Page 745 - Industrial Power Engineering and Applications Handbook

Grounding practices 22/705

Y

Generator transformer Generator

@ - E, - Step voltage
Indoor/ @ - E, - Touch voltage
@ - E,,, - Mesh voltage
(max touch voltage)
@ - - Transferred voltage

Utility auxiliary transformer Switchgear

Figure 22.9 Likely positions in which a human body may come in contact with phase and the ground conductors and the corresponding voltage
gradients (illustrated through the layout of Figure 13 21)

0.1 16 22.9.3 Mesh voltage or safe design voltage (E,)
E,,,,,, 5 (1.5 c, ' p, + 1000) x ~
\f (22.7) This is the maximum touch voltage ofa grounding station
and E,,7o1 5 (1.5 C, p,. + 1000) x - that may occur under thc worst situation (position 3,
for ;I SO kg body
Figure 22.9). The design of the grounding station must
0.157
\t ensure that in actual service this voltage does not exceed
for a 70 kg body (22 8) the permissible tolerable limits noted in Section 12.9.6.
Of the de step and touch voltagcs, the requirement of 22.9.4 Ground potential rise (GPR)
the safe touch voltage E, is more stringent. These are
basic design parameters, which will decide the required This is the maximum voltage, that a station grounding
size of ground mat and the design of mesh. In all our grid (ground mat) may attain relative to a remote ground
future assumptions. we consider the average weight of a en route to the grounding network considered to be at
human body to be 70 kg. the potential of the remote ground. In normal conditions