characteristics of multiphase transmission lines lecture 11 power engineering - egill benedikt...

26-Oct-11

1Lecture 11 Power Engineering - Egill Benedikt Hreinsson

Characteristics of Multiphase Transmission Lines

26-Oct-11


The Electrical Transmission LineThe major components

are:• Shield (ground) conductors for

lightning protection.• Tower (lattice or tubular)• Phase conductors

(Transposed?, Bundled conductors?)

• Insulators (V string shown)• Foundation and grounding

grounding grounding

Foundation

26-Oct-11


Examples of Transmission Line Towers

a) Low voltage tower with ground conductor

b) Medium voltage towerc) Concrete towerd) 110-380 kV towere) 110-220 kV tower

Source: Happoldt/Oeding: Elektrische Krafwerke und Netze.

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4Lecture 11 Power Engineering - Egill Benedikt Hreinsson700-800 kV Transmission lines in Canada and Russia

Conductor bundles

Source: Happoldt/Oeding: Elektrische Krafwerke und Netze.

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Electrical Transmission Towers

Conductor bundles

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6Lecture 11 Power Engineering - Egill Benedikt HreinssonSteel and Wooden Transmission Structures in Iceland

SteelWood

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7Lecture 11 Power Engineering - Egill Benedikt HreinssonSteel and Wooden Transmission Structures in Iceland 145-420 kV

•The size and type of towers will generally depend on voltage, climate and general conditions along the right of way

Source: Landsnet, Grid operator, Reykjavik

26-Oct-11


Transmission towers, Hellisheiði, Iceland

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Transposition of Transmission Lines•Objective: To obtain phase symmetry with the

approximate same average inductance and capacitance between phases and to earth for the total line length

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LJªSIFOSS 66 kV

T S R

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132 kV

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BLANDA

132 kVS

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BºRFELL

220 kV

132 kV

PRESTBAKKI

132 kV

KRAFLA

309 312 669 672

363 265 138

920

923

18

314

631

HªLAR

132 kV

132 kV

133 126

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66 kV

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132 kV

ÑRAFOSS

132 kV

220 kV

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132 kV

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132 kV

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132 kV

VATNSHAMRAR

132 kV

A5

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STEKKUR

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RANGñRVELLIR

66 kV

66 kV

66 kV

DALVÑK

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11 kV

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132 kV

220 kV

ìINGVALLASTRÆTI

66 kV

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66 kV

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132 kV

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220 kV

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KOLLUGERïI

SULTARTANGI

220 kV

NE1

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S

T

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RAKRANES

66 kV

AK1

AKRANES

MELUR

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66 kV

ANDAKÑLL

SP 3

132 kV

SIGALDA

220 kV

SIGALDASP1 SP2

SP2 SP1

SP2 SP1

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13.8 kV

T

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HVOLS-

VÖLLUR

66 kV

FLºïIR

66 kV

SP4

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66 kV

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R-FASI (L1)

S-FASI (L2)

T-FASI (L3)

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220 kV

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ST1 STEINGRÑMSSTÖï 66 kV

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Samòykkt LV: BG

LANDSVIRKJUN

26-Oct-11


Transposed HV line in Hellisheiði, Iceland• A familiar view from the

east in Hellisheiði, showing 2 adjacent towers in the HV line from Sog hydro to Reykjavik (Geithals). In these 2 towers next to each other transposition takes place and the conductors are rotated

26-Oct-11


Distribution line13.8 kV

Transformer

240/120V line

Fuse and disconnector

Telephone line

Distribution Cable13.8 kV

Distribution line and Transformer in North America

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Phase Conductors

• Transmission lines use stranded aluminum conductors.

• Typical type of conductors are:– Aluminum-Conductor-steel -

Reinforced (ACSR)– All-Aluminum (AAC)– All-Aluminum Alloy (AAAC)

• Shield Conductors– Aluminum-clad-steel (Alumoweld)– Extra-High-Strength-Steel

ACSR Conductors

Most frequently used is the ACSR conductor. The steel provides mechanical strength, and the aluminum conducts the current.

Aluminum strands2 layers, 24 conductors

Steel strands7 conductors

Transmission Line Conductors

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Cross Section of Conductors

Steel reinforcement

Winding of layers on opposite directions

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15Lecture 11 Power Engineering - Egill Benedikt HreinssonAluminum Conductor Steel Reinforced (ACSR) Conductors

Steel reinforcement

Winding of layers on opposite

directions

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Stranding of ACSR/ACAR

ACAR ACSRSource: Soutwire Cable Co.

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Transmission Line Insulators

Cup and pin Insulator Insulator chain

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Conductors - spacersExtra high voltage lines use bundled

conductors:– to reduce corona discharge by

reducing the maximum electrical field near the conductor.

– to increase current carrying capacity.

• Bundles with two, three and four conductors are used.

• The distance between the conductors in the bundle is maintained by steel or aluminum bars (spacers) as indicated in the figure.

d

d

r

d

r

d

r

Bundled conductors

26-Oct-11


Bundled conductors• More than one conductor per

phase for higher voltages• Approximate increase in the

number of conductors:– 0-400 kV: 1 conductor per phase– 400-500 kV: 2 conductors per

phase– 500-700 kV: 3 conductors per

phase– 700-800 kV: 4 conductors per

phase– 80-1200 kV: 6-12 conductors

per phase (experimental)

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20Lecture 11 Power Engineering - Egill Benedikt HreinssonThe Electrical Field in the Vicinity of Conductor Bundles

The electrical field is at maximum at the outer edge of the conductors

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765 kV and 1100 kV Bundles

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22Lecture 11 Power Engineering - Egill Benedikt HreinssonThe Electrical Field in the Vicinity of Transmission Lines

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23Lecture 11 Power Engineering - Egill Benedikt HreinssonThe Magnetic Field in the Vicinity of Transmission Lines

26-Oct-11


References• O.I. Elgerd: Electric

Energy Systems Theory. McGraw Hill

• J.D Glover, M.S. Sarma: Power system Analysis and Design, Brooks/Cole 2002

• M.E. El-Hawari: Electrical Energy Systems, CRC Press, 2000

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