Papers by Keyword: Flashover

Abstract: The electrical characteristics of insulating materials play a key role on the working performance and operation reliability of power equipment. With the rapid development of superconducting technology in recent years,the working temperature of high temperature superconducting power equipment can be controlled around the liquid nitrogen temperature. Due to its excellent dielectric performance and mechanical properties, polyimide have been widely used in power equipment at room temperature. However, polyimide, as a kind of cryogenic insulating materials, is rarely reported at present. Therefore, the study of the insulating characteristics of polyimide at the cryogenic temperatures is of great significance. The DC breakdown property and flashover performance of polyimide are tested around room temperature (300K) and liquid nitrogen temperature (78K). The results show that temperature has some effects on the DC breakdown property and flashover performance of polyimide.

Abstract: In this paper,the relationship between 50% ac flashover voltage (U₅₀) of long porcelain insulator string and ρ_ESDD and ρ_NSDD was analyzed based on experimental results. It was shown that the relationship between U₅₀ and ρ_ESDD is the same as the one between U₅₀ and ρ_NSDD, in which the U₅₀ reduces with the increase of ρ_ESDD by a power function, and the influences of ρ_ESDD and ρ_NSDD on U₅₀ are mutually independent. By using the least square method, the value of exponent of a and b were determined.

Abstract: Live working (LW) is performed to provide high reliability of transmission lines (TL). Only “bare hand” method of LW is used at voltage systems more than 200 kV. Live working (LW) is possible if the minimum approaching distances are in working place. This requirement provides the safety of LW excluding flashover of insulating gaps under the switching overvoltage impact. In some cases it is impossible to provide the required gaps in LW zone. In order to protect it against possible flashover, special arresters were designed. Their effect on overvoltage magnitude was checked in calculations.

Abstract: Various natural contamination components distributed on the surface of high-voltage insulators play important roles on the flashover hazard. Under the low humidity condition, the flashover voltage could be affected considerably by the sucrose contaminations. Molecular dynamics simulations have been carried out in order to reveal the microscopic mechanisms for the sucrose-involved flashover uptake. It is found that the diffusion of ions decreases significantly and thus the conductivity of aqueous medium is lowered apparently. In the presence of sucrose, the contact ion pairs formed between Na⁺ and Cl^- ions are enhanced because both ions are less coordinated to water molecules. The influence of the external electric fields on the diffusion and conductivity were investigated as well. It is suggested that the sucrose contamination might lead to the uneven electric fields on the insulator surface.

Abstract: Contamination Monitoring is an important means of preventing pollution flashover of electrical equipment, the monitoring data can make the insulator design more economical, leading to a both win in economic and operational safety. The existing monitoring tools are based mainly on ESDD, the measurement data is affected by many factors, limited guidance. This paper will analyze several of factors which have impact on ESDD, and also propose additional measures and many forward-looking recommendations to face the reality, so that we can carry out anti-pollution work better.

Abstract: The flashover phenomenon in biomass boiler causes serious damages to the equipments performance as well as security of people due to people are not clear about biomass boiler running, and thus preventing flashover from happening has a positive significance on boiler running. The characteristics of biomass fuel particles have been analyzed at first, and then simplifying the structure of boiler in order to model conveniently. This essay focus on justifying the stability of combustion system of biomass boiler with catastrophe theory in combination with the measured and calculated data, it demonstrates that swallowtail catastrophe conforms to the flashover mechanism. By building energy equation, conducting dimensionless treatment and carrying out the swallowtail catastrophe research method, the instability point is obtained. The gained critical flashover temperature of hot smoke layer is 686.71°C which is similar to predecessors studies, Then changing the parameters values for the sake of calculating different hot gas layer temperatures. The higher the hot gas layer temperature is, more hazardous the flashover tends to be. The research reveals that increasing the initial temperature of air or aggrandizing area of fire grate (larger than 3.36m²) contribute to increase flashover temperatures. However, augment of vapor heat and heat transfer area have the opposite effects.

Abstract: According to the test result about class insulator string of 32 units, a method of calculating 50% ac flashover voltage U₅₀ based on radial basis function network is put forward in this paper. Inputs of the model are equivalent salt deposit density ρ_ESDD and nonsoluble deposit density ρ_NSDD ,the output of the model is 50% ac flashover voltage of polluted insulator strings, the Orthogonal least squares algorithm was used to select right hide layer neurons and center vectors, and the weight from hide layer neurons to output layer neurons are determined by pseud-inverse method. The calculating result is in concordance with the test result, it is indicated that the model can give some references to access the pollution condition of external insulation.

Abstract: Study on pollution flashover characteristics of EHV system have great reference on engineering.In this paper,the relationship between 50% ac flashover voltage U₅₀ of class insulator string of 32 units and ρ_ESDD, ρ_NSDD was analyzed based on experimental results. It was shown that the relationship between U₅₀ and ρ_ESDD is the same as the one between U₅₀ and ρ_NSDD, in which the U₅₀ reduces with the increase of ρ_ESDD by a power function, and the influences of ρ_ESDD and ρ_NSDD on U₅₀ are mutually independent. By using the least square method, the value of exponent of a and b were determined.

Abstract: Considering that insulator flashover accident frequently occurs in high voltage transmission line, a kind of insulator string flashover positioning system is designed. The positioning system is on based on the fact that ultrasonic and ultraviolet energy is released when flashover occurs. To make sure whether a flashover accident occurred, sensors are used to detect ultrasonic and ultraviolet waves near the insulators in real time. The detecting results and accident position information will be uploaded to the monitoring center wirelessly using GSM/GPRS (Global System of Mobile communication / General Packet Radio Service), which can make it easy and fast for operating personnel to locate the accident, reduce troubleshooting work and quickly recovery power transmission. The experiment shows that the system has lots of advantages such as high sensitivity, high positioning accuracy, more stable and so on.

Abstract: As the improve of voltage class in power system and the aggravation of industrial pollution, flashover of contaminated insulators in HV and UHV system is growing, imperiling the security of power system severely. The linchpin of enhancing the security of system is excavating ways of monitoring status of insulator’s surface by some eigenvalues. In this paper, distinctive spectrum features of leakage current(LC) are computed, including power spectrum and bispectrum. The results show that bispectrum depicts the information of arc discharge in LC more valid than power spectrum, which is a good eigenvalue for flashover identification and risk predictions.