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TRANSCRIPT
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Nirmal-Kumar C Nair
Department of Electrical Engineering
Texas A&M University
EPPE Power Seminar SeriesMay 3, 2001
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PRESENTATION INDEX
De-Regulation
Electric Markets
Transaction Based Power Flow
Conventional Power Flow Analysis
Transaction Based Voltage Margin Allocation
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POWER SYSTEM DE-REGULATION (RESTRUCTING)
GENCO
TRANSCO
DISCO
Tie Lines
GENCO
TRANSCO
DISCO
GENCO
DISCO
GENCO
DISCO
GENCO
TRANSCO
DISCO
Deregulation or Restructuring denotes breaking up of the
Vertically Integrated Utility(VIU) structure into Competitive
Market Entities.
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RESTRUCTURED ELECTRICAL INDUSTRY
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ENTITIES RESULTING FROM DE-REGULATION
SO
GENCO TRANSCO DISCO
SO is the Power System Operator and the Power Market
Operator, which may include other entities depending on the
market structure. SO, is independent of the other entities
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An Integrated Electricity Market
Power Commodity Markets
Real-time Balancing Markets (RBM)
Transmission Capacity Markets
Power Exchange Market (PX)
Bilateral Contract Market (BCM/SC)
Ancillary Service Market (ASM)
New types of transmission directives.
(ISO, ISA, RTO)
Long-term capacity access charge (LCC)
Fixed transmission rights (FTRs)
To perform a security-constrained ED function
To re-dispatch bilateral contracts
RESTRUCTURED COMPETITIVE ELECTRICITYMARKET
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Power Commodity Market Components
A Power Exchange (PX) establishes an auction market where energyoffers/bids by the generators/consumers are matched anonymously based onvolume and prices. The PX may operate a forward (a day-ahead) market as wellas an hour-ahead spot market separately.
A Bilateral Contractis defined as the right to inject a certain amount ofpower at a delivery point iand remove it at another receipt point jat aspecified price Pij.
BCM/SC market shields for pro-conservative market agents against risk ofhedging of electricity price in the central spot market (PX) due to variousstrategic bids/offers.
The Ancillary Service Market is responsible for procuring spinning reserve,non-spinning reserve, AGC, replacement reserves, voltage support and blackstart, to secure stable operation of the system.
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Transmission Capacity Market Components
Within the context of Transmission Open Access (TOA) philosophy, thetransmission entities continue to evolve towards new types of directives like
For-Profit TRANSCO
Non-Profit Independent System Operator (ISO)
Independent Scheduling Administrator (ISA)
Regional Transmission Operator (RTO)
The Capacity Connection Charge (LCC), or power fee, is a long-term (sayone year) charge per MW of connected capacity as a portion of thetransmission tariff package.
The capacity charge could be same for all users connected to ISO, or can berelated to the geographical location or based on other market designs relatedto congestion.
Firm Transmission Rightis defined as A financial contract that entitles theholder to a stream of revenues (or charges) based on the reserved level andhourly LMP difference across the specified transmission paths.FTR protects transmission customers from increased cost due to transmissioncongestion on the condition that energy trades are consistent with firmreservation.
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REAL-TIME BALANCING MARKET
The Real-time Balancing Market is a real-time energy balancingmarket performed by the ISO to revise the preferred schedules whenthere is any imbalance or transmission congestion.
In the RBM, both generators and consumers in the PX can submit
their incremental or decremental energy offers and bids to theISO, who will select the least cost resources to meet the balancingrequirements or to eliminate the congestion on a real-time basis.
In the RBM, the ISO also can curtail the bilateral contracts whose
sensitivity to the violated constraints is high, or call for newbilateral transactions resulting in a negative power flow effect onthe congested lines.
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MARKET COORDINATION MODELS
SO
BUYER SELLER
SO
BUYER
SELLER
C
O
N
T
R
A
C
T
Bid
Transaction
Bid
Transaction
Approve/
Disapprove
Submit
POOLCO OPCO
POOLCO
OPCO
VIU
Regulation
Market Force
ISO
SC PX
SO
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ikkiikkiikkiDiGi
kiikkiikki
ik
DiGi
bgVVPQ
bgVVPP
)]cos()sin([||||
)]sin()cos([|||| 1
Here all N buses fall into 3 categories: PQ bus, PV bus and
one single slack bus .
Since power flow equation is in term of angle difference, areference angle is assigned to the slack bus in advance,
whereas generation of the slack bus is left open to account
for imbalance between the total generation and load in the
system.
