لوله فلکسی روکش دار

Substation potential rise

During the passage of earth-fault current a substation earth electrode is subjected to an earth potential rise (EPR). Potential gradients develop in the surrounding ground area and these are highest adjacent to the substation earth electrode. The EPR reduces to approximately zero (or true earth potential) at some distance from the substation earth electrode.

A person could be at risk if they can simultaneously contact parts at different potential. Thus in a well-designed system, the potential differences between metallic items will be kept to safe levels regardless of the EPR.

Ground potential gradients around the electrode system, if great enough, can present a hazard to persons and so effective measures to limit them should be incorporated in the design.

The three main design parameters relate to touch, step and transfer potentials as defined below. These terms are shown as , and A respectively in Figure 1.

Touch potential

This term describes the voltage appearing between a person’s hands and feet (see Figure 1 below), or between a person’s hands. Hand to foot touch potential arises from the fact that the EPR at a person’s feet can be somewhat lower in value than that present on the buried earth electrode (and any connected metalwork).