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UL Announces New Safety Certification Program for Dry Type High-Voltage Transformer Insulation Systems from UL

February 14, 2018

New UL 1446A provides framework to evaluate, test and certify the electrical insulation systems thermal class rating for use in dry type transformers rated above 1kV

NORTHBROOK, Ill., Feb 14, 2018 — To benefit material suppliers, transformer manufacturers and end-users, 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.

Due to growing demand for electricity, energy efficiency requirements, and the replacement of old transformers, this industry is seeing an influx of new technologies and materials entering this critical global marketplace.  The newly issued UL 1446A Outline For Dry Type Transformer Insulation Systems Rated Above 1 kV 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."

These new requirements more effectively evaluate insulations 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.

UL is pleased to offer testing and certification services to insulating material suppliers and transformer manufacturers to these new requirements. Companies interested in submitting products to UL should contact Customer Service at 1-877-854-3577 or e-mail at

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