Power Frequency Voltage Research Articles

An expeditious calculation approach to consider the influence of power frequency voltage on the calculation of the lightning performance of transmission lines: Validation for different peak current-front time correlation expressions and cumulative peak current distributions

The approach to consider the influence of the power-frequency voltage on the calculated lightning performance of transmission lines with voltage level from 69 kV to 500 kV by means of the 0.88-multiplying-factor applied on critical currents is validated for simulation conditions that assume the correlation between lightning peak current and front time, and several cumulative peak current distributions of negative first strokes. The obtained results confirm that the relation between critical currents calculated in the presence and in the absence of the power-frequency voltage follows the 0.88-factor for all investigated cases. The root mean square errors (RMSE) calculated for the critical currents vary from 3.20 kA to 7.37 kA and for the backflashover probability are not greater than 0.02 %, ensuring the generality of application of the proposed approach. The ratio between the backflashover rates obtained by the 0.88-factor approach and by the Monte Carlo method is around 1 for most of the simulated cases, confirming the quality of the results provided by such expeditious procedure.

Magnetohydrodynamic simulation and test of compression arc-extinguishing device under icing condition

When the weather is cold and wet, the insulator and the transmission line components often undergo icing. In order to study the inhibition effect of the compression arc-extinguishing device with icing on the recovery of arc plasma conductivity and air disruptive strength, this paper will verify it through simulation and test. In the simulation part, a two-dimensional geometric model is established, and the magnetohydrodynamic equation group is used as the control equation group. The breakdown characteristics of the device with and without icing are compared, and the dynamic characteristics of the arc are studied in terms of temperature and conductivity. The results show that the temperature of the arc plasma can be reduced to 3000 K within 1 ms, and the conductivity can be reduced to 0 within 250 µs. In the test part, the suppression effect on arc current amplitude after the device with icing is subjected to high current impact is verified, and the coupling triggering method of impulse voltage and power frequency voltage is adopted to further verify the arc extinguishing condition of the device when the power frequency current continues. The results show that the amplitude of the arc produced by high current impulse decreases from 67 to 35 kA and to 0 within 1 ms after passing through the device with icing, and the current amplitude can still drop to 0 at 2.5 ms after adding the power frequency voltage. It is proved that the device with icing can inhibit the recovery of arc plasma conductivity and air disruptive strength.

Development of nanosecond spike pulse power supply for electrochemical micromachining

The use of pulse voltage can greatly improve the precision of electrochemical microfabrication, and the narrower the pulse width of the applied pulse voltage signal, the higher the machining precision. However, the commonly used chopper circuit topology of pulse power supplies is limited by the maximum switching frequency of the field-effect transistor. To address this problem, this paper proposes a nanosecond pulse electrochemical micromachining power supply based on a differential circuit. The power supply uses the STM32F103C8T6 microcontroller as the control core to output high-performance rectangular waves through a DDS device. After differential, rectification, filtering, and power amplification processing, stable, frequency, amplitude, and pulse width adjustable spike pulse voltage signals are obtained. By establishing a system mathematical model and optimizing the time constant of the differential circuit, theoretically, the sub-nanosecond pulse width can be obtained. Prototype performance tests show that the power supply has a maximum frequency of 20 MHz, a minimum pulse width of 1.8 ns, and a maximum peak voltage of 10 V. By using this power supply for microhole electrochemical machining experiments, nanometer-level machining precision has been achieved.

Research on the Growth Characteristics of the Electrical Tree at Polyethylene/Silicone Rubber Composite Interface Under Power Frequency Voltage

During operation, the composite interface of the cable joint will experience a tangential electric field. When the composite interface has insulation defects, it is easy to experience interface discharge. Electrical tree is a phenomenon of electrical degradation and it’s a precursor of polymer breakdown. It is observed in the laboratory that under the power frequency voltage, the electrical tree will initiate at the composite interface, and the tree growth will finally lead to the interface breakdown. This paper investigates the development of an electrical tree at the composite interface of polyethylene/silicone rubber under power frequency voltage through microscopic observation. The results show that the air gap of the interface is the weak position of insulation, and the electrical tree will be initiated from the triple junction of the air gap and the impacted area of the two materials. The increase in voltage amplitude will speed up the initiation. High amplitudes also promote the electrical tree. The electrical tree shape will be changed from a branch structure at low voltage to a single branch structure at high voltage. The study on the electrical tree at the interface provides a visual display of the degradation process of the material before the breakdown at the composite interface.

