IEEE 7382012 pdf free.IEEE Standard for Calculating the CurrentTemperature Relationship of Bare Overhead Conductors.
IEEE 738 describes a numerical method by which the core and surface temperatures of a bare stranded overhead conductor are related to the steady or timevarying electrical current and weather conditions. The method may also be used to determine the conductor current that corresponds to conductor temperature limits. The standard does not recommend suitable weather conditions or conductor parameters for use in line rating calculations.
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 Working Group on Calculation of Bare Overhead Conductor Temperatures of the Towers. Poles and Conductors Subcommittee has made every effort to ensure that the computer 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.
For the purposes of this docunwnt. the following terms and definitions apply. The IEEE Siandards Dictionary Online should be consultcd for terms not defincd in this clause.
conductor temperature: The temperature of a conductor, is normally assumed to be isothermal (i.e.. no axial or radial temperature variation). In those cases where the current density exceeds 0,5 A/mm2 (I Afkcmil), especially for those conductors with more than two laycrs of aluminum strands, the diff’crcnce between the core and surface may be significant. Also, the axial variation along the line may be important. Finally, for transient calculations where the time period of interest is less than I mm with nonhomogeneous aluminum conductor steel reinforced (ACSR) conductors, the aluminum strands may reach a high temperature before the relatively nonconducting steel core.
efTectke (radial) thermal conductisit: Effective radial thermal conductivity characterlies the bare stranded conductor’s heterogeneous structure (including aluminum strands, air gaps. oxide layers) as if it were a single, homogeneous conducting medium. The use of etTective thermal conductivity in the thermal model simplifies the calculation process and avoids complex calculations on a microscopic level including the assessment of contact thermal resistances between strands, heat radiation and convection in air gaps locked between strands.
heat capacity (material): When the average temperature of a conductor material is increased by dT as a result of adding a quantity of heat dQ, the ratio. dQ/dT. is the heat capacity of the conductor.
maximum allowable conductor temperature: The maximum conductor temperature limit that is selected in order to minimize loss of conductor strength. and which limits sag in order to maintain adequate electrical clearances along the lines.
Re nolds number: A dimensionless number equal to air velocity lime the air density times conductor diameter divided by the kinematic viscosity of air. all expressed in consistent units. The Reynolds number. in this case, is equal to the ratio of inertia forces to the viscous force on the conductor. It is typically used to differentiate between laminar and turbulent flow.
specific heat: The specific heat of a conductor material is its heat capacity divided by its mass.
steadystate thermal rating: That constant electrical current which yields the maximum allowable conductor temperature for specified weather conditions and conductor characteristics under the assumption that the conductor is in thermal equilibrium (steady state).
thermal time constant: In response to a sudden change in current (or weather conditions), the conductor temperature will change in an approximately exponential manner. eventually reaching a new steadystate temperature if there is no further change. The thermal lime constant is the time required for the conductor temperature to accomplish 63.2% of this change. The exact change in temperature is not exponential so the thermal time constant is not used in the calculation described in this standard. It is. however, a useful concept in understanding line ratings.IEEE 738 pdf free download.
IEEE 7382012 pdf free
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