Global Blackouts – Lessons Learned - Siemens

20 |
Limitations of large AC Systems
o Voltage Stability
Interconnected Systems
o Load-Flow Problems (Manage-
Long-Distance Transmission
ment of Congestion required)
Systems
o Frequency Control
o Voltage Stability
o Reactive Power Problems o Oscillation Stability
o Steady-state Stability
o Inter-Area Oscillations
o Blackout Risk due to
o Transient Stability
Cascading Effects
o Interactions between the Power
o Subsynchronous Oscillations Systems in Terms of Physics
Fig. 24: How large can a synchronous System be ?
3.2 Solutions for System Interconnection
There are basically three possibilities to interconnect power systems, ref. to Fig. 25:
� synchronous interconnection (AC Solution)
Benefits,
Efforts
Benefits
� asynchronous interconnection using HVDC (DC Solution)
o HVDC Back-to-Back (without DC-Line)
o HVDC Long-Distance Transmission with DC Line
� hybrid synchronous interconnection (Hybrid Solution)
Cost-to-Performance Ratio
Optimum
Advantages of
interconnected interconnected Operation
Operation
Efforts
Size of interconnected Grid
When the Synchronous System is very large – Advantages diminish
System 1 System 2
AC Interconnection:
many Lines “from the Beginning”,
for Stability Reasons
DC Interconnection:
1 Link sufficient for stable
Interconnection
Hybrid AC/DC Interconnection:
The flexible synchronous Solution
Fig. 25: Alternatives of Power System Interconnections
a) a) Back-to-Back Solution
b) b) HVDC Long Distance Long-Distance SolutionTransmission
By using DC for interconnection of power systems, many benefits can be achieved: with DC,
an easy staging is possible (one link is already stable), whereas an AC-Interconnection must
a)
b)