3. Outline
Design of AC TL.
Design of DC TL.
Design of a 500kV, 2GW AC TL.
Design of a 400kV, 2GW DC TL.
Economic Comparison.
Conclusion.
4. Power Transmission
Importance of power transmission.
Means to transmit and sell power.
Distant energy sources.
Trading energy.
Generation away from cities.
5. AC Transmission
Dominated transmission for a long time.
Needs synchronization.
Simple & cheap terminals.
Expensive towers.
Works well for short distances.
Use of models to represent lines.
6. AC Transmission Design
PLL at 5% VD, 30-45o
AD.
Double or single circuit lines.
Margin to minimize over-loading.
Number of lines=total P/PLL.
7. AC Transmission Design
Entering current.
Appropriate conductor’s CCC.
Transformer (TRF) rating.
Conductors between TRF and TL.
Bundling.
8. AC Transmission Design
Insulation design criteria.
Withstand of standard unit = 15kv.
Adjacent centers at 0.146m.
Minimum clearance.
Sag and tension.
Tower dimensions.
10. Design of 500kv, 2GW AC TL
PLL = 700MW.
Needs 3 lines, margin 2 lines double
circuit.
P/Circuit = 600MW, (670MVA)
I=3376.7A at 380kV.
4 incoming ACSR1033500,54,7
CCC=1060A.
11. Design of 500kv, 2GW AC TL
Each conductor to TRF 380/500kV
700MVA.
TRF Secondary 500kV, 780A.
From TRF Secondary 2 ACSR795,26,7
per bundle CCC=900A to first Tower.
Line Length = 700kM.
Ra=28.175 Ohms.
13. Design of 500kv, 2GW AC TL
Pr=565.5MW.
Efficiency=93.8%.
Voltage Regulation=54.7%. (Very High)
TSSSL=908.662MW.
PLL=618.16MW.
14. Design of 500kv, 2GW AC TL
A withstand voltage of 30kV.
Switching Surge Criteria.
1 MV Insulation.
34 Units.
Two Strings for more mechanical
Strength.
Min clearance from ground is 12m.
15. Design of 500kv, 2GW AC TL
Phase-phase min clearance is 12m.
Surge Arrestors at beginning, 1/3, 2/3
and end of line.
SBD, more wind in the center.
TRF relays slope= 20% pickup 68.6A
on 380kV side, 52.8 on 500kV side.
16. Design of 500kv, 2GW AC TL
Sag = 7m.
Tension = 31222.4 lb.
Lower circuit of tower’s height =20m.
Upper circuit of tower’s height =32m.
19. DC Transmission Design
Converting Station is expensive.
Converting TRF.
Converting Valve. (quad valves).
AC & DC filtering.
DC Transmission Line.
Pole Configuration
Smaller, Cheaper DC Towers.
Line Commutation.
21. DC Transmission Design
12-Pulse Configuration
DC
Side
AC
Side
Mid-point
DC bus
arrestor
Thyristor Quad-valve
Thyristor Module
22. Design of 400kv, 2GW DC TL
400kV DC and 500kV AC.
Converting Valves 400kV.
4kV thyristors, (100 LTT/valve)
Entering AC is 3380A at 380kV, in 4
ACSR 874500, 54, 7 of CCC 950A.
Every 2 conductors terminate in a HV
Bus-Bar at 380kV and 1200MVA.
23. Design of 400kV, 2GW DC TL
From BB to Conv.TRF ACSR 874500,
54,7 CCC=950 in 2 conductors/bundle
to the TRF. I = 1800A.
The Conv.TRF is a 3-windings
380kV/400kV 1200MVA.
24. Design of 400kV, 2GW DC TL
Bus-Bar at: 380kV
1200MVA
2 conductors
entering
1 conductor
leaving.
3p ACSR 874500, 54, 7
2 bundles
CCC=950A/bund
V=380kV
S=600MVA
I=912A
PF=0.9 leading
After 20m of
ACSR 874500, 54,
7cond.:
Drops negligible
Converter TRF:
V=380kV/400kV
S=1200MVA
3p 3 windings
3p ACSR 874500,54,7 2
bundles
CCC=950A/bund
V=380kV
S=1200MVA
I=1824A
After 40m of ACSR
874500,54,7:
Drops and losses
negligible
Delta
winding
Y winding
AC
Filters TRF
protection
TRF
protection
TRF
protection
25. Design of 400kV, 2GW DC TL
400kV
DC
Side
400kV AC
Side
Delta Side:
V=400kV
S=600MVA
I=866A
Conductors are ACSR
795000,26,7 CCC=900
Length 20 m drops &
losses negligible
Y Side:
V=400kV
S=600MVA
I=866A
Conductors are ACSR
795000,26,7 CCC=900
Length 20 m drops &
losses negligible
866
A
Mid-point
DC bus
arrestor
+
D
C
-
3000
A
26. Design of 400kV, 2GW DC TL
From the DC
side of the
converting
Valve
DC
Filters
Transmission Line
ACSR 874500, 54, 7
3 bundles per pole
CCC per pole = 950A
Total I per pole =
2750A
R = 17.18 ohms
Span = 200 m
To the DC
side of the
converting
ValveDC Filters
V = 400kV DC
P = 1100MW
I = 2750
V = 352.75kV DC
P = 970.08MW
I = 2750
27. Design of 400kV, 2GW DC TL
Insulation for 800kV.
Number insulator units = 800kV / 30kV
= 26.67=27 units/ string.
12m clearance from phase-phase and
phase to neutral.
Surge arrestors at withstand of 1MV.
SA at beginning, 1/3,2/3,end of line.
28. Design of 400kV, 2GW DC TL
TRF protection assumes 30% overload.
CT 2400:5 and 1200:5.
Slope is 20%.
25% pickup means:
380kV pickup = 115.2A.
400kV pickup = 56.4A.
29. Design of 400kV, 2GW DC TL
Vr = 352.75kV.
Pr= 970.8MW.
Voltage Regulation = 13%.
Voltage Drop = 11%.
Efficiency = 88%.
30. Design of 400kV, 2GW DC TL
Lower design than AC is for less
voltage.
500kV DC performance is:
8.2% Voltage Regulation.
7.5% Voltage Drop.
93% efficiency.
31. Design of 400kV, 2GW DC TL
Span = 200 M
Sag = 8.94m
Tension = 31433.82
Pole’s Height 13 + 8.9 =21.9m.
32. Design of 400kV, 2GW DC TL
TRF 1
TRF 2
Converting
Valve
Converting
Valve
Converting
Valve
Converting
Valve TRF 2
TRF 1
Diagram of the Line
34. Economic Comparison
Break-Even Distance.
AC Cost Estimation Legend:
TRF >500MVA, 1MVA=150$.
AC Towers 200m span = 80,000$.
1m of conductor for AC = 80$.
DC Cost Estimation Legend:
1 Station = 10,000,000$.
DC Towers 200m span = 45,000$.
1m of conductor for AC = 160$.
35. Economic Comparison
Table of Equipment:
Equipment Number Per Unit Price
TRF 380/500kV
700MVA 8 105,000$
AC Tower 200m
span 3,500 80,000$
AC Conductors 12/m 80$
Converter Station 2 10,000,000$
DC Tower 200m
Span 3,500 50,000$
DC Conductors 4/m 160$
36. AC & DC Costs
1. 98,644,000 $ for AC TL.
2. 91,040,000 $ for DC TL.
37. Conclusion
AC TL higher Tower and conductor
costs and lower terminal costs.
DC TL lower Tower and conductor
costs and higher terminal costs.
Economics determines the design to be
used.
Line length determines which one is
more economic.
