Advantages of neutral earthing in electrical power system

TYPES OF EARTHING

1. System earthing: Neutral of the transformer is connected to the earth.
   
2. Equipment earthing: All non-current carrying metallic parts of the generator, transformers, etc.are connected to the earth.
   

ADVANTAGES OF NEUTRAL EARTHING

1. Arcing phenomenon is prevalent in the case of the three-phase ungrounded neutral system. By neutral earthing, the arcing ground is reduced. This is explained in detail via the following example:

•         As shown in fog.1, under Normal conditions due to shunt capacitance the charging current flows from line to ground and sum of three current are zero and no current flows through neutral.

Fig.1: The Normal operating condition

·         Let us consider, L-G fault occurs at phase C, and charging current from phase A and B  to the ground remains the same. The charging current will be the summation of Ia and Ib. The fault current line Ic connects directly to the ground and hence feeds a high magnitude of the current. Since the neutral is not connected to ground that path is considered open.

·         This means that if the neutral was connected to the ground, this faulty current would have moved in that path. As this is not the case, faulty current will leads to arcing in the two capacitances between phases A, B, and ground. So it will originate from the ground and terminate to the unground neutral.

                  Fig.2: L-G Fault at phase C 

      2. The life of insulation is large due to the prevention of voltage surge.

      3. Overvoltage due to lightning is discharged to earth.

      4. Prevention of unnecessary tripping of circuit breakers.