Uprating of spare transformers: Bio-based oil boosts thermal performance
A joint project with Alliander reaffirms that Nynas’ bio-based transformer liquid NYTRO® BIO 300X can significantly improve the thermal performance of existing distribution network transformers.
Hugo Campelo
Senior Technical Advisor, Electrical Industry, Nynas AB.
“The accelerated energy transition in the Netherlands is driving the need for extensive grid reinforcement. But a scarcity of public space, skilled technicians and resources is causing long lead times and increasing grid congestion,” says Rory Leich from Duurzaam Energieperspectief (DEP), part of the leading Dutch distribution system operator Alliander and a key driver of the joint project.
The proof of concept has been conducted on a spare power transformer from the Alliander Network. The approach involved improving the external airflow by doubling the numbers of fans of the original design while retrofilling the unit with NYTRO BIO 300X. The unit was manufactured in Italy in 2021 and has since served as a backup unit that has never been energized.
“The goal was to assess if a retrofit of the original design involving NYTRO BIO 300X could be a viable strategy to extend the useful life and capacity of aging transformer fleets, providing critical flexibility amid long procurement lead times for new units.” explains Hugo Campelo, Senior Technical Advisor at Nynas.
Being the first of its kind, the researchers carried out their experiments on the retrofitted 50/10 kV 24/30 MVA ONAN/ONAF spare transformer with the aim of assessing its thermal performance along with corresponding power increase enabled by the modifications introduced to the original design. In the original design the transformer was equipped with a standard mineral, naphthenic- based, recycled inhibited oil which was more viscous.
Due to its ultra-low viscosity and low density, NYTRO BIO 300X flows better through the windings, transformer tank and radiators, enhancing the cooling performance of the whole transformer. The researchers wanted to validate up to which extent these properties of NYTRO BIO 300X could lower the hotspot temperature and increase the continuous loadability within IEC Loading Guide temperature limits.
“Based on accumulated field experience, a gain of about 10% of additional loadability was forecast due to the retrofilling, but the combined effect of the bio-based oil and more fans prove to be even more promising!” observes Hugo Campelo.
An uprating of 125% over the original apparent power has been proven possible
The results of this joint project show that the continuous load can be extended, and that an uprating is achievable and the expected benefits can be unlocked. Results showed a significant reduction in hot-spot temperatures up to 17 ºC. Based on those temperature reductions measured, the 100% reference tests have been extrapolated towards the IEC temperature limits for different scenarios as shown in Table 1.
The continuous loadability of the tested transformer was successfully improved to approximately 125% of its original rating, demonstrating the potential of targeted modifications to extend operational capacity. The full set of results and tests has already started to be disseminated in industry forums, and discussions will continue.
