JRC2018-6247
TRANSIENT STABILITY OF ROTARY FREQUENCY CONVERTER FED LOW FREQUENCY RAILWAY GRIDS: THE IMPACT OF DIFFERENT GRID IMPEDANCES AND DIFFERENT CONVERTER STATION CONFIGURATIONS. John Laury, Lars Abrahamsson, and Math Bollen Electric Power Engineering Luleå University of Technology Campus Skellefteå, Sweden Joint Rail Conference - April 18 - 20, 2018 Pittsburgh, PA
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TRANSIENT STABILITY OF ROTARY FREQUENCY CONVERTER FED LOW FREQUENCY RAILWAY GRIDS THE IMPACT OF DIFFERENT GRID IMPEDANCES AND DIFFERENT CONVERTER STATION CONFIGURATIONS 2
Outline • • • • • • • •
Background Motivation Briefly about the model Cases studied Results Conclusions Discussion End
(1) (1) (3) (5) (13) (6) (4) (1) 3
Background • Low frequency AC synchronous railways • SFCs and RFCs – different transient behaviors • More interactions, lower impedances between stations – BT to AT – High voltage low frequency AC transmission – More and geographically closer converter stations
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Motivation • No previous studies mixed RFC feeding – Large disturbance, transient stability – Synchronous low frequency AC railways
• Practical, models more canonical than SFC • Besides current limitation – some resemblance
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Briefly about the model (1/3) • RFCs – Anderson-Fouad 5th order synchronous machine models – Motor and generator sharing the shaft – Assumptions: • Ignore saliency (makes 6th order 5th) 𝑔𝑔
𝑔𝑔
𝑚𝑚 – For Swedish RFCs: 𝑋𝑋𝑋𝑋𝑞𝑞 ≈ 𝑋𝑋𝑋𝑋𝑑𝑑 , but 𝑋𝑋𝑋𝑋𝑚𝑚 𝑞𝑞 ≠ 𝑋𝑋𝑋𝑋𝑑𝑑
– Might overestimate stability on motor side
• Identical excitation systems (lack of data)
–… 6
Briefly about the model (2/3) • RFCs –… – Strong feeding three-phase grid • Ignore 50 Hz-side AVR
– Magnetic saturation neglected
• Phasor models, quasi steady-state • …
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Briefly about the model (3/3) • … • Loads/load-flow – Pre-fault conditions: 𝑃𝑃 + 𝑗𝑗𝑗𝑗 (normal load-flow) – During/after transient: impedance (linear loadflow). Consequences: • Post-fault load might differ from pre-fault • System less prone reaching transfer limit
– Positions fixed – short time frames studied • 200 km/h => 389 m in 7 s 8
Cases studied (1/5) • Q38/Q39: 4 MVA (upgrades exist, not here) • Q48/Q49: 10 MVA
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Cases studied (2/5) km = 0.2 + 𝑗𝑗𝑗.2 Ω/km • BT: 𝑍𝑍BT • AT: init = 0.189 + 𝑗𝑗𝑗.293 Ω – 𝑍𝑍AT km = 0.0335 + 𝑗𝑗𝑗.031 Ω/km – 𝑍𝑍AT
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Cases studied (3/5) km = 0.2 + 𝑗𝑗𝑗.2 Ω/km • BT: 𝑍𝑍BT • AT: init = 0.189 + 𝑗𝑗𝑗.293 Ω – 𝑍𝑍AT km = 0.0335 + 𝑗𝑗𝑗.031 Ω/km – 𝑍𝑍AT
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Cases studied (4/5) • 60 km between converter stations • Trains: – 𝑆𝑆𝐷𝐷1 = 5 + 𝑗𝑗𝑗 sin acos 0.8 , – 𝑆𝑆𝐷𝐷2 = 10 + 𝑗𝑗𝑗,
15 km/45 km 30 km/30 km
• Fault
– Applied after 1.8 s –…
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Cases studied (5/5) • Fault –… – Cleared: • by disconnecting the 15 km section • after 0.2 s
– Train 1 becomes electrically closer to station 2
• 𝑆𝑆𝑏𝑏 = 10 MVA • 𝑈𝑈𝑏𝑏 = 16.5 kV
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Results (1/13), Case 1 Case 1, BT, Voltage
Case 1, BT, Power (station)
Results (2/13), Case 1 Case 1, AT, Voltage
Case 1, AT, Power (station)
Results (3/13), Case 1 Case 1, BT, Rotor speed
