2027 Event Agenda

CELESC (Centrais Elétricas de Santa Catarina S.A.) is the Brazilian electric power distribution utility responsible for serving almost the entire territory of the state of Santa Catarina, Brazil. It serves 3.5 million customer units and operates more than 200,000 distribution transformers. It has been awarded by ABRADEE as the best energy distributor in Brazil and is recognized as one of the top electric utilities in the country, notably achieving the shortest power restoration time in Brazil.

In Brazil, distribution networks are typically overhead, with only a limited number of underground systems implemented, generally restricted to portions of downtown areas in some cities.

At CELESC, in the state of Santa Catarina, until the year 2000, underground networks were limited to small portions of the urban centers of Florianópolis and Blumenau.

In recent years, this profile has changed. With real estate growth—especially in coastal regions—combined with the emergence of high-end developments and the desire to improve urban aesthetics, the demand for expansion and conversion to underground power networks has intensified.

Given the high cost difference of underground systems, which require imported equipment and connections for insulated cables, CELESC developed a simplified construction standard aimed at improving feasibility. This standard offers a more affordable cost structure, high reliability, and reduced technical barriers for expansion.

Beyond financial aspects, there were also significant challenges related to implementing underground networks in new regions. Regional teams lacked adequate training, and CELESC was not prepared with the necessary tools and equipment to scale this construction standard across the state. Because it was a technically new and unfamiliar approach for decentralized technical teams, there was resistance regarding the construction, implementation, and especially the operation and maintenance of underground networks in new areas.

To mitigate these barriers, CELESC designed its underground construction standard to be more user-friendly, often employing solutions analogous to overhead networks. This made it easier to train technical teams already accustomed to working with overhead systems.

Among the various measures implemented to overcome barriers and foster growth in underground networks, several initiatives stand out.

This standard uses aluminum cables in low-voltage circuits and applies H-type compression connectors insulated with heat-shrink sleeves, combined with low-voltage busbars designed for customer connections.

Unlike other utilities that use copper cables, aluminum cables reduce costs; however, they require additional care to prevent moisture ingress into the cables and connection materials.

In the event of faults, the use of H-type connectors prevents water penetration by capillarity within the cables, limiting potential damage and conductor degradation to only a few meters. Additionally, the method adopted for connecting the low-voltage main network to service lines was designed to be simple yet robust, capable of withstanding frequent handling during customer connections, public lighting connections, future maintenance, and even unintended access by unauthorized individuals in cable access chambers.

In Brazil, there are specific regulatory standards that establish special procedures when work must be performed at heights above 2 meters and when personnel need to enter restricted-access environments known as confined spaces. Therefore, large underground chambers with circular access covers require special procedures and dedicated equipment for safe work.

For this reason, CELESC’s construction standard was designed so that electricians never need to enter underground chambers to perform customer connections or disconnections, switching operations, or equipment inspections. Entry into confined spaces is only required in rare and extreme maintenance situations.

In addition to using compact chambers and pad-mounted transformers, a key feature is the installation of underground switching devices designed to be operated at ground level. This allows electricians to open, close, and ground circuits quickly and safely.

The design of the chambers housing these switching devices was specifically studied, resulting in a special technical arrangement in which the switch is positioned just below ground level. Small reduced-size covers allow operators access to handles, voltage indicators, and SF6 pressure gauges. In addition to these covers, a dedicated arrangement enables the installation and removal of the switch when exceptional maintenance is required.

A submersible design standard was adopted by CELESC for switching devices, as flood events occur frequently in the state of Santa Catarina, Brazil. Given the limitations of available urban space for positioning pad-mounted solutions, along with the risks of vehicle impact and debris collisions during flooding, the below-ground switch solution proved to be technically appropriate.

Typically, a switching device has multiple three-phase paths interconnecting feeders from various substations and multiple load circuits. As a result, the underground chamber that houses it contains a large number of cable connections and entry/exit points, making it a higher-risk environment for electricians if entry were required.

The advantage of this arrangement is that all switching operations can be performed quickly, without requiring special confined-space procedures, reducing operator exposure to risk. It also minimizes damage in the event of operational errors, such as incorrect feeder switching or improper grounding that could lead to an electric arc.

In addition to the technical advantages, considering the Brazilian context of technical and economic barriers to underground system expansion, this solution eliminated the need for fully motorized switching equipment, which would require very high investment due to the number of paths needed to interconnect feeders and loads.

As a result, the cost gap between overhead and underground networks has been reduced, technical barriers to expansion have been eliminated, and the feasibility of implementing underground networks across the state of Santa Catarina, Brazil, has significantly increased.

This set of actions—replicable in other utilities and countries—has accelerated the expansion and conversion to underground networks throughout the CELESC Distribuição service area.

Today, the main urban areas of the state of Santa Catarina already have more than 350 transformers and 260 km of medium-voltage underground networks in operation, delivering not only technical and operational benefits to the electrical system but also the urban improvements associated with underground network implementation.