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IEEE Transactions on Dielectrics and Electrical Insulation Vol. 15, No. 2; April 2008 Performance Evaluation of Insulating Links Used for Worker Protection in Cranes George G. Karady, Essam Al-Ammar, and S. Venkataraman Department of Electrical Engineering Arizona State University Tempe, AZ, 85257 USA ABSTRACT Insulating links are used to protect crane workers from accidentally contacting a transmission line. This paper presents the results of laboratory tests that determined the lesikage current produced by sudden energization of polluted and wet insulating links. Two different manufacturers' liiks were tested at heavy and light pollution. The results show that the short duration transient or the root mean square (rms) leakage current is the measure of the ability of the links to provide protection. The leakage cur. rent can endanger the life of a crane worker before flashover occurs. The dependence of leakage current on test voltage under heavy and light pollution conditions was de termined. Obtained leakage current data was compared with IEC 479-1 standard, that provides health effect data. The link protects the crane worker, if the line voltage is less than the maximum voltage determined from the correlated test results. The results were used to assess the efficiency of worker protection. Index Terms - Crane, electrocution, flashover, fatal accident, fog chamber, insula- tor, leakage current, power line, pollution, wetting. 1 INTRODUCTION with a polyurethane impact resistant body. References [2] and [3] provide details of the link construction and technical data. CONTACT of cranes with power lines causes several accidents every year. Significant number of accidents results in fatal injuries and death. [I]. An average 231 accidents oc- cur every year in the USA and of those 113 are fatal [l]. Power line contact causes about 40% of these accidents, which translates to an average of 90-95 power line contacts per year. Most frequently, the victim of the crane-power line contact is the crane worker attaching the load to the hook. Inserting an insulating link in the crane line can reduce the number of accidents. This link isolates the worker from high voltage. Figure 1 shows the concept of Insulating Link provid- ing protection. The operator standing on the ground touches the hook to rig a load, while the crane line contacts the high voltage line. The high voltage flashes over the tiers and drives short circuit cur- rent to the ground, but the operator is isolated from the high voltage and only a small leakage current flows through the operator. Figure 2 shows an insulating link installed on a crane. The crane lifts a billboard when it works near a transmission line. Presently two major manufacturers sell around one hundred insulating links every year worldwide. The insulating link A has a glass fiber core that provides mechanical strength. This is covered by hard polyurethane foam insulation. The surface of the foam is protected by shiny epoxy resin skin. Insulating link B has steel core, insulating bushes and is encapsulated Manuscript received on 27 February 2007, in final form 14 June 2007. Figure 1. Concept of Insulating Link providing protection. Typically the contact between the transmission line and the crane causes a ground fault, which is cleared by the line pro- tection in 5 to 30 cycles or 83 milliseconds to 0.5 seconds. Accordingly the transmission line contact energizes the insu- lating link only for a short time. The voltage switched on the insulating link is the line to neutral voltage. This voltage drives a leakage current through the insulating link and can 1070-9878/08/$25.00 0 2008 IEEE
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