Low Cost Techniques in Rural Tunisia
Transcript of Low Cost Techniques in Rural Tunisia
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LOW COST TECHNIQUES IN RURAL
TUNISIA
Presented by
Moncef AISSA Senior Electrical Engineer Private Consultant-Tunisia
Nov 14, 2011
AEI Practitioner Workshop Dakar 2011
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Situation before RE program -1975
Rural electrification rate: 6% Overall electrification rate 35% MV grid length : 4000 km 3-phase 30 kV Rural population: 53%
• The Government decided to develop RE
INSTITUTIONAL APPROACH Ministry of Economic Development
- Policy-planning-funding of regional integrated development
STEG (Public Utility) - appointed as Operator
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STEG: STRATEGIC CHOICE
Rural area indicators: low income, demand,
density, high cost STEG undertook tech-econ
study / comparison
Main findings
GRID LEVEL SAVINGS
MV network 30 to 40 %
MV/LV substations 15 to 20 %
LV network 5 to 10 %
Overall 18 to 24 %
ADOPTION of MALT technique in January 1976 from existent 30 kV voltage level
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Z
HV/MV Substation inverse time protection
Earthing coil Grounded neutral
MV 4-Wire line
H Type Fused cutout
T Type Fused cutout
1-phase MV line
1-ph. MV/LV transformer
LV 1-ph lines
MALT CONFIGURATION
protection selectivity
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Characteristics of MALT system
148.1 mm² AAAC for 3-Φ+N main lines (12 to 16.8 MW)
54.6 mm² AAAC for rural 1-Φ+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 arrester Fused 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 25 kVA
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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 computerization 2. Training 3. Demand Forecasting –
Network Planning 4. Inventory Management
system- Huge quantity purchase (equipment)
5. Private enterprise: construction (Competition)
6. Private industry: grid equipment supply (Competition)
7. Technical and non technical losses management
8. Operational rules and guidelines
9. Maintenance planning 10.Hot line Works 11.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 tariff < 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
• Cheaper than 3-phase
• Suited to rural area characteristics
• Easy construction • Easy operating
• Reliable and secure
• Numerous opportunities to coordinate between protection devices
• Good quality service
• Upgradeability to duplex and triplex
• Possibility to use 3-phase converter or 1-phase motor
• High permissible load flow (up to 2.6 MW)
• SWER extensions without isolating transformers
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Disadvantages of Single Phase Technique
• Adaptation of existing conventional 3-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-wire backbone 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 WEST96,6%
CENTER WEST96,8%
NORTH EAST97%
CENTER EAST97,9%
GRAND TUNIS97,5%
SOUTH WEST96,3%
HAMMAMET
SFAX
SOUSSE
GABES
GAFSA
TATAOUINE
KEBILLI
SOUTH EAST96,8%
BIZERTE
2004- RE rates (after about 30 years of RE)
% of single-phase lines and substations
• 53% of overhead lines are single phase type
• 72% of public MV/LV substations are single phase type
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Conclusion • After 35 years using single phase
technique STEG still believe they made a good technical choice
• This choice was made early enough to allow maximum savings from using MALT 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 Phase
Technique as soon as possible
• Adapt existent network to MALT system
• Fix neutral conductor at top of poles to prevent cable theft
• Change protection system to Inverse time type
• Use single phase lines for expandable network
• Use SWER or 4 kV single phase technique for remote areas
• Use small single phase transformers (1; 3; 5; 10; 15; 25; 50 kVA)
• Use conductors with small cross-section
• Use ACSR conductors if terrain permits long spans
• Use pin insulator if possible
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stork nest