Supply-Side Spreading Gradients |
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The power line neutral conductor is grounded (connected to the earth) principally for electrical safety.
When an accident occurs or equipment malfunctions on power systems, unsafe and/or dangerous conditions may develop.
Grounding power systems enhances the capability of
protection devices (e.g. fuses and circuit breakers) to detect these unsafe conditions and shut down the power supply before equipment, people, and animals
are harmed. |
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No matter how many precautions are taken, some accidents will inevitably happen (e.g. lightning, auto accidents, etc.).
Grounded supply systems make it easier to detect malfunctions and prevent fire and injuries.
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The current that flows from the neutral wire to the earth or vice versa does so through
grounding electrodes such as the ground rod commonly used at the base of a power pole.
Flowing through the ground rod, the current creates a spreading voltage gradient
much like the one we examined earlier in the two-rod study case
[Spreading Gd].
The following is a visualization of these spreading gradients
on the surface of the earth at the bases of poles with ground rods.
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The voltage gradient typically follows a circular pattern centered around the ground rod.
The amount of voltage that can be measured between gradient lines will depend on both the amount of current flowing into
or out of the earth at a specific pole and the earth's resistance at that location. |
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These spreading voltage gradients tend to be insignificant under normal operating
conditions, although they may appear striking in the figure. Because the current
entering the earth travels from the confines of a very small conductor (ground wire)
to the enormity of the earth, current density decreases rapidly as the current
moves away from the ground rod. Conversely, earth current leaving the earth
increases in density as it approaches the ground rod. Current density depends on the
distance of the current from the electrode. The most significant gradient
changes take place very near the rod, where the current density varies the most.
This is usually away from livestock. |
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