Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Electrical Engineering


Growing concern for the preservation of the natural beauty of this country has spurred the development of underground cable. Overhead circuits, which once cluttered the landscape, are being retired and underground circuits are being installed. At new development sites, whether rural or urban, the question of installing underground circuits is being considered. The advantage of added beauty is not the only favorable consideration for underground distribution systems. In the Midwest, the unpredictable weather often becomes a formidable opponent of the electric utility. Since the underground cable is buried in the earth, the hazards of wind, ice, and lightning are either eliminated or reduced considerably. The added advantage of service quality is augmented by the increased safety of underground systems. There are no poles to be struck by out-of-control vehicles, no live wires lying on the ground to endanger citizens, and no overhead lines to be snagged by large equipment. However, to simply state the advantages of underground distribution systems would be misleading. are disadvantages which, through added research, hopefully can be resolved. The major disadvantage in employing underground systems is cost. To simply revise all of the existing overhead systems by installing underground systems would virtually be an impossibility. Therefore, if there is to be a revision of existing systems, it will have to be a gradual process. The other disadvantage of underground distribution is its inaccessibility in case of a fault. Research is being carried out to develop new methods of fault location. Once these methods are established, part of the problem of inaccessibility can be reduced. Research in the area of underground cable is an expanding field. The never-ending goal of decreasing the cost of cable has resulted in various new designs. The concentric neutral underground cable is one of these designs. The purpose of this thesis is to make a study of a single-phase underground circuit comprised of this concentric neutral cable, and a study of a single-phase underground system that is physically paralleled with a single-phase overhead circuit. Formulas will be developed for the inductance and capacitance of each of these cases. These formulas will be developed, based on the assumption that all of the phase current returns in the neutral conductor. An equivalent circuit will be proposed for each of these cases, and numerical values for each of the circuit parameters will be calculated. Finally, solutions will be obtained using formulas which take into account the earth-return path. Values which are obtained from these formulas will be checked with data measured in the field.

Library of Congress Subject Headings

Underground electric lines



Number of Pages



South Dakota State University