Power System Engineering Lecture 22

8/3/2019 Power System Engineering Lecture 22

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Review of Last Class

Underground Cables Conductors

Insulation materials for cable

Paper (3.6, 20 kV/mm, 800C (continuous), 500 kV (pressurized))

PVC (5.0, 17 kV/mm, 70

0

C (max), 22 kV) XLPE (2.5, 18-20 kV/mm, 900C(continuous), 220 kV (500kV))

TR-XLPE

EPR

Different types of cable

Belted

Screened

Pressure cables


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Cable Structure

http://www.coppercanada.ca/publications/pub21e/21e-Section6.html


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Paper-Insulated Lead-Covered Cables (PILC)

Sub- Marine Cable


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Materials of Cable Component

Conductor Insulation Shield Sheath Jacket Armor

Copper

or

Aluminum

(Stranded)

PaperPVC

XLPE

TR-XLPE

EPR

Vulcanized

rubber

Polythene

Semicondu

-cting

(Insulation

with carbon

impregnati-

on)

Aluminum

Copper

(tape)

LeadAluminum

PVCPolythene

Nylon

Neoprene

Galvanized

steel


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Single Core and Three Core Cables

Single Core Cable Three Core Cable

(Below 66 kV)


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Belted and Screened or shielded Cable

Belted cables are used up to 11 kV.

There are two types of screened cables H-Type (Hochstadter) and

S.L. type (Separate lead). Used up to 33 kV

Belted H-Type Screened S.L. Type

Screened

George F. Moore,Electric cables handbook, Blackwell Science, 1997


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Pressurized Cable (Oil filled & oil pressure)

Above 220 kV, It is necessary to avoid

void formation.

Voids are generally formed by cyclicheating and cooling and can be

prevented by use of oil under pressure.

Oil channel is made by spiral steel

tape.


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Gas Pressurized and Gas Filled Cables

Mainly two types: 1. impregnated gas pressure cable 2. gas filledcables.

More revolutionary are the cables incorporating cryogenic cooler.

Used up to 132 kV to 500 kV


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Electrical Characteristics of Cables

Insulation resistance

Conductor inductance

Cable capacitance

Electrical stress inside insulation Grading of cable

Capacitance grading

Inter-sheath grading

Dielectric losses and tan delta (loss tangent) Sheath and armour losses


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Insulation Resistance

Resistance of small section dx is:

Therefore insulation resistance is

Insulation per unit length


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Conductor Inductance

For single core cable:

For three core cable:


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Inductance of Cable

http://www05.abb.com


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Capacitance of Cable

Therefore, capacitance between core

to sheath

Therefore, voltage is


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Capacitance of Three Core Belted Cable


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Electric Stress in The Cable

Maximum stress occurs at the surface of conductor

Minimum stress occurs at the sheath surface


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Underground Cable System

http://www05.abb.com/

Documents

Power System Engineering Lecture 22