power system engineering lecture 22
TRANSCRIPT
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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
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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
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