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Session Six: Arrester Earthing Resistance
Earthing, Lightning & Surge Protection Forum – IDC Technologies
4
Arrester
Earthing
Resistance
(Ohm)
Arrester Current
(Amp)
Arrester Voltage
(kV)
Phase
Conductor
Voltage
(kV)
5 6.6 65.6 323
10 6.5 65 350
30 6.4 64 481
50 6.3 62.5 599
100 5.9 59.4 878
Table 1 – Summary for different arrester earthing resistance values
Note from Table 1 that increasing arrester earthing resistance increases the
phase conductor voltage to earth. At large arrester earthing resistances, the
higher conductor impulse voltage rise will put more voltage stress on adjacent
insulators and also insulators further away. Another way of looking at this is
that for low arrester earthing values more energy is shunted to earth through
the arrester branch and less energy continues along the phase conductor.
While a low value of say 5ohms gives better performance it will be more
expensive to achieve than 30ohms. It is recommended that the current
standard value of 30ohms maximum for arrester earthing resistance be
continued.