PIPE-TYPE CABLE AMPACITIES IN THE PRESENCE OF HARMONICS

This paper explores the effect of harmonics on HPFF pipe-type transmission cable ampacity. Industry currently calculates the current carrying capacity of underground cable based on the assumption of a purely sinusoidal 60 Hz. current. However, increasing levels of harmonics on power systems have raised concern about their effect on cable ampacities. The issue has already been addressed for distribution cables. This paper begins with a discussion of Neher and McGrath's classic equations and some recent revisions, and develops a closed form composite equation accurately reflecting the effect of harmonics. The effect of frequency on the loss ratio is shown and supported by comparison with measured data at 60 Hz. and a finite element analysis at a number of harmonic frequencies. The effect of specific harmonic scenarios is shown in light of the IEEE standard on harmonics. The results are used to develop a derating factor to compensate for current harmonics on transmission systems.