Substation grounding

Question

I am trying to understand a grounding system for substations, fault current is something I am not getting. For example, for a small substation with some transformers, if there is a fault in the system how will the fault current flow into the grounding system? If the system has let's say 50 kA full fault current will all of the current (50 kA) flow into the ground or only certain percentage of the faulty current will flow into the ground?

How does this work? an explanation or link to explanation will be very helpful.

Answer 1

your question is not very precise. However, I will try to give it a direction by following points.

Different types of failuers can occur in a substation. Therefore the fault circuit depends on the kind of failure and the neutral point treatment.

Failure types:

• three phase short circuit
• two phase short circuit without earth contact
• two phase short circuit with earth contact
• one phase short circuit against earth
• earth fault (only for nets with isolated neutral or resonant earth system)
• double earth fault (only in nets with isolated neutral or resonant earth system)

Types of neutral point treatment

• isolated neutral
• resonance earthing
• low impedance earthing