BY: M.Awais Ejaz EE307-070

TO: Sir Salman Bilal

Research: Underground Cables

The University of Lahore

Underground Cables

BY THE TEXT BOOK

Several types of cables are in use depending upon working voltage and requirements. A cable must fulfill the following

requirements.

•The conductor used in cables should be tinned stranded copper or aluminum of high conductivity.•The conductor size should be such that the cable carries desired load current without overheating.•The thickness of insulation of cable must kept proper to restrain uncertainty.•The cable must be provided with suitable mechanical protection (cable tray).

Construction:

•Cores and conductors: Made of tinned copper or aluminum.

•Insulation: Different types an different sizes of insulation depending upon he voltage to be withstood by the cable

•Metallic sheath: To protect cable from moisture.

•Bedding: To protect the sheath from corrosion and mechanical injury.

•Armoring: Layers of galvanized steel wire or tape to protect cable from mechanical injury

while laying it and during course of handling.

•Serving: In order to protect armoring from atmospheric conditions.

Insulation types:

1. Rubber.2. Vulcanized Indian rubber.3. Impregnated paper.4. Varnished cambric.5. Polyvinyl chloride (PVC).

Classification of cables:1. Low tension (LT) up to 1kV2. High tension (HT) up to 11kV3. Super tension (ST) from 22 to 33kV4. Extra high tension (EHT) from 33 to 66kV5. Extra super voltage cables beyond 132kV

3-phase cables:

1.Belted cables up to 11kV2.screened cables from 22 to 66kV3.pressure cables beyond 66kV

Laying:

1.Direct laying.2.Draw in system.

Direct laying

Research

Underground Lines

General:• Underground line installation will be coordinated

with the installation master plan to avoid conflict with construction of future facilities.

• Lines will normally be installed adjacent to roadways in urban, housing, or industrial plant areas, but may be routed as required to meet the project objectives.

• Electrical lines will be at least six feet from any steam or hot water lines, except at crossings where a one-foot separation from such lines is adequate.

Cable

Conductor material:

Since underground conductors are continuously supported, soft-drawn copper or aluminum alloy 5005 provides adequate strength. However, the selection of copper or aluminum will be justified based upon an analysis using life, environmental, and cost factors.

Chapter:7 AFJMAN

Insulation material These should kept following properties

• Non-inflammable.• Unaffected by acids.• High resistance to avoid leakage current.• High dielectric strength to avoid electric breakdown.• Mechanically strong to withstand the handling.• Non-hygroscopic.• Low cost so as to make the system feasible.

Chapter:7 AFJMAN

Insulations types an

parameters:

Cable installation:

Duct lines.

Manholes, handholds and pull boxes

Direct burial cable installationor Direct laying

Chapter:7 AFJMAN

Major underground systems

• New York City – no overhead since 1890’s• Singapore - 100% underground• The Netherlands – Distribution 100%• Belgium ban on OH Lines since 1992• Denmark replaced six 132 kV OH lines with two new 400 kV UG cables in 1997 and 1999• December 1999 storms in France caused many blackouts-new policy 25% HV lines are UG• Connecticut Underground Power Line Legislation Approved• “Overhead Lines Need a Quick Burial” in Atlanta Journal Constitution• Two major developments cancelled in Atlanta one for $150M and the other $100M

BY Harry OrtonOCEI

Vancouver, Canada

Advantages of UG Cables

Environmental

• Minimal visual impact• Low EMF• No corona discharge, RI and TVI• No bush fire problems• Minimal lightning problems• High level of personnel and public safety, no fallen

lines (France 2000, 19 contact deaths with OH lines, 0 with UG cables)

• Good working conditions

Reference:http://jcots.state.va.us/pdf/overheadorunderground.pdf

Distance from circuit (FL)

Advantages of UG Cables

Power Grid Security

• Not affected by ice, snow, rain, wind, dust, smoke or fog• Not affected by Ice storms, Tornadoes, Hurricanes• Nothing to be stolen• French storms in 1999, 8% of OH lines out of service, 90% of substations back in service after 4 days• 6 months to complete repairs to the lines• Total cost of damage Euro1.3 Billion• No estimate for economic losses• Interruption lasted 15 million customer-days• Quebec ice storms in the winter of 1998• Hydro-Quebec hundreds of kilometers of EHV and HV lines collapsed• Thousands of towers• Blackout initiated by OH line at First Hydro in Ohio

Advantages of UG CablesEconomy

• Low maintenance costs• Land use minimized• Value of land and buildings unaffected

Advantages of UG CablesOperation

• High reliability and availability• Few faults, bumps on power system• Major blackouts in NE• Diagnostics available to locate problems

Disadvantages

• Cost, must consider life time costs not just initial• Cost differential decreasing with time• Cost of losses (30-60% less than OH), maintenance and repair• Under grounding 25% of the existing EHV and HV lines in Italy and the UK will increase the price of electricity by 3-5%• Under grounding all of the lines in Italy would increase the cost of

electricity by 16%• Outage time, locate fault and repair (OH one day, UG 7-10 days)• Fault location instantaneous, can have longer repair time• Continuous trench required (sensitive areas, directional boring)• Soil thermal conditions modified• Presence of vaults and manholes• Distance limitation 100 km for ac cables• HVDC Light 600 km - planned• Murray Link 177 km – longest in the World 2002

Increasingly cables are being seen as the lowest cost solution for reliable delivery of power. This recognition is seen in the increasing use of cables within utilities. Within Europe the total amount of underground cable used has risen from 15-20% in 1960 to 40% in 1994. In Japan at 275 kV there was 11.5 % in1980 and in 2001 there was 28%.

