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Power Cable Technology
Contents:
� Importance of Cable
� Construction of Power Cable
� Cable Insulating materials and property� Cable Insulating materials and property
� Cable Rating and rating factors
� Cable laying installation practices
About us:
Kirit Rana Debayan DeyJoined 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)
Why Cable is Important?
• Residential & Industrial load density :Growing trend
• Greater services reliability & increased safety
• High acceptability on aesthetic point of view.
INTRODUCTION
Cables or Over Head Lines ?
*costs cable versus O.H line
- investment costs cable always high- 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
INTRODUCTION
are cable important ?
1. Cables represent large part of the capital 1. Cables represent large part of the capital
(often > 50%) of a network owner.
INTRODUCTION
are cables important ?
2. Reliability cables (and O.H lines) is 2. Reliability cables (and O.H lines) is
dominant for outage time
SAIDI mainly related to mvSystem Average Interruption Duration Index System Average Interruption Duration Index --
SAIDISAIDI
� Importance of Cable
� Construction of Power Cable
� Cable Insulating materials and property� Cable Insulating materials and property
� Cable Rating and rating factors
� Cable laying installation practices
Types of Cable
� LV Cables
HV Cables� HV Cables
� EHV Cables
LV Cables : 1.1kV
� Standard Sizes
� 400,240,150,70 & 25 Sq.mm
� Standard Construction� Standard Construction
� Sector Shaped & Stranded Al Conductor
� PVC / XLPE Insulation
� PVC Inner Sheath
� Flat Stripped G.I Armour
� PVC Outer Sheath
LT Cables:1.1kV
1.1KV ,3.5C, 240 Sq. mm, XLPE
HV & EHV Cables
� PILC Cables (not added after 2000)
11KV & 33 KV
� Gas filled Cables
33 KV (not added after 1960)33 KV (not added after 1960)
132 KV (not added after 1985)
� XLPE Cables
Up to 220 KV.
Types of HV Cables: XLPE
11KV,3C,225 Sq. mm, PILC
Standard Construction
� Sector Shaped Conductor
� Oil Impregnated Paper
Belt Paper� Belt Paper
� Jute/Paper fillers
� Lead Sleeve
� Bituminized Hessian Bedding
� Double Steel Tape armour
� Bituminized Hessian Serving with
anti – termite coating
Electrical Field
What is Electrical Stress (E):It can be defined as the gradient of voltage with
respect to distance.
E = - dU / dx
So Electrical Stress at distance x from conductor
Electrical Field in a Cable
CESCCESC
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.
Limitation of PILC Cables
� Costly due to lead sleeve
� Large bending radius
� Hard to install due to heaver than XLPE� Hard to install due to heaver than XLPE
� Maximum operating temp. 70 Deg C.
� Importance of Cable
� Construction of Power Cable
� Cable Insulating materials and property� Cable Insulating materials and property
� Cable Rating and rating factors
� Cable laying installation practices
Other Insulating Materials
� PE
� EPR
� PILC� PILC
� PVC
� XLPE
POLY
What is XLPE ?
POLY ETHELYNE
Classification of POLYMER
Thermoplastic
Thermoset
1.Presence of Dicumyl peroxide.2.18-20 bar pressure.
3.210 deg C Temperature.
ENVIRONMENT REQUIRED
XLPE Manufacturing Process
• XLPE can hold its property up to 90 Deg C, continuous
•XLPE can hold its property up to 250
Deg C, for 1 second.
XLPE Structure
Types of HV Cables: XLPE
11KV,3C,300 Sq. mm, XLPE
Standard Construction
� Compact & Stranded Conductor
� Conductor Screen
XLPE Insulation� XLPE Insulation
� Insulation Screen
� Cu Tape Screen
� Round fillers
� PVC Inner Sheath
� G.I Flat stripped / Round wire armour
� HDPE Outer sheath
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
Cable with out Insulation Screen
Equipotential Lines
Conductor
Electric Field Lines
Electric stress may concentrate on one side of the cable insulation, possible lead to break down
Insulation Screen
Equipotential Lines
Cable with Grounded Insulation Screen
Conductor
Conductor Screen
Field Lines
Grounded insulation screen ensures that the equipotential lines are evenly distributed through the cable insulation.
