1. System Modeling Discussion
(Open Discussion for WECC SRWG)
By: Ben Hutchins

2. Intro Quote
[We intend] to be candid about [our] errors; for as a wise man once said: "An error does not become a mistake until you refuse to correct it." We intend to accept full responsibility for our errors; and we expect you to point them out when we miss them. -John F Kennedy

3. Discussion Items Short Circuit Model Verification kV Base Issues
Base kV Differences
Operational Voltage Range
Equipment Modeling Buses Shunt Sizes Line Ratings Line Impedances
Conclusion

4. Short Circuit Model Verification
Current Communication Structure: -N Interconnected Entities must communicate. 2 Entities: 2 Requests, 2 Responses 3 Entities: 6 Requests, 6 Responses 4 Entities: 12 Requests, 12 Responses 5 Entities: 20 Requests, 20 Responses … 2*N(N-1) s!

5. Short Circuit Model Verification
MOD has requirements for Short Circuit Modeling Data

6. Short Circuit Model Verification
Motion
Once per year, WECC will request, from all utilities, their Short Circuit Models for the current system, in their native format.
WECC will ZIP the files into a single package, and post in the same location as WECC Base Cases.
First Request: Friday April 14th, 2017
Due Date: Friday June 2nd, 2017

7. Base kV Differences 525kV Base NV Energy’s Equipment Nameplates
NV Energy’s System Protection Group
NV Energy’s Transmission Operations
500kV Base
WECC
PeakRC (West-Wide System Model, WSM)

8. Operational Voltage Range
For NV Energy: Nominal “Target”: 525kV Normal: kV Emergency: kV WECC-CRT-003: If interpreted using PSLF kV Bases, 500kV ± 5%  kV 500kV ± 10%  kV

9. Buses
500kV System: Not Operated at 500kV PSLF ±5% for most reports (475kV-525kV)

10. Shunts
Example Nameplate, provides rated kV Remember: MVAR Output ∝ V²

11. Shunts – 100MVAR @ 525kV Example
Shunt Reactor Common Mistake: Entered in PSLF as B=1.00 This is wrong! At 500kV (PSLF’s Base), this reactor will only output (500/525)^2 * 100 = 90.7MVAR! Error could occur if “borrowing” impedances from a System Protection Case

12. Shunts – 100MVAR @ 525kV Example
Shunt Reactor

13. Shunts – 100MVAR @ 525kV Example
Test Reports: Applied Voltage, Resulting Current

14. Shunts – 100MVAR @ 525kV Example

15. Shunts – 100MVAR @ 525kV Example
Example calculation:

16. Shunts – 100MVAR @ 525kV Example
SCADA Measured Output: = kV Model B= (From Test Report) Calculated Output: * 100 * ( / 500) ^2 = MVAR ~1% Difference from SCADA Measurement. Not too bad!

17. Line Ratings
Line Ratings: Two Limitations 1) How much heat before annealing? 2) How much heat before sag below clearance? I²R  Heat  Sag & Annealing Current drives temperature. Equipment is Temperature Limited. PSLF takes MVA ratings, but converts (using the Bus kV Base) to Amps for comparison.

18. Line Ratings
Common mistake: Maintaining ratings in MVA, without a kV Base Specified. Example: If Operations uses a 525kV base, but Planning uses a 500kV base, your Amp ratings should the same, and your MVA ratings should differ! Planning: 500kV  1732 MVA Operations: 525kV  1819 MVA

19. Line Impedances
Driven by three things: 1) Relative Phase Positions 2) Conductor 3) Length

20. Line Impedances
AspenLC can produce R, X, B per-mile To convert from Ω to PU, divide by Zbase: 𝑍 𝐵𝑎𝑠𝑒 = 𝑘 𝑉 𝐵𝑎𝑠𝑒 2 𝑀𝑉 𝐴 𝐵𝑎𝑠𝑒

21. Line Impedances
Common mistake: “Borrowing” impedances from a different model, which does not have the same base. Potential error: kV² 500kV vs 525kV Bases means up to 10% Error

22. Conclusion
Motion for a WECC Short Circuit Data Request 500kV vs 525kV Base Issues: Potential for not catching low-voltages (488kV) for manual studies in PSLF. Potential for data entry mistakes: -Shunts: 10% -Line Ratings: 5% -Line Impedances: 10% Possibility to use 525kV Base in the future? -Automatic conversion routine?