Danger in one-phase power line

One-phase power lines and direct current power lines can be insulated from the ground, have ground pole or center tap.

During one-pole touching of conductor a person gets connected to another conductor through ground resistance (fig. 3.1).

Since one-phase power lines are not extended capacitance of their conductors can be neglected and as for DC lines such capacitance equals to zero. To simplify formula for current calculation ground currents of both conductors are assumed equal, so are their insulation resistances:

. (3.1)

Current passing through human body can be found out of the scheme (fig. 3.1):

, (3.2)

where U – voltage, V; R_h – human body resistance, ohm; r – conductors’ insulation resistance, ohm.

Fig. 3.1 Scheme of person connection to conductor of insulated power line

Touching not grounded conductor of power line with grounded pole (fig. 3.2) causes current passing through human body that is:

, (3.3)

where R_o – grounding resistance, ohm.

Taking into account that R_o << R_h formula will look as:

. (3.4)

Fig. 3.2 Scheme of person connection to not grounded conductor of power line with grounded pole

Connection to normal conductor when another one is damaged and has short circuit with the ground is shown in the fig. 3.3. That connection causes current:

, (3.5)

where R_sc – resistance of short circuit, ohm.

Fig. 3.3 Scheme of person connection to conductor of damaged power line

If person touches a conductor of power line with grounded center tap (fig. 3.4) he turns out to be under voltage making half of total line voltage, so the current will be:

, (3.6)

where R_ct – grounding resistance of center tap, ohm.

Fig. 3.4 Scheme of person connection to conductor of power line with grounded center tap

Two-pole connection to power line (fig. 3.5) gets a person under total line voltage and current will be:

. (3.7)

Analysis of all studied formulas testifies that case of two-pole connection to power line is the most dangerous irrespective to neutral operation mode, because in this case current passing through person depends only on human body resistance. The least dangerous is connection to conductor of insulated power line in normal operation mode.