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Abstruct-This article reports the procedures used to determine the voltage applied upon several pipelines crossing the 138 kV double circuit Termorio-S.Jose transmission line. During a fault to ground, the current flowing along one of the circuits can differ, in terms of value and direction from the current flowing in the other circuit. This fact gives rise to the need of special simulation techniques which are dealt here. This article also presents a summary of the basic calculation procedures used to determine the voltage difference which appears across the pipeline insulation (between metal and ground), when a fault occurs on the transmission line crossed by the pipeline. This voltage difference should not exceed 5kV for sa€ety reasons.

This paper deals with the modeling techniques necessary to represedt, in a suitable way, the important inductive and resistive couplings existing between a transmission line and a pipeline, when the Iine crosses the pipeline several times.The subject is illustrated using the 500 kV transmission line Cachoeira Paulista-Adrianopolis 111, which belongs to FURNAS transmission system. This line crosses 9 times the OSRIO poliduct; 5 times the CASPAL gasduct 4 times the GASVAL gasduet and the OSVAL poliduct. All these pipelines belong to PETROBRAS. Furthermore the transmission line crosses a CEG pipehe twice. This article shows also how to determine the value of the lengths of transmission line and pipeline which must be represented, in each side o f the crossing towers, in order to take in due account all the inductive and resistive couplings existing between them.Index Terms-Decoupled Method; ladder; characteristic length; pipeline t-IntroductionThe studies dealt with in this article were carried out using the digital program DECOP (version 2) developed by one of the authors, and presented in references [1,2] about the subject, The calculation methodology uses the Decoupled Method, also developed by the same author [3,4,5]. II-Line DescriptionThe program receives the position of each tower center at the ground level by means of X, Y, Z coordinates. To each tower, a code number is assigned, indicating the type and geometry of it. This allows the program to compute the coordinates of each one of the three phases, at the point they join the tower insulators chain.Between two consecutive towers, each phase is represented by a straight tine connecting the mentioned points. Under special circumstances, the straight line representation can be replaced by a catenary (not yet in operation). For each pair of successive towers a code number is assigned, indicating the characteristics of phase, groundwire and counterpoise conductors. ' (*) R.Vice Gov. Rubens Berardo 175 coni 1002 Bloco 1-Gavea-CEP 22451-0700 -RJ -The pipeline geometry is indicated by the X, Y, Z coordinates of inflection points. For each pipeline length between two successive inflection points, a code number is assigned, indicating the pipeline characteristic such as diameter, type and thickness of the insulation etc. 1V-Additional Points Created by the Program Along the Line Figure 1 shows a transmission line with towers 1,2,3,4,5,6 ,...., and a pipeline with inflection points a,b,c,d, .... These points were indicated by the program user. However the program must subdivide the line and the pipeline into additional points, in order to create pairs of line and pipeline segments, in which the mutual zero sequence impedance can be considered as approximately uniform, and submitted to the same values of phase current and ground-wire current.Figura 1-Generation of new points along the pipeline (a,b,c,d) and the transmission line 11,2,3,4,5,6) Figure I shows that two planes perpendicular to the segment (1-2), corresponding to the central phase segment of the line betwe...