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