traversée à huile communicante

Standard Number BS EN 50180-2:2015
Title Bushings above 1 kV up to 52 kV and from 250 A to 3,15 kA for liquid filled transformers. Requirement for bushing components
Title in French Traversées de tensions supérieures à 1 kV jusqu'à 52 kV et de 250 A à 3 ,15 kA pour transformateurs immergés dans un liquide. Exigences relatives aux composants de traversée
https://shop.bsigroup.com/ProductDetail?pid=0000000000303011...

The thermal stability is roughly doubled when such bushings are given very short conical ends, which allows some of the heat to be dissipated axially when provision is made for oil to circulate inside the tubular conductor (m - 2.5). The heat runs per- formed on such bodies have proved that they can be safely used at system voltages up to 525 kV. Fig. 1 shows an example of a completely immersed bushing of this kind.
https://fdocuments.in/document/resin-bonded-paper-bushings-f...

Figure 7.3. — Circulating Oil Cable System.
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Pipe-type cables are terminated in oil-filled porcelain bushings called "potheads".
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Figure 7.5. — Forced-Cooled System Termination
https://books.google.de/books?id=_AxGAQAAIAAJ&pg=RA1-PA64&lp...

The HV series are solid porcelain liquid filled (hollow core oil communicating) designed in accordance with the standards EN 50180 and EN 50243 (formerly DIN 42531-2-3-4 & 42541).
Transformer oil fills the space between the conductor (a rigid cylindrical copper stem) and the porcelain, increasing the electrical insulation and dissipating the thermal energy generated by the high current.
http://www.cedaspe.com/en/bushings/porcelain-bushings-hv.htm...

4.6 HV bushings.
The transformers are equipped with one of the following types of bushings: Porcelain bushings - in accordance with DIN 42531 or EN 50180:2010. These bushings are suitable for outdoor and indoor applications for transformers filled with mineral oil or with other insulation liquid
https://download.schneider-electric.com/files?p_enDocType=Us...
(oil circulation not specified)

The invitation to tender must specify whether the bushings must be made of ceramic materials (porcelain), a polymer or a composite material. Special requests concerning electrical insulation –i.e. oil-filled bushings, gas-filled bushings or other in accordance with DS/EN 60137 –must be stated in the invitation to tender.
https://www.danskenergi.dk/sites/danskenergi.dk/files/media/...
(not sure whether "oil-filled" refers to "communicating oil")

5.4 Oil level indication
Oil filled bushings for highest voltage for equipment Um  245 kV shall be provided with oil level indication.
https://www.svk.se/siteassets/aktorsportalen/tekniska-riktli...

The present invention relates to an improved hollow core composite bushing and, more particularly, to an improved bushing for use within a dead tank circuit breaker
https://patents.google.com/patent/US6140573A/en

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Note added at 14 hrs (2020-06-14 20:55:49 GMT)
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As far as I see, there is no difference between OIP bushings and capacitance-graded bushings, as most OIP bushings contains condenser cores for corona shielding (capacitance-graded insulated cores)

Some details about oil-impregnated paper bushings:

Oil impregnated paper (OIP) is a term used for bushings that utilize plain kraft paper, with the condenser core saturated with transformer-grade mineral oil. OIP bushings usually have upper air-side and lower oil-side porcelain insulators. OIP bushings can also have upper and lower insulators made of other materials, such as epoxy or fiber-wound shells of polymer.
https://new.abb.com/products/transformers/transformer-compon...

Condenser Bushings
At higher system voltages, condenser bushings are used. Compared to bulk type bushings, condenser bushings are relatively complex in their construction. In order to cope with the high electric field stresses generated at high voltage, condenser bushings are formed from an inner capacitance-graded insulated core, which is sandwiched between the central current carrying tube and external insulator.
The condenser core consists of coaxial layers of electrical grade Kraft paper and conducting foil inserts of varying lengths. Foil inserts are located at fixed radial intervals, which aids in distributing and stabilising the electric field across the bushing insulation. These conducting inserts mimic the capacitive elements (connected in series) that link the high voltage conductor of the bushing to ground. For this reason, condenser bushings are sometimes referred to as capacitance-graded bushings.
To further increase a bushing’s dielectric strength, the condenser insulation is saturated with mineral oil, or curable epoxy resin; these two technologies are referred to as oil impregnated paper (OIP) and resin impregnated paper (RIP), respectively.
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OIP condenser bushings are also fitted with a spring-loaded expansion chamber to allow for oil volume fluctuations (expansion/contraction) due to varying temperature (a conservator tank on a power transformer performs a similar purpose).
https://savree.com/en/product/oil-to-air-condenser-bushing/

All materials carrying an electric charge generate an electric field. When an energized conductor is near a material at earth potential, it can form very high field strengths, especially where the field lines are forced to curve sharply around the earthed material. The bushing controls the shape and strength of the field and reduces the electrical stresses in the insulating material.
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The inside of the porcelain bushing is often filled with oil to provide additional insulation and bushings of this construction are widely used up to 36 KV where higher partial discharges are permitted.
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Typically, paper insulation is later impregnated either with oil (historically), or more commonly today with resin. In the case of resin, the paper is film coated with a Phenolic resin to become Synthetic Resin Bonded Paper, (SRBP) or impregnated after dry winding with epoxy resins, to become Resin Impregnated Paper or Epoxy Resin Impregnated Paper (RIP, ERIP).
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To improve the performance of paper insulated bushings, metallic foils can be inserted during the winding process. These act to stabilize the generated electrical fields, homogenising the internal energy using the effect of capacitance. This feature resulted in the Condenser/Capacitor bushing.
https://en.wikipedia.org/wiki/Bushing_(electrical)

See also https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...