Compensation and transient studies on a long EHV overhead line

Illustration with the AGADIR-LAAYOUNE 400kV overhead line project

Study background

Issue Very weak 225kV network

Long antenna (approx. 1200km) Low production Low loads Low short-circuit power

3

PE2 PE1

PE3

Technical solution Extension of the northern 400kV

network to the south Double circuit 400kV overhead line

between Agadir and Laâyoune

LAAYOUNE

Ait MELLOULIMI MKOURNETIZNITGUELMIME

TANTANPHOS .B

CHICHAOUA

AGADIR

ST

EP

A.M

OM

N

Oed TEIMA

Dakhla

Bou

jdou

r

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 Distorted voltage profile Temporary disturbances

Study:

Steady state analysis Transient overvoltage studies Transit capacity optimization

(series compensation)

Modelling

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°39: GUIDELINES FOR REPRESENTATION OF NETWORK ELEMENTS

WHEN CALCULATING TRANSIENTS

One schematic for all cases…

Future network development

Border of the circuit: Propagation # 1/f

For low frequency studies: Thevenin equivalent at 50 Hz

Completion with the southern 225kV grid

6

AGADIRLAAYOUNE

1

1 1

1

1

1

1

2

2

2

2

2

2

2

Components modelling (1)

Basics models, non frequency-dependent: R, L et C

Lines: FD model for temporal simulations PI-exact model for frequency scans

Generators:

+ +

+

ZnO

+

+

Geometrical data

Components modelling (2)

Transformers: standard low frequency model

Trans form er DataBCTRAN

Coupling considerations

Components modelling (3)

Specificity: auto-transformer

UHV – ULV

Winding 1 parameters

ZHV-LV

ULVULVUHV

Winding 2 parameters

LV parameters

HV parameters

2

LVHV

HVLV-HV U -U

U . Z

Validation by simulating the factory tests…

Modelling of magnetic saturation:

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

Shunt compensation

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

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

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

Transient studies

Temporary overvoltage

Load drop Windfarms power generation variation

Single phase fault

Three phase fault

16

overvoltage = 1.2 pu

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

Switching overvoltage (2)

18

Local loadsClosing time of the circuit breaker

One circuit of the 400kV line connectedOne autotransformer energization

Remanent flux

Transformer energization

Neutral grounding reactor

Closing time of the circuit breaker

Single phase faultSingle phase opening of the circuit breaker

Single phase reclosure of the breaker

Fault clearing

Surge arresters in the substationsInsertion resistors in the circuit breakers (R = 400 Ω, t = 10 ms)

Closing time of the circuit breaker

Single-phase fault3-phase opening of the circuit breakers (1 circuit)

3-phase reclosure of the breaker

Fault clearing

Mitigation means

Statistical parameter

ScenarioExamples of study cases

Series compensation

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

Impact of the localisation of the capacitors (1)

21

V1 V2

Vc

I

∆V

V1

V2I

Vc

0 5 10 15 20 25 30-800

-600

-400

-200

0

200

400

600

800

time (ms)

Vol

tage

V1V2VcI

line

Voltage profile along the 400 kV line

Impact of the localisation of the capacitors (2)

22

V1 V2

Vc

I

V1

V2

I Vc

∆V

0 5 10 15 20 25 30-600

-400

-200

0

200

400

600

time (ms)

Vol

tage

V1V2VcI

line

Voltage profile along the 400 kV line

Impact of the localisation of the capacitors (3)

0,75

0,80

0,85

0,90

0,95

1,00

1,05

-50 50 150 250 350 450 550 650

Distance (km)

Vo

ltag

e (p

u)

Compensation at LAAYOUNE Compensation at AGADIR

Compensation at 2 substations Compensation at 3 substations

Laâyoune Agadir

Voltage Low voltage if condensed

compensation Intermediary substation

slightly interesting

Transmitted power ~ no impact

Final compensation scheme: No intermediary

substation Capacitors balanced

between both the substations

Consequences on resonant phenomena

Y1

Y2

D = (Y1-Y2) / Y1

fR

D > 5%

(50-fR) = F0 ± 3 Hz

No impact on transient overvoltage studies

Further SSR studies needed

Impedance at Laâyoune 400 kV substation – transformers disconnected

Impedance at Laâyoune 225 kV substation

Impedance at Safi 400 kV substation

Conclusion

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?