Inclusion of Wire Twisting Effects in Cable Impedance Calculations

Abstract

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.

Modelling of wind power plant transmission system for harmonic propagation and small‐signal stability studies

“…screen conductors). Depending on the cable type and an application, ignoring those effects might lead to inaccurate results [14][15][16][17][18]. This is especially important for offshore WPPs, which are basically large cable networks.…”

“…As a result, incorrect results arise for the current distribution on wires and other conductors, and thereby the effective impedance seen from the cable phases. The most recent work [18] shows a procedure for improving the accuracy of 2D tools by allowing to choose between alternative assumptions for (twisted) wire screens and (twisted) wire armours. The individual wires are either (i) insulated from each other, or (ii) assumed in galvanic contact (bonded).…”

Voltages and AC Corrosion on Metallic Tubes in Umbilical Cables Caused by Magnetic Induction From Power Cable Charging Currents

“…The voltage along the screen is dominated by the resistive voltage drop along the screen that is caused by the capacitively induced screen current. With a PUL screen resistance RS, the screen voltage in the left half of the cable is 12 1…”

“…3 while the steel armoring is assumed to be on ground potential. The impedance matrix of this 12×12 system is calculated at any frequency using the MoM-SO method [11] which includes both skin and proximity effect while enforcing that the net current is the same in all wires in each armor layer [12]. The capacitance calculations assume that the surface of all elements is on ground potential as the umbilical is flooded.…”

A 3D parametric thermal analysis of submarine three-core power cables

“…One of the most employed type of cable is the three-core armored, where the armor is composed of steel wires twisted around the three cores. Mainly due to the presence of this armor, the global and disaggregated cable losses estimation is challenging, and several approaches have been proposed previously [2][3][4][5][6][7][8][9][10], highlighting the fact that the IEC 60287 standard [11] introduces important errors in the computation of the armor losses since it does not take into account the relative twisting between phases and armor wires. This is of importance because, apart from using it for economic analysis, the losses knowledge is a requirement for the temperature estimation inside the cable, and hence the thermal capacity.…”