TRANSMISSION LINE CAPACITY CALCULATION
BY BHAVESH PATEL
Requirement of Trans. Line Capacity CalculationFor Find out
exact System Stability/Reliability & Thermal limit Point in
view of Maximum Permissible line Loading
Criteria of Permissible Line LoadingVoltage Regulation Thermal
Loading Energy Losses SIL (Surge Impedance Loading)
SIL (Surge Impedance Loading)SIL gives a general idea of the
loading capability of the line SIL = V^2/Zs Zs = Surge Impedance =
(L/C)^1/2 Where, L = Inductance of line H/Mtr./Phase C =
Capacitance of line, P to N, F/Mtr. SIL For Short Line > 1 SIL
For Long Line < 1
SIL (Surge Impedance Loading)Line Voltage 132 KV 220 KV 400 KV
SIL 46 MW 129 MW 410 MW
132KV Line: L= 0.001218 H/KM/Phase C=0.00882 F/KM, P to N Zs =
(L/C)^1/2 = 0.3716 SIL = V^2/Zs = 46.89 MW
Thermal Loading of LineThermal Loading is decided on the basis
of Conductor Type & Dimension, Amb. Temp., Max. permissible
conductor Temp., wind velocity, Solar Radiations, Absorption
Coeff., Emissivity Coeff. Etc. Heat Balance Equation for
calculation of Conductor Losses (W/KM) = Heat Lost By Convection
(HC) + Heat Lost by Radiation (HR) Heat gained by solar radiations
(HS)
Thermal Loading of LineAssumption: 1. Wind Speed : 2 KM/Hour 2.
Solar Radiations : 1045 w/sq. mtr 3. Absorption coeff. : 0.8 4.
Emissivity coeff. : 0.45 (0.3 for new conductor & 0.9 for old
or black conductor) 5. Temp. coeff. Of Res. Per deg C (a): 0.00403
6. Normal Atmospheric Pressure (p): 760
Thermal Loading of LineHeat Lost By Convection (HC) = For
Natural Convection, Hc = 12.8*10^-4*Dia. In cm^0.689*Temp.
12.8*10^rise^1.2333 For Force Convection, Hc = 13.8*10^-4*(Effe.
Wind Speed*Dia. In 13.8*10^cm)^0.448*Temp. rise Effective Wind
Speed = Wind speed in cm/sec*(p/760)*(293/(273+Amb. Temp.) p =
Atmospheric Pressure
Thermal Loading of LineHeat Lost By Radiation (HR) = Conductor
Emmisivity * Stefan Constant*{(Max. Conductor
Temp.+273)^4Temp.+273)^4-(Amb. Temp.+273)^4}*(22/7)*Dia. In cm Heat
Gained by Solar radiation = Solar Absorption Co-efficient *
CoIntensity of solar radiation * Dia. In cm
Thermal Loading of LineAmp Capacity for Max. Ambient Temperatur
Conductor Temp. (Deg C) e (deg C) 65 75 ACSR 40 312 413 PANTHER 45
244 366 210 Sq. mm. 48 199 334 50 311 ACSR ZEBRA 40 454 622 420 Sq.
mm. 45 339 546 48 240 493 50 454 Conductor Type & Dimension
THANKS
