Is dry transformer a good choice for underground substation?

Dry-type cast resin transformer is universally recognized as the optimal and preferred equipment for underground substations worldwide,while oil-immersed transformers are largely restricted or even prohibited by most urban fire and electrical codes for underground enclosed power spaces.Unique underground working conditions including poor natural ventilation,high ambient humidity,limited fire evacuation space,confined maintenance passage and strict environmental protection standards make the oil-free,flame-resistant sealed structure of cast resin dry transformer irreplaceable for underground power distribution projects.

Fire safety is the most decisive factor prompting widespread adoption of dry transformers in underground substations.Underground transformer chambers are fully enclosed without open-air ventilation and adequate fire isolation buffer zones;once conventional oil-immersed transformer suffers internal short-circuit damage,flammable mineral insulating oil may leak and ignite,and dense smoke generated by combustion accumulates rapidly inside confined tunnels with no easy exhaust path.Such fire accidents block escape routes and bring huge challenges for fire rescue,posing severe threats to whole underground traffic or underground utility system.In contrast,epoxy cast resin dry transformer contains zero combustible liquid,and the integrated solid epoxy winding shell boasts outstanding flame retardant capability.Even if internal winding breakdown occurs,no flowing combustible medium spreads fire,greatly cutting catastrophic underground fire risks and complying with municipal underground construction fire control regulations.

High humidity and condensed dew inside underground rooms is another tough working environment where cast resin dry transformer performs excellently.Underground spaces always maintain high relative humidity affected by underground water seepage,ground water vapor penetration and temperature difference between day and night,which easily forms condensed water on equipment surface.Fully vacuum-cast epoxy completely wraps high and low voltage coils into an integral solid component,isolating internal copper windings and insulation materials from moist air,effectively preventing moisture infiltration and insulation resistance decline.Many underground-configured dry transformers are equipped with built-in anti-condensation space heaters inside IP20 or upgraded sealed cabinets;the heater automatically activates when ambient humidity exceeds preset value to evaporate internal dew,guaranteeing long-term stable dielectric performance all year round.Open VPI dry transformers with exposed coils are rarely used for core underground main substations,only applicable for tiny independent dry underground cabins with constant dehumidification facilities.

Limited maintenance condition of underground spaces further highlights dry transformer’s advantages.Underground substations usually have narrow equipment layout and restricted access for large maintenance machinery;oil-type transformers need regular oil sampling,oil filtering,seal inspection and waste oil recycling,requiring frequent professional maintenance access and waste oil storage space which underground sites hardly afford.Cast resin dry transformer achieves nearly maintenance-free operation after installation;routine work only includes regular cabinet surface cleaning and winding temperature monitoring,dramatically reducing later-period maintenance frequency and relevant civil auxiliary construction cost.

Cost comparison between different transformer types should also be considered in project design.Though cast resin dry transformer has higher initial procurement cost than equal-capacity oil immersed transformer,underground projects adopting dry-type equipment save massive expenditure on fire containment trench construction,waste oil storage room and fire prevention anti-leakage foundation reserved for oil transformers.Total comprehensive investment of underground substation with dry transformers turns out more economical in overall project settlement.

In conclusion,cast resin dry-type transformer is an excellent and necessary selection for underground substations based on fire prevention,damp resistance and low maintenance requirements,becoming the mainstream specified product for new urban underground power infrastructure globally.

1.APA 7th

Santos,E.,&Silva,R.(2022).Feasibility analysis of cast-resin dry transformers applied in urban underground substations.Electric Power Systems Research,209,107936.

2.MLA 9th

Santos,Eduardo,and Rafael Silva."Feasibility Analysis of Cast-Resin Dry Transformers Applied in Urban Underground Substations."Electric Power Systems Research,vol.209,2022,p.107936,

3.GB/T 7714-2015

SANTOS E,SILVA R.Feasibility analysis of cast-resin dry transformers applied in urban underground substations[J].Electric Power Systems Research,2022,209:107936.