High-voltage transformers and CE Code requirements • Code File, May 2019
May 10, 2019 - Rule 2-024 of the CE Code mandates that all equipment used within the scope of the Code must be approved. ‘Approved’ is a specifically defined term, requiring the certification of equipment to ensure it complies with the applicable recognized standard(s), as listed in Appendix A. One important aspect of approval requirements for equipment is correlation with the provisions of the CE Code. The approval requirement presents a challenge for high-voltage equipment that has no applicable certification standard.
For three-phase liquid-filled transformers, by way of example, there are engineering standards (i.e. CSA C2.1, Single-Phase and Three-Phase Liquid-Filled Distribution Transformers, and CSA C227.4, Three-Phase, Pad-Mounted Distribution Transformers with Separable Insulated High-Voltage Connectors) that can be used to build to their requirements, but there are no certification standards that include testing criteria for approval purposes.
While efforts are still underway by standards development organizations to develop such certification criteria, for now the authority-having jurisdiction (AHJ) can grant permission to use such equipment under the CE Code, which may come with certain conditions.
In the past, these transformers were mainly used by utilities and rarely installed under the scope of the CE Code. Today, however, they are becoming more common in customer-owned installations, so the lack of certification standards for approval is an ongoing issue.
When these transformers are installed under the scope of the CE Code, it is important to be aware of Section 36, which provides requirements for high-voltage installations. Specifically, based on Rules 36-208 and 36-214, any doors giving access to live parts containing fuses in the equipment shall be interlocked with an external means providing visible isolation of all ungrounded conductors (e.g. the load break switch). The doors cannot be opened until the means of visible isolation is locked open and cannot be closed until the doors are locked closed.
Transformer standards do not correlate with these requirements, since they are more geared toward utility-type installations. Therefore, when high-voltage liquid-filled transformers built to CSA C2.1 or CSA C227.4 are customer-owned and installed within the CE Code scope, additional requirements may be imposed by the AHJ.
The two main additional provisions are ensuring the compartment that provides access to fuses (a) does not contain consumer service conductors or other parts that remain energized when the main load break switch is in the open position and (b) is interlocked with the load break switch.
In fact, both standards for high-voltage liquid-filled transformers—the aforementioned CSA C2.1 and CSA C227.4—include a statement indicating “the operation of transformers complying with this standard by other than an electric utility may be subject to additional requirements by the electrical inspection AHJ.”
The rationale for this statement is the recognition that utility personnel are specially trained to work with high-voltage equipment differing from installations within the scope of the CE Code.
There are some transformers available that both (a) are built to the standards and (b) satisfy additional requirements to correlate with Section 36 of the CE Code, but it is important to understand high-voltage equipment built to engineering standards does not necessarily comply with the CE Code provisions.
This column originally appeared in the May 2019 issue of Electrical Business magazine.
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