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New UL safety certification program for transformer insulation systems

February 16, 2018 | By Ellen Cools

February 16, 2018 — UL has launched a new safety certification program for dry type high-voltage transformer insulation systems. These insulation systems are used within the transformer for transmission and distribution of electricity across the power grid.

The newly issued UL 1446A Outline for Dry Type Transformer Insulation Systems Rated Above 1kV covers the test procedures used in the evaluation of Class 120(E) or higher rated electrical insulation systems (EIS) with operating voltages of 1kV and above for use in the following: open wound, cast coil, resin encapsulated and pre-preg flexible sheet rolled, dry-type high-voltage transformers where the thermal factor is the dominating aging factor and where transient over-voltages or partial discharge may be present.

“UL has been evaluating, testing and certifying electrical insulation systems used in magnetic devices, such as motors, transformers, generators and solenoids, for over 40 years,” said Mark W. Raymond, principal engineer with UL’s Performance Materials division. “With UL 1446A, we have expanded that knowledge to develop enhanced and more appropriate requirements specifically for the growing dry type transformer market segment.”

UL says these new requirements more effectively evaluate insulation systems by establishing a Voltage Stress Level (VSL) for the various insulation functions within the transformer, such as turn-to-turn, layer-to-layer, section-to-section, coil-to-coil and coil-to-ground. This allows transformer manufacturers and end-users to have a better understanding of the insulation systems’ thermal and voltage limits, allowing them to better design and specify electrical insulation systems for these products.


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