Transmission Line Flashcards
Conductors
Conductors inside a cable must be insulated to the ground
Overhead Lines
- Cheaper Construction & cable cost
- Advantage of air cooling and insulation of line
-Vulnerable to strong winds and severe weather conditions - Negative Visual impact
- Inductive in nature
Underground Cables
- Expensive pipe work & cable cost
- Expensive insulation required at high voltage
- Immune to severe weather
- Environment and aesthetic advantage
- Less frequent maintenance work
- Capacitive nature
Resistance
- Heat
- Transmission Line losses (I^2R)
Conductance
- Leakage current from insulation
- Types and no of insulators
- Electric field strength strong = electrically ionised = Corona effect
Inductance
Ampere’s Law (Magnetic field)
Capacitance
Gauss’ law (Electric Field)
Impedance matrix (short line)
A = 1,B = Z, C = 0, D = 1
Ignore shunt value, series Y only
Impedance matrix (medium line)
A = (YZ/2 +1)
B = Z
C= (YZ/4 +1)Y
D = (YZ/2 +1)
Receiving End Voltage at No Load
Vr,nl = Vs,fl /A
Voltage Regulation
- Variation of load voltage with different loading conditions
- 10% tolerance between no load and full load
- Measures degree of change in voltage at specific PF
% Regulation = (Vr,nl - Vr,fl) / Vr,fl * 100%
For short line: Vs,fl = Vr,nl as A =1
Transmission Efficiency
n = Re(Vr x Ir)/ Re (Vs x Is) * 100%
Inductor and capacitor are energy storage elements in an electric circuit
True
Loss in a transmission line (i.e. heat) is mainly due to the line reactance
False, resistance provides transmission line losses (heat)
Conductance of the transmission line model captures the di-electric effect
True
A short transmission line model does not account for shunt admittance
True. Only accounts for series impedance.
A = 1
B = Z
C = 0
D = 1
Receiving-end voltage of a transmission line is the same as the sending-end voltage at full-load condition for the medium transmission line model.
False. Only for no load condition where Vr,NL = Vs,FL /A and A=1
The di-electric effect within the conductors is modelled as admittance
True
Underground cable and overhead line have similar inductance per km for same voltage and power ratings
False. Underground Cable has lesser inductance and more capacitance.
