Poly-phase coaxial power line efficiency enhancements

#Electrical power is distributed from central generating plants to homes, offices, and factories as three-phase alternating current. In recent years there has been an increasing public concern about possible biological effects of the low frequency electric and magnetic fields associated with the distribution and use of electrical power. Apparatus and methods for reducing such fields have been addressed by the inventor in his U.S. Pat. Nos. 5,070,441, 5,147,983, and 5,175,442, the disclosures of which are herein incorporated by reference.

#Although much of the recent public outcry has been directed at high voltage transmission lines on designated rights of way, there is also a perception that substations, especially those near schools, may be a public health hazard. Measurements of electrical or magnetic fields near substations show that these fields are almost entirely caused by the power lines that enter and exit the substation. It is known that the use of coaxial cable with the outer conductor connected to an earth ground eliminates the electric field. It is also well known that there are parasitic losses associated with the use of coaxial cable and that in some cases the magnetic field measured on the surface of the earth may actually be higher over burled coaxial cables than immediately under an overhead power line.

#It is an object of the invention to provide apparatus installable at poly-phase alternating current electrical power substations to substantially reduce or eliminate fringing electrical or magnetic fields near the substation and adjacent power lines entering or exiting the substation. It is a specific object of the invention to provide such reduction or elimination of fringing fields at both the fundamental and at higher harmonic frequencies.

#FIG. 1 of the drawing is an electrical schematic depiction of prior art wiring used in a three-phase electrical distribution substation that is supplied by an overhead-wire power line and that uses coaxial power cabling to connect transformer outputs to a three-phase, four-wire output power line. The core of the transformer is omitted from the drawing to aid in the clarity of presentation.

#FIG. 2 of the drawing depicts prior art electrical connection of typical loads to a conventional four-wire overhead distribution power line. The connected equipment includes an overhead single phase distribution transformer, a single phase distribution transformer in a burled vault, and a three-phase transformer bank in a vault. For simplicity, the transformer cores are not shown.

#FIG. 3 of the drawing is an electrical schematic depiction of a wiring arrangement to take power from an overhead high voltage input line into a substation and from the substation to a three-phase load by means of a different coaxial cabling arrangement. This figure does not provide full detail on the output side of the substation transformer or on the output of the wye connected three-phase load transformer.

#Turning initially to FIG. 1 of the drawing, one finds a schematic diagram of a typical three-phase substation 10 that is fed by a three-phase overhead circuit 12. Overhead ground conductors or neutral conductors 25 associated with other power lines are not part of the load carrying conductors; therefore, they are sometimes omitted from the drawing for simplicity. As shown in FIG. 1, it is conventional to connect the overhead neutral 25 to ground by means of a ground rod 74 outside the substation 10. A protective safety fence 14, used to prohibit public access, is indicated by the dashed line. Outside the fence, transmission wires without either insulation or a coaxial outer sheath must be sufficiently elevated to meet safety standards.

#The three-phase conductors 20,22,24 of the feed circuit 12 are carried through insulator bushings 26,27,28 in the metal transformer housing 30 to the delta-connected primary 32 of the substation transformer. The three-phase conductors 34,35,36 from the wye-connected secondary 38 of the substation transformer 40 are likewise fed through the transformer housing 30 by insulated bulkhead connectors 42,43,44, and are then connected to the center conductors 46,47,48 of three coaxial cables 50,51,52 that are conventionally buried in an underground conduit (not shown) that passes under the protective fence 14 around the substation 10. At the ends of the cables 50,51,52 distal from the substation transformer 40, the three center conductors 46,47,48 are connected to the three-phase conductors 54,55,56 of an overhead electrical power distribution line 60. Lightning arrestors and disconnect switches at this juncture are omitted from this figure for clarity. Observe that standard practice at the juncture of the coaxial cables and the output power line 60 is to connect the three outer conductors 62,63,64 of coaxial cables 50,51,52 to a single wire which is led down the support pole (not shown) to a single ground rod 68.

#The configuration of neutral conductors and ground connections that are used in the prior art is also shown in FIG. 1 of the drawing. A neutral conductor 58 is used in both overhead and buried distribution powerlines for carrying an unbalanced current (e.g. as is introduced by a single phase load connected to a three phase line) as well as for safety purposes. The center tap of the wye-connected secondary 38 of the substation transformer 40, the outer conductor of each of the output coaxial cables 50-52, and the substation transformer housing 30 are all connected to a common substation ground 70 (conventionally a metallic grid underlying a substation and bonded to one or more ground rods). That is, as is common practice in the utility industry, the outer conductors on coaxial cables in a cabling run that uses a plurality of such cables are usually interconnected and grounded at every place where a source or load is connected.