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2.9 ULTRA HIGH-VOLT

R

Wednesday, 14th Sep(11.00 - 12.45)Chm: Aki AmetaniRpt: Jinliang He

291 Availability of different transmission systems for long distanC. Neumann B. Rusek U. Sundermann T. Benz N. Christl

292 Experimental study on corona environment effects of 1000-transmission lines - J.L. He, J. Tang, B. Zhang, R. Zeng

293 Desi n stud for 1000 kV UVH-AC - Com osite insulatin st

J.M. Seifert, D. Stefanini, F. Lehretz294 Lightning strike characteristics of +/- 800-kV DC UHV transJ.L. He, R. Zeng

295 Considerations for the standardization of high-speed earthisecondary arc extinction on transmission lines - M. Toyoda, Y. Y

R. Jaenicke, H. Heiermeier, A. Lathouwers, K. Edwards, I.M. Kim

Marquezin, M. Kosa a a



q ,

Availability of different long distance

transmission systems

C. Neumann, B. Rusek, U. Sundermann, Amprion, Germany

T. Benz, ABB, Germany

N. Christl, Siemens, Germany



Availability of long distance transmission systems| CIGRE Bologna 20112

Content

1 Introduction

2 Considered long distance transmission systems

3 Definitions

4 Approach to define the availability of components

Extra high voltage equipment

Transformers

LCC & VSC & SLC

Overhead lines

Cables

5 Results

6 Conclusions

Availability of long distance transmission systems| CIGRE C4 Bologna 20112



Considered transmission systems (500km, 3GW)


D e s c r i p t i o n (AC1a) (AC1b) (AC2) (DC1) (DC2a) (DC2b) (DC2c)

AC

2x380-

kV D

AC 2x380-

kV D with

SC

AC 1x750-kV

F* 2T

HVDC LCC

1Bx500-kV

D*

HVDC VSC 3Bx320-kV

cable

HVDC VSC 2x500-

kV D*

HVDC VSC

1x500-kV D*

P o

w e r

3600 3600 4000 4000 3000 3600 2720

X L P E c a b l e s

O H L

O H L + S e r i e s

c o m p e n s a t i o n

O H L

O H L

O H L

O H L



Definitions

Unavailability derived from forced energy unavailability FEU

If no exact data are available

Thereby :

MDT - mean down time

MTBF – Mean time between failures

λ – failure rate




Availability of EHV equipment

Reliability of the EHV equipment

the worst failure rate value from the past CIGRE surveys and Amprion

database.

The assessment of outage time due to failure

according Amprion service experience

The unavailability is strongly affected by minor failures.


17%

33%

20%

13%17% Circuit-breaker

instrumment transformer

pantograph disconnector

center-break disconnector

earthing switch

Forced EnergyUnavailability

of a 380-kV-bay

1,4 hour / year



Availability of transformers

Data source

different CIGRE Surveys and Amprion experience

Reliability LCC Transformers MTBF = 50 years per unit

VSC (AC) Transformers MTBF = 100 years per unit

Mean Down Time Time to replace a transformer = 48 hours


FEU of transformer

0.48 … 0.96 hour / year



Availability of VSC and LCC poles and SC

Power electronics

MTBF = 5 years / pole

MDT = 7 hours


FEU of power electronics

1.4 hour / year

Share in unavailability for typical LCC and VSC 1-pole stations



Availability of

overhead lines


Interpretation of FNN dataoutages due to galloping conductors

probable less probable

(included) (excluded)

FEU of OHL

3.1 hour / year

Typical towersin FNN

DC towers

Data source FNN - German Forumfor Network technology and Network

operation

90% of single mode failures

fault clearing with auto reclosing

similar behaviour of DC systems

10% of common mode failures

fault end-ups usually with an outage

(except galloping conductors)

MTBF 3.86 years / 100 cct. km

MDT 12h



Availability of DC cables

No data for on-land DC XLPE

Use of data for AC XLPE (CIGRE, TB 379)

λ adjustments: AC 3 phases DC 2 poles

J oint every 0.8 km per cable 2.5 joints per cct. km

MTBF = 8.06 year / 100 cct. km

MDT = 120 h (4 - 5 days) !!


