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
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
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
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
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
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?
