High Quality Product Development: A unique Ensto tension clamp up to 241 mm² medium voltage conductors

Satisfied R&D engineer Seppo Julkunen smiles contentedly and turns over in his hands a new and gleaming metallic SO257S tension clamp for large covered conductors with cross section up to 241 mm². The product has undergone a long product development testing process and is now ready to launch and will be a great complement to Ensto's range of Medium Voltage Covered Conductor (MV CC) overhead line products. But what kind of product development journey has this product meant for conductor terminals undergone? 

The development of a new product in the field of network construction is the result of long-term commitment from people and business. SO257S tension clamp has been redesigned many times by different groups and individuals, drawn, re-drawn, seen prototypes made and ended up being redesigned almost from scratch. Thus, hundreds of hours of labour and dozens of long-term tests run under laboratory conditions went into its creation.

Multi-disciplinary, reliable, strong and timely product development has always been the cornerstone of Ensto's success. Cooperation with our customers' experts is also very important. Ensto aims to design and manufacture high quality durable products that are easy to install and which withstand challenging conditions for several years. Since we are dealing with medium voltage lines and such demanding products as overhead lines, safety is paramount. Therefore, the design of the product has to have precise and individual details that must be perfected before the product can be placed on the market.

The SO257S tension clamp was developed primarily for the needs of Norway, Sweden and Russia, but target countries are found globally. In addition, the product is unique – it is designed up to 241 mm² cross section area and there is no corresponding tension clamp for MV CC lines found on the market. Now Ensto has a complete range of products up to 241 mm² because, simultaneously with the launch of the SO257S tension clamp, a SLW34 connector and the SO183S suspencion clamp are also being launched.


tension sketch

 The first designings of SO257S.


Strong product development knowledge

Before the actual product development of SO257S tension clamp, Product Manager Petteri Pulkkinen had already researched the market and its competitors, ascertained the technical requirements of the product and the general standards, i.e. the project’s specifications were defined. After the initial research, the rest of the product development team, Product Development Manager Timo Vikman, Product Development Engineer Seppo Julkunen, and Laboratory Engineer Ola Forsström joined to this development project.

A fun detail in the early stages of the design came when the tension clamp was christened Big Bell because the product is the big brother to the previously launched SO256S, called the Bell designed for smaller conductor wire up to 157 mm² cross section. The name comes from covered BLL medium voltage wire.

Thus, the product did not have to emerge from thin air as the existing tension clamp worked as a good base from which to start. In the beginning, the R&D team carefully examined the product concept and product requirements. Momentum was gained by further reshaping the existing product but real-life priorities and challenges were quickly met. Even after the first prototype and the short-term mechanical strength test, it was found that if the design of the product followed on the same path, it would become too long, too heavy and not strong enough. Thus, it was decided to seek other solutions while keeping usability and ease of installation constantly in mind.

The design was returned to a slightly earlier state and the product was ideated with a larger group which produced new perspectives and ideas that took flight; in such situations it is good to let the mind wander and break familiar patterns. Brainstorming of this type is important, especially when developing new products. In later development, it was noted that the strength was particularly affected by the screws that hold the device together and increase its durability. In the end, the finished product even could support a few cars.

– The tensile strength of the SO257S must be as strong as the conductor that is going to be terminated with it. Mathematical calculations are central to parts of the design as there are lots of variable parts, says Vikman.


Testing plays a major role

Testing is an integral part of the product development lifecycle. Up to half of the tension clamp’s product development time went on testing the product, involving dozens of different tests from pre-tests to test to attain EN standards to UV and corrosion tests. To conduct those tests, Ensto has its own international criteria fulfilling accredited laboratory in which it is possible to monitor testing moment by moment.

– It's essential for the product designers to be involved in product testing as cooperation with laboratory products testers is crucial. When testing, you gain new perspectives and see different properties for the product. Additionally, the laboratory's employees make useful comments and advise us on directions that support the product’s development. The product is tested until it is ready for the market,” states Julkunen.

According to the R&D team, the development project for the tension clamp was typical: starting from the initial idea, refinement to become a protype, testing, a refined prototype, pre-tests and components and the testing of the finished product. The first products will be installed in Sweden’s medium voltage network in autumn 2018.

– The development of new products is interesting, creative work. I'm especially fascinated by fashioning products by hand, fine-tuning prototypes and mathematical calculations. An important part of this is professional skills and communicative teams, emphasizes Julkunen.

Ensto Tension Clamp SO257S


In order to improve the reliability of electricity distribution, plastic covered overhead conductors without metal sheaths have been developed. User experience over many years has shown covered conductor system to be very functional and safe. Snow, ice and storms cause outages but faults have been significantly reduced. Ensto has been a leader for many years in the development and construction of MVCC products and now for larger conductors of 241 mm² there is a complete range of high quality products. All Ensto's medium voltage products have been tested and certified according to the demanding and comprehensive EN50397-2 standard.