Power Frequency Voltage Research Articles

Study on Lightning Intruding Overvoltage in Yantan Extension Substation

500kV substation is especially important to the grid of our country, once it encounters lightning damage, the safety and reliability of the whole power system will be directly affected. As lightning intruding waves will cause overvoltage on electric equipments by intruding from the transmission line or straightly stroking the substation, which seriously influences the insulation level of equipments, so it is essential to calculate overvoltage on electric equipments when substation struck by lightning to ensure their safe operation under the protection of arrester. As for the new connection mode of extension project of Yantan 500kV substation, numerical model of hydropower equipments is established and electromagnetic transient simulation calculation software of ATP/EMTP is used for calculation of overvoltage on electric equipments. According to the result, conclusions about strong insulating of incoming line towers, importance of lightning shielding failure intruding waves and influence of power frequency voltage on lightning intruding overvoltage in 500 kV substation can be drawn. This is the first-time study on overvoltage in 500kV substation extension project and has certain practical guidance. DOI : http://dx.doi.org/10.11591/telkomnika.v12i4.4796

Experimental Investigations and Ageing Studies on Effects of Insulating Barriers in Transformer Oil during High Frequency High Voltage Transients in Inhomogeneous Field

Insulating barriers utilized in complex high voltage insulation systems has been exploited widely by manufacturers of power apparatus. Barriers have found utility in a variety of power apparatus for protection against direct lightning strokes, as an interface at the boundaries of composite insulation materials etc. Though investigations have been carried out by researchers on the breakdown characteristics, barrier position in the gap, influence of space charge etc these characteristics have been analyzed based on aspects pertinent to classical testing procedures only. Advent of high speed switching devices in power systems provides avenues to investigate the effect of insulation performance due to High Frequency High Voltage (HFHV) also. Further, uncharacteristic failures in oil filled distribution transformers have been reported indicated fast transients as the major cause for failures which was not revealed during classical laboratory testing. This research focuses on the influence and effects of solid insulating barriers placed in transformer oil due to HFHV in inhomogeneous fields. Test cell arrangement has been fabricated for carrying out experimental investigations to adhere international standards. Exhaustive experimentation has been performed to infer the influence of the position of barrier, nature of field and breakdown voltage, erosion characteristics of the barrier at an appropriate range of frequencies. A detailed comparison between HFHV and classical power frequency voltage has been carried out. The nature of ionization at the barrier interface and the subsequent increase in the breakdown voltage as explained by Double Electric Layer (DEL) theory has been cross validated. In addition, a study has also been carried out to assess and characterize the ageing of oil based on Dissolved Gas Analysis (DGA) analysis using Weibull distribution.

Comparison of Surge Arrester Models

This paper deals with the two most used arresters models applied in digital simulations with the Alternative Transients Program, the conventional, and IEEE models. It presents a model analysis and parameter adjustment procedures to the conventional model. It also presents an application to both models of different types of current and voltage surges and even power frequency voltage, with a comparison of the results obtained with both models and with typical manufacturer data. While adjustment of the IEEE model was difficult and laborious, the conventional model presented a straightforward procedure. The results obtained show that there is a close agreement between the two models when the surge front time is above 1/2 μs. The conventional model always presents higher values for the limiting and residual voltages, and better agreement with the typical manufacturer data. Thus, the conventional model presents the advantages of simplicity and more conservative results.

The Distortion Influence Simulation and Experimental Study of Human Body to High Voltage Power Frequency Electric Field

In order to eliminate the distortion influence error caused by human body on the measurement of hand-held high voltage power frequency electric field measurement device, field intensity distortion caused by induced current of human body has been analyzed, and the enhancement factor of the electric field intensity is introduced to reduce the distortion degree of electric field measurement value by electric field measuring instrument. A simple model of the human body is built, the Ansoft Maxwell is used to simulate and calculate the electric field distribution around the high voltage power frequency transmission lines when human body presented, and distortion influence of field intensity distribution caused by human body has been analyzed. In addition, the enhancement factor value of electric field is determined and the electric field distortion is corrected by experiment and comparing the measurement data with the electromagnetic field analyzer EFA300. With the actual measured values of instrument restored the value of the field intensity when the human body away from the measuring equipment, the distortion influence measurement error can be reduced and measurement precision can be improved.

