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AIS Substation Grounding/Earthing Design and Analysis

Soil resistivity measurement is the fundamental and most important concept in grounding studies. Wenner method is the most widely used technique for soil resistivity measurement. Measurements to sufficient probe spacing is very important to identify the deep soil layers. Multiple traverses of measurements should be done and worst case scenario should be identified for conservative design. Seasonal variations of soil should also be accounted. SES provides a tool named “SoilModelManager” to access seasonal variations of frozen or dry soil conditions based on summer measured soil data.

The internationally approved IEC standard 61936-1 entitled Power Installations Exceeding 1 kV ac – Part 1: Common Rules, states clearly in Section 10.3.1 General Clause b:

This requirement means that the designer of a grounding system has the obligation to determine if seasonal soil resistivity variations have an impact on the grounding performance.