Conductor internal impedance

The conductor internal impedance Z which means Zg, is the outer surface impedance given in Equation 1.9—or in Equation 1.10 as far as an overhead line is concerned. However, in the case of a cable, Z, is composed of a number of component impedances, as in Equation 1.9, and also an insulator impedance between metallic conductors because the cable is, in general, composed of a core conductor carrying current and a metallic sheath (shield or screen) for a current return path [4,5]. 

Discuss the difference between conductor internal impedance and earth-return impedance based on the results of Problems 1.1 and 1.4. 

Similar to the conductor internal impedance explained earlier, the earth-return impedance in Equation 1.15 is frequency dependent as the penetration depth hg is frequency dependent. Equation 1.15 is approximated considering ln(l + x) for a small x by... 

The reason for the much smaller wave deformation in the aerial modes than in the earth-return modes is that the conductor internal impedance that contributes mainly to the aerial modes is far smaller than the earth-return impedance that mainly contributes to mode 0. 

The earth-return impedance is far greater than the conductor internal impedance thus, the latter can be neglected. However, in a steady-state analysis such as fault and load flow calculations in a multiphase line, the positive-sequence (mode 1) component is important, and the conductor internal impedance is dominant for the positive-sequence component. 

Each element of the impedance matrix is composed of the cable internal impedance and the cable outer media (earth-return) impedance, as explained in Chapter 1 of this volume. In the overhead line case, the conductor internal impedance is composed of only one impedance (i.e., the outer surface impedance of a conductor). The cable internal impedance consists of the following six components [1] ... 

Noda, T. 2006. Development of accurate algorithms for calculating ground-return and conductor-internal impedances CRIEPI Report H05003 by Central Research Institute of Electric Power Industries in Japan (CRIPEI Tokyo) Report H05003. 

In general, the impedance and admittance of a conductor are composed of the conductor internal impedance Z and the outer-media impedance Zq. The same is applied to the admittance [1] ... 

The current of 1/3 following to the positive direction on each phase and the return current 1 have to flow back through the earth. Because the return current flows through the earth, the mode "0" component is called "earth-return" component. A circuit corresponding to the mode 0 can be drawn as Figure 1.21a. The mode 0 component involves the earth-return path of which the impedance is far greater than the conductor internal impedance as explained in Section 1.5.1,... 

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