Working:
In this method, a reactance is connected between the neutral and grounds as shown in the figure.
The value of the fault current depends on the external reactance connected also in addition to the zero-sequence impedance of the power source and the impedance of the faulty phase.
The fault current can be adjusted to the required value by adjusting the value of the reactance. This method is employed to obtain the characteristic of the solid earth system.
In this method, the value of the earth fault current should be one-fourth of the three-phase fault current. This value is more than the fault current of the resistance earthing.
This type of earthing method can be employed where the value of the charging current is more e.g. transmission line, underground cable, etc.
Advantages :
1. Earth fault protection can be given.
2. Value of the fault current is reduced so the disturbances to the nearby communication lines are reduced.
3. Circuit breaker has to break comparatively less value of the fault current.
4. Problem of arcing ground is avoided or is reduced as the effect of the charging current due to the line capacitance is reduced.
Disadvantages :
1. Transient overvoltages are not suppressed if the value of the reactance is more. So the insulation of the equipment connected to the line may be damaged.
2. Value of the surge voltage increases due to the reactance at the switching operation.
3. Fault current and capacitive charging current are not neutralized properly. So some effect of arcing ground remains.