Overhead conductor

When discussing the mutual impedance between an overhead conductor and an underground cable or a buried gas and/or water pipeline, the selfimpedance of the overhead conductor is given by Equation 1.11, while that of the underground conductor is given by Equation 1.12. The mutual impedance will be explained in Section 2.2.3. 

Because the earth is not perfectly conducting, the earth surface is not the zero potential plane. Instead, the zero potential plane is located at the depth h from the earth surface. Then, the theory of image gives the following inductance [6]  

the outer-media impedance of the single overhead conductor is given by 

Remind that the penetration depth is not a real value but a complex value and thus the zero potential plane at the depth h is just a concept and does not exist in physical reality. 

When the earth is perfectly conducting, that is, pe=0, then hg=0 in Equation 1.13. 

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EET-NEMA Standards for Connectors for Use Between Hluminum or Hluminum—Copper Overhead Conductors, EEIPub. No. TDJ-162, Edison Electric Institute, New York, Aug. 1973. 

On stretches of electric line, according to Ref. 12, filling tracks without overhead conductors are usually isolated from the rest of the rail network with insulating joints in order to keep the rail currents flowing to the tank installation as... 

Tracks on wooden sleepers in ballast have a relatively low leakage load that is a hundred times smaller for a ballast bed than for tracks in the street. Good electrical insulation is, however, only ensured if the rails have no electrical contact with other installations with low grounding resistance. Overhead conductor poles should in principle not be connected to the rails. Exceptions are overhead conductor poles with electrical equipment that is connected to the rails to avoid inadmissibly high contact voltages in the event of a failure. Such overhead conductor poles should be... 

Electricity is generated in large modem Power Stations at 25 kV (25,000 volts). It is then transformed up to 132kV or 270kV for transmission to other parts of the country on the National Grid network. This is a network of overhead conductors suspended on transmission towers which link together the Power Stations and the millions of users of electricity. 

Fig. 1-15 Berlin streetcar in 1882 with double overhead conductor with rod contact.

Equipment location. Outdoor metal structures supporting antennas, as well as self-supporting antennas such as vertical rods or dipole structures, shall be located as far away from overhead conductors of electric light and power circuits of over 150 volts to ground as necessary to avoid the possibility of the antenna or structure falling into or making accidental contact with such circuits. 

Setting and moving poles, (i) When a pole is set, moved, or removed near an exposed energized overhead conductor, the pole may not contact the conductor. 

The conductors used underground are different from overhead conductors in that they are insulated for their entire length and several of them maybe combined under one protective sheath. The whole assembly... 

S] Dcyle, D. P. and Wright, T. E., A Rapid Method for Predicting Adequate Service Lives for Overhead Conductors in Marine Atmospheres, presented at the IEEE Power Meeting, New York, 1971. 

In this chapter, a theory of distributed-parameter circuits is explained starting from the approximate impedance and admittance formulas of an overhead conductor. The derivation of the approximate formulas is described from the viewpoint of the physical behavior of current and voltage on a conductor. 

It should be noted that the impedance and admittance in this equation become a matrix when a conductor system is composed of multiconductors. Remember that a single-phase cable is, in general, a multiconductor system because the cable consists of a core and a metallic sheath or a screen. In an overhead conductor, no conductor internal admittance y exists, except a... 

The outer media of an overhead conductor are the air and the earth since the conductor is isolated by the air from the earth, which is a conducting medium. Therefore, the outer-media impedance Zq of the overhead conductor is composed of the following component ... 

Using the penetration depth for the earth, the outer-media impedance of an overhead conductor is readily obtained based on image theory. Figure 1.2 illustrates a single overhead conductor and its image ... 

This impedance is well known as the space impedance of an overhead conductor, that is... 

Impedance and Admittance Formulation of an Overhead Conductor System... 

Pollaczek derived a general formula that can deal with earth-return impedances of overhead conductors, underground cables, and multiconductor systems composed of overhead and underground conductors in the following form [7,13] ... 

TABLE 1.11 Surge Impedance of an Overhead Conductor with Length x = 4 m... 

Earth is stratified, as is well-known, and its resistivity varies significantly at the top layer depending on the weather and climate. The earth-return impedance of an overhead conductor above the stratified earth was derived in Reference 16, and the stratified-earth effect was investigated in Reference 17. The stratified-earth effect may be far more significant than the accurate evaluation of the homogenous earth-return impedance of Pollaczek and Carson, and this requires further investigation. 

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