What is hermetically sealed oil immersed transformer working principle?

It keeps core electromagnetic transformation+oil insulation&natural cooling same as conventional oil transformers;the core innovation is full airtight sealing+elastic corrugated wall for oil volume compensation,no conservator tank/breather/silica gel desiccant.

1.Basic Electromagnetic Working Principle(same as standard oil transformer)

AC input on primary winding creates alternating magnetic flux inside laminated silicon steel core via electromagnetic induction.

Magnetic flux links secondary winding to induce different rated output voltage to realize step-up/step-down voltage conversion.

Copper loss(winding resistance)+core loss(hysteresis&eddy current)continuously generate heat during loaded operation;all core&windings are fully submerged inside mineral insulating oil.

2.Insulating Oil Dual Function inside fully sealed tank

Electrical insulation:Isolate high/low voltage windings,separate winding from core and grounded tank,prevent partial discharge and breakdown.

Heat transfer:Hot oil with lower density rises upward by thermosiphon,flows into corrugated cooling fins;cooled dense oil sinks back to tank bottom to form ONAN natural oil circulation continuously(can add fans for ONAF forced air cooling optionally).

3.Core Hermetic Sealing&Oil Thermal Expansion Compensation Principle(key difference vs conservator-type transformer)

Transformer oil expands~0.07%volume per 1°C temperature rise;traditional transformers use overhead conservator+breather to absorb volume variation,while hermetic design relies on elastic deformation of pressed corrugated steel tank walls for full compensation:

Hot status(high load/high ambient temperature,oil expands):

Increased oil volume pushes corrugated fins outward to expand total internal tank capacity;tank internal pressure rises slightly within designed safe range(normally≤0.05 MPa),no air enters the fully sealed tank at all.

Cold status(light load/low ambient temperature,oil contracts):

Reduced oil volume pulls corrugated fins inward to shrink tank inner space;internal pressure drops moderately,avoids negative vacuum inside the sealed housing.

Two mainstream sealed structures:

①Corrugated full-oil filling type(most common for distribution transformer≤3150kVA):Tank completely filled with oil,no reserved air space inside;all expansion compensated only by flexible corrugated panels(S11-M/S13-M global standard).

②Nitrogen gas cushion sealed type(large medium-power transformer):Small top chamber pre-filled with sealed inert nitrogen;gas compression/expansion cooperates with corrugated wall to balance oil volume change,still fully isolated from outside air.

4.Full airtight sealing advantage logic

All tank flanges,bushing seats,drain valves are fully welded&gasket-sealed;oil never contacts atmospheric oxygen&moisture:

Stop oil oxidation,avoid sludge generation and water ingress,maintain long-term dielectric strength of insulating oil.

Cancel conservator tank,breather and regular silica gel replacement,achieve nearly zero routine maintenance.

5.Safety protection matching sealed structure

Equipped with pressure relief valve mounted on tank top:When severe internal short/arcing produces massive gas and sharp overpressure inside sealed tank,valve automatically opens to discharge excess pressure and prevent tank rupture,then reseals after pressure back to normal.

References

APA

IEC.(2017).IEC 60076-2:2017 Power transformers-Part2:Temperature rise.IEC.

MLA

Varelen,Thomas."Performance Analysis of Hermetically Sealed Corrugated Distribution Transformers."IEEE Access,vol.12,2024,pp.105211-105220.

GB/T7714-2015

[2]VARELEN T.Performance analysis of hermetically sealed corrugated distribution transformers[J].IEEE Access,2024,12:105211-105220.