Recommended Maximum Allowable Conductor Temperature. The determination of maximum allowable conductor temperatures is left to the discretion of each equipment owner, with due consideration for the conductor material; however, such temperatures must not be less than 100C for any emergency rating. OVERHEAD CONDUCTOR RATING METHODOLOGY IEEE Standard 738, first published in 1986, is based on the methods developed by Xxxxx and Xxxxxx in their 1958 AIEE paper [Reference 3]. These same methods were used in the New England Electric System programs PG92 and PG108, which the System Design Task Force adopted for calculating conductor ratings in 1970, and from which some programs now in use evolved. Programs consistent with the methods of Standard 738-2006 are acceptable for use in rating overhead conductors in New England. Standard 738-2006 and the included rating program, RATEIEEE, address both steady-state and transient ratings. Since the thermal time constant of a conductor is generally greater than 15 minutes, the steady-state calculation is to be applied in determining Normal and Long-Time Emergency ratings. The transient calculation is applied in determining Short-Time Emergency ratings and Drastic Action Limits. In all cases, adequate clearances must be maintained with conductor loadings at the rated values. OVERHEAD CONDUCTOR RATING PARAMETERS Overhead conductor rating calculations are based largely on the resistance and maximum allowable temperature of the conductor, and two environmental factors: ambient temperature and wind speed (the design values of which are discussed in Appendix A). However, other physical characteristics and environmental conditions also influence the calculation of conductor ratings. Some of these vary with the conductor or with location: Conductor Diameter Latitude Elevation 1 Creep can cause permanent increased conductor sag and is defined as the non-elastic deformation or flow of material, which occurs with time under its installed tension and advanced by application of additional wind or ice load. Atmosphere (Clear/Industrial) Line Direction (North – South, East-West, etc.) and the appropriate parameters are left to the discretion of the facility owners. Other parameters can be uniformly applied throughout New England: Wind direction: perpendicular to the conductor as discussed in the SDTF–20 report [Reference 4]. Emissivity and Solar Absorptivity: While these parameters increase with conductor age and oxidation and are influenced by operating voltage and the condi...
