Salt Deposit Density Research Articles

Three-dimensional FEM electrical field calculation for FRP hot stick during EHV live-line work

In February and December 2012, SaskPower experienced two flashovers of Fiberglass-Reinforced Plastic (FRP) hot stick during cold weather live-line work under steady-state 230 kV ac system conditions. As for SaskPower, Manitoba Hydro had two separate live-line tool flashover events, in 1997 and 2002. Clean-fog tests and non-uniform wetting tests at Hydro-Quebec Research Institute (IREQ), and cold-fog tests at Kinectrics and UQAC were carried out to explain these flashovers. The laboratory tests demonstrated that inadvertent contamination of clean tools at a very light level () of Equivalent Salt Deposit Density (ESDD) likely reduced voltage withstand capability of FRP hot sticks, particularly under freezing conditions. The flashover mechanism was identified when surfaces become fully wetted by the environment or surrounding fog. However, the source of moisture in field flashovers well below 0°C, i.e. as low as -19°C, was not identified. This study is based on laboratory tests and on using available pollution flashover models to explain the results. In this paper, the main objective is to determine the potential and electric field distribution along a FRP hot stick under dry condition and non-uniform wetting. A commercial software, COMSOL MultiphysicsTM, based on the finite element method (FEM), was used for the three-dimensional modeling and simulations. The results obtained will be useful to improve knowledge on the determination of discharge initiation conditions based on electric field distributions along a FRP hot stick.

A coupled computational fluid dynamics and heat transfer model for accurate estimation of temperature increase of an ice-covered FRP live-line tool

Controlled laboratory tests validated a hypothesis that extremely light (~2-3 μg/cm2) levels of Equivalent Salt Deposit Density (ESDD) with no Non-Soluble Deposit (NSDD) can reduce voltage withstand capability of Fiberglass-Reinforced Plastic (FRP) hot sticks under cold-fog conditions near the freezing point, where the tool surfaces are fully wetted by the environment or alternately surrounded by fog. However, the source of moisture in flashovers at temperatures below -13 °C was not established. The mechanism of tool surface wetting was explored through coupled Computational Fluid Dynamics (CFD) and Heat Transfer mathematical equations for a FRP hot stick modeled in Commercial software, COMSOL Multiphysics. The results show that the flow of partial discharge current could be sufficient to raise the temperature of an iced pollution layer just below freezing, where the cold-fog flashover mechanism prevails.

Analysis of Natural Pollution Deposit on Optic Sensor for Monitoring of Insulator Contamination

This paper describes a system for the online monitoring of insulators contamination, the system monitors equivalent salt deposit density near insulators on the power system by using optical technology. This paper mainly analyzes contamination components on optical sensor surface of different pollution sources coming from 17 sites in Sichuan, the inland areas of China, and draws the conclusion that calcium sulfate of industrial sources is more than ones of agricultural sources.

Understanding the discharge activity across GFRP material due to salt deposit under transient voltages by adopting OES and LIBS technique

In the present study, breakdown characteristics of a glass fiber reinforced plastic (GFRP) with different salt deposit densities (SDD) under standard lightning impulse (LI)/ switching impulse (SI) voltages are studied. Optical emission during discharge process and the discharge current are measured simultaneously. It is observed that flashover voltage (FOV) reduces with increase in salt deposit density on GFRP material under LI/SI (irrespective of the polarity of applied voltage) voltages. It is also observed that irrespective of level of SDD, the FOV is less with SIV compared with LIV. FOV under negative SIV is less compared with positive SIV. Optical emission corresponding to Na I emission at 589 nm in discharge plasma follows the discharge current profile and also the lifetime of Na I emission is high under switching impulse compared with lightning impulse voltages. Na I emission in the discharge plasma sustains for a longer period in case of negative switching impulse voltages. Plasma temperature is estimated using emission lines and it is observed that the local temperature during discharge process is high under negative switching impulse voltage. With increase in salt deposit density, the optical emission spectrum of GFRP material in addition of Na I line at 589 nm is observed. Laser induced breakdown spectroscopy (LIBS) technique is proposed and demonstrated for the detection of a salt deposit on a GFRP material from a standoff distance of 1 m. In addition, temporal and spatial profile of laser induced plasma on the polluted GFRP material is used to quantify the salt deposit. Laser fluence less than 5 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is ideally suited to rank the severity of a salt deposit on GFRP material at an incident laser wavelength of 1064 nm.

