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Natural polluted insulator surfaces are always coated with various kinds of soluble constituents, and those constituents affect flashover performance differentially. Currently, this fact is not considered either in laboratory experiments or field pollution degree measurements, causing the existing insulation selection method to be deficient. In this paper, a systematic study on insulator flashover voltage gradient correction involving different types of soluble pollution constituents is presented. Using a typical type glass insulator as the sample, its flashover tests, polluted by typical soluble chemicals (NaCl, NaNO3, KNO3, NH4NO3, MgSO4, Ca(NO3)2 and CaSO4), were carried out. Then, the flashover gradient correction was made by combining the flashover performance of each soluble constituent, the equivalent salt deposit density (ESDD) contribution of the seven constituents, and the saturation performance of CaSO4. The correction agreed with the flashover test results of insulator polluted by three types of soluble mixture. Research results indicate that the flashover gradient correction method proposed in this paper performs well in reducing the calculating error. It is recommended to carry out component measurements and flashover gradient correction to better select outdoor insulation configuration. [ABSTRACT FROM AUTHOR]

In this study, icing flashover performance tests of typical DC porcelain, glass, and composite insulators are systematically carried out in a multifunction artificial climate chamber. The DC icing flashover voltages of seven typical insulators under various conditions of icing thickness, pollution severity before icing, string length, and atmospheric pressure are obtained. The relationships between icing thickness, salt deposit density as well as atmospheric pressure and the 50% icing flashover voltage are analyzed, and the formulas are obtained by regression method. In addition, the DC icing flashover voltage correction method of typical porcelain, glass, and composite insulator in the coexisting condition of high altitude, contamination, and icing is proposed. [ABSTRACT FROM AUTHOR]

In the current study, a multi-arc predicting model for DC critical flashover voltage of iced and pre-contaminated long insulator strings under low atmospheric pressure is developed. The model is composed of a series of different polarity surface arcs, icicle-icicle air gap arcs, and residual layer resistance. The calculation method of the residual resistance of the ice layer under DC multi-arc condition is established. To validate the model, 7-unit and 15-unit insulator strings were tested in a multi-function artificial climate chamber under the coexistent conditions of low air pressure, pollution, and icing. The test results showed that the values calculated by the model satisfactorily agreed with those experimentally measured, with the errors within the range of 10%, validating the rationality of the model. [ABSTRACT FROM AUTHOR]

Abstract-The Qinghai-Tibet Railway is the highest railway in the world. Up to now, there were no test and service data for the external insulation of the power-supply project of the railway system above 4000 m above sea level (a.s.l.). The "g" parameter method recommended by IEC Publication 60.1 (1989) has a limited applicable range. Therefore, based on the former tests carried on the artificial climate chamber (ACC), in this paper, a series of test investigations is conducted on the positive switching impulse (PSI) discharge performance of rod-plane air gaps with gap spacing of 0.25 to 3.0 m at the six high-altitude sites along the Qinghai-Tibet Railway with altitudes of 2820 to 5050 m. With analyses of the mathematical optimization method on the test results, the new correction method of discharge voltage is proposed. They are also checked and compared with the test results obtained from the simulation tests carried out in the ACC. It is indicated that the 50% PSI discharge voltage U[sub50] of the air gap at high altitude is a power function of gap spacing d, also a power function of relative pressure of dry air and absolute humidity. The influence law of atmospheric parameters on U[sub50] obtained at high-altitude sites is the same as that obtained in the ACC. U[sub50]. obtained in the ACC, is about 8.15% higher than that obtained at high-altitude sites due to the influence of nonsimulated factors, such as ultraviolet ray and cosmic radiation. The "g" parameter method is not applicable to the regions with an altitude above 2800 m. [ABSTRACT FROM AUTHOR]

Based on the artificial pollution tests, the fiashover performance of various types of dc porcelain and glass suspension insulators as well as composite long-rod insulators were analyzed and compared. The test results show that there is a nearly linear relation between the pollution fiashover voltage and the disc-type insulator string length. The flashover voltage gradients of the insulators are affected by their materials and shed shapes. The antipollution performances of glass insulators are superior to those of porcelain insulators with the same profile. The fiashover voltage gradients of composite insulators are higher than those of porcelain or glass ones. The exponent characterizing the influence of salt deposit density on the pollution flashover voltage is dependent on the profile and the material of insulators, and the values of the composite insulators' exponents are smaller than those of porcelain or glass insulators, namely, the influence of the pollution on the composite insulators is relatively less. The effectiveness of leakage distances of porcelain or glass insulators is less than 0.9 while that of composite insulators is higher than 0.9. [ABSTRACT FROM AUTHOR]

Switching impulse discharge performance of air gaps at high altitudes, which is a fundamental in the extremely high voltage external insulation design, remains an unsolved key technology across the world. Due to the limited applicable range of ‘g’ parameter method recommended by IEC Publication 60-1(1989), this paper aims to explore the relationship between positive switching impulse 50% discharge voltage U50 of rod-plane air gaps and atmospheric parameters, and proposes two new voltage correction methods based on the parameter ‘g’ and the atmospheric pressure ratio, respectively. The two methods have been proved by the experimental investigations carried out on 1-m rod-plane air gap both in the artificial climate chamber and at three spots of different high altitudes in this study. The results show that, if the additional influence of absolute humidity is considered, the positive switching impulse 50% discharge voltage U50 of rod-plane air gaps is a power function of relative pressure and relative air density; the ‘g’ parameter method in IEC Publication 60-1(1989) is not applicable to the regions with an altitude above 2000 m or the condition of h/δ > 15 g/m³ compared with the correction method based on the ‘g’ parameter method, the correction method based on relative atmospheric pressure has a wider applicable range and less error; when the absolute humidity increases 1 g/m³, U50 varies within the range of 1.0%–1.15%. [ABSTRACT FROM AUTHOR]

Based on the results of experimental investigations performed on the polluted and iced IEC standard suspension insulator strings of 3∼21 units, the ac flashover performance and discharge process are discussed in this paper. It is put forward that the icing stress product (ISP), defined as the product of the ice-layer conductivity and the ice layer weight per centimeter of dry arc distance can be taken as a characteristic parameter to indicate the effect of ice accretions and contaminants on the flashover voltage. The flashover stress of an ice-covered insulator string can be expressed as a power function of ISP and has a linear relationship with the length of the insulator string. The partial arc of an iced insulator string is initiated by the breakdown of the air gaps between the tips of icicles and iced insulator surface and the persistence is much longer than that of a polluted insulator string. [ABSTRACT FROM AUTHOR]