21.2 HEAT BALANCE EQUATION OF ELECTRICAL CONDUCTORS
The current carrying capacity rating is computed by using the
following formula under steady state condition of wind velocity, temperature,
solar radiation and electric current.
Q_{c }+ Q_{r }= I^{2 }R + Q_{s
}Where
I^{2 }R = Heat generated in the conductor due to flow of
current ' I ' in Amperes, R is the resistance of the conductor per meter.
Q_{8 }= Solar Heat Gain in Watts per meter of Conductor.
Q_{c }= Convection heat loss in Watts per meter of
Conductor
Q_{r }= Radiated Heat Loss in Watts per meter of
Conductor.
From the above equation, current carrying capacity I can be
determined as
I =
Ö
Q_{c }+ Q_{r}  Q_{s}
/ R_{ }
Ampere
The effect of Heat Gain due to Magnetic Heat and Corona Heating
and Heat Loss due to Evaporation is usually negligible, hence not considered.
21.3 CURRENT RATING OF VARIOUS CONDUCTORS
21.3.1 The size of the conductor used for transmission
lines of various voltage class has now been standardized, which are as fallows
400kv  'Moose' ACSR
220kv  'Zebra' ACSR
132kv  'Panther' ACSR
21.3.2 However, recently in some cases 'moose' conductor
has been used on 220kv lines for evacuation of bulk power from generating
station, such as Unchahar Power Project, In case of 66kv lines which have been
upgraded to 132kv, the conductor used is 'Dog' ACSR. Accordingly, the current
capacities of the above conductors are temperature of 47.5^{0 }C. for
new as well as old conductors for the designed maximum conductor temperature of
65^{0 }C as well as 75^{0 }C.