Table: Amount of Underground Energy Cable installedAt 1994

BY Harry OrtonOCEI

Vancouver, Canada

Table: Public Concerns for cables and overhead lines

“0 no importance, 1 low importance, 2 high importance, 3 compulsory”

BY Harry OrtonOCEI

Vancouver, Canada

Table: Cost ratio of UG cables to OH lines

BY Harry OrtonOCEI

Vancouver, Canada

Prices of OH and Underground cables

Overhead:

Between $1,469 and $1,923 per lot including installation.

Underground:

Between $1,475 and $2,243 per lot including installation.

By FPL electric services

OVERHEAD VS. UNDERGROUND COST COMPARISON5 MILE, 230kV SINGLE CIRCUIT LINE EXAMPLE

1035 MVA CAPACITYINITIAL COST ANALYSIS

1. UNDERGROUND 230kV PIPE TYPE CABLE SYSTEM: $40,577,000

2 – 4 foot wide trenches on 24 foot right of way4 – 8 inch diameter steel pipes12 – 2500 kcmil copper cables5 mile lengthLarge Cost Items Quantity Material Cost Installation CostSteel Pipe 105,700 ft. $ 1,902,000 $15,840,000Power Cable 317,400 ft. $11,109,000 $ 952,000Manholes 26 $ 390,000 $ 370,000Cable Splices 44 $ 1,144,000 $ 2,948,000Terminations 24 $ 840,000 $ 144,000Pumping Plant 2 $ 750,000 $ 106,000Dielectric Fluid 158,000 gal. $ 792,000 $ 158,000Other Misc. Items $ 2,550,000Total Material & Labor $39,995,000Right of Way $ 582,000

Grand Total $40,577,000

2. UNDERGROUND 230kV XLPE CABLE SYSTEM: $32,123,000

2 – 2 foot wide trenches on 20 foot right of way8 – 6 inch diameter PVC conduits8 – 3000 kcmil copper cables5 mile lengthLarge Cost Items Quantity Material Cost Installation CostPVC Conduit 211,200 ft. $ 634,000 $11,880,000Power Cable 212,500 ft. $12,328,000 $ 638,000Manholes 24 $ 360,000 $ 360,000Cable Splices 96 $ 1,104,000 $ 2,112,000Terminations 16 $ 288,000 $ 96,000Other Misc. Items $ 1,838,000Total Material & Labor $31,638,000Right of Way $ 485,000

Grand Total $32,123,000

3. OVERHEAD 230kV CIRCUIT: $5,282,000

Self-supporting steel poles on 100 foot right of wayConcrete foundations6 - 636 kcmil ACSR conductors & 1 - 3#6 Alumoweld shield wire5 mile lengthLarge Cost Items Quantity Material Cost Installation CostPoles with Insulators 40 $ 797,000 $ 334,000Conductor 159,000 ft. $ 149,000 $ 225,000Shield Wire 27,000 ft. $ 9,000 $ 25,000Foundations $ 563,000Other Misc. Items $ 756,000Total Material & Labor $ 2,858,000Right of Way $ 2,424,000

Grand Total $ 5,282,000

Underground cables site

SITARA CHEMICAL IND. Faisalabad

The industry is one of the largest loads of the industrial sector, 60MW.

Running on Wapda, Sitara energy (pvt) LTD. And internal power plant of 32MW.

Plant is generating at 11KV and that is supplied to Grid, from where it is distributed.

Whole distribution with in the plant premises is through underground cable system.11KV is distributed in the whole system and then after auxiliary transformers, 400v to the plant to all motor and to residential area.

for 400v 3-core LT cables of different sizes are being used.120mm at most places. And specifications of 11kv underground lines are given below.

Cables used:

1. CABLE XELPE HT.

– Capacity 12KV– Size 300MM– Type HT-Single core– Length 4500meters

– Rate Rs. 2323.33 per meter– Total amount Rs 10,454,997.6

– Vendor Newage cables (pvt) LTD.

2. CABLE HT-1 Core

– Capacity 11-15KV– Size 500mm – Type HT-1 Armoured Alu– Length 14,400meters– Rate Rs. 1140.00 per meter– Total amount Rs 15,696,000– Vendor Newage cables (pvt) LTD.

Why using underground there?

• Longer Life Expectancy

• Reduced Maintenance Costs

• Service Uninterrupted by Storms and weather

• Reduced Fire Fighting Hazards in plant area

• Conserve Valuable Land

• Enhancement of the beauty of plant area

• Prevention of Accidents and short-circuiting

• Better voltage regulation

View of overhead lines

With underground

What else you need to know about the difference?

Sometimes, being cost efficient does not work