Underground Earthing Grid of a 66kV PowerGrid SubStation in connection with an upper floor GIS Switch Room

Touch Voltage 2D Profile of a 66kV PowerGrid SubStation during a 50kA short circuit

3D Step Voltage Profile of a SubStation Earthing Grid during a 50kA short circuit

Unsafe Touch Voltage zones round a 66kV
PowerGrid SubStation during a 50kA short circuit

A short circuit incident is likely to generate dangerous step and touch voltages within and around a PowerGrid SubStation. A safety earthing grid is therefore designed for each PowerGrid Substation which serves the following objectives:
— To provide means to carry electric currents into the earth under normal and fault conditions without exceeding any operating and equipment limits or adversely affecting continuity of service.
— To assure that a person in the vicinity of grounded facilities is not exposed to the danger of critical electric shock.

The earthing grid design for each PowerGrid SubStation is unique as it depends much on the actual soil conditions of the site. It is therefore necessary to design, model and simulate the effectiveness of the earthing grid.

First, the soil resistivity profile of the site needs to be determined. Thereafter, a 2-layer or multi-layer local soil model is developed. The grid and soil model is then used to simulate the step and touch voltages during a worst case fault scenario to determine any zones that remain dangerous to personnel.

HY can provide the services in designing the earthing grid is in accordance to the IEEE Guide for Safety in AC Substation Grounding - IEEE Std 80-2000.

HY is also able to provide the services to determine the local soil resistivity profile in accordance to the IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System - IEEE Std 81-2012.