Transcript
BY
NAILA ZAREEN
TRANSMISSION LINES PARAMETERS
Transmission Lines Class 6
Transmission Line Concept
PowerPlant
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Transmission Lines
The purpose of transmission network is to
transfer electric energy from generating units at various locations to the distribution system which ultimately supplies the load.
Electrical Properties
All transmission lines in a power system exhibit the electrical properties of
ResistanceInductanceCapacitanceConductance
Equivalent Circuit for an Incremental Length of Transmission
Transmission Line Resistance
Important in transmission efficiency evaluation and economic studies.
Significant effectGeneration of I2R loss in transmission line. Produces IR-type voltage drop which affect
voltage regulation
Transmission Line Resistance
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Conductor resistance is affected by three factors:- •Frequency (‘skin effect’) • Spiraling •Temperature
Skin Effect
When ac flows in a conductor, the current distribution is not uniform over the conductor cross-sectional area and the current density is greatest at the surface of the conductor.
This causes the ac resistance to be somewhat higher than the dc resistance. The behavior is known as skin effect
Skin Effect
Spiraling
For stranded conductors, alternate layers of strands are spiraled in opposite directions to hold the strands together.
Spiraling makes the strands 1 – 2% longer than the actual conductor length.
DC resistance of a stranded conductor is 1 – 2% larger than the calculated value.
Temperature
The conductor resistance increases as temperature increases. This change can be considered linearover the range of temperature normally encountered.
WhereR1= conductor resistances at t1 in °C R2= conductor resistances at t2 in °C
Structure and EM Fields in Co-ax
The inductance and capacitance are due to the effects of magnetic and electric field around the conductor
Diagram of EM Fields Around Wire Pair
Presence of Electric and Magnetic Fields
V
I
I
E
+
-
+
-
+
-
+
-
V + DV
I + DI
I + DIV
IH
IH V + DV
I + DI
I + DI
INDUCTANCE :
A current-carrying conductor produces a magnetic field around the conductor.
The magnetic flux can be determined by using the right hand rule.
For nonmagnetic material, the inductance L is the ratio of its total magnetic flux linkage to the current I given by
L=λ/IWhere
λ=flux linkages, in Weber turns
Flux Linkage
Flux Linkage
Inductance due to Internal flux linkage
Inductance due to Internal flux linkage
Inductance due to External flux linkage
Inductance due to External flux linkage
Inductance of Single-Phase Lines
Inductance of Single-Phase Lines
Flux Linkage in Terms of Self and Mutual Inductances
Inductance of Three-Phase Transmission Lines
Asymmetrical Spacing
Transpose Line
Transpose Line
Inductance of Composite Conductors
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