Users of insulation systems such as transformer manufacturers or electric motor manufacturers are very familiar with this UL standard. Historically, the standard is very old and has not changed significantly over the years. However, technical progress has now finally made a revision and update necessary. As a result, edition 7 has been available since November 11, 2016 with some new features and a number of adjustments.
In addition to the task of adapting to today's industrial conditions, the new edition of the standard should also be internationally harmonized. For this reason, all references to ASTM/IEEE standards, among others, have been removed. Instead, wherever possible, references have been made to the relevant IEC test standards.
UL 1446 is therefore a kind of umbrella standard that characterizes an electrical insulation system (EIS) with the help of tests from other standards.
Without going into the exact test procedures, here are the two main options: either completely new insulation systems can be specified in the full-time ageing test (project duration approx. 1 - 1.5 years; results in the temperature index TI of the EIS) or by comparison with a system already tested in the field (project duration 3-5 months; results in the relative temperature index RTI).
A significant change to UL 1446 is, among other things, the opening of the standard to higher operating voltages than the previous limit of 600 V/1000 V. UL 1446 can now also be used for voltages up to 15,000 V (e.g. ignition transformers, high insulation transformers).
The test procedures for assessing an insulation system in accordance with UL 1446 are described in IEC 61857, Part 1 and Part 2.
Another change is the reorganization of the order of the chapters. This should make it easier to read and assign the various components in an EIS. A new section added to the standard is a corss reference list between wires validated according to "American" standards and those according to IEC standards.
Another significant change is that a distinction is no longer made between major and minor parts. Instead, the products within an EIS are now considered according to their function: If they only have a mechanical reason for their presence in the electrical insulation system (e.g. support molded parts in oil transformers), they are referred to as NIM (None Insulation Material). If, on the other hand, they have a dielectric function, they are called EIM (Electrical Insulation Material).
Depending on the end application, it may be necessary to approve multiple electrical insulation systems, as a NIM cannot mutate into an EIM within an electrical insulation system. It is therefore worthwhile, based on the requirements for the insulation system in the specific end application, to compile its materials in an EIS to be tested (top down, not bottom up).
Electrical insulation systems for defined operating times (DTLA-EIS; Defined Life Thermal Aging)
To facilitate market access (after all, a complete new approval of an insulation system takes over a year), it is possible to define EIS for shortened operating times.
One example is an electric blender in a private household. The motor in such a blender is only in operation for a few hours a month, even when used intensively. To demand a standard service life of 20,000 hours for the electrical insulation system here is overshooting the mark.
For this reason, insulation systems for 1,500 h, 2,500 h, 4,000 h and 5,000 h can now be defined with shortened test times and simplified test procedures (IEC 61857.31; fewer samples, single or dual temperature measurement). In addition to the temperature class (RTI), these systems are also assigned a time class that describes the period of use.
UL 1446, Issue 7 - Everything New?