California
Independent
System Operator
State Estimator for CA ISO Market
and Security Applications –
Relevance and Readiness
IEEE PES General Meeting 2008
PITTSBURGH, PENNSYLVANIA, USA
July 20-24, 2008
Authors:
Dinesh Salem-Natarajan,
Liang Zhao, Wei Shao,
Matthew Varghese, &
Soumen Ghosh
(CaISO, Folsom, CA)
Soumen Ghosh
Mani Subramanian
Gordon Lin,
(ABB, Sugar Land, TX)
Hsiao-Dong Chiang,
Hua Li
(Bigwood-Systems, Ithaca, NY)
Created: 06/15/2008
California
Independent
System Operator
Overview
• Introduction
• CAISO Network Model (EMS Model) footprint;
• The Market Model footprint, Full Network Model (FNM);
• The models in Common Information Model/eXtensible Markup
Language (CIM/XML) format;
• The relevant EMS applications;
• The implementation of Voltage Stability Analysis (VSA);
• Orthogonal State Estimator (SE) and its comparison with Fast
Decoupled SE;
• The relevance of SE solution in Real Time Nodal Market and VSA;
• The SE Readiness Metrics adopted at CAISO and the proposed
acceptable range of the metrics.
• Conclusion
Soumen Ghosh
Created: 06/15/2008
Introduction
California
Independent
System Operator
• Reliability tools and market systems depend on the results produced
by the SE
• Monitoring & Analyzing the quality and availability of every SE
solution
• At CAISO, the SE solution is used for Real Time Power Flow and
Contingency Analysis, Real Time Nodal Market, and for Voltage
Stability Analysis.
• In the evaluation of SE readiness,
• Several metrics used by the Midwest ISO (MISO) and Southwest
Power Pool (SPP) were reviewed
• Several new SE performance metrics of the SE solution at the
CAISO have been identified
• The new SE performance metrics are to identify an unreasonable SE
solution even if the solution is valid.
Soumen Ghosh
• Our hope is to set up a framework for all stake holders to work
collectively in identifying a standard set of SE metrics to determine the
quality of the SE solution
Created: 06/15/2008
California
Independent
System Operator
CAISO Network Model footprint
CAISO - EMS
Soumen Ghosh
CAISO - FNM
Buses
5950
3190
Units
1809
1036
Loads
3150
1974
Lines
5398
3336
Transformers
2327
1082
Shunts
1420
199
Created: 06/15/2008
California
Independent
System Operator
Network Model
• EMS Network Model: This includes the detailed system (including subtransmission) for the state of California and for all other WECC areas, the
system is represented for voltage levels at 161 KV and above.
• Market Full Network Model: Detailed Network Model, mostly derived
from the EMS Network Model,
• The power system model for the CAISO footprint,
• Fictitious injections on inter-ties to areas not part of CAISO
markets and
• Commercial data for the market participants (ex: an association
between a set of electrical buses to a specific LMP pricing node)
• CIM/XML Model Format: A common model format that can be used and
understood by different platforms provided by a variety of vendors.
Soumen Ghosh
Created: 06/15/2008
PSLF Model
Soumen Ghosh
California
Independent
System Operator
Created: 06/15/2008
California
Independent
System Operator
CIM/XML Model
</cim:ACLineSegment><cim:ACLineSegment rdf:ID="Conductor_2003">
<cim:Naming.name>POEPH-RIOOSO_230_BR_1_1</cim:Naming.name>
<cim:Naming.description>30280_POE
_1</cim:Naming.description>
_230_30330_RIO OSO _230_BR_1
<cim:Conductor.x>43.8911</cim:Conductor.x>
<cim:Conductor.r>7.41658</cim:Conductor.r>
<cim:Conductor.bch>16.234</cim:Conductor.bch>
<cim:ACLineSegment.MemberOf_Line rdf:resource="#Line_7448"/>
<cim:ConductingEquipment.BaseVoltage rdf:resource="#230_BV"/>
Soumen Ghosh
Created: 06/15/2008
California
Independent
System Operator
Detailed Model
Soumen Ghosh
Created: 06/15/2008
EMS Relevant applications
California
Independent
System Operator
STATE ESTIMATOR
•State Estimation processes telemetered system power measurements to obtain an estimate of ‘State’ - the magnitudes
and phase angles of bus voltages in the actual power systems.
• This calculation is based on the telemetered analog quantities (MW, MVAr, and KV) and the most current topology
of the power system.
• Knowing the state of the power system, it calculates the MW, MVAr, and MVA flows through all the transmission
lines and transformers and the MW and MVAr injections for all the loads and generation sources.
• These calculated voltage and power values provide useful operational information in cases when no telemetry is
available. When valid telemetry does exist, the calculated quantities can be used to identify measurement errors.
REAL TIME LOAD FLOW & CONTINGENCY ANALYSIS
•Real Time Load Flow provides the system operator with grid information like voltage and line flows for different
short-term study conditions.
•Real Time Contingency Analysis provides the system operator with the information on the ‘system state’ for different
‘what if’ conditions on the existing system.
