parameters of a transmission lines
DESCRIPTION
wefdsfasdfTRANSCRIPT
PARAMETERS OF A TRANSMISSION LINES
PARAMETERS OF A TRANSMISSION LINES
RESISTANCE
For copper conductors:
F = 0.0105d2 f
For aluminium conductors:
F = 0.0063d2 f
Where:
R dc = dc resistance
R ac = ac resistance
Skin effect tendency of current to move outward the surface of the conductor. It increases the resistance of the conductors
At frequency of 60 hz and below the difference between Rdc and Rac is less than 1% for conductors of less than 350 MCM in cross section
Electrical power transmission system includes all loud structures and conversion equipments in a source of supply; all lines , switching and conversion equipment between a generating substation and the distribution substation and all the equipments stations and lines for tying integrating source of supply
Inductance
L inductance of the line GMD Geometric mean distance GMR Geometric mean radius
Transposition is the alternating position of each phase of the line in equal intervals so that each phase has the same inductance.
Capacitance
Cn = Capacitance of the liner - outside radius of the conductors
Leakage Reactance primary due to corona
Corona ionization of the gases around a high voltage conductors characterized by the presence of ozone
D1
D2
Dn
Conductor
Skin effect
Z is constant
r = outside radius of the solid conductors
For equilateral triangle
D1
D2
D3
Spacing
D1
D2
D3
Dielectric substance that separates the plates of a capacitor
Pin-insulators
Aerial ground
Post - insulator
SUSPENSION INSULATOR
Short Transmission Line
Resistance
inductance
Medium Transmission Lines
Resistance
Inductance
Capacitance
Long Transmission Lines
Resistance
Inductance
Capacitance
Leakage reactance
Problems
A 5 mile long 3 phase 3 wire(substation) substransmission line with 410 ASCR, 6/1 strand conductors vertically spaced 3ft apart has a balanced 3 phase load of 4500 Kw at 0.8 pf lagging and 19200 V line to line 60 h for 4/0 / 6/1 strands ASCR conductors , resistance is 0.592 ohms/mile/conductor and GMD is 0.00814 ft at 60 hz and 50 C assuming conductors working tempf.
Determine:
The impedance of the line
The percent voltage drop
The line loss
Line Conductors
ACSR aluminium cable steel reinforced(most common transmission line conductor)
Expanded ACSR has filler usually a paper separates the outer aluminium strands from the inner steel(reinforced) strands , usually used in high voltage lines, the purpose of the fillers is to increase the diameter of the conductors so that corona is minimized
Hard drawn of medium drawn copper used from 200ft spans
Soft drawn copper usually used as the wires(arial ground conductor)
Copper weld usually used as ground conductors
Problems
A short 3 phase 3 wire substransmission wire per conductor of 1 + j4 ohms is supplying an inductive load 220 A at 0.8 pf lagging that requires line current of 90 A. the receiving end phase to neutral voltage is 7650 V. determine:
The % V. R. and efficiency of transmission
What are the disadvantage of having a low lagging p.f
A 3 phase 3 wire medium length transmission line has the ff. data impedance/conductor (2L) = 10+ j5 ohms
Shunt capacitor susceptance Bu = 0.0025 siemens(mho) line to neutral at the middle of the line
Receiving end kVA = 15000 kVA
Receiving end line voltage = 60 kV
Receiving end pf. = 0.8 lag
Det. A. The sending end voltage and p.f.
B. The % V.R. and efficiency of transmission
Long Transmission lines
Zc = characteristic impedance of the linesZL = Series impedance of the linesZSH = shunt impedance of the line
Rl = leakage resistanceRL = series resistanceXL = series inductive reactance
Xc = Shunt capacitive reactance
Characteristics impedance of the line total impedance of the line
Surge impedance also called characteristics impedance , the characteristics impedance of a line
%
=!
%
%
=)%
%
1
#
1
#
=
%
2
#
2
#
%
=%
+ %
)=
1+
1+ #
2
2
=0.7411 10
3
log
%%
%%
#
=
0.0388
%%
10
6
%%=
"
1
"
2
"
3
."
$=+$
%%=(
=0.7411 10
3
log
(
=
1/4
"
1
="
2
="
3
=%%
%%=
"
1
"
2
"
3
3
"
=
"
"
"
= %
%
"
= %
+%