Earthing Layout Design


Earthing systems are required to manage the transfer of fault energy via a low impedance path to limit the risk to people, equipment and system operation to acceptable levels. An earthing system is required to perform this function for the life of the electrical plant for which it is installed, for the range of configurations of the network and nearby infrastructure that are foreseeable. The earthing system may need to be augmented over time so as to continue to fulfill this function.
The energy which earthing systems must manage comes from a range of sources and system events, including:

 Generating plant,
 Conductively coupled earth fault current,
 Inductively coupled earth fault current,
 Lightning discharges,
 Transient discharges (e.g. switching surges)
 Capacitively coupled induction
Identification of these sources and any special considerations is part of the earthing system design and is
outside the scope of this document. Any requirements that impact on the earthing layout design will be provided as an input to the earthing layout design.
The substation earthing must achieve the following objectives:

 Successful Protection Operation
 Safety Compliance
 Interference Minimisation
 Robustness
 Protection of Electrical Plant

The earthing system is required to ensure proper operation of protective devices such as protection relays and surge arresters to maintain system reliability within acceptable limits. It is intended to provide a potential reference for these devices and to limit the potential difference across these devices. The earthing system is required to achieve the desired level of system reliability through: Facilitating the proper and reliable operation of protection systems during earth faults. This entails reliable detection of earth faults and either clearing the fault or minimising the resulting fault current. Limiting equipment damage (by enabling protection systems to operate correctly and thereby limiting the duration of earth faults) and the consequent need for repair or replacement,Limiting or reducing interference to substation secondary system equipment (e.g. SCADA).

The earthing system is required to manage any hazardous potential differences to which personnel or members of the public may be exposed. These potential differences include:
 Touch Voltages (including transferred touch voltages)
 Step Voltages
 Hand-Hand Voltages


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