1. Solid grounding When the neutral pointof a 3-phase system is directly connected to earth(i.e. soil) is called solid grounding or effective grounding. When an earth fault occurs between earth and any one phase , the voltage to earth of the faulty phase becomes zero, but the healthy phases remains at normal phase values. current(IF) completely nullified by capacitive current(IC) 2. Resistance grounding When the neutral of a3-phase system(e.g.3-phasegenerator,3-phase transformer etc.)is connected to earth(i.e.soil)through a resistor, it is called resistance grounding. (iii) Reactance grounding In this system, a reactance is inserted between the neutral and ground The purpose of reactance is to limit the earth fault current. Disadvantages: (i)Inthissystem, the fault current required to operate the protective device is higher than that of resistance grounding for the same fault conditions. (ii)High transient voltages appear fault conditions. If inductance L of appropriate value is connected in parallel with the capacitance of the system, the fault current IF flowing through L will be in phase opposition to the capacitive current IC of the system. If L is so adjusted that IL=IC then resultant current in the fault will be zero. This condition is known as Resonant Grounding. When the value of L of arc suppression coil is such that the fault current IF exactly balances the capacitive current IC, it is called resonant grounding. 8. Explain the overlapping of protective with neat sketch(N/D 2015) 9. Explain in detail about different types of earthing scheme. (N/D- 2016) or earthing may be classified as: (i)Equipment grounding
1. Solid grounding When the neutral pointof a 3-phase system is directly connected to earth(i.e. soil) is called solid grounding or effective grounding. When an earth fault occurs between earth and any one phase , the voltage to earth of the faulty phase becomes zero, but the healthy phases remains at normal phase values. current(IF) completely nullified by capacitive current(IC) 2. Resistance grounding When the neutral of a3-phase system(e.g.3-phasegenerator,3-phase transformer etc.)is connected to earth(i.e.soil)through a resistor, it is called resistance grounding. (iii) Reactance grounding In this system, a reactance is inserted between the neutral and ground The purpose of reactance is to limit the earth fault current. Disadvantages: (i)Inthissystem, the fault current required to operate the protective device is higher than that of resistance grounding for the same fault conditions. (ii)High transient voltages appear fault conditions. If inductance L of appropriate value is connected in parallel with the capacitance of the system, the fault current IF flowing through L will be in phase opposition to the capacitive current IC of the system. If L is so adjusted that IL=IC then resultant current in the fault will be zero. This condition is known as Resonant Grounding. When the value of L of arc suppression coil is such that the fault current IF exactly balances the capacitive current IC, it is called resonant grounding. 8. Explain the overlapping of protective with neat sketch(N/D 2015) 9. Explain in detail about different types of earthing scheme. (N/D- 2016) or earthing may be classified as: (i)Equipment grounding
EE6702-VII%20SEM.docx