Research of Cable PD Detected Technology Based on Variable Frequency Oscillation Wave

With the accelerating construction of strong smart grid, and the grid voltage level rising, performance requirements for the electrical insulation of electrical equipment also continue to increase. The ( XLPE ) cable with good electrical and thermal performance and simple structure, the manufacturing cycle is short, safe and reliable power supply etc, which is widely used in power system ; Partial discharge is in the power cable to run a larger security risks is a sign of deterioration of the cable insulation is caused by insulation deterioration of important reasons . In this paper, based on variable frequency resonant damped oscillatory wave voltage XLPE cables and their connectors partial discharge site detection technology, the damped oscillatory wave voltage and power frequency voltage equivalent; the field test requirements, parameter optimization and performance detection impedance, and use advanced digital signal processing methods to analyze the test data processing, to provide a reference for the cables and their joints more accurately determine the insulation condition.

The Experimental Study on the Influence of Human Body to Measurement of High Voltage Power Frequency Electric Field

Based on the basic theory of electromagnetic field, the Electric Field Distortion (EFD) in power frequency electric field caused by induced current of human body has been analyzed. The enhancement factor of the electric field distortion is introduced to reduce the influences caused by human body in the measurement of high voltage electric fields. The Ansoft Maxwell is used to simulate and calculate the electric field distribution under the influence of the human body to have the value of enhancement factor. In addition, the enhancement factor has been corrected by experiment with the electromagnetic field analyzer EFA300. With the enhancement factor introduced in this paper, the measurement error can be reduced.

A Design of Circuit and its Application of the Power Frequency Voltage Linear Superposition Method

In order to improve the power frequency voltage ratio standard calibration techniques to meet the application of UHV power grid，a measuring circuit based on power frequency voltage linear superposition method was proposed. A three-port network was fromed by connecting two shielding voltage transformer with the same rated voltage ratio in series. The voltage coefficient of a voltage transformer was tested by double voltage method based on the proportionality and superposition of the linear network. The measuring circuit based on power frequency voltage linear superposition method can prevent the shielding error of the voltage transformer during the mearurment, making it used in voltage ratio standard self-calibration system with higher voltage and precision. The test has proved the feasibility and accuracy of circuit of power frequency voltage linear superposition method.

Lightning back flashover double circuit tripping pattern of 132 kV lines in Malaysia

This paper presents a study on flashover patterns due to double tripping using EMTP software. The simulation was performed on a 132kV line double circuit for economic installation of transmission line arresters (TLAs). The simulation results were validated with the field data of 132kV transmission line in Malaysia. A vertically configured double circuit transmission line was modelled and the effects of tower footing resistance, lighting current values, power frequency voltage and the coupling effect of the phase conductors study were taken into account. A good agreement between the simulation and field data was obtained. A specific back flashover phase of the double circuit line can be determined by considering the effects that have been mentioned. Through determination of the tripping pattern, a suitable installation of line arresters and mitigation of line tripping due to back flashover can be achieved.

Electrical Characteristics of Dielectric-Barrier Discharges in Atmospheric Pressure Air Using a Power-Frequency Voltage Source

Dielectric-barrier discharges (DBDs) in atmospheric pressure air have been studied by using a power-frequency voltage source. In this paper the electrical characteristics of DBDs using glass and alumina dielectrics have been investigated experimentally. According to the Lissajous figures of voltage-charges, it is discovered that the discharge power for an alumina dielectric is much higher than that for a glass dielectric at the same applied voltage. Also, the voltage-current curves of the glass and alumina dielectrics confirm the fact that the dielectric barriers behave like semiconducting materials at certain applied voltages.

Design of Triggering Device for VFTO Measurement System

Very fast transient overvoltage (VFTO) can be generated during the operation of disconnect switch (DS). Especially in ultra high voltage (UHV) gas insulated substation (GIS), VFTO is a threat to the safety of the power system equipment. It is very important to measure VFTO waveforms accurately. VFTO waveforms are comprised of high frequency voltage superimposed on the power frequency voltage in source side of DS and high frequency voltage superimposed on step-wise voltage in load side. How to trigger oscilloscope to acquire data is a big problem in measuring process. According to the features of VFTO waveforms, new triggering device consisting of a high pass filter is designed. The output of measurement sensor is used as the input of the high pass filter, and the output of the high pass filter is used to trigger oscilloscope. When the DS is not operated, there are no signals output from the high pass filter and the oscilloscope is waiting for trigger. After the operation of DS, the high frequency signals will pass the filter to trigger oscilloscope to acquire data. The device can guarantee the oscilloscope to complete a data acquisition properly.

