Case Studies

  • High load in a small space

    Customer: New Jersey Transit

    Location: New Jersey and New York

    Application: Rolling stock transformers

    Highest voltage: 25kV / 12kV

    Big Power from Small Units

    When the third largest transport services provider in the United States needs to protect its rolling rail stock, there’s only one transformer fluid they trust.

    New Jersey Transit provides bus, rail and light rail services covering an area of 5,235 square miles, linking major locations in New Jersey, New York and Philadelphia. Moving thousands of passengers every day requires a large fleet, with safety and reliability the top priorities.

    On the electrified sections of the commuter network, NJ Transit use Bombardier ALP46 and ALP46A locomotives, with onboard traction transformers manufactured by ABB and filled with MIDEL 7131 fluid. Using MIDEL enabled ABB to achieve the large power output needed, but within a small unit required to optimize space on board the locomotive.

    The locomotives on the NJ Transit network have one of the hardest operating cycles. Frequent stops require harsh acceleration and deceleration, placing greater strain on the traction transformer. Combined with a regenerative braking system that feeds power back into the distribution network via the transformer results in very large load fluctuations, putting huge demand on the MIDEL transformer fluid. Despite this, MIDEL has delivered consistently excellent performance, with no maintenance needed over more than 10 years’ service.

    To monitor the condition of the transformers and ensure optimum performance of the MIDEL fluid during normal operations, regular samples were taken and analysed using Dissolved Gas Analysis. NJ Transit contacted the MIDEL technical team for support and guidance in interpreting the DGA results. MIDEL made sure a full assessment was quickly returned to NJ Transit, enabling a future-proof plan for monitoring the transformer fleet and ensure the continued smooth running of the network.

    If optimizing transformer performance for safe and reliable operations is on your agenda, find out more about MIDEL fluids.

  • Environmentally Safe

    Customer: CG Power

    Location: Global

    Application: Bio-SLIM transformer

    Highest voltage: 35kV

    Transformer Innovation Where Space is Restricted

    For maximum transformer output with the smallest weight, CG Power needed an alternative to conventional cast resin transformers. MIDEL was the answer.

    Cast resin technology was the conventional solution for wind turbines with onboard transformers. In reality, a number of high profile failures in the field, combined with required increases in power ratings and higher voltages, meant that an alternative was needed.

    CG Power set about developing a compact, fluid-filled transformer in partnership with DuPont, with the aim of fitting it through the tower door of a modern multi-megawatt turbine. This new innovation was dubbed ‘SLIM’. For the first range of these transformers, silicone oil was used for its K-class capability and dependable high temperature characteristics. However, it was soon found that silicone oil has serious shortcomings in these applications due to its poor biodegradability and tendency to leak through gasket seals.

    CG Power searched for a more environmentally friendly solution, and recognized the potential of MIDEL 7131 transformer fluids. Since MIDEL 7131 is readily biodegradable, it has far less impact on the environment than silicone oil if spillage occurs. It is also more compatible with most sealing materials and so less likely to leak. This offers a double benefit in relation to wind turbine applications, since many of the turbines are located in environmentally sensitive areas, including offshore installations.

    The second stage of development defined a smaller footprint than the silicone oil transformers, yet with the same or higher power output. Close collaboration between the MIDEL technical team, CG Power and DuPont pioneered a new transformer design for wind turbine applications. MIDEL experts provided extensive testing of MIDEL 7131 for materials compatibility and long term high temperature performance for use in the latest generation Bio-SLIM transformers from CG Power. These innovations were possible due to the superior thermal and electrical properties of MIDEL 7131.

    There are now several thousand Bio-SLIM transformers in operation around the world. The latest transformers in the Bio-SLIM range have ratings up to 7MVA and highest voltages to 72.5kV.

    For effective alternatives that can optimize transformer performance and innovation,

  • Protecting people

    Customer: PROLEC-GE

    Location: Mexico City

    Application: Power transformers

    Highest voltage: 36/48/60 MVA, 230/23/15 kV, HV OLTC

    Safety in the City

    In 2015, the joint venture between GE and Xignux (PROLEC-GE) stepped in to help when the national Mexican utility, CFE (Comision Federal de Electricidad), set about updating its substations serving greater Mexico City (population – over 20 million people). The transformers were located both indoors and outdoors, within the city’s very dense population centers.

    The aim was to provide safer installations, reduce environmental impact and improve power system reliability. PROLEC-GE was able to meet these criteria by delivering power transformers filled with MIDEL 7131 synthetic ester instead of mineral oil. PROLEC-GE understood that using a synthetic ester liquid as a coolant and dielectric insulator provides a higher fire point along with biodegradability for the transformer fluid; fire risk is greatly mitigated and the potential for soil contamination is eliminated.


    The modernization project involved more than 50 power transformers; the electric substations now satisfy the new technical, ecological, safety and service standards.

    “Fires in transformers can be highly dangerous and devastating, especially in indoor substations or densely populated areas.  That is why we decide to invest in the safety of our installations with this new technology, successfully proven in other countries” commented Federico Ibarra, CFE Technical Manager.

    PROLEC-GE is a joint venture between GE and Xignux, S.A. de C.V. It is one of the largest transformer manufacturers in the Americas, offering a full line of transformer products for the generation, transmission and distribution of electric power.

  • Urban density, maximum safety

    Customer: A major UK grid operator

    Location: London

    Application:  Power transformers

    Highest voltage: 400kV

    Bringing Together Safety and Reliability

    A major UK grid operator needed an innovative solution to the challenge of installing 400kV transformers in a densely-populated area of London. The aim was to combine safety and reliability with a heat exchanging device (directing the captured transformer heat-loss to a nearby school). A world leader in transformer manufacturing provided the operating assets – 400kV transformers – and selected MIDEL 7131 as the best choice of dielectric fluid.

    Safety, reliability and environmental impact are crucial considerations for grid operators and transformer manufacturers, especially for installations in large cities. Residential properties, hospitals and business premises where people work must be protected from the risk of fire or explosion from the installed electrical assets. The environment and appropriate corporate social responsibility considerations are also critical factors. Furthermore, space constraints are very often a key issue in cities.


    MIDEL 7131 synthetic ester insulation was chosen for the project as it greatly reduced the risk of fire and explosion. The firepoint and flashpoint of synthetic ester are very high compared to mineral oil. In order to manufacture the transformers according to the required performance levels (dielectric characteristics, insulation and projected lifetime), specialized constructive changes were calculated and planned in the design phase.

    Waste heat from the power transformer was re-used using heat exchange devices. Planning and construction of this additional feature was done in close collaboration between the transformer factory, the customer and the supplier of the heat exchange device.

    When installing transformers in urban areas, noise plays a key role, as do reliability and safety. The transformer and cooling devices need to operate silently regardless of transformer load. The transformer filled with MIDEL 7131 was manufactured with a low-noise-design. Bespoke housing, as well as noise-optimized cooling with frequency-regulated fans was added to the low-noise-concept.

  • Reliable power

    MIDEL 7131 selected by Siemens in major transformer project

    With MIDEL 7131 synthetic ester, Siemens was able to secure an important project for Swedish power operator Vattenfall. The flash and fire points of synthetic ester are higher than those of mineral oil, this is one of the biggest benefits of this insulating fluid. Other advantages are that it is readily biodegradable and that it has a higher oxidation stability.