Abstract-Cable series impedance modeling is widely applied in electromagnetic transients calculations and power loss calculations. The calculations are usually performed in a 2D frame using FEM or alternative approaches like MoM-SO, thereby losing the 3D effects imposed by twisting of wire screens and armors. One of the implications of using 2D modeling for three-core and closely packed single-core cables is that currents will always circulate among the individual wires of each wire screen or armor. However, in the case of twisted screens/armors where the wires are insulated from each other, such current circulation will in reality not exist. As a result, the calculated impedances become incorrect, as well as the induced currents and losses on individual conductors. A procedure is introduced for preventing such false current circulations in a 2D calculation frame by simple manipulation of the system impedance matrix. The approach is demonstrated for the modeling of single-core and three-core cables, with and without an external armor. It is shown that the representation of the wire screen/armor armor with respect to current circulations can substantially influence the calculated result, both for the 50/60 Hz impedance and the cable transient behavior. The use of tubular screen representations is also investigated.

Formation of hydrates is a well known problem in subsea production systems for oil and gas. As the unprocessed well-stream cools down, hydrates are formed at temperatures up to 250C depending on the water cut and pressure inside the pipeline. Several options are available to

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.Abstract-Offshore umbilical cables often include both power cables and elements such as metallic tubes and signal cables. It was concluded from a recent failure of stainless tubes that AC corrosion was the failure cause. This paper describes how AC corrosion can lead to tube failure if a puncture exists in the insulating tube coating. The variation in power cable charging currents along the umbilical cable causes a non-zero voltage to exist on the tubes, even though they are grounded at both ends. If the current density associated with the puncture current is sufficiently high, AC corrosion will result. The current density is calculated as function of cable length and VSD operating frequency, for three alternative power cable designs. Comparison with measured corrosion rates shows that AC corrosion can corrode a hole in the tube in weeks or months, depending on the cable design and length, and on the electrical operating conditions. Analytical expressions and numerical procedures are presented which can be used to determine if a given umbilical cable installation involves risk of AC corrosion. It is also shown that substantial heating effects in the puncture area can result in case of excessive harmonics in the supply voltage.

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