Skin effect coefficient

Skin effect coefficient for Milliken conductors depending on insulation material and wire stranding orientation for copper conductors or number of segments for aluminium conductors. The skin effect in a single-core cable is substantially the same as the skin effect in a solid round cylindrical conductor having the same d.c. resistance per unit length.

Values are according to IEC 60287-1-1 with extensions from Cigre TB 272. Default value is $k_1$ = 1.0 for cases not covered below. Values for PP are assumed to be identical to PE and for SiR to EPR.

For hollow conductors, the formula from IEC 60287-1-1 Annex B should be used. This value is also applicable to keystone conductors.

Symbol

$k_s$

Formulas

$\frac{d_c-d_{ci}}{d_c+d_{ci}} \left(\frac{d_c+2d_{ci}}{d_c+d_{ci}}\right)^2$	Hollow conductor
$\frac{D_c-D_{ci}}{D_c+D_{ci}} \left(\frac{D_c+2D_{ci}}{D_c+D_{ci}}\right)^2$	conductor PAC/GIL
$\frac{D_{encl}-D_{encl}-2t_{encl}}{D_{encl}+D_{encl}-2t_{encl}} \left(\frac{D_{encl}+2\left(D_{encl}-2t_{encl}\right)}{D_{encl}+D_{encl}-2t_{encl}}\right)^2$	enclosure PAC/GIL

Related

$c_{type}$

Construction conductor

$d_c$

External diameter conductor [mm]

$D_c$

Diameter conductor (outer) [m]

$D_{ci}$

Diameter conductor (inner) [m]

$d_{ci}$

Internal diameter conductor [mm]

$D_{encl}$

Diameter enclosure (outer) [m]

$k_p$

Proximity effect coefficient

$M_c$

Conductor material

$M_i$

Insulation material

$t_{encl}$

Thickness enclosure [m]

Used in

$x_s$

Factor for skin effect on conductor

Choices

$c_{type}$	Material	Insulation	Direction	Value
3	Cu	PE	unidirectional	0.62
3	Cu	PE	bidirectional	0.8
3	Cu	PE	insulated	0.35
3	Cu	HDPE	unidirectional	0.62
3	Cu	HDPE	bidirectional	0.8
3	Cu	HDPE	insulated	0.35
3	Cu	XLPE	unidirectional	0.62
3	Cu	XLPE	bidirectional	0.8
3	Cu	XLPE	insulated	0.35
3	Cu	XLPEf	unidirectional	0.62
3	Cu	XLPEf	bidirectional	0.8
3	Cu	XLPEf	insulated	0.35
3	Cu	PVC	unidirectional	0.62
3	Cu	PVC	bidirectional	0.8
3	Cu	PVC	insulated	0.35
3	Cu	EPR	unidirectional	0.62
3	Cu	EPR	bidirectional	0.8
3	Cu	EPR	insulated	0.35
3	Cu	IIR	unidirectional	0.62
3	Cu	IIR	bidirectional	0.8
3	Cu	IIR	insulated	0.35
3	Cu	PP	unidirectional	0.62
3	Cu	PP	bidirectional	0.8
3	Cu	PP	insulated	0.35
3	Cu	SiR	unidirectional	0.62
3	Cu	SiR	bidirectional	0.8
3	Cu	SiR	insulated	0.35
3	Cu	PPLP		0.435
3	Cu	Mass		0.435
3	Cu	OilP		0.435
3	Al			0.25
3	Al		4 segments	0.288
3	Al		5 segments	0.195
3	Al		6 segments	0.118
3	Al		7 segments	0.07
3	AL3			0.25