FEU of DC cable

14.8 hours / year



Forced energy unavailability – comparison of

different long distance transmission systems


0,0

0,2

0,4

0,6

0,8

1,0

1,2

(AC1a) (AC1b) (AC2) (DC2b) (DC2c) (DC2a) (DC1)

F o r

c e d E n e r g y U n a v a i l a b i l i t y % Transmission lines (OHL/cables)

EHV switchyard

UHV switchyard

Transformer

Converter stations (VSC,LCC, SLC)

73%

27%

82%

8%

19%

10%

52%

9%

20%

8%

58%

34%

11%

41%

48%

28%

42%

30%

12%

88%

2,5 2.48



Conclusions

Comparable forced energy unavailability of AC & DCsystems with overhead lines⇒ 1.7 - 3.3 days/year

Availability of the transmission lines is crucial

Slightly worse availability of VSC systems caused by higher

number of components and some power restrictions

VSC option using cables as transmission system is stronglyaffected by the presumed availability of the XLPE cables

Since many new LCC and VSC systems are going to beinstalled, the service performance should thoroughly beobserved




DESIGN STUDY FOR 1000/1200 kV

UHV-AC COMPOSITE INSULATOR STRINGDr. J. M. Seifert; Ing. D. Stefanini

Ing. Fabian Lehretz



„Technology Survey“

Transmission Distance in km

C a p a c i t y i n

G W

0.01

0.1

1

10

100

0.001

1 10 100 1000 10000

UHV

1200kV

HVDC

765kV

400/500kV

Subtransmission

„Smartgrids“HVDC - Smart



Tab. 1: Insulation coordination for 1000/1200 kV

Composite Insulator - 1100kV



Tab. 2: Maximum electrical design field stresses at the composite insulator

Location Evaluation Criterion (EPRI)

Insulator

shank

Path length on which Etg > 4.2

kV/cm shorter than 10 mm

Triple point Etg

< 3.5 kV/cm

Composite Insulator - 1100kV Field Control



Fig. 3: Tangential Field distribution along the insulator axis and field plot of HV region



0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 10 20 30 40 50 60 70 80 90 100

ATH content (by weight)

P e r f o r

m a n c e

HTM

Tracking & Erosion Resistance

Outdoor performance

p.u.

%

HTV - Composite Insulator - Pollution Performance



0

20

40

60

80

100

120

140

0 4 8 12 16

Transfer Time

S t a t i c C o n

t a c t A n g l e

RTV-2

RTV-1

HTV-Gen III/IV

HTV-Gen II

HTV-Gen I

LSR

Generation III/IV HTV-

PDMS² / ATH filled

°

d

HTV Composite Insulator - Pollution Performance

RODURFLEX®



Pollution Severity: 2% ESDD Level (mg/cm²)

0,001 0,01 0,1 1

I n s u l a t i o n L e n g t h ( m )

11,0

10,5

10,0

9,5

9,0

8,5

8,0

7,5

7,0

6,5

6,0

5,5

5,0

4,5

U n i f i e d S p e c i f i c C r e e p a g e D i s t a n c e ( m m / k V i n s u l a t o r )

56

54

52

50

48

46

44

42

40

38

36

34

32

30

28

26

2422

Fig. 6: Insulation Length in m and USCD in mm/kV in dependence on ESDD 2% site pollution.

The IST sensitivity analysis in Fig. 3 for the “study” insulator will result in a 2%-ESDD pollution performance of 0.22 mg/cm² (“heavy pollution”). More performancecan be reached if more underrib sheds will be added (up to CF of 4.0). At samelength 2%-ESDD of 0.6…0.8 mg/cm² can be achieved with silicone rubberinsulators of this design.

