Wilmarth-Lakefield 345 kV Line Series Compensation
Study Summary
Presentation to Northern MAPP Sub-regional Planning
Group
October 27, 2004
Warren Hess
Excel Engineering, Inc.
www.exceleng.net
Outline
 Project Background & Goals
 Conditions Studied & Models employed
 Technical Considerations
 Study Results
 Conclusions & Recommendations
Project Background & Goals
 Wind generation additions in Southwest MN & gas
generation in SE South Dakota (Buffalo Ridge area
& Anson) have “flowgate problems” on “Ft Cal S”
& “Cooper S” interfaces (PTDFs exceed 5%)
 November 2001 Buffalo Ridge outlet report
identified need for flowgate mitigation
 Recent Midwest ISO Transmission Service Request
studies identified a few new constraints on
neighboring systems due to other projects -- such as
wind development in Iowa.
 Series compensation of Lakefield 345 kV line was
one possible solution
 Wind in SW MN: problem after addition of Split
Rock-Nobles-Lakefield Junction 345 kV line
 Anson: problem before and after Split RockLakefield Junction 345 kV line
 Proposed solution: series compensation!
 Task: determine amount & location of series comp.
Conditions Studied & Models employed
 Year 2006 and 2008 Summer
 Peak and off-peak load
 Powerflow cases derived from 2001 Series 2007
model
Generation additions represented
 Buffalo Ridge 425/825 MW
 Wilmarth 667 MW
 Lakefield 100 MW
 Faribault 300 MW
 Anson 232 + 170 MW
Contingencies:
 NSP, Alliant-W, WAPA, GRE, SMMPA, MEC
areas
 all 115 kV & above
 n-1 & multiple circuits over 1 mile
Monitored:
 NSP, Alliant-W, WAPA, GRE, SMMPA, MEC
areas
 all 69V & above
Technical Considerations
 PTDFs
 Line & transformer loadings (system intact & postcontingency)
 Voltage profiles
 Arrestor (MOV) energies
 Fault levels
 Losses
 Dynamic Stability
Study Results (1)
 PTDFs: need at least 40% comp to achieve <5% on
Ft Cal & Cooper
Anson Distribution Factors
Year 2008 Summer, Off-Peak Load,
9%
8%
Distribution Factor (%)
7%
6%
5%
4%
3%
Cooper S (PTDF)
Ft Cal S (PTDF)
2%
Spencer-Triboji (OTDF)
1%
0%
0
0.1
0.2
0.3
0.4
0.5
Series Comp Level
 Spencer-Triboji OTDF goes up!
0.6
0.7
0.8
Line & transformer loadings
 Only “new” overload is Lakefield JunctionLakefield 345 (rating is 574 MVA)
 Some existing overloads eliminated or alleviated
(e.g. Marshall-Lyon Co 115 kV)
 Wilmarth area 69 kV loadings increase
Study Results
 Voltage profiles not limiting consideration, but midline is best
 Series comp reduces system losses, increases NSP
losses
Fault levels increase slightly
 13% at Wilmarth 345 kV
 5% at Wilmarth 115
 1% at Wilmarth 69
 8% at Lakefield Junction 345
Dynamic Stability


Generally, imperceptible change
Slight improvement (0 – 2%) for EI2 & NBZ
voltages
 Lakefield wind farm may trip for Wilmarth area
faults
Recommended Plan (Preliminary)
 Series Comp Amount: 60% (20.0 Ohms)
 Location: mid-line (based on MOV energy, not V
profile)
 Protection: bypass breaker & MOV (approx 42 MJ)
Resultant Anson PTDFs, % (2008 off-peak)
before after
Ft Cal S
8.3
2.5
Cooper S
5.8
2.7
 Spencer-Triboji OTDF: Anson to use tripping
scheme for outage of Lakefield Junction-Raun 345
kV
Next Steps
 Confirm results on Midwest ISO TSR model
(facility study).
 Investigate cost.
 Finalize plans and make decision.