power cable technology in cesc ltd

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

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.

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.

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

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.

power cable technology in cesc ltd

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