Distribution Programs

Overhead Networks

Overhead Electrical Network Protection · TECHNOLOGY IN SERVICE OF URBAN TREE MANAGEMENT

The commitment to environmental quality is the ruling principle of all Cemig’s activities. An audacious company directive, which includes expressive investments in the implementation of new distribution network technology, seeks to reduce the amount of tree pruning conducted.

Urban trees furnish increased comfort, dust and gas absorption, protection against the wind, a reduction in noise pollution and a healthier environment for the fauna.

Protected and Insulated Overhead Lines

Developed over 50 years ago, the conventional overhead networks (RDA) are characterized by its lack of sheathing. Due to their being unprotected against the elements, they present high rates of failure such as interruptions in energy output, caused by contact with tree branches, household appliance burnouts, disruptions in public lighting besides presenting risks to pedestrians and require excessive and dramatic pruning.

The solution pioneered by Cemig was to develop and implement, beginning in the 80s, new types of distribution networks such as: protected medium voltage overhead networks (RDP) and insulated low and medium tension overhead networks (RDI).

Through the pilot-projects conducted in the cities of Belo Horizonte, Governador Valadares, Divinópolis, Curvelo and Alfenas, Cemig was able to verify the cost/benefit ratio of these networks, and refine the project’s criteria for the construction, maintenance and operation while taking into consideration the experience garnered by North-American, Japanese and European projects.

Starting in 1998, Cemig began employing the RDP and the low voltage RDI networks as the Standard for urban supply to all the municipalities in the state, due to the excelling results obtained from the pilot-projects.

Technical Specifications

Protected Overhead Networks: featuring plastic spacers, installed every eight to ten meters, which function as conductor supports, creating a triangular configuration. A steel messenger cable sustains the spacers, absorbs all the mechanical force and subjects the conductors to less traction.

Despite featuring polyethylene sheathed aluminum conductors, RDPs must be regarded as bare lines for personnel safety as this kind of sheathing does not insulate the electric field, in spite of allowing occasional contact with tree branches and leaves, avoiding disruptions in the energy supply.

Therefore, the dramatic and sometimes unnecessary pruning may be replaced by simpler techniques such as the removal of those branches and leaves that are in physical contact with the network.

Insulated Overhead Networks: employed in those circumstances made necessary by the environment, that is, in densely forested areas where branches constantly make physical contact with the conductors.

This kind of network features three types of conductors: insulated, armored, and braided, all united around a supporting messenger cable. This system is fully insulated.

Results

Cemig has replaced 1,200 kilometers of bare network lines with protected lines. The reduction in the rate of energy supply interruptions, an increased level of personnel safety and the decrease in the frequency and intensity of pruning are just some of the advantages of these network lines. As for the insulated lines, they already account for 140 kilometers of the network.

Cemig has been implementing this transformation little by little, over its 28 thousand kilometers of primary circuits in need of being protected or replaced. This is, clearly, part of the great challenge faced by the company, which is to achieve international levels of quality in the supply of energy desired by companies in the electrical sector that seek to meet the needs of its customers and their communities.