Types of Neutral Earthing in Power Distribution:

§  In the early power systems were mainly Neutral ungrounded due to the fact that the first ground fault did not require the tripping of the system. An unscheduled shutdown on the first ground fault was particularly undesirable for continuous process industries. These power systems required ground detection systems, but locating the fault often proved difficult. Although achieving the initial goal, the ungrounded system provided no control of transient over-voltages.

§  A capacitive coupling exists between the system conductors and ground in a typical distribution system. As a result, this series resonant L-C circuit can create over-voltages well in excess of line-to-line voltage when subjected to repetitive re-strikes of one phase to ground. This in turn, reduces insulation life resulting in possible equipment failure.

§  Neutral grounding systems are similar to fuses in that they do nothing until something in the system goes wrong. Then, like fuses, they protect personnel and equipment from damage. Damage comes from two factors, how long the fault lasts and how large the fault current is. Ground relays trip breakers and limit how long a fault lasts and Neutral grounding resistors limit how large the fault current is.

 Importance of Neutral Grounding:

§  There are many neutral grounding options available for both Low and Medium voltage power systems. The neutral points of transformers, generators and rotating machinery to the earth ground network provides a reference point of zero volts. This protective measure offers many advantages over an ungrounded system, like,

1.     Reduced magnitude of transient over voltages

2.     Simplified ground fault location

3.     Improved system and equipment fault protection

4.     Reduced maintenance time and expense

5.     Greater safety for personnel

6.     Improved lightning protection

7.     Reduction in frequency of faults.

Method of Neutral Earthing:

§  There are five methods for Neutral earthing.

1.     Unearthed Neutral System

2.     Solid Neutral Earthed System.

3.     Resistance Neutral Earthing System.Resonant Neutral Earthing System.

1.     Low Resistance Earthing.

2.     High Resistance Earthing.

4.     Resonant Earthing System.

5.     Earthing Transformer Earthing.