Determination of the effect of harmonics on pipe-type power cable AC/DC resistance ratios

The authors present a closed-form expression for computing the AC/DC resistance ratio of high-pressure fluid-filled (HPFF) pipe-type cable in the presence of harmonics. Industry computes this factor with the assumption that the currents are purely sinusoidal at 60 Hz. However, as levels of harmonics increase on power systems, concern for the effect of harmonics on system ampacities rises. The authors develop a closed-form hybrid of the resistance ratio equations presented by J.H. Neher and M.H. McGrath (1957), and they compare the results with measured data at 60 Hz. No measured data are available for the resistance ratio at higher frequencies, so a two-dimensional finite element model is developed to view the effect of frequency on the resistance ratio. The effect of a specific harmonics scenario on the resistance ratio of a given system is discussed, and results are presented for some example systems