Upload
others
View
5
Download
1
Embed Size (px)
Citation preview
Workshop on Power Grid Interconnection in Northeast AsiaMay 14-16, 2001, Beijing, China
Felix WuFelix WuThe University of Hong Kong andThe University of Hong Kong andUniversity of California, BerkeleyUniversity of California, Berkeley
Technical Considerations for Technical Considerations for Power Grid Interconnection in Northeast AsiaPower Grid Interconnection in Northeast Asia
Outline
Cost-benefit analysis» Probabilistic production
costingOperation and control» Frequency control» Protection» Reliability
Interconnection alternatives» HVAC, HVDC, Hybrid
Reinforcement of existing networks» FACTS devices» EMS
Simulations and analysis» Power flows» Stability
NEA interconnection» Technical assessments
Potential Benefits of Interconnection
Economical» Utilization of most favorable energy resources» Use of larger and more economical power plants» Flexibility of building new power plants at favorable
locations» Sharing generation as a result of non-coincidental load
demand» Cost reduction through joint economic dispatch.» Sharing spinning reserve
Potential Benefits of Interconnection
Environmental» Coordinated use of environmentally friendly resources» Replacing resources with adverse environmental effect.» Generating electricity away from population.
Reliability» Providing emergency support.» Strengthening network connection
Others» Stimulating economic cooperation and growth.» Technology transfer
Benefit Analysis
SystemA
SystemB
InterconnectionSystem
ASystem
B
InterconnectionInterconnection
Comparative study» For each system, compare the costs of production
of alternative plans (interconnection included).Tool» Probabilistic production costing
Production Simulation
Load» Forecast load-B
Generation» Existing generation B» Import from the
interconnection.» Merit order
Simulate power system operationTo calculate production cost
From each generator and for the whole systemEnergy, fuel, pollution, etc.
Load» Forecast load-A.
Generation» Existing generation A» Export to B» Merit order
Production Costing Simulation
0
20
40
60
80
100
120
140
0 4 8 12 16 20 24 28 32 36 40 44 48 52
ExpensiveThermal
Hydro
CheapThermal
Load (GW) Annual Load Curve
Production Costing Simulation
0
20
40
60
80
100
120
140
0 4 8 12 16 20 24 28 32 36 40 44 48 52
ExpensiveThermal
CheapImport
Hydro
CheapThermal
Load (GW) Annual Load Curve
Probabilistic Production CostingTaking into account of uncertainties in generator scheduling, forced outages, hydro availability, etc.Multi-year breaking down to a series of monthly or weekly simulationsOutput provides detailed information of » Fuel usage and cost» Pollution generated» Loss of load probability» Long-run marginal cost
Can be used to assess benefits (economical and environmental) of interconnection.Data requirements
Transmission Cost
Capital costsOperational costs» Losses» Maintenance, etc.
Transmission Costs
0
0.5
1
1.5
2
2.550
0kV
DC
2 50
0kV
AC
2 73
5kV
AC
650k
V D
C
3 50
0kV
AC
2 73
5kV
AC
2 10
50kV
AC
750k
V D
C
3 75
0kV
AC
2 10
50kV
AC
USc
/kW
h
Loss costCapital cost
Based on 1200km
0
0.5
1
1.5
2
2.550
0kV
DC
2 50
0kV
AC
2 73
5kV
AC
650k
V D
C
3 50
0kV
AC
2 73
5kV
AC
2 10
50kV
AC
750k
V D
C
3 75
0kV
AC
2 10
50kV
AC
USc
/kW
h
Loss costCapital cost
Based on 1200km
Factors Determining Cost/Benefit
Benefit» Transfer capability
Cost» Interconnection site» Interconnection method
How much
Where
What
Operation and Control
Where, what, and how much to interconnect affects operation and control of both systems.Existing systems are AC.Will look at AC system operation and control requirements.
AC Networks
Power flow control» Power flows and voltage distribution in an AC power
network are determined by Kirchhoff and Ohm laws. » Individual element has very little control over the whole
system.System dynamic performance» Quick and wide-spread response to local disturbance.» Disturbance may cause cascading outages.» Mitigating measures are designed and built into the
system.
