ESCOM :: Power Transmission

About Electricity

ELECTRIC POWER TRANSMISSION

Definition

Electric power transmission is one process in the transfer of electricity to customer. The term refers to the bulk transfer of electrical power from place to place. Typically, power transmission is between the generation plant and a substation near a populated area.

This is distinct from electricity distribution, which is concerned with the delivery from the substation to the customer. Due to the large amount of power involved, transmission normally takes place at high voltage (66kV , 132kV or above). Electricity is usually transmitted over long distance through overhead power transmission lines. Underground power transmission is used only in densely populated areas (such as large cities) because of the high cost of installation and maintenance; however ESCOM has no underground transmission installations yet.

Apart from conveying electricity to major centres of use, the transmission system also links separate generating stations to improve reliability and system security. In a liberalized market, the transmission system also provides independent power producers with access to the electricity market.

Therefore the transmission system is the backbone of the electricity supply industry. A strong transmission system supports consumer needs in terms of cost-effectiveness, security and reliability. ESCOM Transmission is putting a lot of effort in improving quality and reliability of electricity in the country despite the many challenges it is facing.

Overhead power transmission lines

Transmission Infrastructure

Transmission infrastructure includes high voltage power lines, power transformers and switchgear. Overhead transmission lines are not insulated; hence design of these lines requires minimum clearances to be observed to maintain safety. Engineers design transmission networks to transport the energy as efficiently as feasible, while at the same time taking into account economic factors, network safety and redundancy.

ESCOM has a transmission network comprising of 1250 km of wood pole lines and 815 km of steel tower lines. These lines transmit bulk power at 66000 volts and 132000 volts, and feed power to over 70 transformers which are located at 39 substations in the country. Power transformers step-up generation voltages of 11000 volts to 66000 or 132000 volts for transmission to major load centres where these voltages are then stepped down to 33000 and 11000 volts for distribution to customers. In future it is expected that a 220000 volts transmission line will link Malawi to Caborra Bassa in Mozambique thereby enabling the two countries’ power utilities to conduct power trading.

Challenges

Whenever transmission of power is interrupted due to a fault or shortage of capacity, many customers both domestic and industrial are affected. This is so because the transmission system transports bulk power from generation centres to major load centres for distribution.

Some of the challenges confronting ESCOM Transmission include:

How to deal with problems of termite attacks on wood structures, bush fires leading to burning of wood poles, vandalism on both wood and steel tower structures
Floods which erode tower foundations and bring the towers down, lightning strikes
How to maintain some of the transmission lines and transformers with minimum disturbance to customers. This is especially a problem for radial wood pole lines and load centres with only one transformer. Such cases include places like Nkhotakota, Chintheche and Mzuzu where customers have to be switched off to enable ESCOM engineers work safely on transmission equipment

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