2013 Issue 2—Form meets function for comfort, aesthetics and safety

DuPont™ Zytel® flame retardant nylon matches demanding solar switch requirements

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Image: Courtesy of ABB
OTDC switch disconnectors for 16 to 32 amperes have various DC voltage ratings with the same footprint area. The application benefits from DuPont™ Zytel® FR performance in CTI, ductility and easy processing.


In the power generation industry direct current (DC) rated switches—even those used for solar power—can experience extremely high voltage levels, up to 1,000 volts. For this reason the switch bodies must deploy materials that offer the correct mix of functional attributes to help ensure correct operation and arc containment.

To address these demands, ABB, a leader in power and automation technologies, has turned to DuPont™ Zytel® FR nylon for the casings of a new range of DC rated switch disconnectors.


As well as its good functional features with regards to its impact resistance and strength, ABB chose Zytel® FR because it also provides a relevant Comparative Tracking Index (CTI), a measurement used industry-wide to measure the electrical breakdown (tracking) properties of an insulating material.


The ABB devices—called ‘OTDC 16 … 32’—have been designed to suit the specific demands of photovoltaic applications, which include the significant arcing generated by high-voltage DC switching. The CTI value of the housing material has to be significant, especially in these small switches, where there is not much space to create buffer zones. Therefore, Zytel® FR has to stand up to extremely high instantaneous temperatures in the event that electrical arcing occurs.


"DC is more difficult and challenging than AC," explains Oskari Uitto, product manager, breakers and switches, ABB Oy, Finland. "AC fluctuates and DC doesn't, so there are no natural zero points; as a result, the breaking features have to be more powerful than an AC switch.”


"Arcing concerns us," he said. "With DC there is always arcing when you break a load. This means that any material used in the switch's construction has to be able to withstand the extremely high instantaneous temperatures.”


"We had to take a very hard look at the materials out there," Uitto explains, "due to the high CTI values we needed. In this case we had to see what we wanted and balance it against what was available. We have manufactured switches for a very long time. We know the materials and the ones we typically use, and we really had to dig deep in the design of this switch range due to the required CTI value and the small space we had available."


With its UL rating, weld ability, excellent flow and proven mechanical properties, Zytel® also offers cost savings against thermoset alternatives or high temperature thermoplastics. Zytel® combines good mechanical properties, such as flexural strength and elongation, together with superior electrical properties such as CTI and RTI, which has been put to use in a huge range of applications across the globe and it has undergone significant development by scientists at DuPont in order to create grades tailored to specific applications. Sustainability is also a high priority and DuPont has addressed industry needs with the development of non-halogen and renewably sourced variants.


ABB has developed a whole range of products dedicated to photovoltaic applications and is able to meet all installation requirements, from the strings on the DC side to the AC grid connection point. Its product range includes circuit breakers, switch disconnectors, fuse disconnectors and fuses, residual current circuit breakers, grid-connection relays, metering devices, surge arresters, consumer units and enclosures suitable for outdoor installation, all specially designed for these applications.