The Electrical Insulation Property of PTFE Cannula in High Elevation

The polytetrafluoroethylene (PTFE) with the good dielectric property is a kind of nonpolar material. Made from the PTFE, the cannula has the high electrical insulation performance. This cannula can be applied to the equipment which requires for the high electrical insulation. There are 3 kinds of power-frequency voltage resistant experiments on PTFE cannulas with the inner diameter and outer diameter of 0.55/1.35, 0.7/1.5, 0.96/1.6, 0.46/0.96, 1.5/3.0 in the 1970m elevation. The PTFE cannulas are tested at the 85kV power-frequency voltage with the pure condition, the humidity condition, and the polluted condition separately in 1 minute. The result induced that the PTFE cannula did not be destroyed in all of the above experiments with no puncture sound, no smoke, no flashover and no burning. The insulating quality of the PTFE cannula is satisfied with the insulation requirement of the 85kV, i.e., the pollution level I.

Simulation and measurement of the voltage distribution on high voltage suspension Porcelain insulator string under pollution condition

Satisfactory operation of suspension insulator strings is intimately related to the voltage distribution of the string. At operational voltage, the voltage distribution along insulator string is affected by stray capacitances, which causes a non-uniform voltage distribution. In addition, the performance of insulator changes by the accumulation of environmental pollution over its surface that will deteriorate by absorption of moisture sharply. In order to explain this dilemma clearly, a full equivalent circuit, which takes into account the insulator material properties and the stray capacitances, is derived from the Finite Element Method Based Software, which is implemented in the EMTP-ATP package to calculate the voltage distribution, power loss and the leakage current, flowing through the string with and without pollution under power frequency voltage. Finally, the simulation results of voltage distribution have been compared with experimental results, which were obtained in the High Voltage Laboratory. In experimental procedure, an attempt to form the pollution on the surface of the insulator has been carried out. For this investigation the dry pollutant on the insulator surface has been approached according to IEC60507, which has led to the resistance of pollutants. Then, the voltage distribution of clean and polluted insulator strings has been measured by sphere gap method.

A Self-healing Scheme of Single-phase-to-ground Fault in Smart Power Distribution System

The paper presents a self-healing scheme of single-phase-to-ground fault in smart power distribution system. The scheme consists of three parts: single-phase-to-ground fault detection, faulted feeder selection and faulted feeder isolation. Fault detection is based on power-frequency voltage measured by a voltage transducer. A single-phase-to-ground fault is detected when measured voltage is greater than threshold. A fault generated current traveling waves are used to identify faulted feeder. The feeder with different initial traveling wave's polarity to other feeders is selected as faulted feeder. When faulted feeder is identified, the interconnection switch between different bus-bar is switched on firstly, then the switch at the load side of faulted feeder is switched off to isolate the load from the fault, the switch at the power source side of faulted feeder is switched off to isolate the source from the fault lastly. Simulation studies show that the scheme can meet the requirements of isolating single-phase-to-ground fault without affecting power supply to the load.

Investigation on a Novel Four-Quadrant Power Electronic Transformer

Power Electronic Transformer (PET) has potential application value in distribution network. This paper presents a novel PET with only one stage single-phase to single-phase AC/AC converter at the primary side of the transformer, the high voltage end, which generates high-frequency alternating voltage. The secondary side of the transformer, the low voltage end, is also one stage AC/AC converter, by which low power frequency voltage can be created. The final stage is a resistive converter obtaining low DC output voltage and unitary input power factor. Consequently, the unitary power factor can be reflected to the mains side and the PET owns a four-quadrant operation capability. The theory of four-quadrant PET is analyzed and the simulation analysis using MATLAB/SIMULINK is also provided. The result shows that this kind of PET holds some prominent advantages such as simple structure, easy to control, safe commutation, unitary input power factor, bidirectional power flow and easy to cascade. So it has application value.

