The number of single-phase faults in the transmission networks in wintertime increases substantially during cold atmosphere precipitation and after ice accretions followed by a rise in air temperature above 0/spl deg/C. >

Flashover problems caused by ice build up on insulators

Test methods for evaluating flashover voltage of ceramic and nonceramic insulators under ice, snow, and cold-fog conditions are recommended. The paper describes the procedure to be followed at various stages of an evaluation test including preparation of the test object, insulator precontamination, ice, snow, and cold-fog deposits as well as voltage applications and flashover voltage evaluation. Some relevant parameters for ice accretion, flashover voltage evaluation, artificial pollution, and power source requirements are taken from IEC 60129, IEC 60507, and IEEE Std.-4-1995 on standard techniques for high-voltage testing.

Insulator icing test methods and procedures: a position paper prepared by the IEEE task force on insulator icing test methods

A field observation of ice accretion on Hydro-Quebec HV insulators was carried out, as well as a laboratory investigation of the AC flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8/spl times/2.8 m/spl times/3.8 m climate room using a HV transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V/sub WS/) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V/sub WS/ of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm/sup 2/ on the same insulators. >

AC flashover performance of insulators covered with artificial ice

Internationally comprehensive studies were performed to analyze the effect of clean or contaminated snow and ice accretions on high-voltage insulators. The authors' experience with transmission lines in inland mountainous areas reveals a substantial contribution of pollution from anthropogenic (man-made) contaminants. One observation of a flashover case with thin rime ice layers in contrast to the many cases with thicker accretions without similar failures led to the question of the role of the ion content of the ice. Fifty-five ice samples were analyzed. The contributions to the conductivity from natural (sea salt) and man made ions (sulphur and nitrogen components) are given. It is shown that long-range transported anthropogenic ions contribute to more than 50% of the conductivity in 33 of the 55 cases. In 21 cases, the contribution was more than 80%. >

Long range transported pollutants and conductivity of atmospheric ice on insulators

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

Study on AC Flashover Performance and Discharge Process of Polluted and Iced IEC Standard Suspension Insulator String

Test apparatus and procedures were developed to test energized, non-contaminated, 120 kV system insulators under simulated freezing rain conditions. The flashover performances were compared between non-ceramic composite transmission line insulators and standard porcelain 53/4 x 10 inch suspension insulators. Standard and long leak Multicone porcelain insulators were also compared in the icing tests to standard porcelain station post insulators. Icing tests at several voltage stresses provided the full flashover-range of the insulators from the minimum or zero flashovers in ten trials up to the maximum or 10 flashovers in 10 trials. Using the desired insulator voltage stress flashover curve for specific insulator types and the voltage stress applied to the insulator, the comparative probability of flashover due to ice storms on the system can be evaluated for 120 kV, 230 kV and 345 kV systems.

Flashover test of Artificially iced Insualtors

Test apparatus and procedures were developed to test energized, non-contaminated, 120 kV system insulators under simulated freezing rain conditions. The flashover performances were compared between non-ceramic composite transmission line insulators and standard porcelain 5 3/4 x 10 inch suspension insulators. Standard and long leak Multicone porcelain insulators were also compared in the icing tests to standard porcelain station post insulators. Icing tests at several voltage stresses provided the full flashover range of the insulators from the minimum or zero flashovers in ten trials up to the maximum or 10 flashovers in 10 trials. Using the desired insulator voltage stress flashover curve for specific insulator types and the voltage stress applied to the insulator, the comparative probability of flashover due to ice storms on the system can be evaluated for 120 kV, 230 kV and 345 kV systems.

Flashover Tests of Artificially Iced Insulators

Testapparatusandprocedures were developed totestenergized, non-contaminated, 120kV systeminsulators undersimulated freezing rainconditions. Theflashover performances were compared between non-ceramic compositetransmission lineinsulators andstandard porcelain 53/4 x 10inchsuspension insulators. Standard andlongleak Multicone porcelain insulators were alsocomparedintheicing teststo standard porcelain station postinsulators. Icing tests atseveral voltage stressesprovided thefullflashover- range oftheinsulators fromthe minimumor zero flashovers intentrials up tothemaximumor 10 flashovers in10trials. Usingthedesired insulator voltage stress flashover curve forspecific insulator typesandthevoltage stress applied totheinsulator, thecomparative probability offlashover due toicestormson thesystem can beevaluated for120kV,230kV and 345kV systems.

G. L. Gaibrois

Papers

Flashover test of Artificially iced Insualtors

Flashover Tests of Artificially Iced Insulators

Flashovertestsof artificially icedinsulators