This is a short presentation about line model and performance

1. Line Modeling and
Performance Line
Presented by,
Nafis Shahriar Munir
Student ID: 170021026
Tamanna Tajin
Student ID: 170021033

2. Why do we
need line
modeling
?
Transmits power
from one end to
another over a
distance with high
efficiency and low
voltage
regulation.

3. Parameters of
transmission line
Performance of
transmission lines

6. • Z: per-phase impedance
of the short line
• r: per-phase resistance
per unit length
• L: per-phase inductance
per unit length
• l: length of the line
• R: per-phase resistance
of the line
• X: per-phase inductive
reactance of the line

7. Two-port network model of
short transmission line
The ABCD parameters are given
as in
Short line transmission line can be
translated into a two port network-

8. Voltage Regulation
Voltage Regulation:
Voltage regulation of the line may be defined as the percentage change
in voltage at the receiving-end of the line (expressed as percent of full-
load voltage) in going from no-load to full-load.
Voltage regulation is a measure
of voltage drop of the line and
depends on the power factor of
the load

10. Nominal π-Model
• Half of the shunt capacitance may be considered to be lumped at each end of
the line.
• g represents the leakage current over the insulators and corona effects
• g is generally ignored in normal operating conditions
Y: total shunt admittance of the line
g: shunt conductance per-unit
length
C: Line-to-neutral capacitance per
unit length
l: length of the line
Z: Total series impedance of the lineNominal π-model for medium
length line

12. Long line with distributed parameters
z: series impedance per
phase per unit length
y: shunt admittance per
phase per unit length
z = r + jwL
y = g + jwC
Δx = small segment
Using KVL we get :

13. Voltage and Current Waves for a Long Transmission Line
Placing gamma’s value and transferring voltage
Equation in time domain we get:
First term second term
At any point along the line,
the voltage is the sum of
these two components
• As x increases (moving away from receiving-end),
the first term becomes larger because of e^ax.
• The first term is called ‘incident wave’.
• As x increases (moving away from receiving-end),
the second term becomes smaller because of e^- αx
• The second term is called ‘reflected wave’.

14. Surge impedance
• In summary, when line losses are
neglected (g = r = 0);
• Attenuation constant α becomes
zero
• Phase constant β becomes
w*sqrt(LC)
• Characteristic impedance ZC
becomes sqrt(L/C) which is a
real number and purely resistive
• Characteristic impedance ZC
is also known as “surge
impedance”

15. Since,
• In a lossless line under surge impedance loading,
the voltage and current at any point is constant
in magnitude
• Since ZC is real number (no reactive part), there is
no reactive power in the line (QS = QR = 0)
• For SIL condition, the reactive power losses due to
line inductance are exactly offset by reactive
power supplied by the shunt capacitance
• SIL is a useful measure of the transmission line
loading capacity
• For heavy loads (LOAD > SIL), shunt capacitors
can be required to minimize voltage drop along
the line
• Generally transmission line full load is much higher
• than SIL, so shunt capacitors should be used
Surge Impedance Loading

16. Real and Reactive Transmission Line Losses

17. Power Transmission Capability
The power carrying capacity of an
AC transmission line is limited
by three factors:
• Thermal loading limit
• Voltage stability limit
• (Angle) stability limit

18. Thermal Loading Limit
The excess amount of current flowing on the line produces heat leading to
undesirable results such as
• Increase sag due to stretching the conductors
• Decreased clearance to ground due to conductor expansion at higher temperatures
• Stretching the conductors may be irreversible
• Gradual loss of mechanical strength of the conductor caused by temperature
extremes

19. Voltage
Stability

20. Transmission Line
Compensation
Two types of
compensation:
1.Series Compensation
2.Shunt Compensation

21. Shunt
Reactors
• Shunt reactors are
conventional solutions to
compensate for the
undesirable voltage effects
associated with line
capacitance.
• Shunt reactors are used to
control voltage during low-
load period.
• Shunt reactors are usually
unswitched

22. Shunt
Capacitive
Compensation
• Compensating reactive power of lagging
power factor load
• Supplying reactive power to maintain
the receiving-end voltage at satisfactory
level (around ~ 1.0 pu)
• Capacitors are connected either
directly to the bus
to the tertiary winding of the main
transformer

23. Series
Capacitive
Compensation
Series capacitors are used
for-
• Reducing the series
reactance between the load
and the supply point.
• Reducing the series
reactance between the load
and the supply point.
• Yielding more economical
loading.

24. Thankyou