PROJECT: NJT Commuter Trains | USA

ESTER TYPE: MIDEL 7131 synthetic ester

PURPOSE: To improve traction transformer performance


New Jersey Transit (NJT) is the third largest provider of bus, rail and light rail services in the USA. It covers an area of 5,235 square miles, linking major locations in New Jersey, New York and Philadelphia. NJ Transit operates a large fleet of commuter trains, providing transport for thousands of passengers every day.

NJT is keen to promote its approach to developing a sustainable role for public transportation. The NJT website states “In 2019, NJ TRANSIT’s annual passenger trips totaled just over 260 million, and average weekday trips were just over 925,000. By providing these passengers with an alternative to driving cars, NJ TRANSIT reduces automobile vehicle miles traveled in New Jersey by 1.5 billion every year and is one of the single greatest mitigators of auto congestion on New Jersey roadways.” This case study describes MIDEL’s contribution to helping the NJT deliver safer, greener rail travel.


On the electrified sections of the NJ Transit commuter network, Bombardier ALP46 and ALP46A locomotives are used, all of which use onboard MIDEL 7131 filled traction transformers. By using MIDEL the traction transformer manufacturers ABB were able to get the large amount of power needed from a relatively small unit. In addition, on the original ALP46 models, MIDEL was used to cool the power electronics in the converters onboard the train. As a point of interest the original ALP 46 trains were based on a proven E101 design utilised on the German rail network, where the locomotives also used MIDEL in the main transformers and converters. There were over 145 of the E101 series trains successfully running in Germany from 1996 onwards.

The New Jersey Transit locomotives have one of the hardest working lives of any rail network, as they are subject to frequent stops, meaning harsh acceleration and deceleration. The trains also utilise a regenerative braking system, which can feed power back onto the distribution network. All of this power is transferred through the main traction transformer, which in turn experiences very large load fluctuations, placing a huge demand on the MIDEL transformer fluid. Despite this, MIDEL has given excellent service, without needing any maintenance over decades of service.


During normal operation of the trains, regular samples of fluid were taken and put through Dissolved Gas Analysis (DGA) in order to monitor the condition of the transformers. NJ Transit contacted the MIDEL technical team to help interpret the DGA results. A full assessment was carried out by the technical team and quickly fed back to NJ Transit, allowing them to devise a plan for monitoring the other transformers to ensure smooth running of the network.

The use of MIDEL ester fluids in these sectors supports the following UN Sustainable Development Goals:

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