Purpose of Cu Tape Screen
� Used only in 3-core Cable
� Provide circular earth path over Insulation Screen� Provide circular earth path over Insulation Screen
� Connected with armour at Joints & Termiations.
Purpose of Armour
� To carry Earth Fault current during fault condition
� To provide Earth path for Screen current� To provide Earth path for Screen current
� To provide mechanical Protection.
Purpose of Outer Sheath
Provides Protection against
� Soil pressure
� Spiking of external Agencies� Spiking of external Agencies
� Damages during Cable laying
Types of EHV XLPE Cables
33KV,1C,300 Sq. mm, Poly-AL, XLPE132KV,1C,Cu,800 Sq. mm, Poly-AL
sheath, XLPE
TR-XLPE
Tree Retardant XLPE Cables:
� XLPE with regard to resistance to water treeing.
� It gives more life to cable.� It gives more life to cable.
� Using polar co-polymer in place of polyethylene homo-
polymer.
� AC Breakdown strength is increased.
� Importance of Cable
� Construction of Power Cable
� Cable Insulating materials and property� Cable Insulating materials and property
� Cable Rating and rating factors
� Cable laying installation practices
Cable Losses
� Losses in conductor
Losses in Insulation� Losses in Insulation
� Losses in sheath.
�Losses in Conductor
Types of EHV Cable Conductors
Skin and Proximity effects.
Rac = Rdc ((1+Y5+Yp) Rac = AC resistance of conductor
due to self- induction causing
a higher current density towards the
outer surface of the conductor
effect is due to mutual induction
between conductors of adjacent cables
causing a higher current density along one
Side of the conductor
Rac = Rdc ((1+Y5+Yp) Rac = AC resistance of conductorRdc = DC resistance of conductorY5 = skin effect factorYp = 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.
Insulation Loss:
� Losses in insulation (minor effect)
� Partial Discharge in voids (medium effect)� Partial Discharge in voids (medium effect)
� Friction from rotating dipoles (larger effect)
�Sheath Losses
�Cable Ratings
Sl No.
Size mm2 x No. Of Cores
Guiding IS Code
Type Of Insulation
*Current Rating In Amps
End Use In
Ground In Air
1 25 x 3 ½ 7098 Pt I XLPE 96 90 Service
Service /
RATINGS OF 1.1 KV PVC/XLPE CABLES OF
DIFFERENT CROSS-SECTIONS (ALUMUNIUM
CONDUCTOR)
2 70 x 3 ½ 7098 Pt I XLPE 176 170 Service / Distributor
3 150 x 3½ 7098 Pt I XLPE 255 294 Service / Distributor
4 240 x 3½ 7098 Pt I XLPE 333 402 Distributor / Service
5 400 x 4 7098 Pt I XLPE 426 542 Feeder
Rating Factors:
� Thermal Resistivity of Soil.
� Ground Temperature.
� Thermal Resistivity of Insulation.� Thermal Resistivity of Insulation.
� Depth of Laying
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
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� DIRECTLY BURIED IN GROUND
� BOTH END EARTHED
� Importance of Cable
� Construction of Power Cable
� Cable Insulating materials and property� Cable Insulating materials and property
� Cable Rating and rating factors
� Cable laying installation practices
Cable Laying and Installation
practices
� Fixing of Route
� Process of Laying� Process of Laying
� Inspection for Service
Route Fixation
� Straight Cable route..
� Adequate Width of route
� Avoid major Road/Railway tracks Crossing.� Avoid major Road/Railway tracks Crossing.
� Maximum usage of Footpath.
Plan Sanction
� Preparation of detailed plan of route
� Approval of the concerned Authority.� Approval of the concerned Authority.
� Intimation of tentative programme of work.
� Permission of Public Common Passage
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� This determines exact cable alignment to be followed
during laying. Thus creating minimum interference with
underground obstructions and installations of other
agencies.
B) Process Of Laying
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.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
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� 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.
� Exposed cables and pipes should be suitably
supported.
� In case of damage to installation of other agencies they
should be immediately informed.
b) Trenching Work
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.
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.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”.
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
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:� Serving Test:
Test to check any damaged occurred at outer sheath
during laying.