What is Solid Grounding or Effective Grounding?
In a power system, solid grounding refers to the practice of directly connecting the neutral point of a generator, power transformer, or grounding transformer to the ground through a conductor with negligible resistance and reactance. This type of grounding is also known as effective grounding.
Solid grounding is used to ensure that fault currents in the system are kept within safe limits. When a single-phase fault occurs in a solidly grounded three-phase system, the voltage of the faulted phase becomes zero, while the voltages of the other two phases remain unchanged. When a fault occurs, the power source not only supplies the charging current but also feeds the fault current.
For a solidly grounded neutral system, it is important that the ground fault current does not exceed 80% of the three-phase fault current. This helps to prevent damage to equipment and ensure the safety of personnel. Solid grounding is typically used in power systems to keep fault currents within safe limits and improve system reliability.
Advantages of Solid grounding:
Solid grounding has several advantages, including:
- The neutral point is effectively held at earth potential, which can help to prevent electrical accidents and improve system reliability.
- Equipment can be insulated for phase voltage, which results in cost savings.
- The arcing ground phenomenon and overvoltage conditions cannot occur due to phase opposition between the resultant capacitive current and the fault current.
- Solid grounding is less expensive for all operating voltages compared to other grounded systems, as the voltages of healthy phases in the case of a line-to-ground fault do not exceed 80% of the line-to-line voltage.
- Discriminative protective gears can be used due to the availability of a large fault current between the fault point and grounded neutral.
- Ground fault relaying is simple and satisfactory in a solid grounding system.
A disadvantage of Solid grounding:
However, there are also some disadvantages to solid grounding:
- High fault currents may cause the system to become unstable.
- Circuit breaker contacts may burn due to high fault currents.
- Interference in neighboring communication lines may be greater due to high fault currents.
Application of Solid grounding:
- This type of grounding is used to protect people and equipment from electrical shock and to provide a path for fault current to flow in the event of a ground fault.
- One of the main advantages of solid grounding is that it can help to keep the earth fault current within safe limits. When a ground fault occurs, the fault current will flow through the grounding conductor and into the earth, which will help to reduce the amount of current that flows through the rest of the circuit. This is particularly important when the circuit impedance is high, as it helps to prevent overloading and damage to the electrical system.
- Solid grounding is typically used for voltages up to 33 kV with a total power capacity of not more than 5000 kVA. This is because the resistance of the grounding conductor and the earth can be relatively low at these voltage levels, which allows for sufficient fault current to flow and clear the fault in a timely manner.