1. Reading a GE PSLF *.epc into PWS
Tracy Rolstad
Avista System Planning
WECC PWSUG, 14 March 2012
We are going to discuss how a GE *.epc power flow case should be read into PWS, what to watch out for, how the results are the same, and why the results might be somewhat different. Both programs yield “correct” answers…any notable differences should certainly be examined with an eye towards modeling “error budget.”

2. Open Case, Select <GE EPC format (with options)>
Make use of the proper epc read form to understand what you are doing.

3. What Options (these are defaults)?
Matching up options…understand what ignoring the generators with less than 2 MVAr bandwidth does across the case. Is this really the right thing to do? Note that GE doesn’t enjoy very tight bandwidths whereas PWS will solve fine.

4. Start with GE Nothing is sacred about the GE defaults. Change them!
Solve the case, multiple times…
GE uses an estimated mismatch
So, solve in GE three times or so
Save the solved case as an *.epc file
If you have GE you should play around with the settings and see how GE does with different settings. Read how the recommended PARM settings are NOT the same as the WECC default solution settings. Note that at least the GE *.epc file tells you how a case was solved. The PTI *.raw format has no provision for that.

5. Read into PWS and Solve Read in case, note mismatches, understand them
Lock all controls down, solve in PWS (set gen voltage control)
Check Interface flows against GE…
GE allows double counting the same line
PWS does NOT allow double counting
Note Mismatch resolution in log
PWS Zero Impedance Line is very, very small
GE uses X= ( kV)
PWS uses X= ( kV)

6. Mismatch Table
Why are these mismatches there? What does this all mean? Guesses?

7. Mismatches in State Variable View
Note the lack of arrows in the state variable view…thoughts?

8. Mismatches in Input Data View
Try the input data view?

9. Bug or feature. When should software NOT do what you tell it
Bug or feature? When should software NOT do what you tell it? It is fair to assume that someone wanted to add the same line twice…but PWS doesn’t because we understand how WECC intends to represent the Path Rating Catalog. There is NO right way to implement the software, but there is certainly a right way to submit the data.

10. After Fixing GE Bface Error
Errors after removing extra BFACE entry
Total MW Error (i.e. sum) = -19.5
Max MW Error = 3.7 (North to South California, Path 24)
Min MW Error = -4
After fixing the error we get really about the same answer

11. Read the Log, Understand and Take Action
See the IID to SCE entry

12. Read into PWS and Solve Unlock all controls, solve in PWS
Check log for AGC movement
May need to “Zero out transactions”
If GE transaction table isn’t manually updated by WECC staff
Check Interface flows against GE…
Should get pretty much the same answer on path flows
Check for multiple islands

13. Zeroing Out Transactions

14. Voltage Control for Generators
Allocate across buses using the user-specified remote regulation percentages. This option is what is used by default and most closely matches the sharing seen in RAW files.
Allocate so all generators are at same relative point in their [min .. max] var range. This option most closely matches the sharing seen in a few EMS solutions PowerWorld has seen.
Allocate across buses using the SUM OF user-specified remote regulation percentages. This option most closely matches the sharing seen in EPC files.
Note: Generators at the same bus always allocate vars so they are at the same relative point in their [min…max] range

15. Var Sharing
Note what is going on here with the same setpoint. At the highside bus the Var injection is almost exactly the same

16. Comparing PWS to GE VAr “Answer”
Which method do YOU think is right.

17. Check Case Summary and Slack Bus Generator
Quantity GE
PWS
Load MW
Gen MW
Losses MW
6269.8
6263.5
Buses count
18205
18585
Load MVAr
(t_area)
Load MVAr*
Slack MW
538.0
543.01
The TABR report t_area seems to have a bug. Never trust summation tools in software without doing a basic check once in awhile.
* Summed directly from load record

18. Look for Places to Establish “Test Flows”
Cut and paste depiction of PWS flows on a GE scan diagram

19. Check Performance in Contingent Environment
GE pasted on a PWS diagram

20. Participation Factor Note (Added Post Meeting)
During the second WECC PWS Users Group we noticed that PWS was parsing the Gen MVA field of the *.epc file and setting Participation Factors on that field. In many cases this value is merely set to 100 MVA (for example the large units located in the third power house at Grand Coulee).
Users should be alert to this behavior and manually set Participation Factors to be based on Pmax
Typically setting Participation Factors to Pmax is the desired setting for dispatching make-up power during contingency analysis, etc.

21. Setting Participation Factors

22. Questions?
PWS will provide similar, but not exact results when compared to GE (or PTI)
Heuristics abound…
What is “right?” Good reason to use multiple tools
VAr dispatch of generation has an impact, especially on the initialization point for transient stability
Zero impedance line representations have some impact
Recommendation
Presume that both software provide reasonably accurate possible solution points
Take five minutes to understand the case read!!!
In general, going through this sort of procedure should let users verify that PWS and GE produce substantially the same results in Power Flow. Such an activity is being proposed as part of the certification process of software. Note that if you stress the case you are likely to seem MORE differences in the solved cases…

23. Dump truck providing smart grid to a home in Othello, WA…losses should be low if your alarm clock operates at 13.2 kV