Calculating single phase ground fault and

Solved Step by Step With Explanation- Earthing Design Substation Report

Questions

• Single phase to ground current calculation - Figure 1

• The earth grid for the entire substation - Figure 2

3. Earth Conductor Sizing A calculation is required to determine the size of the earth conductor used for the bonding of all steel structures throughout the facility (refer to IEEE Std 80).

Answers

The single phase to ground fault level at the 22 kV side of the 22/0.433 kV transformer T1 needs to be determined. The single phase to ground fault level for a 1-second clearance time at 22 kV can be calculated using the following formula:

Fault Current (I) = Transformer Rating (MVA) / (3 * Rated Voltage (kV))

The single phase to ground fault current at the 22 kV side of the transformer is approximately 22.73 kA.

2. Earth Grid for the Entire Substation

• Define the size and material of the earthing conductors and rods.

• Perform FEA to calculate the ground resistance and potential distribution across the substation area.

To calculate touch and step potentials, the following information is required:

• Ground fault current (from the single phase to ground fault calculation).

The sizing of the earth conductor for bonding all steel structures throughout the substation should be based on the requirements specified in IEEE Std 80. This standard provides guidance on the minimum size of the conductor to ensure effective bonding and to facilitate the safe dissipation of fault currents.

The sizing of the earth conductor depends on factors such as the soil resistivity, fault current magnitude, and the type of steel structures to be bonded. The calculations should consider the worst-case fault scenarios to ensure adequate protection.