Reactance of Large Cables in Steel Pipe or Conduit

The determination of reactance of large conductors in steel pipes or conduits has not been susceptible of practical computation but is required for estimating the voltage regulation of pipe cable systems. The present paper gives the results of tests made by Electrical Testing Laboratories (ETL) under the auspices of the Insulated Power Cable Engineers Association, on cables from 750,000 to 2,500,000 circular mils. These data have been supplemented by data from other sources, extending the lower limit of size to 4/10 American wire gauge. Empirical formulas have been developed to include all intermediate sizes and spacings. These formulas are based on the principle of deriving a self-GMD (geometric mean distance) from the a-c/d-c resistance ratio, and using an augmented axial spacing to allow for the magnetic effect of the pipe.