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- 1. Compensation and transient studies on a long EHV overhead line Illustration with the AGADIR-LAAYOUNE 400kV overhead line project
- 2. Study background
- 3. Issue ■ Very weak 225kV network CHICHAOUA Long antenna (approx. 1200km) STEP A.MOMN PE3 AGADIR Low production LAAYOUNE Boujdour Low loads Low short-circuit power Oed TEIMA Dakhla PHOS .B GUELMIME TIZNIT IMI MKOURNE PE2 PE1 TANTAN Ait MELLOUL ■ Incoming generators in the southern part of the grid Winfarms (~ 800 MW) in the south Reversal of the usual power flow Heavy loaded 225 kV network Study: Distorted voltage profile Temporary disturbances ■ Steady state analysis ■ Transient overvoltage studies ■ Technical solution ■ Transit capacity optimization Extension of the northern 400kV (series compensation) network to the south Double circuit 400kV overhead line between Agadir and Laâyoune 3
- 4. Modelling
- 5. Many different phenomena ■ Different frequencies Power frequency (50 Hz) Low frequency (~ 500 Hz) Transient disturbances (~ 5 kHz) ■ Different simulation cases Load flow Temporal Frequency scan ■ References: Guide CEI 60071-4: Computational guide to insulation co-ordination and modelling of electrical networks Brochure CIGRE n° GUIDELINES FOR REPRESENTATION OF NETWORK ELEMENTS 39: WHEN CALCULATING TRANSIENTS
- 6. One schematic for all cases… 2 ■ Future network development ■ Border of the circuit: Propagation # 1/f 2 2 2 1 2 1 LAAYOUNE AGADIR 1 For low frequency studies: Thevenin equivalent at 50 Hz 1 1 2 1 1 6 ■ Completion with the southern 2 225kV grid
- 7. Components modelling (1) ■ Basics models, non frequency-dependent: R, L et C + + ZnO + + + ■ Lines: FD model for temporal simulations Geometrical PI-exact model for frequency scans data ■ Generators:
- 8. Components modelling (2) ■ Transformers: standard low frequency model Trans form er Data BCTRAN Coupling considerations
- 9. Components modelling (3) ■ Specificity: auto-transformer ■ Modelling of magnetic saturation: HV LV Winding 1 Winding 2 parameters parameters parameters parameters UHV ULV UHV – ULV ULV 2 ZHV-LV U HV Z HV - LV . U -U HV LV Validation by simulating the factory tests…
- 10. Validation of the model ■ Quite impossible to validate so complicated a network To many components Very simplified modelling Which data to compare to? ■ Load-flow simulations Compilation of the model No misconnections of the components Production / consumption configurations ■ Time domain simulations Compilation of the model Predicted behaviour
- 11. Shunt compensation
- 12. No-load compensation ■ Determination of the total reactive power needed Energization of the line (extremity disconnected): 800 Mvar needed ■ Which compensation scheme? Intermediary substations needed? Which repartition between substations? Reactors on the line or in the substation? Many steps needed? New specifications for reactors? Common mode? ■ 10 cases studied: 12
- 13. No-load compensation (2) ■ Observation of the voltage profile along the line Line connected at Agadir substation Line connected at Laâyoune substation Line connected to both substations 13
- 14. On-load compensation ■ Evolution of the compensation needs with the load Progressive increase of the generated power Adaptation of the compensation ■ Final compensation scheme: No intermediary substation Line reactors, all connected with circuit breaker =>new operation rules Minimal step = 40Mvar
- 15. Transient studies
- 16. Temporary overvoltage ■ Load drop ■ Windfarms power generation variation ■ Single phase fault overvoltage = 1.2 pu ■ Three phase fault 16
- 17. Switching overvoltage (1) ■ Frequency scan Different configurations • Substation analysed • Lines configuration • Compensation scheme Identification of potentially harmful situations ■ Statistical studies for each scenario Parameter variation • Apparition of the fault • Opening time of the circuit breakers • Closing time of the circuit breakers Maximum overvoltage ■ Statistical studies have no ending… 17
- 18. Switching overvoltage (2) Examples of Scenario Statistical Mitigation study cases parameter means ■Single-phase fault ■Closing time of the ■Surge arresters in the ■3-phase opening of circuit breaker substations Fault the circuit breakers (1 ■Insertion resistors in circuit) the circuit breakers clearing ■3-phase reclosure of (R = 400 Ω, t = 10 ms) the breaker ■Single phase fault ■Closing time of the ■Neutral grounding Fault ■Single phase opening of the circuit breaker circuit breaker reactor clearing ■Single phase reclosure of the breaker ■One circuit of the ■Closing time of the ■Local loads Transformer 400kV line connected ■One autotransformer circuit breaker energization energization ■Remanent flux 18
- 19. Series compensation
- 20. Series compensation ■ Why compensating? 225kV => stability constraint ■ What solutions? Series capacitors Phase shifting transformer FACTS (UPFC, …) ■ Method: Amount of compensation • Increase of the power generation • Stability limit in faulty conditions • Determination of the optimal compensation rate Objective: stability limit = thermal limit Compensation scheme 20
- 21. Impact of the localisation of the capacitors (1) Vc V2 I line I Vc V1 V1 V2 ∆V 800 V1 V2 600 Vc I Voltage profile along the 400 kV line 400 Voltage 200 0 -200 -400 -600 -800 0 5 10 15 20 25 30 time (ms) 21
- 22. Impact of the localisation of the capacitors (2) Vc V2 line I I Vc V1 V1 V2 ∆V 600 V1 V2 Vc 400 I Voltage profile along the 400 kV line 200 Voltage 0 -200 -400 -600 0 5 10 15 20 25 30 time (ms) 22
- 23. Impact of the localisation of the capacitors (3) 1,05 ■ Voltage 1,00 Low voltage if condensed 0,95 Voltage (pu) compensation 0,90 Intermediary substation 0,85 slightly interesting 0,80 0,75 ■ Transmitted power -50 Laâyoune 50 150 250 350 450 550 650 Agadir Distance (km) ~ no impact Compensation at LAAYOUNE Compensation at AGADIR Compensation at 2 substations Compensation at 3 substations ■ Final compensation scheme: No intermediary substation Capacitors balanced between both the substations
- 24. Consequences on resonant phenomena Impedance at Laâyoune 225 kV substation Impedance at Laâyoune 400 kV substation – transformers disconnected Y1 D = (Y1-Y2) / Y1 D > 5% (50-fR) = F0 ± 3 Hz Y2 fR Impedance at Safi 400 kV substation No impact on transient overvoltage studies Further SSR studies needed
- 25. Conclusion
- 26. Main points ■ Definition of the simulation schematic Which phenomenon? What level of detail? Validation? ■ Operation usages Simulation cases based on operation usages Operation usages adapted to simulation results ■ Parametric studies Prior work is important Which end criteria?

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