AISSA-Dakar-Nov2011

7/28/2019 AISSA-Dakar-Nov2011

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LOW COST TECHNIQUES IN RURALTUNISIA

Presented by

Moncef AISSASenior Electrical EngineerPrivate Consultant-Tunisia

Nov 14, 2011

AEI Practitioner WorkshopDakar 2011


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Situation before RE program -1975 Rural electrif ication rate: 6%

Overall electrif ication rate 35% MV grid length : 4000 km 3-phase 30 kV Rural population: 53%

The Government decided to

develop REINSTITUTIONAL APPROACH

Ministry of Economic Development

- Policy-planning-funding ofregional integrateddevelopment STEG (Public Uti lity)

- appointed as Operator


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STEG: STRATEGIC CHOICE

Rural area indicators:low income, demand,

density,

high cost

STEGundertooktech-econstudy / comparison

Main findings

GRID LEVEL SAVINGS

MV network 30 to 40 %

MV/LVsubstations 15 to 20 %

LV network 5 to 10 %

Overall 18 to 24 %

ADOPTION ofMALTtechnique in January 1976

from existent 30 kV voltage level


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Z

HV/MV Substationinverse time protection

Earthing coil

Groundedneutral

MV 4-Wire line

H TypeFusedcutout

T Type Fused cutout

1-phase MV line

1-ph. MV/LV transformer

LV 1-ph l ines

MALT

CONFIGURATION

protection

selectivity


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Characteristics of MALT system

148.1 mmAAACfor3-+N main lines (12 to 16.8 MW)

54.6 mmAAAC forrural 1-+N branch lines (2.6 MW) Inverse time protection- Selectivity of protection

Neutral conductor earthing every 300m

17.3 kV phase to neutral voltage

Lightning

arresterFused cutout


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Recent cost cuttings estimate (2001)

27% cost-cutting with suspension insulators

37% cost-cutting with pin insulator

Distribution of cost reductions in %

Main savings come from

Conductors 7%

Line accessories: 13%

Poles: 7%(suspension insulators) / 17%(Pin Insulators)

Single phase transformer: 44% for 25kVA


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Further cost reductions

26-30% additional cost reduction compared to

single-phase technique

1200km SWER lines-425 villages No need for isolating transformer installation

Additional Cost reduction

7-14% if houses are fairly dispersed 31-33 % if houses are widely dispersed

1.SWER technique

2. 4,16 kV single phase


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Non technical approach:

Continuous efforts to optimize costs

1. Early computerization2. Training3. Demand Forecasting

Network Planning

4. Inventory Managementsystem- Huge quantitypurchase (equipment)

5. Private enterprise:construction (Competition)

6. Private industry: grid

equipment supply(Competition)

7. Technical and nontechnical lossesmanagement

8. Operational rules andguidelines

9. Maintenance planning10.Hot line Works11.Customer Management


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Funding Households STEG Government through loans

Affordability

Easy terms for STEG consumers

Agriculture Bank- Loans to farmers

Sustainability: thru TARIFF STRUCTURE

Lifeline tarif f< 50 kWh/month (= 600 kWh / year /

Customer) Special tariffs for Rural development

irrigation, olive oil plant, milling/grinding

Socio-Economic Impact Education, health, security, economic opportunity


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Advantages of

Single Phase Technology

Cheaperthan 3-phase

Suited to rural areacharacteristics

Easy construction Easy operating

Reliable and secure

Numerousopportunities tocoordinate betweenprotection devices

Good quality service

Upgradeabil ity toduplex and triplex

Possibili ty to use 3-phaseconverter or 1-phase motor

High permissibleload flow (up to 2.6MW)

SWER extensionswithout isolatingtransformers


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Disadvantages of

Single Phase Technique

Adaptation ofexisting conventional3-phase network to MALT technique

power cuts (adding of neutral conductor)

fixing neutral on every pole keeping requested conductor clearance

for every span

Changing protection system

Extension upfront cost (4-wirebackbone lines +9%)

High losses level if high load flow


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-- OVERAL Electrification Rate 98.9%-- National Rural ER 97%

-- Minimum REGIONAL Rural ER 96.6%

NORTH WEST

96,6%

CENTER WEST

96,8%

NORTH EAST

97%

CENTER EAST

97,9%

GRAND TUNIS

97,5%

SOUTH WEST

96,3%

HAMMAMET

SFAX

SOUSSE

GABES

GAFSA

TATAOUINE

KEBILLI

SOUTH EAST

96,8%

BIZERTE

2004- RE rates

(after about 30 years of RE)

% of single-phase

lines and substations53% of overhead lines are single

phase type72% of public MV/LV substations

are single phase type


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Conclusion After 35 years using single phase

techniqueSTEG stil l believe they made agood technical choice

This choice was madeearly enoughtoallow maximum savings from usingMALT technique

What To Do Differently

More SWER lines / more 4.16 kV single phase lines

Use more pin insulators Fix neutral conductor at top of pole on main lines


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Some Recommendations

Start Single PhaseTechnique as soon aspossible

Adapt existentnetwork to MALTsystem

Fix neutral conductorat top of poles toprevent cable theft

Change protectionsystem to Inverse time

type Use single phase lines

for expandablenetwork

Use SWER or 4 kV

single phasetechnique for remoteareas

Use small singlephase transformers(1; 3; 5; 10; 15; 25; 50kVA)

Use conductors withsmall cross-section

Use ACSRconductors if terrainpermits long spans

Use pin insulator ifpossible


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stork nest

Documents

AISSA-Dakar-Nov2011