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Quantify in watts Sheath losses with transposition

Quantify in watts Sheath losses with transposition

Quantify in watts Sheath losses with transposition

(OP)
It is possible quantify in watts sheath losses with regular transposition?

The std 525-1992 and other stds show many equations to determinate sheaths losses in many arrangements including flat formation, but do not have to flat formation with regular transposition.

iec 60287 quantify these losses with factor lambd1, but is a value without dimensions.
 

RE: Quantify in watts Sheath losses with transposition

The shield losses-for non-magnetic shield-can be divided in two sources:
Circulating current losses and eddy current losses.
For cross bonding, the cable length is divided into three approximately equal sections. Each of the three alternating magnetic fields induces a voltage with a phase shift of 120° in the cable shields. The cross bonding takes place in the link boxes. Ideally, the vectorial addition of the induced voltages results in Uires = 0. In practice, the cable length and the laying conditions will vary, resulting in a small residual voltage and a negligible current. Since there is no circulating current flow, there are practically no losses in the screen. The total of the three voltages is zero, thus the ends of the three sections can be grounded.
Cross bonding the cables also would reduce more the residual voltage so circulating current too.
In shielded three-phase cable systems, the ac currents flowing along the cable conductors induce eddy currents in the metal shield which produces an additional resistive loss.
If high frequency harmonics are involved then eddy current could be significant.
But for low frequency [50-60 Hz] this may be neglected. See IEC 60287-1-1 for eddy current evaluation.
Also see:
http://www.eea.co.nz/images/Events/APEX/Southern%20Summit%2007/Presentations/Pres%205%20Zhou,%20Zoseph%20-%20Presentation.pdf
And IEEE 575-1988  " IEEE Guide for Application of Sheath-Bonding Methods for Single-Conductor Cables and the Calculation of Induced Voltages and Currents in Cable Sheaths"
 

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