Measure Characteristic of UHV Power Frequency Voltage Ratio Standard

In order to meet the urgent needs of voltage measurement traceability and transfer in the construction of ultra-high voltage power grid, 1000kV series standard voltage transformer is developed as the standard instrument, and then its measurement characteristics is tested. According to the theory and construction of the series power frequency voltage ratio standard, semi-insulating transformer voltage summation is proposed to make the voltage ratio measurement of SSTV whose accuracy can reach the 0.02 level trace to the source of national power frequency ratio standard of 500kV successfully. The compatibility is better than compared to traditional voltage coefficient measuring method.

Enhancement of Power System Stability Using Adaptive Combinational Load Shedding Methods

In the modern power systems operating at lower stability margins, conventional non-adaptive schemes cannot offer adequate protection for securing the power system, especially against combinational events. For major disturbances, the active power deficit is usually accompanied by reactive power deficit and frequency stability and voltage stability of the system are jeopardized simultaneously. In this paper, three adaptive combinational load shedding methods are proposed to improve operation of the conventional underfrequency load shedding scheme in order to enhance power system stability following severe disturbances. The proposed methods use locally measured frequency and voltage signals to counteract such events. In the proposed algorithms, load shedding is started from the locations which have higher voltage decay for longer period of time. The speed, location, and amount of load shedding are changed adaptively depending on the disturbance location, voltage status of the system, and the rate of frequency decline. Operation of the conventional and the proposed load shedding methods have been simulated in an actual large network. Obtained simulation results confirm that the proposed methods provide considerable enhancement in the power system voltage stability margin, and by using the proposed algorithms, various power system blackouts could be prevented.

Design of 33kV Transformer Bushing Insulator from NR and HDPE

Abstract This research presents a design of transformer bushing insulation at high-voltage wire connection side. The bushing insulator is made from composite materials between natural rubber (NR) and high-density polyethylene (HDPE). The HDPE has been utilized to increase a weather resistance property of natural rubber, such as ultraviolet resistance, temperature, heat resistance, and so on. The blend ratio of materials depends on NR 60% and HDPE 40%. To study properties of insulator material, it is tested by using ASTM D2240, ASTM D412, ASTM D257-99 and ASTM D149-05 standard. The test results shown that the composite material has a tensile strength equal to 4.28 ± 5.4 MPa, volume resistivity more than 2.14 × 1016 Ω-cm and surface resistivity about 5.56 × 1016 Ω/square. This insulation material can be withstanding a maximum AC power frequency voltage about 19.7 kV/mm. In additional to design, the electric field distribution around the bushing insulator is analyzed by using a finite element method (FEM). The highest electric field strength occurs at wire connector and equal to 0.95 kV/mm. Finally, the developed bushing insulator has been installed on 33 kV distribution systems at Saraburi province.

A novel protection and control strategy for high-voltage power frequency control system

The complicated structure and high power density make the protection and control of high voltage power frequency control system difficult. This paper proposed the novel protection and control strategy covered different parts of the system. Taking advantage of microprocessor protection system realised the system-level protection covered the fault of rectifier input, DC link, inverter output and even the induction motor. Improve the main circuit to strengthen security and stability in device level. The paper also analysed the cooperation of the protective trip and PWM pulse blocking and validated the feasibility of dual breaker setting to restrain feedback energy.

Finite element analysis of electric field around an ice-covered semi-conducting glazed insulator using a form of Kelvin transformation

This paper describes electric field distributions around a semi-conducting glazed standard post insulator for power frequency, lightning impulse(1.2/50 μs) and switching impulse(250/2500 μs) voltages under icing conditions, which were computed numerically using finite element method. Thin glaze coating on the insulator requires a very large number of elements for finite element analysis because of an open boundary around an ice-covered insulator. To reduce number of elements and hence computation time, the region between domain of interest and infinity was modeled by a form of Kelvin transformation. Simulation results are compared with laboratory experiments and are found to be in agreement.

Research of Zero-Cross Modulation Technology

The zero-cross modulation technology is a communication technology for distribution network, different from the traditional distribution network power line carrier communication technology. Its basic principle is to use the TWACS of the power frequency voltage fundamental wave to realize the signal transmission, and the modulation signal frequency is low It can be long-distance communication across the transformer. The data reliability and data through rate are high. It has broad application prospects in real-time communication less demanding situations. This paper first introduces the principle of the zero-cross modulation technology, and then details the generation and the identification of the voltage modulation signal. Practice shows that the transmission success rate of zero-cross modulation signal is up to100%. Meet the actual needs.