CAISO OUTAGE MODELING TOOL (COMT)
•The COMT application is a Web-based tool which allows the users to search the CAISO Outage database and
identify scheduled outages that impact the network topology. The tool allows the users to develop switching
instructions (based on Network Model components) that need to be automatically applied to the network model at the
appropriate time.
• In the Real-Time COMT is used to update the status of non-telemetered points and the status points with failed
telemetry.
Soumen Ghosh
Created: 06/15/2008
California
Independent
System Operator
Voltage Stability Analysis (VSA) Tool
Soumen Ghosh
•
VSA Real-Time Mode (VSA/RT)
•
VSA Real-Time Look-Ahead Mode (VSA/LA)
•
VSA On-line Study Mode (VSA/OS)
Created: 06/15/2008
VSA Tool Input and Output
Soumen Ghosh
California
Independent
System Operator
Created: 06/15/2008
VSA-User Interface, RT/LA
California
Independent
System Operator
System Load Margin: the maximum total real power transferred from source to sink before the system hits
the voltage collapse point under a proposed stress pattern. Interface flow: the power flowing through an
interface flow gate. The Interface Margin is the portion of the total power transferred that flows through the
Interface. If the interface is defined properly in relation to the stress pattern a sizable portion of total power
transferred will flow through the defined interface
Soumen Ghosh
Created: 06/15/2008
VSA -User Interface, OS
California
Independent
System Operator
Study mode VSA runs as a stand-alone process, which can be launched directly from the workstation as well as from the Viewer.
Study mode VSA can retrieve an archival case from the VSA viewer or a Dispatcher Load Flow case directly from the data bridge.
Soumen Ghosh
Created: 06/15/2008
Orthogonal vs. Fast Decoupled Comparisons
California
Independent
System Operator
Stage 1
Run with existing ‘Convergence Tolerance’
Run with existing ‘Global Measurement
Errors’
COMPARISON : INVALID RUNS for ORTHOGONAL vs. FAST DECOUPLED
Stage 2
Set MW/ MVAR convergence tolerance for
all Areas to 0.05
Revise the MW/ MVAR mismatch on ‘Zero
Injection Buses’ measurement error
tolerance to 0.1
Stage 3
Re-set convergence tolerance to values
before Stage 2
Reduce the minimum values for ‘Global
Measurement Errors’
For Voltages, use decrements of 0.001
For Circuits, use decrements of 0.5 (then)
.05
For gen/loads, use decrements of 0.1
(then) .01
180
160
140
120
100
orthogonal
fast decoupled
80
60
40
20
0
stage 1
stage 2
stage 3
stage 4
Stage 4
Repeat steps of Stage 2 with parameters of
Stage 3
Soumen Ghosh
Created: 06/15/2008
California
Independent
System Operator
State Estimation & Real Time Market
Real Time Market
• Real Time Pre Dispatch (RTPD)
• Executes every 15 minutes
• Real Time Interval Dispatch (RTID)
• 5 Minutes dispatches
• RTPD & RTID
• Utilizes the Full Network Model updated
by the real time State Estimator solution
to get the current operating conditions to
initialize the power flow. State Estimator
Solution resides in Enterprise Integration
Bus to be used by RTPD and RTID.
Soumen Ghosh
Created: 06/15/2008
California
Independent
System Operator
State Estimation & Market
•In the RTM environment the static model is
updated with dynamic data based upon real
time operations that comes from the State
Estimator application which is merged with
commercial Market and Supplemental Market
Data Maintenance (SMDM) system data for the
various Market runs.
Outage Derates
Load, Generation,
and Reactive
Distribution Factors
Voltage/Tap
Schedules
Constraints/
Exceptions
Static Model
From EMS
Contingencies
Full Network Model
• The static market model from the GDB and the
dynamic model of the power system are
exported from the EMS to the RTM system.
• For the RTM analysis, the State Estimator
solution along with Topology Information from
the EMS is transmitted to the RTM System and
used to initialize the Power Flow.
Soumen Ghosh
Market Analysis Engine
(Topology Process, Power Flow, Security Analysis, Unit
Commitment, Unit Dispatch, Congestion Management, Loss
Management, Locational Marginal Pricing)
Dynamic Model
from EMS for
RTM only
RTM
IFM
Created: 06/15/2008
SE/ DLF Solution Quality Monitor
Soumen Ghosh
California
Independent
System Operator
Created: 06/15/2008
SE/ DLF Solution Quality Monitor
Soumen Ghosh
California
Independent
System Operator
Created: 06/15/2008
California
Independent
System Operator
Conclusion
• Importance of the quality of the information provided by the SE to
the various reliability and market tools
• At the California ISO, the SE solutions are required for (1) The Real
Time Market and for (2) Security Applications such as Voltage Stability
Analysis.
•This paper proposes the formulation of metrics to study the availability
and quality of the SE solution.
Soumen Ghosh
Created: 06/15/2008
California
Independent
System Operator
Questions and Answers
Soumen Ghosh
Created: 06/15/2008