Very Light Light Medium Heavy Very Heavy

IEC 60815

0,22 mg/cm²



600 / 800 kV HVDC

533 kV 600 kV 800 kV

Glass / Porcelain 9.8m 12.6m 15.1m

Silicone Rubber Composite

6.4m 7.3m 9.6m

Required Insulation Length:

HEAVY (IEC 60815): ESDD=0.1mg/cm² - NSDD=0.3mg/cm²



2011 BOLOGNA SYMPOSIUMThe Electric Power S stem of the F

Integrating Supergrids

and

Microg

13‐15 September 2011, Bologna, Ita

Lightning Strike

Characteristic

800‐kV DC UHV Transmission

Jinliang He and

R.

Zeng

g o age esearc ns



2. Fractal Model

Lightning current magnitude Q=f(I m ),

charges are assumed uniformly distributedin the fractal channels

without with fractal channels

6 2/3

16.5 10I

6 2 / 3

43 10 I

Upward leader inception

Local field criterion

enera groun e o ec :

Transmission line:

mc

/03.013000 r m E c “Hot‐spot” concept

Hot‐spots distribute every several meters

along the

line

edges,

corners

and

tips

of the tower



4. Application in +/‐800kV DC UHV

Distribution of the initiating point and falling point

EGM and LPM develop vertically or near vertically, this property leads to

But the fractal model has scattered distribution of the initiating point and

leader. This

means

downward

leader

initiating

from

far

place

can

still

hav



4. Application in +/‐800kV DC UHV

Shielding failure is most probable to occur in middle part of transmiss

Our statistical results lead to the ratio between numbers of shieldin fof (+) and (‐) conductors (~8:1), very close to the operation data (8~10:1)lines of China Southern Power Grid

+/ ‐800kV DC line



Cigrè International Symposium



P-2

HSESs (HSGSs)

HSES for 550kV system in BPA

13-15 September 2011 – Bologna (Italy)



Cigrè International Symposium13-15 September 2011 – Bologna (Italy)



P-6

Direct lightning strokes to phase lines

Direct lightning stroke to the

upper phase line

Direct lightning stroke to the

middle phase line and flashover



P-13

Comparison between four-legged reactor and HSES four-legged reactor HSES

Secondaryarcextinction

- Effective for single-phase fault that

hold the majority of the faults.- Difficult to choose a reactance value

of reactors that effectively reducethe secondary arc current for allfault modes.

- Quick extinction for all fault modes.

Flexibility to

the changeof network

- In case a substation is constructed inthe middle of a line, it might be

required to substitute a reactor thathas already installed.

- Not affect on the substation

equipment that has alreadyinstalled.

Control/Protection

- Special control is unnecessary for secondary arc extinction.

- Automatic sequential control such as“fault detection CB open HSES close HSES open CBclose” is necessary in each phase,and it can be easily realized.

Economy- Four-legged shunt reactor is appropriate for transmission lines which require

shunt reactors for voltage control, while HSES would be economical for thelines without shunt reactors.

Concern

- Detailed analysis is necessary so asnot to cause resonance betweenshunt reactor inductance and linecapacitance not only in power frequency of 50/60Hz but also inthe high frequency band.

- Highly reliable control system isrequired since a mal-function leadsto a ground fault.

C l i




P-14

Conclusion

★ PT48 in IEC SC17A works for HSES standardizationfrom 2009-1

• Effect of system parameters to the interrupting duties isstudied and ５ categories are introduced as interruptingduties

• Contacting with CIGRE WG A3.22 and A3.28

★ Principal topics discussed in this paper are…;

• coordination with CB re-closing systems

• timing coordination of HSES operation with CBs’

• consideration for successive fault on transmission line



1

Considerations and Recommendations

for the Specification of UHV Substation Equipment

CIGRE Symposium in Bologna, 13-14 September 2011

Hiroki Ito, Mitsubishi Electr ic

Anton Janssen, Liander Denis Dufournet, Alstom Grid

Yoshibumi Yamagata, TEPCO

Scope: Review the state-of-the-art of project specific and national technicalspecifications for all substation equipment within the scope of CIGRE Study Committee

A3 at voltages exceeding 800 kV.

Recommend future specifications and standardizations of 1100 kV and 1200 kV

equipment and provide technical backgrounds on the collected information to IEC TC17.

