Earthing of Steelwork in HV SUBSTATION
Earthing of Steelwork in HV SUBSTATION
(OP)
HI,
Currently designing a 110/11kV indoor GIS substation and the main earthgrid conductor has been calculated at 240sqmm. I am trying to find standards or information on how to size the earthing cables for earthing of gates, steel beams, columns, louvres etc located both inside and outside of the substation.
Currently designing a 110/11kV indoor GIS substation and the main earthgrid conductor has been calculated at 240sqmm. I am trying to find standards or information on how to size the earthing cables for earthing of gates, steel beams, columns, louvres etc located both inside and outside of the substation.






RE: Earthing of Steelwork in HV SUBSTATION
Akcmil= If Kf( t c)1/2 or Amm2~ 0.5 If Kf( t c)1/2
Where:
A= Area of conductor: (Akcmil in kcmil & Amm2 in mm2)
If = Fault current in kA rms (injected current in the earth)
t c = Duration of fault current in seconds (typ. Backup relay time).
Kf = Constant for the material from table or determine at various values of fusing temperature conductors (~1084 oC for most Cu conductors) or limited conductor temperature (250 oC for Cu commercial hard-drawn) considering ambient temperature typically 40 oC
Per IEC Std for bare Cu : Kf =1/[226(ln(1+(Ti –Tf)/(234.5+Ti)
Where:
Ti =Initial Temp in oC (max. Ambient Temp)
Tf= Permitted final temperature as follow:
Tf1=500 oC: for visible conductor in location that are not generally accessible.
Tf2=200 oC: for non-visible conductors in location that are generally accessible.
Tf3 =150 oC: Where hazards are greater (non-visible in location with increased fire risk or for earthing conductor laid together with PVC cables)
NOTES:
a- the standard eng practice consider normally two different conductor path in most structure.
b- Most steel structures connected to the ground via anchor bolts carry significant part of the part of the ground current; however, in conventional engineering calculation this is ignored and indirectly is considered as a safety margin.
c- For additional information, see IEC Std 60621-2, IEEE Std 80 and article 9.6 in the enclose publication based in IEEE. http://ww
RE: Earthing of Steelwork in HV SUBSTATION
1. The wire size has 19 strands which means that crimping and exothermic welding are more likely to have ALL of the wire strands conducting.
2. Fault currents spread out into the soil in such a way that larger sizes are a moot point - several 4/0 wires in parallel in say a 10 foot by 20 foot grid works.
3. 4/0 copper has reasonable ability to handle lightning current.