Earthing

Earthing in solar power plants provides a zero potential surface to all the electrical equipment installed in the system. To achieve this objective, the non-current carrying parts of the electrical equipment are connected to the Earth which prevents them from over-voltage surges and also provides safety to the staff. 

The earthing requirements depend on two factors: Effective resistance and fault current.  Fault Current is the electrical current that flows through a circuit during an electrical fault condition.In a DC system, the fault currents are smaller and hence not significant, but for an AC system, fault currents are in the range of kA. The soil resistivity can’t provide a low resistance path by itself, therefore, earth pits are dug with specific clearance and electrodes are installed inside these pits. 

While designing earth pits, few soil samples are taken and tested for the resistivity. A caution here is that the samples should be collected randomly so that it is a close representation of the actual soil conditions where the pit might be dug.

There are a few points that needed to be taken care of while Earthing:

1. GI strips should have appropriate galvanization thickness to prevent rusting for proper contact with the earth

2. The rod or metal plates available as an electrode for earthing must be certified

3. Continuity must be ensured in the connection so that fault currents always get a low resistance path to earth

If a single earth pit is not sufficient, multiple pits may be created and connected in parallel to reduce the effective resistance of the system. The earthing is considered good if the effective resistance of the system if less than 1-2 Ω. 

Maintenance: The earth pits need to be moisturized periodically depending on the location and type of soil to prevent effective resistance from increasing. Quarterly continuity checkup of the complete system must be conducted to ensure that all earthing locations are still active.