Transient characteristics and sites of pre‐breakdown in spark conditioning for high‐voltage vacuum interrupter under power frequency voltage

AbstractThe objective of this paper is to determine the transient characteristics and sites of the pre‐breakdown (pre‐BD) in the spark conditioning under power frequency voltage (PFV) in vacuum. A multi‐angle optical path system was designed and made the determination of the pre‐BD sites in spark conditioning possible, through one camera at two viewing angles. The experimental results indicate that, in the spark conditioning under PFV, the pre‐BDs continuously occurred at a random moment. Within several half‐waves, the number of the pre‐BDs could reach dozens of times, which was the key for the treatment of the electrode surface in conditioning. Under the application of PFV, the single pre‐BD occurred at a random moment, in which it would last for several microseconds and the peak value of the current would reach several amperes. Moreover, the pre‐BD sites randomly distributed in the surface of the electrode and almost covered the whole surface of the electrode. The pre‐BDs took place independently in both time and space, in which there should be no effect between each other of two sequential pre‐BDs. To sum up, the transient characteristics and the sites of the pre‐BDs determined in this paper could reveal the physical mechanism of the pre‐BD on the treatment of electrode surface in the conditioning process, which is quite significant to improve the BD voltage of vacuum interrupter.

A method for tracing impulse voltage peak value using weighted frequency components

This paper studies a method for synthesizing impulse voltage peak error based on frequency energy weight. The research designed three capacitive voltage dividers with a voltage rating of 1 kV, 10 kV, and 200 kV, respectively, and measured their response characteristics using the step wave response test. The scale factor and linearity of the 1 kV capacitor divider were measured at different frequencies and impulse voltages to verify the equivalence of voltage coefficients under power frequency and impulse. Using boundary conditions obtained from AC voltage standard sources and impulse voltage standard generators, the equivalence of 200 kV power frequency voltage coefficient and impulse voltage coefficient was derived.

Energy harvesting using variable stiffness piezolaminated shallow shell panels exposed to hygrothermal environments

The effect of hygrothermal environment on the energy harvesting capabilities of piezolaminated shallow shell panels made of variable stiffness composite layers (VSCL) is investigated. The use of curvilinear fibers to tailor the characteristics of the energy harvester is also explored. To model the deformation of the harvester, a finite element model based on a first-order normal shear deformation theory (FNSDT) is developed. Nonlinear strain–displacement relations based on Green–Lagrange strains are considered for nonuniform stress distribution due to temperature and moisture. A nine noded isoparametric element is used to discretize the domain. The effects of temperature and moisture concentration change on Power frequency response functions (FRFs), Voltage FRFs and Motion FRFs are presented. Power FRFs, Voltage FRFs and Motion FRFs are plotted for optimum load resistance when the shell structure is excited at short and open circuit frequencies. The current study is expected to help design and optimize the vibrational energy harvester to power sensors used in different automotive, aerospace, nuclear applications, subjected to elevated temperature and moisture conditions.

A New Approach for Considering the Effect of the Power-Frequency Voltage on the Calculated Lightning Performance of Transmission Lines

The effect of power-frequency voltage on the backflashover rate of 138 kV to 500 kV transmission lines was assessed by means of an elaborate computational approach, based on the Monte Carlo method. Accurate results were obtained using this approach and were taken as reference for assessing the quality of results of the main methodologies available in literature for considering this effect that significantly increases the backflashover probability. The results showed that the effect is more pronounced for low tower-footing grounding impedances and for transmission lines with higher voltage level. With the exception of the approach recommended by CIGRE Brochure 63, the other tested approaches showed to yield reasonable results. Two new alternatives were proposed in this work for considering the effect. Particularly, the work developed an impactful original result: the use of a simple 0.88-multiplying factor to correct the critical currents. This approach yielded top-quality results, exhibiting very small average error (1.2%) and lowest maximum error (9.2%) in relation to the reference results.

Current Situation Analysis for the Integration and Detection Methods of the Primary and Secondary Switch

The distribution equipment is core to intelligent distribution and directly determines the reliable operation of distribution networks. The primary and secondary integrated switchgear is an integration of the traditional primary switch, sensor, and secondary controlling terminal. It is influenced by temperature, pressure, electromagnetic interference, etc. To guarantee the quality of the primary and secondary integrated switchgear which is accessed to the power grid, the inspection outline of the primary and secondary integrated switchgear in the State Power Grid includes the structure and configuration, appearance inspection, insulation resistance test, power frequency voltage withstand test, and lightning impulse test.

Time Synchronization Method of Low-Voltage Distribution Network Based on Wi-Fi and Voltage Detection

Under the background of frequent electric fires caused by leakage and arc faults, the low-voltage distribution network uses the Internet of Things technology to solve the problem of low-voltage monitoring, so as to ensure the safe use of electricity. In order to tag the collected data with time tags, a large number of low-voltage terminal units need to have time synchronization function, while the cost and accuracy of existing time synchronization methods cannot adapt to the demand of low-voltage distribution network monitoring system. Based on analyzing the demand of low-voltage distribution network monitoring function for time synchronization, this paper puts forward a time synchronization method combining WiFi communication with voltage detection by taking advantage of the characteristics of short low-voltage line and small voltage phase angle change at both ends of the line. Time synchronization of low-voltage terminal unit at the time when the power frequency voltage crosses the zero point, using WiFi communication to transmit time synchronization commands. This method is economical and does not require additional equipment. Finally, the feasibility of the method is verified by building a test system, and the time synchronization accuracy can be within 1 ms.

