28 November 2019

Nomex® Edge Protection Rings

Geometrically Edge Protection Rings are characterized as Angle Rings, which protect the inner diameter of a winding, or as Caps to protect the outer diameter. The rings are specified using the following main dimensions; diameter, flange and collar, thickness and edge radius.

While the Angle Rings and Caps of the end insulation divide the respective oil gaps, the Edge Protection Rings reinforce the insulation of the conductor and are placed directly on its surface.

The ratio of dimensions is adjusted according to individual specification, however they are typically small collars and flanges with a sharp edge radius of 1 – 1.7 mm. Beyond the dimensional differences between Edge Protection Rings and “classical” Angle Rings and Caps of an end insulation, is the difference in thermal exposure. Placed directly on the hot conductor insulation, cooling occurs only from one side via the oil gap. Specifically, designs that assume higher temperatures can be challenging in the long term as they promote accelerated aging of the particular component.

Weidmann developed a new fabrication process that allows Edge Protection Rings to be manufactured out of Nomex®. Adjusted to the specified dimensions, it provides protection for that critical section of the transformer, close to possible hot-spots. Using Nomex® the risk of mechanical weakening of the particular part due to aging is eliminated. This meta-aramid based material is in the temperature class of 180°C.

According to the Weidmann E-catalogue article E2D55, the spectrum of dimensions that are offered in cellulose covers the same range as Edge Protection Rings.

Please do not hesitate to contact us for further information or advice.