pengoperasian pembangkit tenaga listrik 4

Pengoperasian Pembangkit

Tenaga ListrikDosen

Ir.Syariffuddin Mahmudsyah,M.Eng.

4/30/2014 360 Topic 3. Transmission Lines 2

TRANSMISSION LINE

Construction

The major components are:

• Shield conductors for lightning

• protection. (When necessary)

• Tower (lattice or tubular)

• Phase conductors

• Insulators (V string shown)

• Foundation and grounding

Typical Extra High Voltage Line

grounding grounding

Foundation


TRANSMISSION LINE220kV


TRANSMISSION LINE69 and 13.8kV

69kV

13.8kVkV


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Cup and pin Insulator

Insulator chain


Cup and pin Insulator


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 strands

2 layers,

24 conductors

Steel strands

7 conductors

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Conductors

• Extra high voltage lines use

bundle conductors:

– to reduce corona discharge.

– 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.

Bundle conductors

d

d

r

d

r

d

r

TRANSMISSION LINE


Parameters

• Series AC Resistance

• Series Inductance

• Shunt Capacitance

AC Resistance

• The stranded conductor resistance is larger than the solid conductor

resistance because spiraling of the strands increases the actual length.

• AC resistance is larger than the DC resistance because the skin effect forces

the current toward the conductor surface.

• Resistance increases with the temperature.

• Resistance of most line conductors is determined from conductor tables.

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Typical conductor table from EPRI Red book (ACSR):

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Three Phase Line.

• The conductors of a long transmission line are usually transposed.

The concept of transposition is shown in the figure below.

• In an actual line, the difference of the flux linkage is relatively small.

This permits the calculation of an average distance GMD

(Geometrical Equivalent Distance) and uses the equation derived for

symmetrical (triangular) arrangement. This method is correct only if

the line is transposed. However, a good approximation is obtained

even if it is not transposed.

A

A

AB

B

B

C

C

C

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3BCACAB DDDGMD


Three Phase Line Parameters Calculate inductance and

capacitance:

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mHenry

0

7-104 m

Farad

36

10-9

0

mHenry

0

bundle

AGMR

GMDln

2

L

mFarad

0

undleb

AG

r

GMD ln

2C


Three Phase Line Parameters

1. Find the r, the GMRc and the resistance from the conductor tables.

2. Calculate the equivalent radius or GMR for bundle of two, three and four

conductors :.

One conductor (no bundle):

rbundle = rc GMRbundle = GMRc

Two conductor bundle

TRANSMISSION LINE

cr dr bundle Cbundle GMR dGMR


Three Phase Line Parameters

2. Calculate the equivalent radius or GMR for bundle of two, three and four

conductors :

. Three-conductor bundle:

Four-conductor bundle:

3. Calculate the equivalent distance GMD:

TRANSMISSION LINE

3 BCACAB D D DGMD

3C

2

bundle GMRdGMR 3

c

2

bundle r dr

4c

3

bundle r d1.09r 4C

3

bundle GMRd1.09GMR


Three Phase Line Equivalent Circuit

Short line

• The transmission line is considered short if the lengths is less than 50

miles.

• The capacitance in a short line is negligible. Only the resistance and

reactance are considered.

• The equivalent circuit represents the A phase and is energized by the

line to neutral voltage.

• The equivalent circuit is:

VS

IR

VR

IS RjX

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Medium line

• The medium line length is between 50-150 miles.

• The medium line is represented by a circuit.

• The equivalent circuit represents the A phase and is energized by the

line to neutral voltage.

• The equivalent circuit is:

j X

VS VR

IS R

C/2C/2

Ics I ICR

Ir

TRANSMISSION LINE



Long line

• The long line has a length of more than 150 miles.

• The long line is represented by a circuit with distributed parameters.

• The voltage and current is described by a distance and time functions.

• These functions are calculated by solving the line partial differential

equations.

TRANSMISSION LINE


Three-Phase Line. Numerical Exercise

A 220 kV transmission line serves a variable load with a pf = 0.9

(lagging). The maximum load is 200MW. The load voltage is maintained

at 220 kV. The line length is 85 miles.

The line is built with two bundle CARDINAL conductors arranged

horizontally. The distance between the conductors in the bundle is 18”.

The distance between the adjacent phases is 26 ft. The ground clearance

is 50 ft.

a) Draw the line arrangement.

b) Calculate the line parameters.

c) Calculate and plot the required supply voltage, the input apparent

power, the regulation, and the efficiency of the line as a function of the

load.

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Numerical Exercise. Solution steps

1. Draw the line arrangement.

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26ft 26ft

50ft

18”



2. Calculation of the line parameters

– Find conductor: radius, GMRc and resistance from conductors

table

• From the conductors table, the CARDINAL conductor has the following data:

• GMR =0.0404 ft

• R =0.1191 ohm/mile at 75 C

• conductor diameter = 1.196”

– Line resistance

– GMR of the bundle conductors

– Equivalent phase distance or GMD

– Line inductance

– Line Capacitance

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3) Calculation of supply voltage, and

input apparent power.

Order of calculation:– Load current

– Capacitive receiving

current (ICR)

– Line current

– Source voltage

– Capacitive sending current (ICS )

– Source current

– Input apparent power

All of these quantities are calculated as a function of the load

VS

IR

VR

IS RjX

CAG/2CAG/2

Ics I ICR

Equivalent circuit.

TRANSMISSION LINE


Questions to ponder:

• What has caused public discussions regarding transmission line

generated magnetic fields in recent years?

• What is the reason that a 500 kV line in Arizona has two shield

conductors and most 15 kV line have none?

• The insulators are in vertical position on most transmission line

towers. However, insulators are in a horizontal position on some

towers. Explain.

TRANSMISSION LINE


Distribution line 13.8 kV

Transformer

240/120V line

Fuse and disconnector

Telephone line

Distribution Cable 13.8 kV

Distribution line and Transformer

pengoperasian pembangkit tenaga listrik 4

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