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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ANSI/UL2737 (Withdrawn)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MIL-L-24410 (Withdrawn)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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392 that "the flashaver voltage obtained with constant Safety Code permits a step voltage of 263V. The step potential decreases rapidly with increasing horizontal distance. seem to indicate that there is a decrease in flashover The large CEUle may have a 40-50 ft (12-15 m) boom. If the authors and describe the constant energization boom's projection is larger than 4-5 meters, the test procedure effect of step potential seems to be negligible. energization corresponds to the 75-85% flashover probability with one second energization " This would voltage with the time of the applied voltage. Would the Manuscript received March 6, 1995. G. Karady Arizona State University, Tempe, AZ : In reference to Dr. Gela's remark about the acceptable risk, we did not intend to imply that the one-out-of-ten or two-out-of ten is an acceptable risk. We merely tried to show that even an imperfect link can protect a worker to some degree. The short duration energization was achieved by a low voltage time switch installed at the supply side of the transformer. The high voltage side used an RC load that practically eliminated Of touch and step potential. We a@ee that separating the monitored at each switching and the oscillograms showed less worker from the crane and the application of auxiliary low resistance grounding improves the worker's safety. However, this paper deals with the insulating link and not the overall we have safety problem. In spite of this, we performed a cursory potential using the data 'Om The results are shown in Figure 1. Both Dr. Gela and hk. Gillies discussions show the impmm both the switch on and off transients. The voltage was 5% overshoot. the minor errors pointed out by Gels. Of the paper' In reference to Mr. Gillies questions about flashover voltage- time characteristics, during short duration tests, the link was wetted by fog, when the leakage current reaches its peak value the link was energized 25 times for 1 or 10 seconds, respectively. At the constant voltage test, the link was wetted by fog, when the leakage current reached its peak value, the link was energized and voltage was maintained for five minutes. If no flashover occurred, the voltage was raised slowly, by 5%. This process was repeated until flashover occurred. Contamination flashover is a slow process where the R- lOOcm 360V 12OV 60V 36V 24v leakage current-caused heating produces dry bands. Repeated flashover of the dry bands ultimately leads to flashover of the insulator. This process requires time, which explains why flashover voltage decreases with an increase of energization time. Last but not least, the authors thank the reviewers for their Transmission Line step size: 3 ft ____I,. _____I _-__- -I ------' ------I ---- -J-----J 72V 46V R i 50 cm 720V 240V 12ov Rs25cm 1440V 480V 240V 144v 96V Ground plate .I Emax - 263 V. T = 0.5 SeC Figure 1. Step voltage, 3 ft step, 7.5 kV line to ground voltage. R is the radw of the grounding plate The diagram indicates that step voltage increases by reducing the electrode's sue, which is equivalent with increasing gomd resistance. For 0.5 sec exposure time, the National Electric Teceived *Pnl lo* I9g5.
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