Compact Transformers in Urban Areas Rely on Nomex® Insulation
Noise is a major concern for transformers in urban areas. When Gaz Electricité de Grenoble (GEG) needed a low-noise transformer with a higher power rating to fit in an existing substation located in a densely populated area, the utility chose a liquid-immersed transformer with a hybrid insulation system utilizing DuPont™ Nomex® brand insulation.
GEG, the power utility in southeastern France, is responsible for many transformers in urban areas. When GEG needed to replace an aging 10 MVA (63 kV/5kV) transformer in the city center of Grenoble, the replacement unit had to be a low-noise transformer with a much higher rating than the previous transformer. It also had to fit in the existing substation, so the dimensions were strictly limited.
“Transformers to be located in densely populated urban areas must meet all the usual technical requirements such as size, weight, overload capacity, safety and reliability. In addition, noise is a major constraint,” explained Jean-Paul Giraud, CEO of GEG.
GEG chose a 36 MVA (63 kV/21 kV) liquid-immersed transformer—with natural air ventilation to reduce noise—that uses a hybrid insulation system based on Nomex® insulation to allow higher temperature rise. Nomex® paper is used to insulate the conductors and Nomex® pressboard is used for spacers.
Low noise emissions: This transformer does not generate the unacceptable noise levels of transformers with forced ventilation systems and the use of Nomex® insulation helps ensure that it operates reliably at full load with only the existing air-entry points in the substation.
Compact size: This transformer with hybrid insulation of Nomex® paper and pressboard is smaller and lighter weight for the given power rating than most conventionally insulated units, enabling GEG to install a low-noise transformer with a much higher rating in the existing substation.
Reliability: The use of Nomex® insulation helps this low-noise transformer take load variations and overloads in stride, helping to ensure uninterrupted delivery of electricity to the homes and businesses in Grenoble.
Safety in use: Transformers in urban areas with hybrid insulation of Nomex® paper and pressboard operate safely and reliably, even with winding temperature rises of more than 65 K.
Materials Selected and Why
The use of a hybrid insulation system based on Nomex® paper and pressboard allows this low-noise transformer to have the significantly higher power rating required by GEG while being small enough to fit in the existing substation—a power-to-size ratio not possible with most conventionally insulated units.
Nomex® insulation provides reliable, long-term service even under challenging conditions. It has a proven ability to withstand overloads and features excellent thermal stability. In addition, this hybrid insulation system—Nomex® paper on the conductors and Nomex® pressboard for the spacers—meets IEC 60076-14, an important consideration for this electricity utility.