Pollution flashover calculation model based on characteristics of AC partial arc on top and bottom wet-polluted dielectric surfaces

A double-arc model, which considers the differences between characteristics of AC partial arcs on top and bottom surfaces, was proposed for predicting the flashover voltage of polluted insulators in this paper. The arc constants parameters, the arc reignition criteria, as well as the radii of arc columns in the proposed model were determined by measuring partial arcs on the top and bottom wet-polluted surfaces of a triangular glass plate separately. A “II” type glass model was made to investigate the partial arc propagation process by using an ultra-high speed camera. It has been found that the arc length increased linearly with leakage current amplitude, the ratio of arc length increments on top and bottom surface was related to salt deposit density (SDD) rather than leakage current. Based on above-mentioned researching results, the double arc calculation model was established, and the calculated results were in good agreement with the experimental results.

Contribution of Design Parameters of SiR Insulators to Their DC Pollution Flashover Performance

Compared to HVAC, the application experience of composite/polymer insulators in HVDC transmission lines is limited. However, the tendency to utilize them in HVDC transmission lines, where pollution flashover is a major problem, is growing due to their water-repellent feature. This trend demands understanding insulator flashover performance and recognizing key parameters in the design and dimensioning of insulators. This paper presents the measurement and analytical results for dc pollution flashover of silicon rubber insulators at extra heavy pollution conditions. Two approaches are employed to model flashover voltage gradient and quantify the contribution of salt deposit density, specific leakage distance, average diameter, shed spacing to shed depth ratio, and form factor to insulator pollution performance. Developing a nonlinear regression model, the effect of the mentioned parameters on pollution flashover is studied. Then, the artificial neural network (ANN) and randomization method are used to develop a model to interpret parameters contribution to pollution flashover, and the results are validated with those of the regression method. Finally, by applying an ANN-based randomization approach, a multi-input model is created to quantify the significance of different parameters in flashover voltage gradient. The model ranks specific leakage distance and average diameter, respectively, as the most and least important geometrical characteristics in pollution flashover performance of SiR insulators. The method and results can be a source of information to optimize the design and dimensioning of HVDC SiR insulators especially in severe pollution conditions.

Artificial pollution flashover performance of porcelain long rod UHVDC insulators at high altitudes

Porcelain long rod insulators are recommended for outdoor insulation of UHV/EHV dc transmission lines because of their excellent service experience obtained in Central Europe. However, very few studies have been conducted on dc pollution flashover performance or the UHVDC insulators at high altitudes. Artificial pollution tests on 300 kN and above porcelain long rod insulators were carried out with dc voltage in natural high altitude areas (about 2000 m), in which the solid layer method was used and the 50% flashover voltage (U50%) was measured with the up-and-down method. Test results show that dc pollution flashover performances of the 300 and 400 kN insulators are similar. The exponents characterizing influence of salt deposit density on the flashover voltage vary from 0.46 to 0.57. A nearly linear relationship between the flashover voltage and the string length of the insulators is presented. Both double suspension strings and tension string patterns have a significant influence on the flashover voltage. The influence of non-uniform pollution distribution between the top and bottom surfaces of the insulator sheds on the flashover voltage is analyzed, and a correction coefficient for the insulators is proposed.

The Research on Deposition Saturation of Disc Suspension Porcelain Insulator

The equivalent salt deposit density (ESDD) is an important characteristic of our country which is used to measure insulator deposition level. The contamination of the insulator would reach saturation after a period of time.In order to increase the specific creepage distance, disc suspension porcelain insulator lower surface inward concave, which makes the rain washing the upper surface difficult, that cause the saturation time of lower surface longer than upper surface .For studying the operation insulator contamination saturation time and reflecting the ESDD of the actual operation line accurately,this paper adopts a comparison method between empty hanging insulator surface and operation insulator surface to measure the ESDD , the field experimental results further verify that the saturated time of disc suspension insulator lower surface is longer, so as to lay the foundation for the ESDD measurement.

Silicone rubber insulators for polluted environments part 2: textured insulators

The design principles and prototype manufacture of 11kV silicone-rubber composite textured insulators are described. The moulded surface texture increases the maximum creepage length from 375 mm to 503 mm for the four-shed profile used. The trunk sections of the insulator are patterned with a square-section array of hemispherical protuberances, and the shed undersides with interlaced logarithmic spirals of hemispherical ridges. Both textures are sufficiently shallow to facilitate fabrication, to allow effective washing and to avoid an increased salt deposit density (SDD) in artificial pollution tests. The test procedures which were developed in Part 1 of the paper are applied here to the textured prototypes. These procedures had been shown to quantify reliably the performance of conventional non-textured insulators of the same profile: the variation of flashover voltage and leakage current due to the silicone-rubber formulation, SDD and wetting rate could be measured. For textured insulators, it is found that the increased creepage distance improves the flashover voltage by up to 27%, with a corresponding reduction of pre-flashover leakage current. Comparative tests for two silicone-rubber formulations of different hydrophobicity and pollution performance were performed. Although very severe pollution causes a large reduction in flashover voltage, surface texturing mitigates this reduction effectively. This is particularly relevant to recent concerns expressed in IEC-TS 60815-3 (2008) relating to the selection and dimensioning of high-voltage a.c. polymeric insulators for use in heavily polluted conditions.

