Observations from Avista Short Circuit Analysis WECC Short Circuit Workgroup January 2018 Tracy Rolstad

Transcription

1 Observations from Avista Short Circuit Analysis WECC Short Circuit Workgroup January 2018 Tracy Rolstad

2 The Driver (TPL-001, R2.3) With apologies to Protection folks this is all about a Planner s perspective. And from a single utility! But to be clear Protection is the ultimate authority. Avista Planners talk to Avista Protection folks ALL THE TIME

3 Fundamental Point FERC told us to study and document short circuit analysis Why? They believed that we (Transmission Owners) had over-dutied circuit breakers in-service They were correct! We continue to be poor advocates for ourselves My take Do not fear doing more studies (full employment!) Software is more willing than we seem to be Submit the data please Data needs are modest

4 Some Observations (TPL-001-4, R2.3) Avista Discovery (oil filled breakers get rid of them) Six 230 kv breakers that are over Two 115 kv breakers that are over Actions Others Short circuit analysis are now done routinely We now spec a 253 kv class breaker for 230 kv (Type F ) Breakers are not that expensive ($109K) Foreign utility results indicate others need breaker replacements (some vocal critics had issues) FERC & NERC were right!

5 SCWG Endstate Is this just to check breaker duties? The existing WECC tools are likely adequate Talking powerflow here We can do better on the data Subtransient reactances and mutuals Do we want a single data source for coordination? Tools are up to the job (communicate our needs) Data grooming might be needed Match powerflow bus nomenclature (WECC and/or WSM) We already do this in the Northwest btw

6 Challenge the SCWG statement The software is quite capable But mapping the few to the many is fraught with peril We can easily perform short circuit duty analysis using the present WECC data formats Just need to submit mutual and check for subtransient data submissions These should come with gen testing

7 If you will indulge me What are we talking about? The ability to interrupt and extinguish the arc

8 The Basic Approach Identify the data needs Topology Buses, stations, lines, transformers, breakers, impedances, mutual coupling, etc Hmmm, this data ALL fits in our power flow software Identify the desired outcome Apply most conservative test and measure breaker fault interrupting capability against results 3 phase bus faults deemed most conservative (yes?) Document the results, replace breakers ASAP, and feed the TPL beast

9 Assumptions The short-circuit current occurs simultaneously on all three phases (no arc resistance). During the short circuit, the number of phases involved does not change, i.e. a three-phase fault remains three-phase. During the short circuit, the voltages responsible for the flow of the current and the short-circuit impedance do not change significantly. All WECC generation is statused on MW output=0 for units whose status was changed from OFF to ON.

10 Avista Data Stream Same data Planning & Protection Impedances System Data Book (test reports, etc single source) Basic Topology (same bus numbers mostly) Substation level is ok Different data Planning & Protection Protection adds buses for their own purposes These appear to be driven by software limitations Software seems to be undergoing upgrades Protection likes to equivalence at the seams With modern hardware is this even needed?

11 Existing Fault Duty Data Capabilities epc file Has everything we need for 3 phase bus faults What data might be submitted Seq file Gen record: Zgenr, Zgenx, Mbase If you have huge short circuit currents R & X are likely missing This appears to be THE place for short circuit data What data might be submitted Gen record: Zgenr, Zgenx, Mbase Clobbers power flow data Branch data Transformers, mutual, etc

12 Data Needs Subtransient reactances WECC data submission (*.epc/*.seq/*.dyd) has this In maybe three places Power flow Sequence data Transient stability Various impedances Generally power flow and sequence data Mutuals Transformers

13 PowerWorld Environment Loading sequence data, IF it is available

14 But, No *.seq data is available So just run it using the power flow data No R might want that X is submitted

15 Branch Data (just positive sequence)

16 Choose a Method (PowerWorld)

17 Various Options

18 Avista: ASPEN vs Powerworld (6 over) Circuit Breaker Rated Maximum Voltage (kv) Circuit Breaker Interrupt Capacity (ka) Aspen Short Circuit Phase Current (ka) PowerWorld Short Circuit Phase Current (ka) Flat voltages (solved voltages) % delta (14.02) -2.3% (-2.03%) (14.02) -2.3% (-2.03%) (14.02) -2.3% (-2.03%) (14.02) -2.3% (-2.03%) (14.02) -2.3% (-2.03%) (14.02) -2.3% (-2.03%) (18.79) -9.3% (-7.07%) (18.79) -9.3% (-7.07%) Powerflow programs can do short circuit fault duty. The entire fault study took 2 minutes to perform.

19 Conclusions and Questions Avista performed short circuit fault duty analysis Using ASPEN and PowerWorld for 3 phase bus faults Source data is conceptually the same ASPEN is equivalenced (unknown WECC case origin) PowerWorld is a full WECC case Missing some subtransient reactances No mutuals, no xfmer data NO seq data We found over dutied breakers replacement program is an ASAP program (50% complete) A power flow program is adequate? Yes?

20 Discussion Items Why not submit *.seq data? Missing subtransient reactances are easily found Monster short circuit values Do we need a modeling bus feature? An object that can be reduced by software to show a real vs modeling needs system Fault duty and coordination are not the same thing The topology features are the same The data used might not be