Prolec GE Transformers: Power, Pad-Mounted, Pole-Type

What it is and where it is used

Prolec GE is a transformer manufacturer that began in Monterrey, Mexico. It started as a joint venture between GE and the Mexican group Xignux, and on February 2, 2026 GE Vernova reported that it had completed the purchase of the 50 % it did not already own, so the company is now wholly owned by GE Vernova. Its current website uses the Prolec brand and lists nine plants in Mexico, the United States and Brazil, with names such as Prolec Monterrey, Prolec Waukesha and Prolec Shreveport.

Its transformers are installed at utilities, in industrial substations, at solar and wind plants and in underground distribution networks in Mexico, the United States and Latin America. For the technical background, see power transformer and distribution transformer.

Variants: power, GSU, pad-mounted, pole-type and special units

Rating, voltages, vector group and tap changer type are read from the nameplate. Catalog ranges are in the next section.

Ranges published by the manufacturer

In its power transformer brochure (English, 2022 edition), Prolec GE describes five integrated product lines with ratings from 5 kVA to 1,000 MVA. It also states more than 8,000 power transformers and 3.5 million distribution transformers installed in more than 35 countries. For the power line, the brochure gives these maximums:

According to the brochure, all power units accept an on-load tap changer (OLTC), a de-energized tap changer (DETC) or a combination of both, and the power line can be supplied with mineral, vegetable or synthetic oil. These are catalog maximums; what a specific unit has is stated on its nameplate and in its test report.

In its Spanish-language brochure on power transformers for electrical distribution, Prolec GE also describes the PST Industrial. It is a substation-type unit (delta-wye) of up to 40 MVA, with high voltage from 69 to 138 kV and low voltage from 12 to 34.5 kV. It is offered with or without an on-load tap changer and with circular coils. The on-load tap changers can be reactive or resistive, and the standard cooling systems are ONAN, ONAN/ONAF and ONAN/ONAF/ONAF. See transformer cooling system.

Accessories and options to recognize in the field

The same brochure lists as standard accessories the sudden pressure relay, the liquid level gauges and the winding temperature indicator. It adds the vacuum gauge with bleed valve, the drain valves and the detachable radiators. The list is completed by the sealed tank for oil preservation and the external grounding connection. As options it mentions the oil conservator with Buchholz relay, the automatic gas preservation system, multi-ratio current transformers, surge arresters, forced-oil cooling, preparation for Schnabel tests and vegetable oil. Knowing whether a unit is sealed-tank or has a conservator changes what to expect in the gas analysis and in the inspection: see mechanical protection of the transformer, devices 63 and 26.

Factory tests the test report should include

According to the brochure, every transformer receives the standard tests, with a report per serial number. The report includes, among others: polarity and phase displacement, ratio, no-load losses and excitation current, and load losses and impedance. It also includes impulse, low-frequency dielectric tests, insulation power factor, induced voltage, partial discharge and dissolved gas analysis, and the temperature rise test. If your transformer arrives without any of these, the omission should be clarified with the supplier. The values in the test report are the reference against which the receiving tests are compared.

Points of attention in commissioning and maintenance

• Nameplate and documentation. Before energizing, verify that the nameplate matches the design: vector group, tap changer positions, insulation levels and cooling system.
• Moisture and oil. In power units, the water content and the dielectric strength of the oil are measured before energizing and compared with the factory values. See dielectric oil analysis.
• Baseline gases. A dissolved gas sample before energizing and another after the first hours under load give the baseline for future monitoring.
• Solar and wind plant step-up units. They carry variable load and inverter harmonics; confirm that the protection, the tap changer and the alarms respond to the plant’s real operating cycle.
• Transport. An impact recorder and positive dry-gas pressure during transport are part of the delivery; their record is reviewed on receipt.

Main features

• Oil-immersed power transformers, with an on-load tap changer depending on the application, a cooling system and mechanical protective devices.
• Distribution units, pole-type and pad-mounted, for underground networks.
• Lines for renewables: pad-mounted units for inverters and collector step-up transformers.
• Other units: the company also lists Prolec LABS, Prolec Celeco and Prolec Energy Solutions among its sites.

Communications and integration

A transformer does not communicate by itself. In power units, the temperature, oil level, Buchholz relay, pressure relief device and tap changer position reach the protection and the SCADA through contacts and transducers, or through an online monitoring system. In distribution, it is usual to supervise only the upstream protection. In step-up units at solar and wind plants, these signals are integrated into the plant SCADA together with the substation protection, and the utility may require some of them.

Frequently asked technical questions

• Prolec GE transformer manual: the installation and maintenance manual and the factory test report come with each unit; request them with the serial number.
• Receiving on site: before energizing, compare the receiving tests with the factory report; see factory tests of transformers.
• Trip on energization: the inrush current can operate the differential or overcurrent protection if they are not properly set; see transformer trip on energization.
• Oil and dissolved gases: periodic analysis is the best early warning; see dielectric oil analysis.
• On-load tap changer: it is the part of a power transformer with the most mechanical wear; its maintenance follows the accumulated operations and the instructions of the tap changer manufacturer, not the transformer manufacturer.
• Prolec pad-mounted units in underground networks: before energizing, check the fuses, dead-front bushings, elbows and grounding, in addition to the electrical receiving tests.

How we can help

At Tiza Group we do not sell transformers. We test and commission transformers from any manufacturer, Prolec units included: ratio, winding resistance, insulation, power factor, frequency response analysis, tap changer and the unit’s own protective devices, as well as the protection scheme. See power transformer testing within testing and commissioning. Field work is done in Colombia, or elsewhere on request. If you are going to expand a substation with a new transformer, we design the change under engineering design and studies, which we can deliver remotely worldwide. Write to us through contact.

Related guides

• Power transformer
• Distribution transformer
• Factory tests of transformers
• Transformer protection scheme
• Hitachi Energy (ABB) transformers

References

• IEEE C57.12.00, general requirements for liquid-immersed distribution, power and regulating transformers.
• IEC 60076-1, power transformers: general.
• Prolec, corporate website (product lines and plants).
• Prolec GE, Power Transformers brochure (English, 2022) and Transformadores de Potencia para Distribución Eléctrica brochure (Spanish), published by GE Vernova and Prolec.
• GE Vernova, press release of February 2, 2026 on the purchase of Prolec GE.

Frequently asked questions