Substation Grounding. High voltage is used for long-distance transmission of electrical power. The line going to the consumer is usually under 6 to 10 kilovolts and to reduce the voltage to the usable 0.4 kV substations are required.
Substations are grounded by the external and the internal circuits. The external grounding circuit is a horizontal grounding assembled from vertical electrodes. Steel strips are used to make horizontal electrodes. If the mean resistivity of the ground is below 100 Ohm×m, the total resistivity of the circuit should be below 4 Ohm. This correlation may be achieved by taking 8 vertical electrodes with the length of 5 meters each, made of a 16 mm diameter circle. It is also possibe to use 10 vertical electrodes with the length of 3 meters each, made of 50x10x5 angle beams. The external circuit must be located no farther than 1 meter from the substation wall.
The need for the internal grounding circuit is due to the fact that transformer substations consist of several structures. Each must be equipped with grounding along the perimeter. All energized metal components must be grounded.
After laying of the grounding and neutral conductors through walls or ceilings and floors, they must be sealed off, using special casings filled with inflammable material which can easily be extracted if necessary.
A power transformer is grounded as follows. The presence of a dead-grounded neutral allows to connect the neutral bus of the transformer to the grounding circuit. To connect the metal case of the transformer to the grounding circuit, a flexible short circuit is used.