How
many types of Neutral grounding system?
§ There are primarily
three types of grounding system which are:
§ (1)Solid grounding – The neutral
point of the system is grounded without any resistance. If the ground fault
occurs, high ground current passes through the fault. Its use is very common in
low voltage system, where line to neutral voltage is used for single phase
loads.
§ (2) Low Resistance
grounding (LRG) – This is used for limiting the ground fault current to minimize
the impact of the fault current to the system. In this case, the system trips
for the ground fault. In this system, the use of line to neutral (single phase)
is prohibited. The ground fault current is limited to in the rage from 25A to
600A.
§ (3) High Resistance
Grounding (HRG) – It is used where service continuity is vital, such as process
plant motors. With HRG, the neutral is grounded through a high resistance so
that very small current flows to the ground if ground fault occurs. In the case
of ground fault of one phase, the faulty phase goes to the ground potential but
the system doesn’t trip. This system must have a ground fault monitoring
system. The use of line to neutral (single phase) is prohibited (NEC,
250.36(3)) in HRG system, however, phase to neutral is used with using the additional
transformer having its neutral grounded. When ground fault occurs in HRG
system, the monitoring systems gives alarm and the plant operators start the
standby motor and stop the faulty one for the maintenance. This way, the
process plant is not interrupted. The ground fault current is limited to 10A or
less.
§ There are other two
types such as Corner Grounding (for Delta system) and ungrounded system but
they are not commonly used.
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