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Preview

Distribution system

Overhead vs. underground system

DC vs. AC systems

Choice of working voltage

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Transmission Cost as Function of

Voltage Level.

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Choice of Working Voltage

100

3

6.1

5.5

1506.15.5

PLV

kVALV

Vis the line voltage in kV

L is the line distance in km

P is the estimated

maximum power in kW

per phase

Using these empirical relations preliminary estimate is

made. Then voltage level is chosen by doing complete

economic study of existing interconnected system.

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Line Parameters

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Electrical Parameters

Resistance

Inductance

Capacitance

Conductance

Conductance is due to leakage over line insulators. It isvery small and can be always neglected.

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Types of Conductor

Copper

Aluminum: Cheaper, lighter, but less conductive and less

tensile strength than copper

ACSR (Aluminum Conductor Steel Reinforced)

AAC (All Aluminum Conductor)

AAAC (All Aluminum Alloy Conductor)

ACAR (Aluminum Conductor Alloy Reinforced)

Expanded ACSR

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ACSR Conductor

Internal steel strands increase the tensile strength

Outer aluminum strands carry the current

Stranded conductor with twisted wires for strength and

flexibility of mechanical handling.

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Resistance

The DC resistance of conductor at specified temperatureis:

T is the resistivity of the conductor at temperature T

l is the length of the conductor in m

A is the cross-sectional area of conductor in m2

A

lR

T

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Resistance

Temperature dependence of resistance:

R0 is the resistance at 00C

0 is the temperature coefficient of the resistance of conductor

at 00C

Thus, if the resistance at temperature T1 is known, the

resistance at any other temperature T2 can be computedusing:

)1( 00 TRRt

)1(

)1(

10

20

1

2

T

T

R

R

t

t

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AC Resistance:

Skin and Proximity Effect

Currents in same direction Currents in opposite direction

Skin Effect

Proximity Effect

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Resistance

Resistance depends on:

Temperature

Dimensions

Frequency

Material % Conductivity Resistivity (200

C)m

Copper 100% 1.72

Aluminum 61% 2.83

Iron 17.2% 10

Silver 108% 1.59

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Inductance

Most dominant line parameter

Therefore

In linear magnetic systems

Mutual inductance is:

dt

diL

dt

di

di

d

dt

de

di

dL

iL

2

12

12

IM

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Steps in Calculating Inductance

Magnetic field intensity (H) using Amperes law

Magnetic flux density B (=H)

Flux linkages ()

Inductance from flux linkage per ampere (L=/I)

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Internal Inductance

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/Course_home-1.htm

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Internal Inductance

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/Course_home-1.htm

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External Inductance

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/Course_home-1.htm

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Inductance of Single-Phase Line

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/Course_home-1.htm

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Inductance of Single-Phase Line

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT-KANPUR/power-system/ui/Course_home-1.htm

If r1 = r2 = r , then