Why should HV neutral earth and LV neutral earth not be given to the same earth pit in the switch yard?
Earthing System
Electrical link with the Earth for safety & functionality which connects components of an electrical power system to the earth’s conductive surface for safety & functionality. Used to protect towering structures, telegraph lines, & radio antennas from lightning strikes.
Reasons for separate HV & LV Neutral Earths
HV (High Voltage) and LV (Low Voltage) neutral earths should not be fed into the same earth pit in a switchyard for the following reasons:
Safety
HV and LV systems run at various voltage levels, hence the earth resistance needed for each differs. If they are linked to the same earth pit, the higher voltage system may be unable to efficiently discharge its fault current, increasing the risk of electrical shock and fire.
Fault Current Discharge
HV systems often require reduced earth resistance to ensure that fault currents are safely discharged. If the LV system is linked to the same earth pit, it may be unable to adequately discharge its fault current, which could result in equipment damage (or) electrical shock.
Soil Resistivity
Soil resistivity can vary greatly based on location and conditions. If the HV and LV systems are linked to the same earth pit, the soil resistivity can not be appropriate for both systems, resulting in problems with fault current discharge and overall safety.
Separate Earth Resistance Requirements
HV systems need lower earth resistance values (0.5 ohms for power stations) than LV systems (2.0 ohms for 33 kV stations). Connecting both to the same earth pit may jeopardize the safety & effectiveness of the earthing system.
It is essential to keep separate earth pits for HV & LV neutral earths in a switchyard to assure the safety and reliability of both systems.