On behalf of CIGRE WG A3.22 / A3.28

Uwe Riechert, ABB

Paulo Fernandez, EletrobrasMasayuki Kosakada, Toshiba

David Peelo, Consultant



DC time constants in fault currents



5

Tower and conductor designs

Calculations predict a large DC time constants in fault current in UHV transmission systems due

to usage of multi sub-conductor bundles and the existence of large capacity power transformers.

16.5m

16m

15.5m

19m

7 2 . 5 m

9 0 m

1 0 7 . 5 m

1 2 0 m

810mm sq. -8 conductors

1100kV transmission lines

2 7 . 4 m 4

0 . 3 m

15.24m

42.7m



3 5 ( 5 4 . 5

) m

2 2 . 6

( 4 2 . 1

) m

12m 12m

20.12m



Influences of the high DC component on test-duty T100a does not show any signi ficant

difference when the constant exceeds around 120ms. Therefore, it was recommended to

use a time constant of 120 ms for rated voltages higher than 800 kV.

ConductorsHighest voltage(kV)

Size(mm2 ) Bundle

DC timeconstants(ms )

800Canada 686 4 75

800USA 572 6 89800

South Africa 428 6 67

800Brazil 603 4 88800

China 400 6 751200

Russia 400 8 911050Italy 520 1001100Japan 810 150

1100China 500 120

8

8

81200India 774 1008

5

UHV TRV requirements



6

Voltage

Uc

ti0

Ui

t2 Timet1

U1U1: First reference voltage= 0.75 x Kppx Ur 2/3

U1/ t1: Rate of rise of TRV

Uc/ t2

U1 / t1

RRRV

TRV peak

ITRV

t2 : time to TRV peak

Uc: TRV peak = Kpp x Kaf x Ur 2/3

t2 = 4 x t1for T100, t2 = 6 x t1 for T60

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (μs)

U ( k V )

T60, kpp=1.2, kaf =1.5, t2=3xt1

T100, kpp=1.2, kaf =1.5, t2=3xt1

T60, kpp=1.2, kaf =1.5, t2=4.5xt1

T100, kpp=1.3, kaf =1.4, t2=4xt1

T60, kpp=1.3, kaf =1.5, t2=6xt1

T60, kpp=1.2, kaf =1.5, t2=6xt1

TRV for T100 and T60 with Ur=1100 kV

q

1.2 (1.3)T100 1617

TLF

Out-of-phase

UHV

DUTY

T60

T30T10

First-pole-to-clear factor

Kpp

2.0

1.2 (1.3)

1.2 (1.3)

1.2 (1.3)

1.2 (1.5)

Amp lit udefactor

Kaf

1.5 (1.4)

1.5

1.541.76

0.9*1.7

1.25

1100 kV

TRV peak (kV)

1617

16601897

1649

2245

1764

1200 kV

TRV peak (kV)

1764

18112076

1799

2450

Rate of Rise of TRV

RRRV (kV/µs)

2

3

57

(*)

Time to TRV peak

t2

3.0*t1 (4*t1)

4.5*t1 (6*t1)

Time to TRV peak

t3

t3 (t3)

t3 (t3)

(*)

Values ( ) are standards for 800 kV and below.

1.38*t1 (2*t1)

t1 and t3 are based on Kpp=1.2

(*) : RRRV= Uc / t3 with t3 =6 * Ur / I 0.21 shown in the ANSI C37.06.1-2000 for t ransfo rmers up to 550 kV

For UHV transformers, RRRV and t3 are determined by the transformer impedance and its equivalent surgecapacitance (specified as 9 nF)

Effect of MOSA on TRV waveforms



7

0 4Time (ms)

1 52 3

Uc=1635kV (Kpp=1.3, Kaf=1.4)

0

500

V

o l t a g e ( k V )

1000

1500

2000 T60, Breaking current : 26.2kA

TRV for T60 with twic e TRV peak value of existi ng 550kV standard

Without MOSA

With MOSA (A type characteristic)

With MOSA (B type characteristic)

Uc=1751kV (Kpp=1.3, Kaf=1.5)

