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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ANSI/UL2737 (Withdrawn)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MIL-L-24410 (Withdrawn)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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320 impedance and grounding resistance is also negligible. If the insulator capacitance is less than 25pF, the leakage current is lessthan 1.OmAwhichiswellbebwtheletgothresholdlimit.The use of an insulating sole will further reduce the current. This reduction isnoticeableat 25pFinsulatorcapaatance,butnegliiible at lower capacitance values. The voltage across the sole is high. For example, the sole voltage is 1.6 kV when the source voltage is 12.47 kV and 15.1 kV at source voltage of 115 kV, assuming that the insulator capacitance is 25pF in both cases. These voltages may produce breakdown of the shoe’s soh?, when a transient current pulse is generated, which may endanger the worker. 0.5 0.4 4 E 0.3 z L t 0.2 0 0.1 K 3 0.0 0 20 40 60 80 100 120 VOLTAGE IN kV Figure 8. Current through the worker when the crane is equipped with an insulating link In polluted conditions the resistance of the polluted layer has a major effect on the leakage current. Fgure 9 indicates that the leakage current is higher than the fibrillation limit of about 30 mA for all voltages. At the 69 and 115 kV voltage level the current most probably will cause lethal shocks. This emphasizes the need for regular cleaning of the insulator links and prohibition of the operation in wet conditions. It is interesting to observe that the link capacitance, and source and body impedance have no practical effect on the current. TRANSIENT CONDITIONS When the crane touches the line, a transient current will flow through the crane worker. This cumnt will be superimposed on circuit of FQure 6, the parameter values are listed in Fgure 5. 0 20 40 60 80 100 120 VOLTAGE IN kV Figure 9. Cumt lhrough the crane worker when the insulator link is polluted and wet The result of a typical analysis is shown in Figure loa, and b for an insulator capacitance of 25pF. Figure 1 Oa gives the voltage developed across the operator. Fgure 10b gives the current through the operator. the steady-state current. The peak value of the current depends on the time when the crane touches the high-wlta@ line. The transient current will be maximum when the voltage is maximum Fgure 10. Transient voltage and current oscillation Maximum Energy = 0.0405 Wsec and zero when the voltage is zero. Due to the small inductances It is important to notice that the peak current is close to 4 A and and capacitances in the circuit the transient current will be of a the peak voltage ismore than 2 kV. However, the voltage duration shortduration damped sine-wave oscillation. The transient is very short. The oscillation frequency is around 333 kHz and it conditions were analyzed by the MICROCAP transient analysis attenuates to negligible value within 50-100 usec. During this program, which solves the differential equations of the equivalent short period, the steady state current is practically constant. A circuit of Fgure 2. The body impedance was represented by the sensitivity analysis indicated that the peak current is affected by
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