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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ANSI/UL2737 (Withdrawn)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MIL-L-24410 (Withdrawn)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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318 2.5pF and 25pF during the analysisto determine the sensitivily of the system. For the calculation of the steady state current in dean conditions, a resistance of 200 Mn was selected. For the simulation of the polluted conditions the resistance value was vaned between 200 kn and 700 K2. The equivalent impedance of the human body was studied by Freiberer [2], who measured the impedance of corpses and living personsat differentvoIfagelevels.Thisbasicworkcondudesthat the body impedance can be divided into three parts. a) The skinelectrode interface impedance. b) The body internal impedance. c) The skinground interface impedance. The skinelectrode interface can also be represented by a resistance and capacitance connected in parallel. In addition, the skin-ground interface may be represented by the Same circuit, if the person iswell grounded. However, if the person wears shoes withinsulating (rubber) soles,acapacitance, connected in series, has to be added to the equivalent circuit as shown in Figwe 2. The capacitance value is calculated by using the shoe's sole surface and thickness. In this paper, the sole surface was assumed to be 300 sqcm and the sole thickness lcm, which resulted in a capacitance of 170 pF for a pair of shoes. The skinelecbPde and the skinground resistance and capacitance depend on the wetness of the skin, the electrode surface, voltage, frequency, etc. The meawed values show a large spread and significant variation from person to person. The most important factor is the voltage used for the measurement. The impedance value decreases by the increase of voltage. The tvplcal values for low voltageandlowfrequencyarearound 100-300ohmand0.150.3 PF. The body itself can be represented by a resistance. In the studies performed by Bieglemeier and Rotter [3], Beglemeir [4] derived a relationship between the kdy impedance and touch voltage. The results show that the total body impedance decreases rapidly with the increasing voltage as an example, 6100 f2 was measured at 25 Vand I500 Rat 100 V. The asymptotic value for very high voltage is 850 a. The equivalent circuit for low-voltage ac current is shown in Fgure 4. In this circuit the skin-electrode and skin-ground resistances have been combined together. Fortrans'ents, Ta~or[5]~po~aresista~~~tor~~. Taylor's work indicate sthat the body impedance for transient high voltages is significantly different from the impedance determined by low-voltage measurements. He measured a capacitance discharge that produced body current and voltage by a high- speed digital oscilloscope and calculated the equivalent transient body impedance. The results of this investigation are shown in Figure 5. CS rK1 CS I/ Skin 0 0 Figure 4. Equivalent human body impedance Calcuhllon Calculation: cs - 625 pF 1 OL I I I I 0 1 2 3 Tim in w Figure 5. Body impedance as a function of Cme [SI This figure demonstrates that the total body impedance is a nonlinear function of time. However, this nonlinear impedance can be approximated by the circuit of Figure 6, if the resistances and capacitances are selected properly. If can be seen that the impedance calculated from the circuit, with the values shown in Fgure 5, resultsinan acceptable andconservativeapproximation because the calculated impedance is lower than the measured OM. The ground is represented by a resistance, the value of which depends on the conditions affecting the sole. When the ground is wet the calculated resistance value is around 50-100 ohm, but in dry conditions the resistance could be more than lo00 ohm. The circuit shown in Figure 2, with two body impedance models, has been used for the steady state analysis . The most simple body impedance model consisted of only the body resistance of 750 f2. The other model, shown in Fgure 4, included both the
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