0 4Time (ms)

1 52 30

500

V

o l t a g e ( k V )

1000

1500

2000 T100, Breaking current : 33.8kA

TRV for T100 with twic e TRV peak value of existin g 550kV standards

Without MOSA

With MOSA (A type characteristic)

With MOSA (B type characteristic)

TRVpeak=1586kV

TRVpeak=1411kV

Uc=1635kV (Kpp=1.3, Kaf=1.4)TRVpeak=1502kV

TRVpeak=1380kV

The clipping or suppression level of 1400 kV would lead to a specified TRV level of

1617 kV considering a certain margin between the circui t-breaker performances and the

MOSA protection levels. This recommendation corresponds to the inherent peak value

for T100 and close to the inherent peak value for T60. 7



Publications of CIGRE WG A3.22



10

2007

Technical paper presented at IEC-CIGRE UHV symposium in Beijing

2-4-1 “ Technical requirements for UHV substation equipments”

2008

First Technical Brochure published in December

TB 362 “ Technical requirements for substation equipments exceeding 800 kV”

CIGRE Session paper presented at 2008 CIGRE session in Paris

A3-211 “ Technical requirements for UHV substation equipments”

2009

Technical paper presented at IEC-CIGRE UHV symposium in New Delhi

3-1 “System impacts on UHV substation equipment”

4-1 “CIGRE state of the art & prospects for equipment”

2011Second Technical Brochure publ ished in April

TB456 “Background of technical specifications of substation equipment exceeding 800 kV”

Technical paper presented at 2011 SC A3 col loquium in Vienna

A3-101 Background informat ion & study results for specifications of UHV substation equipment

> WG A3.28 will cont inue the studies on UHV / EHV switching equipment



Cigrè International Symposium Bologna 13-15 Sept. 2011



Presentation Outline

• Introduction

• The Sardinian Power System

• Power Generation and Load Demand in Sardinia

• Renewable Energy Sources integration in Sardinia

• Scenarios in 2020 and 2030

• Results

• Remarks

Bologna 14 Sept. 2011 - Session 2.9 Ultra High Voltage2




The Sardinian AC Grid

±500 kV HVDC

200 kV HVDC

220 kV AC

380 kV AC

380 kV AC Transmission Lines [km]

Total 304,9

220 kV AC Transmission

Lines

[km]

Total 1335,1

150 kV AC Transmission [km]

Total 2064,6

Bologna 14 Sept. 2011 - Session 2.9 Ultra High Voltage

380 kV EHV transmission network

from North to South of Sardinia

connects the two areas with the

biggest power plants.

A shorter 380 kV EHV line connects

the two HVDC stations.

3




500 kV, 1000 MW HVDC (SAPEI)

• Connection from Sardinia to the mainland.• Two HVDC converter stations (Fiume

Santo, Latina).

• The HVDC system is a bipole of 1.000 MW.

• Each pole has a capacity of 500MW at ±500kV with 1.000 A as nominal current.

• The DC cable is laid beneath the Tyrrhenian

Sea at depths of up to 1,600 meters.

Sardinian DC Grid 200 kV, 300 MW HVDC (SACOI)

Currently the SA.CO.I. is under scheduling arevamp to increase reliability and power

capacity

Bologna 14 Sept. 2011 - Session 2.9 Ultra High Voltage4




The energy production in Sardinia on 2008 was dominated by thermal plants

which covers 72% of the total Sardinian electricity generation


2008 vs 2010 Power Generation Capacity

The expansion of RES power plants installed in Sardinia, especially wind

and PV power, has reduced the share of traditional power plants

12.46%

74.59%

0.41%

12.11% 0.42%

Hydro

Thermoelectric

Photovoltaic

Wind

Biomass

10.21

%

71.94

%

2.23%

13.99

%

1.63%

5




In the last 5 years there has

been a great increase of wind

power production that will be

doubled in the next ten

years (1750 MW on 2020).

A fast growth of the PV

integration in the power systems with reference to the

number of power plants and

power capacity


Renewable Power Generation in Sardinia

The orography and

hydrography of the Sardinian

territory do not allow large

hydro generation capacity.

