The document discusses power cable technology, including: 1) The importance of cables for reliable power distribution and aesthetic reasons with growing load density. 2) The construction of different voltage cables, from LV to EHV, using materials like XLPE, PILC, and gas insulation. 3) Factors that determine cable ratings like soil conditions, depth of laying, and allowable operating temperature. 4) Best practices for cable laying including fixing routes, trenching, laying procedures, and post-laying inspections.

1. Power Cable Technology

2. Contents:
Importance of Cable
Construction of Power Cable
Cable Insulating materials and property
Cable Rating and rating factors
Cable laying installation practices

3. About us:
Kirit Rana Debayan Dey
Joined CESC in 1989 Joined CESC in 2008
From Distribution to Technical From Distribution to Project
to Power to Technical Cell.
B.E.E from Jadavpur University B.E.E from Burdwan University
Attached as Manager (Jointing) Attached as Mains Engineer (Tech Cell)

4. Why Cable is Important?
• Residential & Industrial load density :Growing trend
• Greater services reliability & increased safety
• High acceptability on aesthetic point of view.

5. INTRODUCTION
Cables or Over Head Lines ?
*costs cable versus O.H line
- investment costs cable always high
- maintenance and operational costs are less
- investment costs + operation costs
* 10 kV cable : costs = costs O.H line
* 110 kV cable : costs = 7 x costs of O.H line
* 380 kV cable : costs = 20 x costs of a O.H line
•For transmission, arguments pro cable are often :
-public requirements and environmental reasons
-sometimes technical reasons

6. INTRODUCTION
are cable important ?
1. Cables represent large part of the capital
(often > 50%) of a network owner.

8. INTRODUCTION
are cables important ?
2. Reliability cables (and O.H lines) is
dominant for outage time
SAIDI mainly related to mv
System Average Interruption Duration Index -
SAIDI

13. Importance of Cable
Construction of Power Cable
Cable Insulating materials and property
Cable Rating and rating factors
Cable laying installation practices

14. Types of Cable
LV Cables
HV Cables
EHV Cables

15. LV Cables : 1.1kV
Standard Sizes
400,240,150,70 & 25 Sq.mm
Standard Construction
Sector Shaped & Stranded Al Conductor
PVC / XLPE Insulation
PVC Inner Sheath
Flat Stripped G.I Armour
PVC Outer Sheath

16. LT Cables:1.1kV
1.1KV ,3.5C, 240 Sq. mm, XLPE

17. HV & EHV Cables
PILC Cables (not added after 2000)
11KV & 33 KV
Gas filled Cables
33 KV (not added after 1960)
132 KV (not added after 1985)
XLPE Cables
Up to 220 KV.

18. Types of HV Cables: XLPE
11KV,3C,225 Sq. mm, PILC
Standard Construction
Sector Shaped Conductor
Oil Impregnated Paper
Belt Paper
Jute/Paper fillers
Lead Sleeve
Bituminized Hessian Bedding
Double Steel Tape armour
Bituminized Hessian Serving with
anti – termite coating

19. Electrical Field
What is Electrical Stress (E):
It can be defined as the gradient of voltage with
respect to distance.
So Electrical Stress at distance x from conductor
E = - dU / dx

20. Electrical Field in a Cable
CESC
CESC

22. Development of PILC Cables for Higher
Voltage
Particular Designs fails at more than 22KV
Failure analysis: High Electric flux outside core
insulation led to deterioration of filler papers.

24. Limitation of PILC Cables
Costly due to lead sleeve
Large bending radius
Hard to install due to heaver than XLPE
Maximum operating temp. 70 Deg C.

25. Importance of Cable
Construction of Power Cable
Cable Insulating materials and property
Cable Rating and rating factors
Cable laying installation practices

26. Other Insulating Materials
PE
EPR
PILC
PVC
XLPE

27. What is XLPE ?
POLY
ETHELYNE
Classification of POLYMER
Thermoplastic
Thermoset

28. XLPE Manufacturing Process
ENVIRONMENT REQUIRED
1.Presence of Dicumyl peroxide.
2.18-20 bar pressure.
3.210 deg C Temperature.
• XLPE can hold its property up to 90
Deg C, continuous
•XLPE can hold its property up to 250
Deg C, for 1 second.

29. XLPE Structure

30. Types of HV Cables: XLPE
11KV,3C,300 Sq. mm, XLPE
Standard Construction
Compact & Stranded Conductor
Conductor Screen
XLPE Insulation
Insulation Screen
Cu Tape Screen
Round fillers
PVC Inner Sheath
G.I Flat stripped / Round wire armour
HDPE Outer sheath

31. Effect of Conductor Screen
Electrical stress will follow the less di-electric
strength path, means through the air inclosure,
possible lead to breakdown of insulation

32. Cable with out Insulation Screen
Equipotential Lines
Electric Field Lines
Conductor
Electric stress may concentrate
on one side of the cable
insulation, possible lead to
break down

33. Cable with Grounded Insulation
Screen
Equipotential Lines
Insulation Screen
Conductor
Conductor Screen
Field Lines
Grounded insulation screen ensures that the equipotential lines are
evenly distributed through the cable insulation.

34. Purpose of Cu Tape Screen
Used only in 3-core Cable
Provide circular earth path over Insulation Screen
Connected with armour at Joints & Termiations.

35. Purpose of Armour
To carry Earth Fault current during fault condition
To provide Earth path for Screen current
To provide mechanical Protection.

