The Finnish electricity distribution company ESE-Verkko constructed a 20 kV connection line between two substations to ensure electricity supply particularly in service and fault situations. The work was conducted using new innovations to the Covered Conductor (CC) system by Ensto, including composite insulators and robust crossarms.
People in Mikkeli can face the coming storms with peaceful minds, as there is a new medium voltage connection between the Siekkilä and Suojalampi substations serving the northern part of the city centre. It replaces the line that used to run by the roads and streets. This old line cannot be repositioned after modification work made to the routes.
For some part of the distance, the new line received lots of surrounding space, as it was run in the same line route with the 110 kV high voltage line. The aim was to improve the reliability of the critical medium voltage connection to the top level by using covered conductors and some of the latest accessories designed for them.
“Although positioning a part of the line in the same route with a larger power transmission line reduces the risk of a failure caused by falling trees, we also wanted to reduce interference caused by branches, for example”, says Mikko Romo, Network Service Engineer for ESE-Verkko Oy, responsible for planning and construction of the new distribution line.
Minimising the failures with right choices
Operating in the central district of Mikkeli, the distribution company builds new distribution lines for dozens of kilometers each year. When a bare conductor line is on the design board, using covered conductors is always considered because of their unbeatable properties. Choosing a covered conductor system with high-quality accessories is guaranteed to pay for itself in the form of fewer faults, lower maintenance costs, and higher-quality electricity. Romo continues that if the final choice will be covered conductor, it must be ensured that the heavy-duty wire is securely attached to the pole and that the consequences of a possible breakdown of the wire are minimized.
“Firm attachment of the covered conductor is extremely important because of their weight. We chose new and durable composite insulators in order to avoid failures due to vibration of the wire, for example. Using robust horizontal crossarms, we also ensure 100% mechanical strength. In addition, we chose a current-limiting protection instead of the traditional arc protection”.
The Field Manager for Empower PN Oy, Heikki Konttinen, responsible for implementation of the new line, says that construction of the line is completed, apart from final connections at the substations, and that the work will be completely finished during the summer of 2016. This is the first line in Finland implemented with the new CC accessories by Ensto. In addition to the composite line post insulators and crossarms, they include the CIL joints.
“The joints are based on a tested and functional concept; the peeled wire ends are taken inside the joint, where they are locked in place. After this, installation of the heat shrink shield is the only work phase left. Installation is easy and the end result is reliable”, Konttinen sums up.
New CIL joints are used to joint covered conductors. The package contains all the necessary items, that is, tension splice, heat shrink tube, abrasive band, peeling rope, and installation instructions. Using tension splices, the work runs smoothly, providing a reliable result, as the shape of the splices ensures a secure joint. The extension has a broad range of use, which reduces the number of the stock items.
Mechanical and electric durability
Ensto’s new SDI82, SDI83, and SDI84 composite line post insulators and composite tension insulator SDI 90 provide lightness and durability to the covered conductor world, realizing the concept of trouble-free distribution of electricity. They meet the requirements set for medium voltage lines, complying with IEC standards.
The surface of the insulators is of silicone, which provides an excellent dielectric strength and a long life cycle for the insulators even in extremely demanding conditions. The neck of the insulator is of insulating material, so that the electromagnetic field of the wire is not accumulated around the insulator. This helps to avoid the partial discharges that can be harmful for the wire covering.
The line post insulators are attached directly to the crossarm, using bolts included in the product package. The entity with its crossarms is designed in cooperation with energy companies to make the installation easier. The crossarms are delivered pre-assembled, almost complete and without any separate accessories.
The frame structures of the crossarms are made of high-quality rectangular and square tubular sections that help to make as light-weight and strong structures as possible. To ensure high corrosion resistance, all crossarms and crossarm accessories are hot-dip galvanized.
Product support reaches all the way to the site
The covered conductor wires were developed to improve the reliability of electricity supply and distribution of electricity. To realize this, high-quality accessories play a crucial role: designing them requires taking the electrical requirements, environmental conditions and easiness and safety of the installation into account. Ensto is committed to determined R&D with the aim of a reliable electricity network and network power quality.
Mikko Romo at ESE-Verkko praises Ensto, as product support is at a high level and personnel are always willing to solve problems. As an example, he highlights the product training Ensto gives from time to time in Mikkeli.
“Our installers are keen on the products, as, for instance, joints and terminations of the medium voltage cables do not include a high number of parts to install. Delivery always includes extensive instructions, and if any further training is needed, then it is arranged at the site, as necessary.”
For further information, please contact: www.ensto.fi
Petteri Pulkkinen, Manager, Overhead line solutions, petteri.pulkkinen@ensto.com
Jukka Kokkonen, Sales Manager, Finland, jukka.kokkonen@ensto.com