Using natural and synthetic ester fluids in power transformers


Critical transformers require high performance fluids

Power transformers (generally, those rated above 33 kV) are critical assets in energy infrastructure. They are also expensive, difficult to transport and the largest units must be drained after testing and then shipped without fluid, making the residual fluid film prone to oxidation. Power transformers are often deployed in areas of high density population or environmental sensitivity, so fire safety and eco-protection are also prime considerations.

That’s why the world’s leading utilities and transformer manufacturers turn to MIDEL ester fluids.


The MIDEL Ester Fluids


MIDEL eN 1204 and MIDEL 7131 are all suitable for use in power transformer applications up to 400kV. The fluids all offer the benefits of being readily biodegradable (avoiding environmental damage should leakage occur) and enabling reductions in containment measures. MIDEL 7131 is perfectly suited for non-breathing and breathing transformers (due to its excellent oxidation stability) located indoors or outside. In 2016, MIDEL 7131 was specified and used in a 433kV urban transformer installation in London.

The natural ester fluid MIDEL eN 1204 (rapeseed) is produced from renewable vegetable oils, providing an effective, environmentally friendly solution for non free-breathing power transformers. MIDEL eN 1204 (rapeseed), with its pour point of -31°C, is better suited to colder installation climates than soy-based natural ester fluids.


Retrofilling transformers at high voltages

MIDEL fluids are approved for use at transmission voltage levels by several leading OEMs. MIDEL 7131 has been used for multiple projects at 400kV and in mobile test equipment up to 500kV. In common with other ester-based fluids, some design adjustment may be needed for higher voltage levels due differences in permittivity and dielectric performance.


Case Studies: Power Transformers