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Hydro One’s Experience of Using State Estimation for Model
Validation
Yinhua Guo Jeff Penrice Vivian Cheuk
Ontario Grid Control Centre
Hydro One
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Hydro One Power System
• Major Transmission Company in Ontario
– 29,000km High Voltage Transmission Grid
– Peak Load 27,000MW
– Interconnect with New York, Michigan, Minnesota, Manitoba, and Quebec (asynchronously)
• Largest Distribution Utility in Ontario
– 123,000kv Low Voltage Distribution Network
– Serving 1.3million Rural Customers
– Extensive Distributed Generation (Wind & Solar)
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Courtesy of WorldAtlas
Hydro One EMS Applications
• State Estimation(SE): every 30sec.
• Thermal Limit Calculation: time limited ratings
• Contingency Analysis(CA): every 3min. ctg case redefinition, extensive SPS simulation
• Short Circuit Calculation: every 6min.
• Real Time and Study Environment
• Dispatcher Training Simulator(DTS)
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SE Solution Validation
• What is a Valid/Good SE solution?
– Estimated value against measured values
– SE solution against power flow solution
– Power flow solution against CA solution
– Pre-outage CA solution against post-outage system state (real time or DTS Replay)
• Sources of Problem
– Data/Model errors, poor application tuning, software defects, inadequate theory.
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Transformer/Phase Shifter
• Actual Physical Device:
– ULTC tap on HV or LV side
– DETC tap on HV or LV side
– Both ULTC & DETC taps: on different or same side
– Combined voltage transformer and phase shifter
• Typical Model Representation:
– ULTC tap on “from” side only
– Tap step size static (vs. function of DETC position)
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Transformer/Phase Shifter…con
• Symptoms for Wrong Tap Model:
– MW circulation for parallel phase shifters
– MVAr circulation for parallel transformers
– Excessive MVAr/voltage
– Unrealistic estimated tap positions
• Problems with Impedance Parameters:
– Unbalanced flows on parallel transformers
– Too small value causing numerical difficulties
– Impedance variation with tap positions
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Parallel Transformer/Phase Shifter
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The first set is a voltage transformer & a separate phase shifter in series
The second set is one combined voltage and phase shifter transformer
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T3 is a very different transformer model from the other 3 transformers
Transmission Circuit
• Typical Model and Assumptions
– π model per circuit, typical per kilometer value ranges available for data error check
– Balanced 3 phase assumed, mutual coupling between circuits ignored (small), but 500kv circuit rarely transposed
• Parameter Estimation
– Single scan vs. multiple scan solution
– Fluctuating results suggest other problems
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Mutual Coupling Effect Example
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Mutual Coupling Effect Modeled
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Generator/Load Injection
• Generator Capability Limits
• Load Limits and DG impact (if modelled as negative load)
• Model Values (pseudo-meas) for Generator and Load Derived from Measurements.
• Injection Residue Distribution Between Generators and Loads
• Voltage Sensitive Load Model (at nominal kV)
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Telemetry Model & Errors
• IEEE/ANSI C57.13 Defines Accuracy Classes
– Transformer correction factor(TCF) limits
– CT @100% rated current(+meter@10%, relay@20x)
– VT @90% and 110% rated voltage
• Transducer/IED:
– A/D bit length, digitizing error
– Scaling factor, resolution error
• Measurement/Device Mapping:
– Fixed in model, may be dynamic in field
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VT location, multiple CT combined input
Measurement set up for normal configuration, switching operation may
make the mapping invalid
Weighting Factors
• Measurement Weighting in SE Relates to its Standard Deviation(Gauss Error Distribution)
– The product/ratio of 2 normal random variables is NOT a normal random variable
– Lack of source data and procedure
– Differ from ANSI Accuracy Class Definitions
• Impact to SE: Make or Break!
• Tuning: Science & Art or Trial & Error?
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Performance Monitoring
• SE Solution Quality and Availability
– Large Residues/Biases by Measurement Types
– Bus Injection Residues
– Bad Voltage Solutions (too High or Low)
– Run every 30 seconds
• Monitoring Procedures and Tools
– Shift Control Engineer (7x24), issuing tickets
– Application Staff, 2nd level support
– Watchdog application, running in real time
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