 |
|
|
 |
Correction factors for the current carrying capacity
Correction factors for underground installation
The following tables of correction factors are to be applied to the current carrying capacity
when installation conditions vary from the given presumptions. The rating for the most conditions
can be quickly estimated by multiplying the continuous current carrying capacity value by the
correction factors given in the appropriate tables below.
Correction factors for adjacent cables buried directly in ground, for multi-core cables and
for groups of three single-core cables.
|
Free space between the
multi-core cables or between the groups of single-core cables,
mm
|
Number of adjacent multi-core
cables or groups of three single-core cables
|
|
2
|
3
|
4
|
5
|
6
|
8
|
10
|
|
0
(touching)
|
0,79
|
0,69
|
0,63
|
0,58
|
0,55
|
0,50
|
0,46
|
|
70
|
0,85
|
0,75
|
0,68
|
0,64
|
0,60
|
0,56
|
0,53
|
|
250
|
0,87
|
0,79
|
0,75
|
0,72
|
0,69
|
0,66
|
0,64
|
Correction factors for different laying depths
|
Cable
|
Laying depth in ground, m
|
|
0,50...0,70
|
0,71...0,90
|
0,91...1,10
|
1,11...1,30
|
1,31...1,50
|
|
0,6/1 kV
|
1,00
|
0,97
|
0,95
|
0,93
|
0,92
|
|
6/10...18/30 kV
|
1,00
|
0,99
|
0,98
|
0,96
|
0,95
|
|
26/45...220/400kV
|
1,05
|
1,02
|
1,00
|
0,97
|
0,95
|
Correction factors for different thermal resistivities of soil
|
Thermal resistivity in the
ground, Km/W
|
0,7
|
1,0
|
1,2
|
1,5
|
2,0
|
2,5
|
3,0
|
|
Factor
|
1,10
|
1,00
|
0,92
|
0,85
|
0,75
|
0,69
|
0,63
|
Examples of thermal resistivities of soil:
| · dry sand (moisture content 0 %)
|
3,0 Km/W
|
| · dry gravel and clay
|
1,5 Km/W
|
| · semi-dry gravel and sand (moisture content
10%)
|
1,2 Km/W
|
| · semi-dry clay and moist gravel
|
1,0 Km/W
|
| · moist clay and sand (moisture content 25%)
|
0,7 Km/W
|
Correction factors for different ground temperatures
|
Conductor temperature
°C
|
Ground temperature, °C
|
|
-5
|
0
|
+5
|
+10
|
+15
|
+20
|
+25
|
+30
|
|
+90
|
1,13
|
1,10
|
1,06
|
1,03
|
1,00
|
0,96
|
0,93
|
0,89
|
|
+80
|
1,14
|
1,11
|
1,07
|
1,04
|
1,00
|
0,96
|
0,92
|
0,88
|
|
+70
|
1,17
|
1,13
|
1,09
|
1,04
|
1,00
|
0,95
|
0,90
|
0,85
|
|
+65
|
1,18
|
1,14
|
1,10
|
1,05
|
1,00
|
0,95
|
0,89
|
0,84
|
Correction factors for underground installations in unfilled plastic tubes (pipes), for
parallel tubes with one multi-core cable or three single-core cables in each. The cables are
equally loaded. If the correction factor of this table is applied, the correction factor of
adjacent cables buried directly in ground is not used.
|
Free space between the tubes,
mm
|
Number of tubes beside each
other
|
|
1
|
2
|
3
|
4
|
5
|
6
|
8
|
10
|
|
0
(touching)
|
0,80
|
0,75
|
0,65
|
0,60
|
0,60
|
0,55
|
0,55
|
0,50
|
|
70
|
-
|
0,75
|
0,70
|
0,65
|
0,60
|
0,60
|
0,55
|
0,55
|
|
250
|
-
|
0,75
|
0,70
|
0,70
|
0,70
|
0,65
|
0,65
|
0,65
|
Correction factors for different cable covers and troughs
|
Type of covering
|
Factor
|
|
A concrete or brick slab more
than 10 cm above the cable in the well-compacted sandy ground
|
1,00
|
|
Bricks all around the cable,
gaps sealed up tightly with sand
|
0,90
|
|
A concrete trough on the
cable, compacted sand between the trough and the cable
|
0,90
|
|
A concrete or plastic trough
on the cable, loose sand filler between the cable and the trough
|
0,80
|
|
|
|
 |
