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Customer Success Story

Delivering safe urban substation solutions

The largest high voltage HiDry transformers ever made are in the center of Seville, Spain

In 2013 Spain’s largest electric utility, Endesa, needed to replace four conventional oil transformers with dry-type transformer technology in the country’s fourth-largest city, Seville (pop. 700,000). Conventional oil transformers may contain polychlorinated biphenyls (PCBs), which have useful dielectric properties but produce dangerous dioxins when burnt. Since transformer oil is a potential fire hazard, dry technology is considered the safest option for inner city substations.

Energy demand in downtown Seville’s Arjona and Osario substations is high and increasing. Both installations are located in densely populated urban areas, so Endesa needed to find the safest possible solution to eliminate the risk of fire and environmental hazards. Hitachi Energy’s innovative solution consisted of four HiDry dry-type power transformers, rated 34 megavolts ampere (MVA) 66 kilovolts (kV), with on-load tap changers (2 pieces per substation), to replace lower capacity 31.5 MVA oil-type units.

Hitachi Energy’s HiDry transformers significantly increase the quality of electricity supply in Seville, and lower the risk of fire, explosions and environmental pollution from leaking oil or gas. They also provide easy assembly, low maintenance, easy on-site repairs, and reduced civil works requirements.

Endesa ordered four 34 MVA, 66 kV HiDry units including on-load tap changers for a completely oil-free solution. They have since been very satisfied with this solution because it practically eliminates all fire and environmental risks. These units are particularly suitable for urban centers and enclosed areas. They can operate at a temperature of 165°C (compared to 100°C for conventional models), and have an average lifespan that is from 20 to 40 years longer than conventional transformers.  

Hitachi Energy introduced the HiDry transformer to serve direct sub-transmission voltage with a higher power rating, while providing superior safety and environmental advantages. To date, the transformers in Seville are the largest HiDry dry-type transformers ever manufactured.

Main data


Endesa S.A


4 HiDry dry-type power transformers


Urban (inner-city) indoor substation           

Power rating

4 x 34 MVA, 66 / 22 kV, with OLTC         


Seville, Spain