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Standards for Insulating links
ANSI/CPLSO-14
ANSI/UL2737 (Withdrawn)
ASTM F2973
MIL-L-24410 (Withdrawn)
Tests by Independent Organizations
Load Insulator
Miller & Hirtzer
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cause flashover. If the insulating link is polluted and sirnulta- neously wetPkd the citrrei?t can be large md ;can errdangex the operator. Flgure 2. Insulating Liak A instded on a em. The capacitive cqt cmsed by sudden excitation was analyzed using compu@r simulation [4]. Several groups [5-81, including one at Arizona State University [9], have performed laboratory tests on poilutdmt insulating links. The probabil- ity of flashover in case of a power line contact was previously detenmgd [lo]. The objectives of this paper are as follows: a) To understand the relationship between insulating link leak- age current pollution severity, and line voltage using data obtained fiom laboratory experiments. b) Asswment of the level of protection provided by the insu- lating link with the use of laboratory data. c) Investigation of arcing due to transient currents arising from the application of s-m. Figure 3. Insulating Link Aand B. 2 TESTMETHOD Arizona State University (ASU) investigated the perform- ance of two commercially available insulatfng links. Figure 3 shows Insulating Links A and B. Also, Figure 3 shows that the shapes of the two insulating W are different. insulating link A is a simple cylinder; Insulating Link B has a more eiabo- rated shape wiSb a pthlly amgated iwfme. Corngation increases the creepage distance, Insulating Link B is equipped with sensm, whi& records the voltage across the link. A lap- top computer is used to download the stored data periodically. Figure 3, shows that a uniform layer covers the polluted Link A and Link B has only trace of poilution. Table 1 presents major~tschnical data of the links. Table 1. Technical data of the tested insulating links. Insulating links were tested to determine Zbe leakage current caused by sudden energization of the polluted links in dry and wet conditions. The main differtince between the transmission line "insulators and the insulating link is that the former is con- tinuously energized, while the latter is energized only for a few seconds. The standard insulator contamination test was modifled to simulate the short. energization of the insulating link. The modified clean fog method was used to test the links [I I]. The modification was that the insulating link was ener- gized repeatedly 25 times for 5- 1 0 seconds. - 2.1 ARTIIEICLAL POLLUTION PROCEDURE The insulating link was polluted by salt-kaolin mixture, (slurry) based on IEC Standard 60507 [l 1 1. This sIurry con- tains de-ionized water, 40 g/l kaolin and a trdable amount of salt. The kaolin acts as a binder in the slurry. The amount of salt wm selected suitably to obtain light and heavy pollution on the insulating link surface. For heavy pollution, 28 mg fl salt was used in the slurry and for light poIlution; 10 mg/l salt was used. The insulating link was placed vertically in a plastic tank, which contained few inches deep slurry (water-salt- kaolin mixture). Brushing of the slurry on the surfme formed a uniform contamination layer. The polluted links were dried overnight. Equivalent-Salt-Deposit-Density (ESDD') measures the kwl ~f pollution. Using deionized water, 518 contamination samples were collected from circular areas in each link and the ESDD values were determined using the method in IEEE Sxd 4-1995 [12]. Typically ESDD > 0.1 mg/cm2 correspands to heavy and ESDD = 0.01-0.06 is light pollution. The Nm- Soluble-Deposit-Density NSDD was 7-8 mg/cm2. The brushing of slurry on the link saturated the surface with pollution. At the beginning of the drying period, the excess pollution flows off. This assured high repeatability. However if the difference between the desired and actual ESDD was more than 5%, the pollution was washed off and the link was re-polluted.
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