Distribution transformers for Mexico

Medium and low voltage in CFE specifications

13.2 kV, 23 kV and 33 kV (the 34.5 kV class) are therefore the three levels in CFE’s specifications; the exact nominal values are the ones in the table. Three-phase low voltage is 220Y/127 V.

Construction details CFE asks for

• Altitude: pole-mounted and submersible units are specified for a minimum of 2300 m. State the altitude of your site — it affects insulation and cooling.
• Pole-mounted three-phase units: delta primary, star secondary. Submersible units: grounded star on both sides.
• Temperature rise: 65 °C average winding rise for pole-mounted units.
• CFE recommends 15, 30, 45 and 75 kVA for three-phase pole-mounted units; submersible units are 75, 112.5, 150 and 225 kVA.
• CFE applies NOM-002-SEDE/ENER-2014 to the efficiency of the units it buys.

NOM-002-SEDE/ENER-2014: scope

The standard applies to domestic and imported distribution transformers of the pole, substation, pad-mounted and submersible types, self-cooled in insulating liquid, destined for the end consumer, when sold in Mexico. It defines a distribution transformer as 10 to 500 kVA with up to 34 500 V on the primary and up to 15 000 V on the secondary: single-phase 10–167 kVA, three-phase 15–500 kVA, in three insulation classes (BIL up to 95 kV, 150 kV and 200 kV). The standard is in force; its latest systematic review (November 2024) confirmed it.

Dry-type units are not named in the scope, which covers liquid-filled units.

Maximum total losses under NOM-002-SEDE/ENER-2014

Total losses at 80 % load, referred to rated voltage, frequency and current; no tolerance is allowed. The standard also sets minimum efficiency at 80 % load (for example 98.86 % for 75 kVA in the 15 kV class). An intermediate rating must meet the values of the next higher rating in the table.

Product certificate and what must go with the transformer

• Certificate issued by a product certification body accredited under the Federal Law on Metrology and Standardisation (LFMN). Two routes: periodic product testing (certificate valid 1 year) or a certified production-line quality system (valid 3 years).
• Certification is by product family: same type, same number of phases, same factory, and the capacity and insulation-level band of the standard. The largest rating of the family is the one tested.
• The test report has to be issued no more than 120 days before the application. The certificate can be granted to a Mexican manufacturer, an importer or a trader, and cannot be transferred.
• Nameplate in Spanish, including efficiency at 100 % load and the certifier’s mark. A routine test report for each transformer, operating instructions and a warranty of at least 12 months from installation or 18 months from shipment must accompany the unit.

What our published ratings cover

• Pad-mounted transformers (IEEE/ANSI C57.12, 60 Hz): the published HV list includes 13.2 kV at BIL 125 kV; three-phase ratings 30–3000 kVA, including 30, 45, 75, 112.5, 150, 225, 300 and 500 kVA. The published LV options are 240Δ/120 (tap), 480Y/277, 240Δ, 480Δ and 600Y/347.
• 220Y/127 V low voltage, 15 kVA, 23 kV and 34.5 kV primaries, CFE construction details and NOM-002-SEDE/ENER certification: on request, per order.
• Oil-immersed S11 / S13 loss values on this site are 50 Hz guarantees. 60 Hz units for Mexico are designed and quoted per order.

Send with your enquiry

• Utility or end user, site (city, altitude), CFE specification number if the tender names one
• Type: pole-mounted, pad-mounted, substation or submersible; single- or three-phase
• Rated power (kVA), HV and BIL, LV (for example 220Y/127 V), vector group
• Maximum losses or efficiency you must meet, and who will hold the NOM certificate (you as importer, or the supplier)
• Quantity and required delivery date