low cost techniques in rural tunisia
TRANSCRIPT
LOW COST TECHNIQUES IN RURAL
TUNISIA
Presented by
Moncef AISSA Senior Electrical Engineer Private Consultant-Tunisia
Nov 14, 2011
AEI Practitioner Workshop Dakar 2011
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
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
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
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
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
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
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
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
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
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
-- 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
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
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
stork nest