Ground Grid Design and Analysis

Ground grids are very much an invisible component of high voltage electrical installations but serve an important role to provide a degree of safety and protection to persons and equipment. PowerSafe provides measurement of soil resistivity, ground grid resistance, step & touch potentials and ground grid integrity for new and existing high voltage electrical ground grids. Ground grids depending on their size, arrangement and location can make getting valid test results challenging. PowerSafe is ready to assist and provide our expertise for your next high voltage grounding installation project.

Soil resistivity measurements are necessary to determine ground electrode requirements for the design of new electrical ground grid installations. An earth resistivity instrument is used for measurements using the 4-point Wenner method. PowerSafe will perform a check of the data in the field and make corrections as required to ensure the measured values we provide will not cause problems for your engineering team during the ground grid design phase.

Ground grid resistance or impedance measurements are normally performed after construction of new electrical ground grids in high voltage substations to validate that the design meets safety requirements for ground potential rise. The equipment used to measure ground resistance or impedance can be a simple battery operated switched DC output instrument or a complicated frequency selective AC output instrument. The site to be tested should be reviewed so that the correct technology is selected, measurement locations and paths are planned to minimize sources of error, and to ensure it is possible to perform the test with consideration given to geography and surrounding terrain.

Using the same equipment used for the ground grid resistance tests, a survey of step and touch resistances are performed. The resultant step and touch potentials are calculated to determine if the installation is within permissible limits of the applicable safety code.

Ground grid integrity surveys are performed to assess the condition of an existing electrical ground grid installation. The buried conductors are not visible so a method of injecting current into the ground grid between two points and measuring the resistance between the two points is performed. Measurements are performed at multiple locations throughout the substation, normally using the ground grid layout map as a guide if available. Higher than normal resistances measured could help to discover weak, broken, severed or corroded joints that cannot be normally identified.

Ground Testing Services include:

  • Fall of Potential tests
  • Step and Touch calculations and reports on 15kV and 25kV systems
  • Field Soil Resistivity (Ground Resistance) testing using
  • Werner four-electrode method
  • Earth continuity testing
  • Earth Potential Rise (EPR) calculations and reports on 15kV and 25kV systems

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