IEEE 798:2006 pdf download IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors
For the purposes of this standard, either the electrical current is assumed constant for all time or it is as- sumed to undergo a step change from an initial current to a final current. The ambient weather conditions are assumed to be constant with time in both the steady-state and transient calculation methods described in this standard. This standard includes mathematical methods and indicates sources of the values to be used in the calcula- tion of conductor temperatures and conductor thermal ratings. However, because there is a great diversity of weather conditions and operating circumstances for which conductor temperatures and/or thermal ratings must be calculated, the standard does not undertake to list actual temperature-current relationships for specific conductors or weather conditions. Each user must make their own assessment of which weather data and conductor characteristics best pertain to their area or particular transmission line. The calculation methods in this standard are also valid for the calculation of conductor temperature under fault conditions.
1.2 Disclaimer A computer program is included in this standard as a convenience to the user. Other numerical methods may well be more appropriate in certain situations. The IEEE Conductors Working Group of the Towers, Poles, and Conductors Subcommittee has made every effort to ensure that the program yields accurate calculations under anticipated conditions; however, there may well be certain calculations for which the method is not appropriate. It is the responsibility of the user to check calculations against either test data or other existing calculation methods.
2 Definitions
For the purposes of this document, the following terms and definitions apply. The Authoritative Dictionary of IEEE Standard Terms [B21] 1 should be referenced for terms not defined in this clause.
2.1 conductor temperature: The temperature of a conductor is assumed to be isothermal (i.e., no axial or radial temperature variation) for all steady-state calculations and for all transient calculations where the time period of interest exceeds 1 min or the conductor consists of a single material. With transient calcula- tions for times less than 1 min with non-homogeneous aluminum conductor steel reinforced (ACSR) con- ductors, the aluminum strands are isothermal, but the heat capacity of the steel core is assumed to be zero.
2.2 heat capacity (material): When the conductor temperature is increased by dT c as a result of adding a quantity of heat dQ c , the ratio, dQ c /dT c , is the heat capacity of the conductor.
2.3 maximum allowable conductor temperature: The maximum temperature limit that is selected in order to minimize loss of strength, sag, line losses, or a combination of the above.
2.4 Reynolds number: A non-dimensional number equal to air velocity (V w ) times conductor diameter (D) divided by kinematic viscosity (µ f /ρ f ).
2.5 specific heat: The specific heat of a conductor material is its heat capacity divided by its mass.
2.6 steady-state thermal rating: The constant electrical current that would yield the maximum allowable conductor temperature for specified weather conditions and conductor characteristics under the assumption that the conductor is in thermal equilibrium (steady state).

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