Mitigation of electrical treeing at high temperature in nano‐SiO2 doped epoxy resin

AbstractIn this work, electrical tree inception and ageing experiments were conducted to investigate the initiation, growth characteristics and structural characteristics of electrical trees of nano‐SiO2 doped epoxy resin at different temperatures. Electrical tree inception and ageing experiments were conducted using power frequency voltage of 15 kV at 20, 40, 60, 80 and 100°C. Electrical breakdown properties of epoxy resin were investigated by applying AC and DC voltages at 20, 40, 80 and 120°C. There are two major observations based on the experimental results. With the increase of temperature, the morphological structure of the electrical trees changes from dendritic to plexiform, the tree inception voltage decreases and the growth rate of the electrical trees increases obviously. Either under DC or AC voltage, the breakdown strength of the nano‐SiO2 doped epoxy resin decreases as the temperature increases. Finally, based on the space charge and the trap level measurement, the mechanism of the electrical tree propagation and breakdown in nano‐SiO2 doped epoxy resin was analysed.

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

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

Analysis of A Few Continuous Ferromagnetic Resonance PT Faults in Power Plants and Improvement Measures of Harmonic-free Suppression Technology

Many vicious faults of burning PT and high-voltage fuse caused by ferroresonance occurred in power plants. Microcomputer harmonic elimination device and silicon carbide harmonic elimination device did not work; particularly silicon carbide harmonic elimination devices burnt together with PT. This paper, enumerating the excitation conditions of PT ferromagnetic resonance, analyzes the circuit characteristics of PT circuit ferromagnetic resonance in the power plant and the power frequency voltage characteristics of the sound phase when the single-phase grounding fault occurs in the neutral point ungrounded system. The defects of the existing harmonic elimination device are summarized, and the technical improvement measures are proposed to add the current-sensitive intelligent harmonic elimination device. Practice shows that this kind of harmonic elimination device can effectively avoid PT bursts and fuse-fusing faults caused by the resonance of the intermittent grounding of the system.

The Design of Calibration System Based on Cable Accessories

In today’s society, people can’t live without electricity. During the operation of power equipment, there may be various potential safety risks. In particular, partial discharge is easy to occur at the terminal. If people can not deal with the problem of partial discharge in time, equipment continue to live.Setting can cause security, so the electric power industry staff attaches great importance to the local discharge monitoring problem.Ultrasonic technology is better so it is gradually into the application of partial discharge detection.But the ultrasonic detection technology is to detect the intensity of ultrasound, and our traditional method is to measure the discharge of partial discharge method, Therefore, in order to obtain the relationship between ultrasonic intensity and partial discharge, the following experiments are made. After we pass the power frequency voltage withstand device, the transformer is continuously pressurized.Gain DB and discharge PC were obtained by digital partial discharge instrument and ultrasonic partial discharge instrument. After fitting, the linear relation is obtained and the quality inspection of PD detector is completed.It can make the detection effect of partial discharge detector more complete, and provide the basis for the quality inspection of the detector, This system also provides a strong support for the wide application of ultrasonic partial discharge detector.

Broadband radio frequency signal measurement based on quantum compression sensing

With the rapid development of radio frequency technology such as radar, electronic warfare and 5G communication, the measurement and real-time spectrum characterization of broadband radio frequency signals become increasingly important. The traditional radio frequency signal real-time measurement technology is limited by the sampling rate of analog-to-digital converter and the ability to process digital signals, and encounters the problems of narrow measurement band, large data volume, and susceptibility to electromagnetic interference. This work is to study a radio frequency signal measurement technology based on quantum compression sensing, which uses integrated electro-optical crystal as radio frequency sensor, and constructs a compression sensing machine by modulating the photon wave function of the measured radio frequency signal to realize the compression measurement of broadband radio frequency signal, significantly improving the spectrum sensing bandwidth. The experiment demonstrates the long-term spectrum monitoring of power frequency and intermediate frequency high voltage signals, and the real-time spectrum measurement of high frequency radio frequency signals. Under the Fourier limit spectrum resolution, the real-time spectrum analysis bandwidth of GHz magnitude is realized, and the data compression rate reaches 1.7×10<sup>–5</sup>, which can meet the needs of 5G wireless communication, cognitive radio and other applications for broadband radio frequency signal spectrum measurement, and provide a new technical path for developing the next-generation broadband spectrum sensing technology.

