Radial Temp Condutor

Radial Temperature Difference for Bare Stranded Conductors
Research Sponsored by Southern Company & EPRI Bernie Clairmont, EPRI Dale Douglass, PDC, Inc. February 14, 2011
1

A balance of energyat conductor surface


Heat is removed by:
– Convection – Conduction – Radiation



Heat is generated within the conductor by:
– Ohmic (R*I2) Losses – Solar Heating

Heat Balance atConductor Surface

Heat Balance within Conductor


54/7 ACSR Heat Generation
– – – – 2% steel core 22% inner 12 wires 33% middle 18 wires 44% outer layer





56% of heat must flow tosurface through layers Heat flow requires temp drop from core to surface.

Why Radial Temp is a problem now?








Thermal models for OHTL were developed many years ago when 75oC and 1amp/kcmil were typical maximums. Today HTLS conductors operate up to 250oC with current densities up to 2.5 amps/kcmil. With ACSR, above knee-point temp (50 to 120oC) there is no tension in aluminumlayers (poor contact). With ACSS and ACCC (annealed aluminum) there is no tension in alum most of the time. Heat flow between strand layers is proportional to I2 so radial temp differences are 4 to 7times higher with HTLS or with ACSR at very high current.

A simulation of the aluminum strand interface

Calculate Thermal Conductivity - Example
Can be rearran ged to: • A = 12 inch square =0.0929 m2 •b = 0.367 inches = 9.3 mm
Pressure [lbs] Ttop [degC] Tbottom [degC] Q [watts] kth[w/m-C] 10 79 98 86 0.91 100 89 98 93 2.07

Author Z. Peter

Previous Measurements on StrandedConductors

Thermal conductivity calculated with CIGRE formula

Formulation in steady state or in quasi steady state as per CIGRE TB207
 CIGRE WG 22.12, IEEE 738 TF (‘85), Dale (‘86):
2 1 PT D2 D Tc Ts   ln    2 2 2    k  2 D  D2 D2 

 D – external conductor diameter
 Pt – total heat gain  Tc – core temperature  Ts – surface temperature

 D2 – internal diameter = core...