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Standards for Insulating links
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316 IEEE Transactions on Power Delivery, Vol. 6, No. 1, January 1991 EFFICIENCY OF INSULATING LINK FOR PROTECTION OF CRANE WORKERS G.G. KARADY, Fellow IEEE Arizona State University Tempe, A2 85287-5706 ABSTRACT current pulse. This short duration capacitive current may cause heart failure or Cbrillafon. The purpose of this study is the A crane worker can be exposed to a dangerous electrical shock development of a model and calculation method to analyze the when the crane touches high-voltage electrical lines, so an protection value'of an insulating link and compare the current insulator link is used to protect workers. This paper analyses the Wi through the body of the crane wotker with and without the protection efficiency of insulating links under different operatiing link. conditions. Both a steady state and transient model have ken developed for simulation of the system. The models simulate the electrical supply, the crane insulator link, the body impedance of the worker and the grounding resistance. The MICROCAP AC, DC and Transient Analysis program was used to calculate the current and voltages which endanger the crane worker. The results show that the insulating link in clean conditions reduces the current under the harmless let-go level. However, pollutining andwetting the insulating linkmay increase the current above the dangerous ventricular fibrillation level. The contact between the power line and crane causes a shortduration high-amplitude transient current which, in adverse conditions, can cause heart fibrillation. The paper concludes that in spite of the shortcomings, the insulator link increases the safety of the crane operation. Furthermore, the developed model and calculation method can be used for the evaluation of new crane insulator systems. c INTRODUCTION One of the most frequent electrical accidentsoccurwhen a crane touches a high voltage power line while the crane -er works on the load. The line voltage will drii a current through the crane chain and the worker. This results in severe electric shock and sometimes the electrocution of the crane worker. Forthe protection of personnel, crane manufacturers insert a high-voltage insulator in the crane line. The insulator reduces the electric current and protects the crane worker. However, the value of protection is dependant on the resistance and capacitance of the insulator. If the insulator is contaminated and wet, the protection capability of the insulator is reduced significantly. Also, if the insulator has large capacitance, the initial capacitive current may cause a large Fgure 1. Crane protected by insulated link touching a transmission line. EQUIVALENT CIRCUIT Fgure 1 shows the arrangement when a crane touches a high voltage line. The system shown in Figure 1 has five major components: ' crane structure ' insulator link ' crane worker ' ground power line and electrical network. For the analysisof the system operatiin an equivalent circuit has 90 SM 338-4 PWRD the IEEE Transmission and Distribution Committee of the IEE Power Engineering Society for presentation at the IF,EE/PES 1990 Summer Meeting, Minneapolis, Minnesota, July 15-19, 1990. Manuscript submitted January 31 > A paper recommended and approved by been developed and shown in Figure 2. Thehigh-voltagelineandtheelectrical networkis represented by its Thevenin equivalent, which consists Of a voltage source and an inductance connected in series. The source voltage is the system's line to ground voltage. The source impedance is 1990; made available for printing April 24, 1990. O885-8977/91/0loO-03 16$O1 .OO 0 1990 IEEE
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