Study on equivalent circuit of the human body and its transient response against electric shock

To solve the problems of the incorrect operation, the failure action and the low operational percentage on Residual Current Operated Devices (RCDs) in the domestic rural power distribution network, an amount of electric shock signals were demanded to study identifying and extracting method of electrical shock current. In this paper an equivalent circuit model of the human body against electric shock was studied. The frequency characteristic of let-go current according to proposed equivalent circuit model of the human body tallied with the testing results of Dalziel [1–2]. Considering the skin was in the dry condition, wet condition and broken-down condition, touch voltage at 106 V rms, electrical contact making at the peak of touch voltage respectively, the simulation results in low-voltage distribution system based on Matlab indicated the feasibility of explaining certain electrical shock phenomenon by the transient response of the equivalent circuit model. The individual responses against electric shocks were simulated by selecting parameters of the human body circuit model correctly. The results showed great potential value for the application of residual current protected devices (RCDs) of different action time as well as the research and development of new type and high reliability RCDs.

1 Introduction

The effect of electricity on the human body is related to the waveshape of the applied voltage, its points of application, and the subsequent current in the body [1]–[4]. While it is the current delivered that primarily determines the effect, usually only the applied voltage is known so that the current must be calculated by appropriate impedance of the human body. However the impedances of the human body depend on a number of factors. Two impedances are generally used to describe the pathway impedance of the human body: the internal impedance of the body and the impedance of the skin at a contact point [5]. These two combine vectorially to produce the total pathway impedance. Figure 1 presents the equivalent circuit appropriate for shock studies [6]. The shock can be applied to any combination of extremities or points on the torso, and as shown in the figure, the shock current through the body is a function of the source voltage and source impedance as well as body impedance. In some cases, it may be acceptable to model the body as a single lumped-element impedance. But the ranges of situations for which this model will provide valid results are quite narrow. Incorporating all of the known effects in a circuit model is extremely challenging. Much work on the subject has been done. Figure 1 Equivalent circuit shock scenario conditions