Case 1, AT, Rotor speed
Results (4/13), Case 2 Case 2, BT, Voltage
Case 2, BT, Power (station)
Results (5/13), Case 2 Case 2, AT, Voltage
Case 2, AT, Power (station)
Results (6/13), Case 2 Case 2, BT, Rotor speed
Case 2, AT, Rotor speed
Results (7/13), Case 3 Case 3, BT, Voltage
Case 3, BT, Power (station)
Results (8/13), Case 3 Case 3, AT, Voltage
Case 3, AT, Power (station)
Results (9/13), Case 3 Case 3, BT, Rotor speed
Case 3, AT, Rotor speed
Results (10/13), Case 3 Case 3, BT, Power (machine)
Case 3, AT, Power (machine)
Results (11/13), Case 4 Case 4, BT, Voltage
Case 4, BT, Power (station)
Results (12/13), Case 4 Case 4, AT, Voltage
Case 4, AT, Power (station)
Results (13/13), Case 4 Case 4, BT, Rotor speed
Case 4, AT, Rotor speed
Conclusions (1/6) • Oscillations increase, AT • Voltage drops during fault deeper, AT • Sharing: – Voltage overshoots are shared, AT – Active power loads are shared, AT
• Never forget: 𝑆𝑆 = 𝑈𝑈𝐼𝐼;̅
– excitation system impact on power – power impact on voltage
• …
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Conclusions (2/6) • … • Load, larger impedance share, AT • Oscillation frequencies, AT – 2.32 Hz for Q38/Q39 – 2.54-2.57 Hz for Q48/Q49 – 2.45 Hz equal mixes (cases 3 & 4)
• Oscillation frequencies, BT, unclear pattern • … 28
Conclusions (3/6) • … • Rotor speed: – Seems correlated with 𝑃𝑃𝐺𝐺 , not totally – Less synchronized between stations, AT • Almost opposite phase
– Mixed stations • BT: similar type swing together initially • AT: unorganized; stations slightly more together
• … 29
Conclusions (4/6) • … • Mixed stations and active power: – BT: • Machine types synchronized • Stations (or different machines) opposite phase
–…
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Conclusions (5/6) • Mixed stations and active power: –… – AT: • Machine types – Synchronized during fault – Opposite phase over time after clearing
• Within station: same as above
• …
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Conclusions (6/6) • … • Active power of stations opposite phase
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Discussion (1/4) • Future work – Other ways reasons for lowered impedances • More converter stations • Multiple tracks, meshing • Transmission lines
– AVR modeling • Different for different machines? • DC and AC brushless field machines
–… 33
Discussion (2/4) • Future work –… – Load modeling improvement – Eigenvalue analysis for deeper understanding – PSS? (rumors of some experiments)
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Discussion (3/4) • Space and information overflow – Currents, angles and reactive powers missing
• Observations: – Rotor speed double frequency components • Most pronounced: AT case 3 – also AT case 1, BT case 4
• How to interpret?
–…
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Discussion (4/4) • Observations: –… – Case 4 – rotor speed • BT synchronized – exception 2.5 s – 5.5 s • AT: – – – – – –
Station 1 peaking at 2.5 s Station 2 second peak at 3.5 s During fault – station 1 peculiar After clearing – opposite phase – station 1 faster At 3.0 s – opposite phase – station 2 faster At 4.0 s – a similar shift again 36
End • Please, – ask questions, or – discuss afterwards!
• Interested in possible similarities NE corridor! • Contact: – me:
[email protected] – corresponding author:
[email protected]
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