fault rating of OHSW

[mersin33]

Could anybody help me with calculating the short circuit and lightning capacity of an overhead shield wire on a double circuit 230kV transmission line?

The OHSW material is 7 #8 alumoweld (7 strand).

I also need to learn the difference between thermal power rating and current carrying capacity. These are required by the client for a transmission line. As far as I know, thermal power rating depends on many factors like line direction, line lattitude, line elevation, outdoor temperature, max conductor temperature, emissivity, etc as described in IEEE Std 738-1993 and can easily be calculated. I am having difficulty in understanding what "current carrying capacity" is.

Thanks in advance,

saltan

 

[jghrist]

The short circuit capacity of the shield wire can be calculated using formulas and constants in IEEE Std 80-2000, IEEE Guide for Safety in AC Substation Grounding, Section 11.3. This assumes no heat loss during the short circuit duration and that the conductor has a constant heat capacity and linear variation of resistivity with temperature. If you want to get complicated and not assume constant heat capacity, see Rating of Conductors For Short Duration Currents, V.T. Morgan, Proc. IEE, Vol. 118, No. 314, March/April 1971.

The current at the "thermal power rating" is the "current carrying capacity" as the term is normally used.