The comparison between AC and Dc Transmissions are explained in this presentation

1. Comparision of ac and dc transmission
content
 Introduction
 Economics of Power Transmission.
 Technical performance.
 Reliability.
Prepared By
Mr.K.Jawahar, M.E.,
Assistant Professor
Department of EEE
Comparision of AC and DC Transmission
Kongunadunadu College of Engineering and Technology Department of EEE

2. DC POWER TRANSMISSION
TECHNOLOGY
INTRODUCTION:
• Power Demand is doubled every year.
• So Generation and Transmission of power should be ECONOMIC.
DC TRANSMISSION SYSTEM:
• Used for long distance and high power transmissions.
• Power Flow control is important for new line Planning.
(SENDING END)
Generation Station AC Rectifier DC Transmission Line
(RECEIVING END)
Transmission Line DC Inverter AC Loads
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

3. INTRODUCTION
Cons...
• In first DC Transmission between SWEDISH MAINLAND and ISLAND
of GOTLAND (100KV, 20MW, DC Line).
• At First, Mercury Arc Valves are used for (AC to DC).
• Now Rectifier is used for (AC to DC).
• Rating of Semiconductor Devices (10KV, 5KA, 125mm sized)
• Highest Voltage Transmission reached by this devices is +600 KV.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

4. COMPARISION OF AC AND DC
TRANSMISSION
Two modes : AC and DC Transmission.
Factors:
1. Economics of Power Transmission.
2. Technical performance.
3. Reliability.
1.Economics of Power Transmission:
Economics = (Investment Cost + Operation Cost)
Investment Cost Right way of cost, Towers, Conductors, insulators and
Terminal equipments.
Operation Cost  Cost of Losses.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

5. COMPARISION OF AC AND DC
TRANSMISSION Cons....
DC Line:
Two Conductors used (+ve, -ve).
Pdc = 2 Vp x I
• Less ROW, Simple &Cheaper Towers, less Conductors & Insulators cost,
Less Power loss (Two Conductors only).
• No Skin effect, Less Corona Loss, Less Dielectric Loss.
• Size of conductors is economic.
• No need of compensation.
• Terminal Equipment Cost is high ( Converters and Filters)
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

6. COMPARISION OF AC AND DC
TRANSMISSION Cons....
AC line:
• 3 Same size Conductors are used.
P ac =3/2 (Vp x I) CosØ
Vp - peak voltage of conductors,
I- effective Current rating of conductors.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

7. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

8. COMPARISION OF AC AND DC
TRANSMISSION Cons....
• Distance is < Break even Distance AC Transmission is Economic (Less
Distance).
• Distance is > Break even Distance DC Transmission is Economic (Long
Distance).
• Break even Distance is 500 to 800 Km.
Technical Performance:
In DC lines Controllability of Power is Fast than AC lines (By Converters).
Advantages:
1. Full Control over power Transmitted.
2. Fast Control limits the Fault currents in DC Lines.
3. No need of DC breakers in two terminals.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

9. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Stability Limits:
• AC Transmission – Power depends the Voltage Phase at two ends.
• Distance increase  Phase Angle.
• Power Transmission Limited by transient and Steady State Stability.
 Ac Transmission- Affected by Distance increased.
 Dc Transmission- Not Affected by Distance increased. (Only Current
Carrying Capacity of Conductors ).
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

10. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Voltage Control:
Ac Transmission:
• Voltage Control is Complicated by Line Charging Currents and Inductive
Voltage Drops.
• AC Voltage is Flat for Fixed level of power (P=Pn).
• It Depends on surge impedance loading and Line loading.
Midpoint Voltage (V) is increase  Line Loading> SIL (P<Pn).
Midpoint Voltage (V) is Decrease  Line Loading< SIL (P<Pn).
• Capacitive Control is used instead of inductive Control to reduce the
reactive power Control.
DC Transmission:
• No Need of reactive Power Control.
• No charging Current Problems.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

11. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

12. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Line Compensation:
• Ac lines – Needs shunt and series Compensators to overcome stability and
Line charging Problems.
• Series C and shunt L used for compensation.
• SVC (Static Var compensator) used in high Power transfer. It needs in regular
intervals in AC lines.
AC Interconnection Problems:
• Two Power Systems connected by AC ties.
• Automatic control is coordinated both systems in power(P) and Frequency(F).
Problems:
• Large Power oscillations leads Tripping frequently.
• Increase in fault levels.
• Problem of one system affects the second.
• In DC lines we can overcome these problems by asynchronous ties.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

13. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Disadvantages of DC Transmission:
• High cost breakers needs.
• No usage of transformer for voltage level change.
• Generation of AC and DC harmonics Leads AC and DC Filter usage.
It increases the equipment cost.
Reliability:
• DC- GOOD compare than AC.
• It is done by improvement of thyristor converters (Advanced switches).
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

14. Applications of DC Transmissions
• Long distance bulk power transfer.
• Underground and under water cables.
• Asynchronous interconnection systems with different frequencies.
• BTB and MTDC Systems.
Kongunadunadu College of Engineering and Technology Department of EEE

15. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

16. COMPARISION OF AC AND DC
TRANSMISSION Cons....
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission

17. Reference:
• Padiyar, K. R., “HVDC power transmission system”, New Age
International (P) Ltd., New Delhi, Second Edition, 2010.
Kongunadunadu College of Engineering and Technology Department of EEE
Comparision of AC and DC Transmission