Summary of unscheduled flow analysis
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Summary of Unscheduled Flow Analysis. Raj Hundal Dec 19, 2012. Summary of PWG results. PWG and WECC staff performed analysis on 30 events based on a snapshot in time and using the WECC Wide System model to determine effects of RBC on system flow by limiting BAs to L10.

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Summary of Unscheduled Flow Analysis

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Summary of unscheduled flow analysis

Summary of Unscheduled Flow Analysis

Raj Hundal

Dec 19, 2012


Summary of pwg results

Summary of PWG results

  • PWG and WECC staff performed analysis on 30 events based on a snapshot in time and using the WECC Wide System model to determine effects of RBC on system flow by limiting BAs to L10.

  • PWG Study Results showed that in 25/30 events (83.3 %) when BAs were within L10 the system flow was reduced by a total of 2034.8 MWh

  • PWG Study Results showed that in 5/30 events (16.7 %) when BAs were within L10 the system flow increased by a total of 209.1 MW

  • PWG Study Results showed that Overall system flow was reduced by 1825.7 MW if BAs operated within L10 during the 30 events

  • Powerex analyzed this study further against information provided by UFAS for the same 30 events, and using simple method determined that the relief required in webSAS would have decreased by approx.1258 MWh. Powerex understands that this is a simple linear projection and there could be a margin of error of approx. +/- 10 %.

  • On average for each event the relief requested would have been decremented by 57 %


Issues with pwg study

Issues with PWG Study

  • PWG members have expressed reservations of the study and its methodology:

    • The study is a snapshot in time but may not consider what has occurred prior to that minute or after that minute

    • The study does not always take the worst minute when the Actual Flow was impacting the path the most, so the MW flow reduction could be larger in 25/30 events.

    • The study does not analyze or count the number of times the RC has instructed individual BAs to bring ACE within L10, so the Actual MW flows could be larger prior to instruction to reduce.

  • Powerex understands the limitation of the study, but the study does provide an indication that significant portion of Unscheduled Flow is due to RBC and that portion could be in the range of 57 %.


Ufas methodology and analysis of ace contribution

UFAS Methodology and Analysis of ACE contribution

  • UFAS provided initial ACE Data and methodology to determine how the cumulative BA ACEs North of Path 66 and South of Path 66 would have an effect on unscheduled flows.

  • The methodology developed by UFAS stated that when the ACE North of Path 66 is greater than 0 and the South of Path 66 is less than 0, and the minimum value of the two could be considered the ACE contribution Southbound on Path 66

  • Powerex expanded upon this methodology by taking the ACE data from 30 events provided by WECC and re-calculating NO66 and SO66 ACE by moving ACE values beyond L10 back to L10 limit

  • Powerex continued to use the ACE contribution calculation developed by UFAS

  • Powerex calculated COI USFs using weighted-avg of TDFs for NO66 BAs, under both RBC and CPS2


Ufas methodology and analysis of ace contribution1

UFAS Methodology and Analysis of ACE contribution

  • Powerex then compared the worst-minute by event, for RBC and CPS2 independently, and showed the results in a summary sheet.

  • Powerex calculated the implied RBC contribution by determining the percentage between the ACE contribution under L10 and ACE contribution under RBC.

  • Powerex then calculated the average RBC contribution for all 30 events to determine the reduction in flow if L10 limit was applied under CPS2

  • Powerex notes that the ACE data as given by participating BAs has 7 BAs missing which can account for on average 20 % of the overall WECC ACE


Summary for 100 l10 case

Summary for 100% L10 Case


Further analysis of ace contribution

Further Analysis of ACE contribution

  • Most BAs operating under CPS2 requirements try to operate their ACE as close to 0 as possible with fluctuations occurring within the L10 dead band.

  • BAs do not intend to operate at or above the L10 limit due to the possibility of failing the overall CPS2 requirement for the month.

  • BAs do not operate in a relaxed state at the end of the month even if they have achieved a good CPS2 score for the month. It is not considered to be good utility practice to try to take advantage of the ten-minute average calculated score, and try to incur violations by exceeding L10 close to end of the month.

  • Powerex expanded its previous analysis to determine the possible RBC contribution levels if BAs operated under CPS2 and within a % limit of L10.

  • It stands to reason most BAs operating under CPS2 would have most ACE data points within the 0 – 75 % of L10 and would incur spikes in ACE that would reach the > 75 % of L10


Powerex findings

Powerex Findings

  • RBC contribution could be in the range of 46 – 57% or possibly higher depending on the methodology.

  • There is a direct correlation between ACE and Unscheduled Flow and higher ACE fluctuations will have an effect on Unscheduled Flow

  • The graphs highlight that for the 29 events that ACE under RBC has significantly more points that are above and beyond L10 limits.

  • Unscheduled Flow will decrease as a result of having more BAs operate their ACE as close to zero or within 25 – 50 % of the L10 limit.

  • ACE fluctuations are not100 % attributed to RBC, and those ACE fluctuations will incorporate generation trips or forced outages, as well as transmission outages effecting the system.

  • Powerex assumes that planned outages of generation and transmission would already be factored into ACE through BA NSI and path limits.

  • UFAS needs to determine if during those 29 events were there forced (not planned) outages (generation or transmission) that occurred and did they have any effect on ACE.


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