The Method of Calculating Polluted Insulator's Flashover Voltage Based on ANN

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 ρESDD and nonsoluble deposit density ρNSDD ,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.

New Methodology of Monitoring for the Contamination Degree of Insulators

Insulator is an essential part of overhead line. In recent years, the news about the insulator flashover is increasing. The main reason of insulator flashover is insulator surface contamination. Insulator flashover is a serious threat to the safe and stable of transmission lines operation. With the development of China's comprehensive national strength, power companies and power users demand on grids stability is highly increased. Currently usual methods of insulator monitoring are ESDD (equivalent salt deposit density), experiment and on-line detecting of leakage current [. But they can't fully meet our requirements. Now this paper will present a new method, which is made correlation analysis by harmonic analysis based on two ends of the existing lines to the data acquisition apparatus of voltage and current signals. Without additional hardware devices online monitoring of insulator surface contamination can be achieved.

Prediction of Insulator's Equivalent Salt Deposit Density in Power System

The equivalent salt deposit density (ESDD) of insulator in power system is the main basis of defining pollution classes and mapping pollution areas. However, The meteorological factors on it is complex, using traditional methods is difficult to establish accurate mathematical model to express the relationship, In this paper, the gray theory and neural network model to reflect the changing trend of data series on the apparent effect, Gray neural network model used to predict the insulators ESDD under certain meteorological factors, and to design a neural network compensator correction on the predicted results. The simulation results show that the model has higher prediction accuracy, better than a simple gray neural network model, and have certain theoretical value and practical application value.

Prediction of flashover voltage of insulators using least squares support vector machine with particle swarm optimisation

This paper describes the application of least squares support vector machine combined with particle swarm optimisation (LS-SVM-PSO) model to estimate the critical Flashover Voltage (FOV) on polluted insulators. The characteristics of the insulator: the diameter, the height, the creepage distance, the form factor and the equivalent salt deposit density were used as input variables for the LS-SVM-PSO model, and critical flashover voltage was estimated. In order to train the LS-SVM and to test its performance, the data sets are derived from experimental results obtained from the literature and a mathematical model. First, the LS-SVM regression model, with Radial Basis Function (RBF) kernel, is established. Then a global optimiser, PSO is employed to optimise the hyper-parameters needed in LS-SVM regression. Afterward, a LS-SVM-PSO model is designed to establish a nonlinear model between the above mentioned characteristics and the critical flashover voltage. Satisfactory and more accurate results are obtained by using LS-SVM-PSO to estimate the critical flashover voltage for the considered conditions compared with the previous works.

Study on Method and Device Used for Evaluating the Contamination Condition on the Surface of Composite Insulator

In this paper, method and device Used for evaluating the contamination condition on the surface of composite insulator was proposed. The method proposed in this paper considered the hydrophobicity and pollution degree on the surface of composite insulator at the same time. Under the condition of different basic Salt deposit density and different migration time the suitability of dissolution Salt deposit density method was studied. The test results show that the dissolution Salt deposit density with the increasing of migration time gradually reduced at the same basic Salt deposit density. The dissolution salt deposit density with the increasing of basic Salt deposit density gradually increases at the same migration time. It is found that the dissolution salt deposit density method proposed in this paper can well evaluate the contamination condition on the surface of composite insulator.

Study on AC Flashover Performance for Different Types of Porcelain and Glass Insulators With Non-Uniform Pollution

The ratio <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> of top to bottom surface salt deposit density (SDD) affects the ac pollution flashover performance of disk insulator strings. The ac pollution flashover stress was established for fifteen different combinations of SDD and T/B in a systematic study, making use of seven-unit suspension strings with six different disk profiles in this paper. Then a comparison was made of pollution performance for glass and porcelain disks with the same profile. The observed relation of ac flashover stress <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EL</i> to SDD and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> followed an equation of the form <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EL</i> = <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> ·SDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> ·(1- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> ·log( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> )) . The values of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> were fitted to test results for glass and porcelain disks of identical bottom-rib profile, and to four other bottom-rib and external-rib profiles. A reduction in the ratio <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> from 1/1 to 1/15 gave a median 26% ± 8% increase in flashover strength, corresponding to the calculated increase in overall pollution layer resistance. Extrapolation of results for the seven-unit strings to UHV dimensions suggests that some reduction in leakage distance can be accepted in areas where there is frequent natural washing of the top surfaces of disk insulators.