),( V
THE CONVENTIONAL POWER
FLOW ANALYSIS
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Provides reference angle
Accounts for energy imbalance
Makes N power flow equations a consistent set
Causes dependency of the PF solution on the slack
bus when specified real power of N bus is inconsistent.
Difficulty in determining loss responsibility for
individual generators/loads/transactions.
Causes PF sensitivity factors being slack bus
dependent.
NECESSITY
NECESSITY & PROBLEMS WITH
CLASSICAL SLACK BUS
PROBLEMS
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KEY TO TBPF FORMULATION
Nodal power balance equations (a) vs. nodal
current balance equations (b).
...3,2,1)cossin()(
)sincos()(
i
bgVQQ
bgVPP
ijijijijijiDiGi
ij
ijijijijiDiGi
(b)
(a)
i
i
j
n
j
n,nn,
,n,
n
eV
.
eV
y.y
...
y.y
I
.
I1
1
1111
*
i
j
iii IeVjQPi
Can we build a bridge between certain real power
and particular nodal current ?
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R/X ratio and branch angle difference are small.
Strongly Coupling relation betweenP and .
Strongly Coupling relation between Q and V.
Strongly Coupling relations between and, and between and V, provided nodalphase angle is small enough (say | max|< /9).
)Re(busI)Im( busI
SOME GENERAL FACTS
Note that PandQare coupled withIthrough associated
phase angle and voltage magnitude, thus it is impossibleto find the exact contribution ofP onI.Fortunately,transmission grids hold several characteristics like:
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APPROXIMATIONS LEADING TO TBPF
Exact expression Piin terms of nodal current is
We make the following approximation according
to the discussed basic facts:
The aggregated reactive power of the system takes
care the remaining current components, includingall Im(Ii) terms and residual errors of Im(Ii), which
are
)Im(sin)Re(cos iiiiiii IVIVP
ii
ii
V
PI
cos)Re( , assuming Vi sini Im(Ii) is small.
ii
ii
V
PI
cos)Re(
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Main Features of The TBPF Analysis
Decompose complex AC power flows directly intotransaction components, in the light of Physical Laws.
Evaluate interaction quantities of different energytransactions on particular power flows and losses
Show effect of reactive power scheduling on reactiveloss and transmission losses.
Assure satisfactory decomposition accuracy when
realistic network conditions are satisfied. Sustain a simple and fast computation procedure.
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Transaction loss evaluations
Parallel flow evaluation and compensation
Conducting FTR purchase/sale and settlement
Congestion Management
Reactive power support charge for energy delivery
Responsibility settlement of voltage stability
TBPF APPLICATION SCOPES
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VOLTAGE STABILITY INDICATOR
G
L
GGGL
LGLL
G
L
G
L
V
I
YK
FZ
V
I
HI
V
2
jjj
j
j
VY
S
L
jcorrjj SSS
jiLi
j
i
i
jj
ji
jcorr V
V
S
Z
ZS )(
jj
jj
Z
Y
1
[I bus] = [Y bus] * [E bus]
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TRANSACTION BASED VOLTAGE
MARGIN ALLOCATION (TB-VMA)
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TB-VMA Application Scope
Responsibility Settlement of Voltage Security
Node-wise Voltage Stability Margin UtilizationEvaluation
Evolve Transaction Based Pricing Mechanism forVoltage Security
A Tool to confirm whether a Transaction could be
committed from voltage security margin viewpoint
A Tool to decide which transaction if curtailed givesmaximum effect in case of potential voltage collapse
situation
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CONCLUSION
A Transaction Based Voltage Margin Assessmentprocedure has been formulated
The TB-VMA is able to evaluate voltage securitymargin utilization on a node wise basis with respectto individual transactions
TB-VMA has been effectively demonstrated using acomposite market model containing both PoolCotype and Point-To-Point type transactions
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REFERENCES Hongming Zhang,Transactions-based power flow analysis and its
application s to a competitive power market Ph.D dissertation
submitted to Texas A&M University, June 2001
P Kessel, H Glavitsch,Estimating the voltage stability of a powersystem, IEEE Trans on Power Delivery, vol. PWRD-1, No.3, July 1986,pp. 346-354.
G M Huang, N C Nair,An OPF based algorithm to evaluate loadcurtailment incorporating voltage stability margin criterion,
Conference Proceeding of NAPS 2001, TX, October 2001.
G M Huang, N C Nair,Voltage stability constrained load curtailment
procedure to evaluate power system reliability measures, ProcIEEE/PES Winter Meeting Jan 2002, NewYork.
G M Huang, N C Nair,Incorporating TCSC into the Voltage StabilityConstrained OPF Formulation submitted to the IEEE/PES Summer
Meeting, Jun 2002.
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