Underground Cables
What is Underground
Cable????
 A flexible bunch system of conductors for carrying
rated electrical currents
 Insulated to withstand rated applied voltage
 Protected from ingress of water
 Designed to withstand mechanical impacts &
chemical corrosion
 Which can be buried underground
Power cable History
Selection of Cables
 Insulation Based
 Voltage Based
 Conductor Material based
Insulation Based
 PILC-Paper Insulated Lead Covered
 XLPE-Cross Linked Polyethylene
 PVC- Poly Vinyl Chloride
 EPR-Ethylene Propylene Rubber
Voltage Based
 LV-Low Voltage- 600/1000V
 MV-Medium Voltage -11 kV to 33 kV
 HV-High Voltage -132 kV & above
Conductor Material Based
 Aluminum – for LV cables
 Copper – for HV & LV cables
Low Voltage Cable
600/1000V ????
Low Voltage cable 600/1000V???
BS 6231:2006 Electric cables. 600/1000 V PVC insulated
cables for switchgear
 Intended for use at alternating voltages not exceeding
600 V to earth
 Direct voltages not exceeding 1000 V to earth
Points to be considered while
selecting cables
 Application
 Place
 Voltage grade
 Current rating
 Atmosphere
Cable components
 Conductor
 Insulation
Inner sheath
 Armor
 Outer sheath
Cable Construction
LT/HT, XLPE/Paper, 1C/3C, Compact conductors & non compact
Conductors, Semiconducting tape, lead sheath, PVC/HDPE,
Water blocking tape,
Importance of each layer
Graphite coating
Abbreviations
 GSW- Galvanized Steel wire
 SWA – Single Wire Armour
 DWA – Double Wire Armour
 STA – Steel Tape Armour
 SL – Separately lead sheathed
Color coding of phases (Old & new scheme)
Rating Factors – To be applied to the main
current for
 Variation in ambient temperature
 Variation in ground temperature
 Variation in depth of laying
 Variation in soil thermal resistivity
 Grouping factors based on number of parallel circuits
Cable Handling
Cable transport to site
Cable storage (Use of folk lifts, stacking cable drums)
Cable transport to site
Cable drums should be
stored so that the
drum flanges do not
contact cable on
another drum.
Cable laying
Use of rollers
Cable laying
 Depth of laying
 Use of cable rollers
 Minimum bending radius
 Different Cable circuit formations
 De-rating factor when cables are laid in ducts
 Minimum free space in ducts to allow heat transfer
 Precautions to avoid damages to cable during installation (Do
not drag on carpet road surfaces)
 Use of cable tiles or warning tapes
Cable laying – Depth of laying
Rating factors –Depth of laying
Minimum Bending Radius
Voltage(kV) PILC PILC PVC,XLPE PVC,XLPE
Single
Core
Multicore
Single
Core
Multicore
0.6/1V
20D
15D
15D
12D
1.1 to 11kV
20D
15D
15D
15D
Above 11 kV
25D
20D
20D
15D
Different Cable circuit formations
To protect the cable from mechanical damages
Cable warning tapes
Minimum free space in ducts to allow heat
transfer ???
More than 50%+++++++ is required….
Electrical Stress Distribution
Electrical Stress Distribution
Thank You