Operation and Control of AC Network
Frequency control» Frequency is an indication of power balance
between generation and load.» Frequency deviation from normal (50Hz or
60Hz) requires immediate action to balance supply/demand.
» Limitation on generator response.
Operation and Control of AC Network
Fault protection» Disturbances or faults such as short-circuit
caused by lightening, tree falling, etc. happen frequently on power system.
» Protective relays are used to sense a fault.Circuit breakers are used to isolate the fault.
» Fast clearing of faults is essential to prevent the effect to spread and propagate.
Operation and Control of AC Network
Reliability operation» System should be able to withstand credible
disturbances, called n-1 criteria, in the west.» Steady-state: no transmission line overload and
no abnormal voltage immediate after a disturbance.
» Transient: no stability problem.
Stability
0 2 4 6-2 0 0
0
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
s e c o n d s
ang
le in
de
gre
es
m a c h in e a n g le s
0 2 4 6 8 1 00
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0m a c h ine a ng le s
s e c o nd s
ang
le in
de
gre
es
0 2 4 6-2 0 0
0
2 0 0
4 0 0
6 0 0
8 0 0
1 0 0 0
1 2 0 0
s e c o n d s
ang
le in
de
gre
es
m a c h in e a n g le s
0 2 4 6 8 1 00
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0m a c h ine a ng le s
s e c o nd s
ang
le in
de
gre
es
Interconnection Alternatives
System A System BHVAC
System A System BHVDC
System A System BHybrid
System A System BHVAC System A System BSystem A System BHVAC
System A System BHVDC System A System BSystem A System BSystem A System BHVDC
System A System BHybrid
System A System BSystem A System BHybrid
HVAC Interconnection Pre-conditions
Adjustment of frequency control» Adding interchange schedule into frequency control» Area control error = (interchange schedule) + B x δ f» Enough generators under control to respond» Joint responsibility
Protection coordinationCommon reliability criteria
Stability of Weak Interconnection
HVDC Interconnection
Technical advantage» No need for common frequency control.» Stable operation at low power interconnection.» Back-to-back HVDC connection is used.
Technical disadvantage» Generating harmonics» Need reactive power source at converter station» Might bring about subsynchronous oscillation
Bipolar HVDC Transmission
Hybrid AC/DC Interconnection
HVDC can damp oscillations
Example: Pacific intertie
Reinforcement of Regional Networks
Reinforcement may become necessary after interconnection» Stability and other reliability considerations
Flexible AC transmission system (FACTS) devicesComputer-controlled energy management systems (EMS)
FACTS Devices
Power electronics devicesProviding reactive power/voltage support» Static var compensator (SVC)
Improving transfer limit» Static synchronous copensator (STATCOM)
Improving stability limit» Thyristor controlled series compensator (TCSC)
Power flow control (both real and reactive)» Unified power flow controller (UPFC)
Damping power oscillations» STATCOM, UPFC
UPFC
Energy Management System
Generator
Substation
Large load
Tie line
RTU
Communication Operator’sconsoleComputer
Application programs
Interconnected System Performance: Simulation and Analysis
Steady-state performance» Power flow analysis
System dynamic performance» Synchronization after a fault: Transient stability, long-
term dynamics» Low frequency oscillations: small-signal stability» Voltage collapse: voltage stability» Subsynchronous oscillations
Summary
Technical issues arising from large system interconnection are very complex» Power flow and voltage» Dynamics
Cost-benefit analysis and technical issues and solutions need to work out in parallel.
Northeast Asia Interconnection
Technical Factors Considered
Long-distance DC links/ Short-distance AC linksPotential benefits» Balancing surplus and deficiency» Utilizing more desirable resources » Leveling summer and winter demands
Technical difficulty with » Reducing reserve» Joint dispatch» Savings (economical and environmental) from
exchanges over multiple regional networks.
Technical Assessment of NEA Interconnection
Difference of regional networks in» Strength» Planning & operational criteria» Technical standards
Coordination and AgreementResults of technical analysis depends on» Models» Data» Assumptions
Objectivity and Consensus