1. Next Steps in Load Modeling
Presented by Dmitry Kosterev, BPA,
NERC LMTF Chair
August 2016

2. History

3. History of Load Model Development in WECC
1980s – static models
Active power – constant current
Reactive power – constant impedance
Represented limitations of the computing technology of that time
1996 Western Interconnection outages
Need to model a part of load with induction motors to capture power oscillations
Reinforced by August inter-area oscillation event
Led to “interim” load model implementation in 2002

4. History of Load Model Development in WECC
1980s and 1990s
Events of delayed voltage recovery observed in Southern California, Florida and Atlanta area
August Lugo event (more than 3,000 MW of load lost)
Complex load models were developed to study these events:
Representation of distribution equivalent
Special modeling of single-phase air-conditioners
Models were used for special regional studies

5. WECC Load Modeling Task Force
2002 – work begins 2005 – Explicit load model was implemented in WECC-wide studies (Anatoly Meklin at PG&E) – only three phase motor models included 2007 – GE PSLF successfully implements first version of composite load model 2006-now – testing of residential air-conditioners, model development 2011 – adopted phased approach, seeking approval for Phase I (no AC stalling) 2011 – 2013 – system impact studies are completed for Phase I, model approved for use in WECC

6. Phase I is likely to be around for while
Phase I is likely to stay around for next 3 to 5 years, as Phase II development, implementation and validation will take time and resources
Several data revisions are planned:
Motor protection and control data
AC stall feature can be used with lower stall thresholds 0.4 to 0.45 per unit
Your feedback is needed on Phase I studies

7. Phase II

8. Phase II Model Developments
Modular model structure
Need for model flexibility
Improved data management
AC Model Improvements
Revise “stall” and “reaccelerate” characteristics of performance model
Validate MOTORC model, integrate in the composite load model

9. Phase II Model Developments
Distributed Generation
Protection and Control Models
Revise protection and control models for gradual behavior
Load Composition
Continue load composition analysis
Model Validation Studies
- Continual deployment of load monitoring devices

10. Phase II Model Validation Milestones
July Hassaympa fault – small FIDVR, loss of load July Mid-Valley delayed clearing fault – loss of load August Lugo event – wide-area FIDVR, large loss of load Valley events – local FIDDDDVR

11. System Studies

12. Hassayampa Event July 28, 2003 at 18:54
3-phase fault at Hassayampa 500-kV substation west of Phoenix, AZ, cleared in 3 cycles
2,685 MW of generation tripped following a fault
Estimated load loss about 1,500 MW due to tripping and thermal protection

13. Hassaympa 3-phase fault

14. Phase I – 2PV no fault

15. Phase I – 2PV 3p fault

16. Phase II – 2PV 3p fault

17. Phase II, Vstall=0.5 – 2PV 3p fault

18. Phase II, Vstall=0.4/0.45 – 2PV 3p fault

19. Phase I+ Load Model
Simulations using “Vstall” of 0.4 to 0.5 per unit have good correspondence (in principle) with actual system events
Vstall of 0.4 to 0.5 is consistent with what Bernie showed yesterday
Additional sensitivities with respect to motor protection are planned

20. Looking Forward

21. Paradigm Shift “Conventional” power system “Emerging” power system
Generation: synchronous machines
Loads: motors, (resistive) lighting
Main stability concerns: first swing stability, power oscillations
“Emerging” power system
Generation: increasing percentage of electronically-connected generation, increasing distributed generation
Loads: increasing percentage of electronically connected loads
Fault: details become important
How much load will trip ? How much will reconnect ?
Will motors stall ?
Will generators trip ?
Main stability concerns: disturbance ride through, voltage stability, power oscillations, frequency stability

22. Expectations Actual Loads Load Models 3-phase
Distributed along feeders
Diverse operating states
Diverse controls and protection
Diverse load composition
Positive sequence equivalent
Aggregated
Uniform operating state
Uniform “guestimate”
Loads are playing increasingly greater role in power system stability
Grid-scale load models are not able to get the same level of modeling accuracy as the models of synchronous generators
Load models can represent the phenomenon in principle, but not detail
While load models can be tuned to reconstruct past events, it does not guarantee that they will predict in detail load response to future contingencies

23. Model Complexity: Detail vs Manageability
Possible two load modeling directions (complementary, not mutually exclusive)
A detailed load model
Understanding how load characteristics impact power system performance
Development of equipment standards
Scenario planning
Inform development of “simplified” equivalent models
Detail is not same as accuracy
Simplified equivalent model
Used for production studies

24. Looking Forward Loads of the future are likely to get much simpler
Most loads will become electronically connected – chargers, motor drives, solid state lighting
However, it does not mean the problems get easier
BPA technology innovation project researched the impact of power electronic loads on grid stability