in optimization design. By use of Visual C++ language, the optimization design software of electromagnetic voltage transformer is finished on the plat of Windows XP. According to users requirement, the basic design and the optimized design of electromagnetic voltage transformer can be conveniently and quickly realized.

Research on Ferroresonance Detection in Small Current Neutral Grounding System

A novel method to detect ferroresonance was proposed based on the drastic characteristics of the electromagnetic voltage transformer (PT) current rate. This scheme takes current rate which is greater than a threshold value as starting signal and judges the occurrence of resonance by detecting duty ratio of the peaks and interval angles. Then, it identifies the periods and patterns established on the interval time of spikes. Through simulation testing of MATLAB, it can distinguish the occurrence and types of ferroresonance accurately, which verifies the validity of the detection method.