36. Purpose of Outer Sheath
Provides Protection against
Soil pressure
Spiking of external Agencies
Damages during Cable laying

37. Types of EHV XLPE Cables
132KV,1C,Cu,800 Sq. mm, Poly-AL
33KV,1C,300 Sq. mm, Poly-AL, XLPE sheath, XLPE

38. TR-XLPE
Tree Retardant XLPE Cables:
XLPE with regard to resistance to water treeing.
It gives more life to cable.
Using polar co-polymer in place of polyethylene homo-
polymer.
AC Breakdown strength is increased.

39. Importance of Cable
Construction of Power Cable
Cable Insulating materials and property
Cable Rating and rating factors
Cable laying installation practices

40. Cable Losses
Losses in conductor
Losses in Insulation
Losses in sheath.

41. Losses in Conductor

44. effect is due to mutual induction
due to self- induction causing
Types of EHV Cable Conductors
a higher current density towards the
between conductors of adjacent cables
causing a higher current density along one
outer surface of the conductor Side of the conductor
Skin and Proximity effects.
Rac = Rdc ((1+Y5+Yp) Rac = AC resistance of conductor
Rdc = DC resistance of conductor
Y5 = skin effect factor
Yp = proximate effect factor
Calculation methods indicated in IEC : 287
The phenomena of skin and proximity effect
is responsible for increased in the AC resistance of the conductor.

46. Insulation Loss:
Losses in insulation (minor effect)
Partial Discharge in voids (medium effect)
Friction from rotating dipoles (larger effect)

50. Sheath Losses

52. Cable Ratings

53. RATINGS OF 1.1 KV PVC/XLPE CABLES OF
DIFFERENT CROSS-SECTIONS (ALUMUNIUM
CONDUCTOR)
Size *Current Rating In
Sl mm2 x Guiding Type Of Amps
End Use
No. No. Of IS Code Insulation In
In Air
Cores Ground
1 25 x 3 ½ 7098 Pt I XLPE 96 90 Service
Service /
2 70 x 3 ½ 7098 Pt I XLPE 176 170
Distributor
Service /
3 150 x 3½ 7098 Pt I XLPE 255 294
Distributor
Distributor /
4 240 x 3½ 7098 Pt I XLPE 333 402
Service
5 400 x 4 7098 Pt I XLPE 426 542 Feeder

54. Rating Factors:
Thermal Resistivity of Soil.
Ground Temperature.
Thermal Resistivity of Insulation.
Depth of Laying

55. RATINGS OF 11 KV PILC CABLES OF DIFFERENT
CROSS-SECTIONS (ALUMUNIUM CONDUCTOR)
Continuous Current Ratings
Maximum allowable conductor temperature = 650C
SIZE BURRIED UNDER
GROUND(Amps)
3 X 50 mm2 105
3 X 150 mm2 190
3 X 225 mm2 240
3 X 300 mm2 280

56. INSTALLATION CONDITIONS FOR 6 / 11 KV CABLES
GROUND TEMPERATURE = 30O C
AIR TEMPERATURE = 40O C
SOIL THERMAL RESITIVITY = 150O C-CM / WATT
DEPTH OF LAYING = 900 MM
DIRECTLY BURIED IN GROUND
BOTH END EARTHED

57. Importance of Cable
Construction of Power Cable
Cable Insulating materials and property
Cable Rating and rating factors
Cable laying installation practices

58. Cable Laying and Installation
practices
Fixing of Route
Process of Laying
Inspection for Service

59. Route Fixation
Straight Cable route..
Adequate Width of route
Avoid major Road/Railway tracks Crossing.
Maximum usage of Footpath.

60. Plan Sanction
Preparation of detailed plan of route
Approval of the concerned Authority.
Intimation of tentative programme of work.
Permission of Public Common Passage

61. Trial Pits
Trial pits are to be dug approx at 10 meters intervals or
less as necessary.
This determines exact cable alignment to be followed
during laying. Thus creating minimum interference with
underground obstructions and installations of other
agencies.

62. B) Process Of Laying

63. a) Pipes and Pipe Laying
Pipes used now for cable laying below ground are
made from HDPE.
Pipes are laid for crossing roads, tram tracks, petrol
pumps garage entry or entry to multistoried buildings.
For wide roads pipe laying is done by excavating half
the road width at one time. Preferred to be done at
night

64. b) Trenching Work
The CESC notice board should be deployed at site and
work area should be cordoned off.
Depth of trench should not be less than 75 cm and 60
cm wide.
The trench should not be continuous to enable
pedestrian crossing.
Holes should be bored into the earth at uncut
pedestrian crossings.
Excavated earth should be retained besides the trench
on either side.

65. b) Trenching Work
Exposed cables and pipes should be suitably
supported.
In case of damage to installation of other agencies they
should be immediately informed.
An attempt should also be made for temporary
repairing of damaged installations.
Standby pumps and shuttering planks are required for
exigencies.

66. c) Laying Procedure
Before placing drum at site the following needs checking -
condition of drum, cable size, cable length and integrity of
cable end sealing.
The drum is then placed around spindle and lifted by
Jacks, both of suitable capacity.
A few lashings of a manila rope of adequate strength are
made around outer sheath of cable end.
Cable payout is done by rolling drum in direction opposite
to marked “Roll This Way”.

67. Depth of Laying
The desired minimum depth of laying from ground
surface to top of the cable as per IS: 1255 – 1983 are
as follows:
LV, MV (230V, 400V) 750 mm
11 KV 900 mm
33 KV 1050 mm

68. Tests after Laying
For 11 KV: Only moisture test along with IR value
checking
For 33KV : Moisture test and Serving test to be done
Serving Test:
Test to check any damaged occurred at outer sheath
during laying.