7430 therefore defines selection parameters
for the earthing arrangement, e.
The design and specification appropriate
earthing arrangement for substations essential
to provide low impedance path for earth fault,
and lightning currents, and protect personnel
on site from potentially fatal step and touch
voltages. and
ENA 41-24 reference the requirements for
earthing substations.
119
TECHNIC REFERENCE ARTHING STANDARDS
. These standards provide guidance on
(but not limited to):
• Maximum permitted step and touch voltages
• Methods for calculating earthing system design
• High voltage earth electrode selection,
including type, material and size
• Switching and busbar arrangement
• Equipotential bonding
• Insulation co-ordination
Primary these standards limiting earth
potential rise (EPR) under earth fault conditions
so that step and touch potential limits are not
exceeded, and earth resistance remains low
as possible. These earth rods
mitigate seasonal variations earth grid
resistance the grid’s burial depth.
Taking actual measurements the site is
important gauge the expected effectiveness
of the earthing arrangement, and guidance is
provided for measuring resistance calculations
for earth plates, earth rods, ring conductor and
foundation earth electrodes. the size and
material for conductors, earth electrodes etc, and
makes clear the need for careful consideration of
site conditions (soil composition and resistivity).
Substation earthing
BS 50522, 7354, IEEE std.
Where necessary high resistivity areas on
rocky ground, treatment the soil through use
of earth electrode backfill recommended to
improve earth contact resistance.g. Essentially, use earthing grid
consisting horizontal cross-bonded earthing
conductors recommended, augmented by
earth rods where the site includes low resistivity
layers beneath the surface