Optical Fiber Sensor Salt Dense On-Line Monitoring Research

To detect the pollution level of insulators in operation, based on light energy loss theory of medium optical wave guide and mathematical modeling of least squares supporting vector machine, by a lot of contrast tests, this paper designed and developed monitoring terminal of optical sensor. Collecting live temperature, humidity luminous flux attenuation etc. and sending the collected data to data monitoring centre through GSM data communication module, the workstation of data monitoring centre could calculate to get equivalent salt deposit density (ESDD) using mathematical model, so that insulators pollution level can be detected on-line automatically and continuously.

Effect of ultrasonic fog on AC flashover voltage of polluted porcelain and glass insulators

Three wetting methods are frequently used for polluted insulators in artificial fog tests, i.e. cold fog, steam fog and mixture fog. IEC recommended the steam fog wetting method. However, experimental experience shows that, it is difficult to control wetting time with this steam input rate. In addition, the temperature in climate chamber rises over the duration of the test. Both factors make the steam fog test less representative. Porcelain and glass insulator strings of 3 units are wetted by ultrasonic fog in an artificial climate chamber. The flashover performances of polluted insulators are studied. The test results revealed that the relationships between flashover voltage and Salt Deposit Density (SDD) can be expressed as negative exponential functions for porcelain and glass insulators. However, the fitting formulas, which are simulated ac pollution flashover voltages at various pollution degrees for the same type of insulator, are consistent at various conductivities of the applied water. Moreover, the relationships between flashover voltage and conductivity of the applied water can also be expressed as a negative exponential function.

Volcanic ash contamination: limitations of the standard ESDD method for classifying pollution severity

The pollution severity of airborne contamination on high voltage insulation has traditionally been quantified by calculating the contaminant's equivalent salt deposit density (ESDD). Volcanic ash is a rare but severe form of airborne pollution, and the high conductivity of wet volcanic ash (often >1.3 × 10-4 S/cm) can cause pollution-induced insulator flashover. This paper presents the ESDD and non-soluble deposit density (NSDD) for four different fresh volcanic ash samples and two ash proxies measured at different thicknesses using a standardised plate test. Results show that there is a log-linear increase of ESDD with increasing NSDD. Tests indicate that a 3 mm thick deposit (NSDD between 158 and 231 mg/cm2) of fresh volcanic ash yields an ESDD between 0.02 and 0.7 mg/cm2, suggesting that ash can have high contamination severity and therefore potential to cause pollution-induced insulator flashover. Whilst the ESDD/NSDD method provides direct analysis of the ionic content of a contaminant, the procedure is time consuming, cannot accommodate the high NSDD of volcanic ash for site pollution severity classification and does not account for changes in the contaminant's electrical conductivity under different environmental, chemical and physical conditions. Given these limitations, this study proposes an alternative, simple yet more comprehensive technique for investigating the electrical properties of volcanic ash by means of direct resistivity analysis.

Comparative evaluation of the leakage current and aging performance of htv sr insulators of different creepage lengths when energized by ac, dc+ or dc– in a severe marine environment

This paper compares the performance of HTV (high temperature vulcanized) silicone rubber power line insulators under AC and both polarities DC when subjected to natural pollution. The investigation was conducted at Koeberg Pollution Test Station (KIPTS) which is situated near Cape Town and is known for its severe coastal pollution and high humidity during the night. High rainfall is experienced during winter. Five insulators of different creepage lengths and of the same manufacture were energized by each voltage type, while being exposed to the environment for 310 days. The leakage current data of all insulators were logged, together with the weather data. Pollution levels were measured on a regular basis, using the ESDD (equivalent salt deposit density) method and directional dust deposit gauges (DDDG). High leakage current levels were recorded in summer due to the high pollution levels and high humidity. During winter, in contrast, lower levels of leakage current were recorded, confirming the washing effect of the winter rain. The leakage current levels for the silicone rubber insulators were of a similar order of magnitude for AC and positive DC, but lower for negative DC. Electrical discharge activities on the insulators were recorded at night and surface erosion was monitored at set intervals. A polarity effect relating to pollution performance and aging was confirmed on DC energized insulators.

Online measurement of equivalent salt deposit density by using optical technology

In this paper, the optical technology is used to monitor ESDD near insulators on transmission line. This technique is based on the light energy loss and the distribution of optical field in the dielectric waveguide. Under the same measure environment, there has the certain correlation between the ESDDs of the polluted insulators and the ones of the quartz glass rod. Based on the experimental results, artificial neural networks (ANN) has been developed to model the relationships between ESDD by the optical technology and the measured ones. The contrasts reveal that the ANN-calculated ESDDs have the same corresponding with the measured ones for a practical system.