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How to navigate transformer and power supply system standards

Ten answers that will help transformer and power supply manufacturers understand the requirements of IEC 61558-1.

transformer and power supply

February 22, 2019

Navigating global regulations is a challenge for any size company. UL is here to help you understand the complex compliance requirements for transformers and power supplies. We will help you prepare for accelerated market access for successful installations and increased profits.

Here are the top ten questions that will help transformer and power supply manufacturers understand the requirements of IEC 61558-1.

  1. What is/are the appropriate EN standard(s) that cover(s) transformers larger than 40 kVA?

    Power limitations described in the scope for all part 2s (i.e. IEC 61558-2-X) may be exceeded based on the agreement between the purchaser and the manufacturer.  This exception is referenced in the scopes of all part 2s. Depending on the type of transformer it could be IEC 60076-1, which covers power transformers greater than 1kVA single phase and 5kVA three phase.
  2. What is the difference between 61558-1, 62638, and 60950-1?

    IEC 60950-1 is applicable to products that are intended specifically for information technology equipment applications (i.e. datacenters, computer applications, etc.). IEC 60950-1 is being replaced with the standard for AUDIO/VIDEO, Information and Communication Technology Equipment, IEC 62368-1. IEC 61558 is for power supplies and transformers for general applications.
  3. What (if any) distinction is there between "functional earthing" and "earthing"?

    Functional Earthing is established only for the purpose of proper operation of the unit and to comply with EMC requirements. Functional earthing is never relied upon for protective earthing.  "Earthing" or "Protective Earthing" is a reliable bond between all accessible conductive parts of a CLASS I unit to earth.
  4. If a transformer has multiple secondary windings, some have the output voltage<50V and some have the output voltage>50V, then which standard under 61558 shall apply?

    If a unit has multiple aspects (e.g. windings, ratings, etc.), where multiple part 2s are exclusively applicable, then a MAIN test report will be issued in accordance with one of the part 2s.  The test report for the remaining applicable part 2s will be included as an enclosure to this MAIN test report.  All applicable standards will be referenced in the MAIN test report.
  5. Can a transformer certified to IEC under CCN XNXA be used in lieu of transformers certified under UL Standards?

    If the end-product UL Standard references IEC 61558, then this is allowed. Generally, most end-product UL Standards reference UL 5085 for transformers. Transformers evaluated to IEC 61558 cannot be used to represent UL 5085 and vice versa.
  6. When measuring working voltages, do you use an isolating scope so 60 Hz is not part of measurement?

    Yes, UL uses calibrated oscilloscopes rated for the proper bandwidth accompanied with appropriate impedances on measuring probes.
  7. I have not heard of accelerated aging test option for insulation systems. Can you talk about this option and how it works?  What standard is this method described in?

    Accelerated aging test is an end-product alternative to declaring an insulation system. The methods are explicitly described in sections 14.2 and 14.3 of IEC 61558-1.
  8. I thought SELV is below 60VDC, but you mentioned a few times that it was below 50VAC or 120VDC.  What is the correct maximum SELV voltage?

    Unlike Standard Class 2 parameters, different applications have different limitations and definitions for SELV.  SELV for IEC 61558 is 50 Vac, 120 Vdc.  SELV defined by other standards may be higher or lower.
  9. For a transformer using FIW, if the FIW wire vendor has met all the relevant IEC requirements for a particular product line of FIW wire, does this allow for certain IEC 61558 tests to be skipped when evaluating a transformer that uses that FIW in its construction? In other words, the FIW doesn't need to be re-evaluated within the transformer construction?

    All part 2s are evaluated together with part 1 (IEC 61558-1).  The 2005 version of IEC 61558-1 does not allow the use of FIW, except in the case for SMPS applications (i.e. specifically IEC 61558-2-16).  Sections 19.101 and 102 of IEC 61558-2-16 require FIW to comply with IEC 60851-5 and IEC 60317-0-7.  Nominal diameters and test voltages are defined in table 111 of IEC 61558-2-16.  If peak working voltage exceeds 750 Vpk, then a partial discharge test is additionally required as indicated in section 18.102 of IEC 61558-2-16.

    However, the new 2017 version of IEC 61558-1 does allow the use of FIW, whose requirements are similar to those mentioned in the above paragraph.
  10. I have manufacturing facilities in Europe and China; does UL have resources in these areas?

    UL has offices located all over the world to meet all your certification needs. We have four Notification Certification Bodies (NCB’s) and over 50 CB Test Laboratories (CBTL’s), several of which are located in Europe and China.