Distribution of wind capacity

6


2008 L d D d d L ti



•Strong increasing of load in

summer

Agricolture Industry Tertiary Residential Total

Zone GWh GWh GWh GWh GWh

SS 38,6 683 449 458 1.629

Ca 37,4 2.593 927 775,6 4.333

CI 11,7 3.187,9 135,2 172 3.506

OT 11,4 128,9 351,1 289,4 780,7

NU 24,6 289,1 183,9 190,2 687,7

OR 61,7 103,4 178,7 194,4 538,2

VS 18,8 71,6 100,5 111,1 302

OG 7,2 29,6 60,9 60,5 158,2Tot 211,2 7.086,2 2.386,4 2.251,4 11.935


2008 Load Demand and Location

• One third of demand is concentrated in

the south

•Load is widespread with very low density7





Seasonal Daily Load Profile

0

400

800

1200

1600

2000

0 2 4 6 8 10 12 14 16 18 20 22

D a i l y l o a

d [ M W ]

16/04/2008 30/07/2008 15/10/2008 02/12/2008

Hour

The 2008 peak demand in Sardinia was 1825 MW registered in August

due to the high use of air conditioners

• Maximum peak load appears around 8-9 p.m. during summer

• Minimum valley load around 3-4 a.m. during winter

• Average summer peak and winter valley load data were chosen to create

worst conditions for grid operation with high RES shares.8




G id E i i 2030




1) HVDC monopolar connection to the

mainland (SA.CO.I) is put back intoservice with the same capacity of the

existing one (300 MW);

2) Upgrades of the existing 150 kV low

capacity lines in the North-West of Sardinia;

3) Refurbishment of the old 70 kV lines in

the middle of the island with 150 kV new

lines;

4) A possible new monopolar 500 MW/500

kV HVDC link between Algeria and

Sardinia to import “green” energy from

North Africa

Grid Expansion in 2030

10





Load Forecast

- PEAK LOAD

- VALLEY LOAD

2008-2020 + 1,5%

2020-2030 + 1%

2020-2030 + 1%+ 0,9%2008-2020

The PV generators reduce the energy demand from power supply, the

overall yearly power supply and the number of possible congestions

caused by excessive demand11




Methodology

The AC power flow studies have been performed using a Newton-

Raphson iterative method to characterize the steady state operation.

RES production has been dispatched with the highest priority

The dispatching of the thermal generation units has been scaled

down in accordance with their technical constraints (e.g. minimum

power production).

For the inflow of energy from Algeria two alternative assumptions:

The CSP power has always higher dispatch priority versus Sardinian

wind production: the export capacity of the Sardinian grid is practically

halved

The Sardinian wind production has higher dispatch priority versus the

Algerian power import. In this case, it has been assumed that the

import from the Algerian CSP power plants could be curtailed in order

to allow full wind production.13


R lt ( i 2020)



0

2

4

6

8

10

12

14

16

1 2 3 4 5 6 7 8

≥ 70% ≥ 80% ≥ 90% ≥ 100%

SCENARIOS


Results (scenario 2020)

CASE STUDIES

1 Peak Load-Wind 50%- SAR.CO. 50%-NO PV



4 Peak Load-Wind 90%- SAR.CO. 100%-PV

5 Peak Load-Wind 90%- SAR.CO. 100%-PV & CHP

6 Valley Load-Wind 50%- SAR.CO.100%-NO PV

7 Valley Load-Wind 90%- SAR.CO.100%-NO PV

8 Valley Load-Wind 89%- SAR.CO.100%-NO PV & CHP

Number of branches within each congestion level

Scenario with the greatest

losses:

SAR.CO. exploited up to 100% 90% wind generation

No reduction given by the PV

generation

Scenario with the smallest

losses valley load scenarios in the

same conditions.

The increased power

production causes a greater

exploitation of the 380 kV networkand HVDC connections.