Development and Experimental Research of VFTO Measuring Sensor

Very fast transient overvoltage (VFTO) generated by an operating disconnector is one of the main reasons for electromagnetic disturbance in gas-insulated switchgear (GIS) substations. Generally, the amplitude of VFTO can be used as one of the references for the insulation design of GIS primary electric power equipment, so it is necessary to obtain its accurate amplitude. In this study, a new VFTO measuring sensor is developed and its measurement performance is demonstrated through hundreds of operations by a disconnector in a 220 kV GIS test circuit. The validation shows that the low cut-off frequency of the new VFTO measuring sensor has been greatly expanded to 0.01 mHz, which is improved by about 50% compared with the old sensor. The measurement accuracy of amplitude of VFTO micro-pulse improves greatly by about 80% compared with the old one. Thus, the new VFTO measuring sensor can fully meet the measurement needs of trapped charge voltage, power frequency voltage, and high-frequency transient voltage in VFTO waveform. It can be used to provide more accurate data support for insulation design of GIS primary power electric equipment in extra-high voltage (EHV) and ultra-high voltage (UHV) GIS substations.

A Novel Composite Sensor for Overvoltage and UHF Partial Discharge Measurement in GIS

The presence of overvoltage can cause the insulation deterioration and excite the partial discharges (PD) in gas-insulated switchgear (GIS), and it is necessary to detect the overvoltage and PDs simultaneously to evaluate the insulation performance. A novel GIS internal composite sensor for PD detection and overvoltage measurement is proposed in this paper. The proposed sensor is mainly formed with a disc-type monopole UHF sensor and an overvoltage sensor. The effectiveness and sensitivity of the sensor are tested on a designed platform under power frequency voltage, switching impulse, lightning impulse, and oscillating lightning impulse, respectively. Experiment results show that the proposed sensor can be used to detect overvoltage and UHF signals effectively and is expected to help in the GIS condition evaluation.

Retraction Note: Characteristics of electric tree initiation in glass fiber reinforced epoxy resin under power frequency voltage

Retraction Note: Characteristics of electric tree initiation in glass fiber reinforced epoxy resin under power frequency voltage

Electrical Tree Characteristics of Bisphenol A Epoxy Resin/Maleopimaric Anhydride Curing System.

Epoxy resin insulation materials are mainly derived from petrochemical materials which have the disadvantages of resource consumption and environmental pollution. In order to cure bisphenol A epoxy resin, a maleopimaric anhydride (MPA) curing agent was prepared from rosin, a renewable resource, and blended with a petroleum-based curing agent (methylhexahy-drophthalic anhydride). The influence of maleopimaric anhydride content on the initiation and growth characteristics of electrical trees was studied and analyzed in this paper using molecular dynamics simulation (MD) and electrical tree tests at an 18-kilovolt power frequency voltage. When the MPA content used was ≤10%, the free volume percentage of the curing system increased with MPA content, and thus the initiation voltage became lower; when the MPA content was ≥20%, the hydrogenated phenanthrene ring structure content increased significantly with increasing MPA content, and the rigidity of the curing system increased significantly; thus, the initiation voltage gradually increased. MPA4 had an 11.11% higher initiation voltage than the petroleum-based control group. The effect of the polar rigid structure within the curing system significantly inhibited the growth rate and length of electrical trees as MPA content increased. Electrical trees developed into light-colored, thin, and narrow dendritic structures when the MPA content reached 40%. The results show that curing epoxy resin with the rosin-based curing agent maleopimaric anhydride (MPA), in place of a petroleum-based curing agent, can produce environmentally friendly resins with excellent electrical tree resistance and potential application prospects.

EVALUATION OF ENERGY STRESS ON LINE ARRESTERS

Line Surge Arresters (LSAs) are efficient means for the improvement of the lightning performance of transmission lines. Determination of optimal LSA number, location and rating is important for the improvement of the reliability and availability of a transmission system. In selection of the LSA special attention should be paid to their energy stress which depends on complex interactions between the arrester locations, grounding, shielding and the local lightning environment. LSAs experience higher energy stress compared to station arresters, because the incoming surge to a station is limited by insulator flashover on the transmission line and impulse corona. In this paper calculations of energy stresses were carried out for a double-circuit 220 kV line with a single shielding wire. Parametric studies were conducted in which arrester discharge energy was a function of: time to half value of stroke current, number of towers with arresters, footing resistance, span length and angle of power frequency voltage. Arrester energy stress is analyzed in case of stroke to tower and shielding failure. From conducted analysis it can be concluded that energy stress on LSAs is lower for shorter span lengths. Tower footing resistance has only minor effect on the discharge energy. Arrester discharge energy strongly depends on time to half of the stroke current, number of towers with installed arresters and angle of power frequency voltage.