What is a Solid Grounding system?
When the neutral of the system is directly connected to the ground through a conductor which having negligible or small resistance or reactance between the equipment and ground is called a solid grounding system. The solid grounding system is also called an effective grounding system.
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| Solid Grounding system |
The generator, transformer or grounding transformer neutral is earthed by using plate type or pipe or plate type earthing. This method of grounding is used where the impedance of the circuit is more. The solid grounding system is used for voltages up to 33kV.
A system is called a solidly grounded system when the ratio of zero sequences reactance to positive sequence reactance is less than 3 or the ratio of zero sequence resistance to positive sequence resistance is less than 1. In a solid grounding system, zero sequence impedance is greater than or equal to the positive sequence resistance of the system.
In the solidly grounded system. fault current should not be increased from 80 % of the three-phase fault. The solidly grounded system is only used to keep the fault current within the controllable limit.
If the earth fault takes place on phase 'a' as shown in fig. On the occurrence of earth fault in any phase of the three-phase supply system, phase to earth voltage of the phase on which the phase to earth fault occurs become zero. Here fault occurs in phase 'a' so the voltage of phase 'a' to earth becomes zero and Phase 'a' and neutral have become at earth potential. The phase to ground voltage of healthy phases or unaffected phases are remain unchanged.
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| Phasor Diagram of solidly Grounded system |
From the above phasor diagram, fault current IF is in phase opposition with the capacitive charging current ICF. So fault current neutralize the capacitive current. The capacitive current ICF is a resultant of ICR and ICY.
Advantages of solid grounding system
1. In a solid grounding system, the potential of the faulty phases have become zero, but the potential on the healthy phases are remain unchanged. So only insulation is required only for phase to phase. the voltage between faulty phase to earth becomes zero, so insulation is not required for phase to earth, hence there is a saving in cost.
2. In a solid grounding system. the fault current and charging current become out of phase by 180 degrees so fault current and charging current get neutralised and it reduces the problem of arcing ground.
3. In a Solid grounding system, neutral is connected at earth potential.
4. The solidly grounded system is less expensive than other grounding systems.
5. The discrimination type protection is given in a solid grounding system as a heavy fault current can flow.
6. There are no any bad effects on the insulation of the equipment connected to the fault section because there is no any increase in voltage of healthy phases of the system.
7. In a solid grounding system, protective relaying are very simple and satisfactory in operation.
8. In a solid grounding system, there are easy to locate the fault point in the system.
9. The solid grounding system reduces the possibility of overvoltages.
10. In a solid grounding system, heavy fault current flows between the neutral and ground,
so it can easily be sensed by the current transformer and relays and faulty sections can quickly be isolated by the circuit breakers.
Disadvantages of Solid grounding system
1. In a solid grounding system, during the fault very high fault produce which may cause the system to unstable.
2. The very high fault current interrupted by the circuit breaker causes the burning of circuit breaker contacts.
3. In a solid grounding system, Interference with neighbouring communication lines will be high due to the high fault current is produced during the fault.
4. In a solid grounding system, the ground fault current is limited by the system impedance only. So the ground fault current is very high which cause the arc flash at the fault point and damage the insulation of the equipment.