The 150 and 220 kV network is

less used with a reduction of

power flows on those lines14




R lt (S i 2030)




Results (Scenario 2030)CASE STUDIES

1

Peak Load-Wind 90% - SAR.CO.0% - NO PV-Algeria

100%2 Peak Load-Wind 90% - SAR.CO.0% - PV - Algeria 47%

3Peak Load-Wind 90% - SAR.CO.0% - PV - CHP -

Algeria 6.5%

4 Peak Load-Wind 90% - SAR.CO.100% - Algeria 60%

5Peak Load-Wind 90% - SAR.CO.100% - CHP-Algeria

40%

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5

≥ 70% ≥ 80% ≥ 90% ≥ 100%

SCENARIOS

Number of branches within each congestion level

The SA.PE.I. HVDC link

capacity available to export the

Sardinian RES power generationhas been reduced, causing the

RES generation curtailment.

The SA.CO.I. revamping

increases the export capacity to

the mainland.

The scenario with the largest

losses:

maximum wind generation

utmost import from Algeria

The balance between the

power locally produced and the

local consumption allows not

exceeding the rated capacity of

the lines 16





Remarks (scenario 2030)

The HVDC connection with Algeria will significantly impact theSardinian power system with possible curtailment of the power

generation:

The generation of the conventional thermoelectric power plants

should be reduced to preserve the wind production at the evening

peak load.

Storage devices and electric vehicles are necessary to preserve

adequate reserve margin and comply with technical constraints of

thermal generation when PV generation is maxima.

At off-peak hours, the wind production has to be limited (80%) if

Algerian power gets dispatch priority. On the contrary, if the

Sardinian RES generation gets highest dispatch priority, the HVDCconnection with Algeria will be used at 60% of its capacity.

The 150 kV network is the most critical asset of the Sardinia

transmission grid.

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18Bologna 14 Sept. 2011 - Session 2.9 Ultra High Voltage

Question I

According the analysis of the paper, in order not to curtail the

wind production during the evening peak load, it is necessary to

limit the maximum generation level of the conventional

thermoelectric power plants (around 50% of the nominalinstalled capacity). What’s the suitable ratio between RES and

thermoelectric power?





Answer I

- The suitable ratio between RES and thermoelectric power is the one

expected for 2020:

1000 / 3358 ≈ 30%

because a greater increase of wind generation, such as those planned for

2030, requires generation curtailment.

- The dramatic increasing of PV (250 MW already installed, 400 MW

expected by 2013) will probably cause wind and thermal generation

curtailment in summer windy days





Question II

The author has been demonstrated with the study that the 150

kV network is the most critical asset of the Sardinia

transmission grid where the majority of wind farms are

connected particularly in the north-east part of the island.

Connecting the wind farms to higher voltage systems such as220 kV or 380 kV networks can alleviate network congestions,

but at very high costs for power producers and system

stakeholders. What’s the best high voltage grade for the

network with RES？


A II



21

0

1

2

3

4

5

6

7

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≥ 70% ≥ 80% ≥ 90% ≥ 100%

150 kV Voltage Level 220 kV voltage Level


Answer IINumber of branches within each congestion level

By moving wind farms to 220 kVlevel:

- A drastic reduction of congestions;

- An improvement of active power

losses (37,13 MW versus 34 MW)

The best high voltage grade for the network with RES is 220 kV level, because:

- The 380 kV network is poorly developed and the connection costs are too

high;

- the 220 kV level is the best compromise between cost and reliability of the

connection





Question III

Large RES generation facilities are far from the main urban

consumption areas, long distance power transmission

infrastructures are required, an increase in active losses takes

place and some additional difficulties in local voltage controlmay also arise. How do the renewable energy sources affect

the structure of power transmission network? And How does the

power transmission network affect the application of RES?


A III




Answer III

The structure of the transmission network of the future is affected by a high

penetration level of RES and it will be necessary a re-sizing of some

connections in order to export the RES energy to the north and then to the

mainland.

The power system affects the application of RES introducing some limits to

the distributed generation connection to the grid mainly due to the fact that

the grid has not been constituted to receive high level of RES




THANK YOU FOR YOUR KIND ATTENTION

29 Ultra High Voltage

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