Theoretical formula of sequence currents

As mentioned earlier, it is a common practice for underground cable systems which are longer than about 2 km, to cross-bond the metallic sheaths of three-phase cables to reduce sheath currents and to suppress sheath voltages at the same time [3]. Submarine cables, which are generally solidly bonded, are now becoming a popular type of cable due to the increase of offshore wind farms and cross-border transactions. 

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In this section, we derive theoretical formulas of the sequence currents for the majority of underground cable systems that is, a cross-bonded cable that has more than two major sections. We also derive theoretical formulas for a solidly bonded cable considering the increased use of submarine cables. 

Using Equation 3.65, the theoretical formula of the positive-sequence current simplifies to... 

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