The present disclosure relates to subsea power transformers. More particularly, the present disclosure relates to fault tolerant three-phase subsea power transformers suitable for long-term seafloor deployment.
In the subsea oil and gas industry, it is often desirable to perform certain fluid processing activities on the sea floor. Examples include fluid pumps (both single phase and multiphase) and compressors (both gas compressors and “wet gas” compressors). The subsea pumps and compressors are commonly driven with electric motors, which are supplied by three-phase electrical power via one or more umbilical cables from a surface facility. Especially in cases where the umbilical cable is relatively long, it is desirable to transmit the electrical power at higher voltages through the umbilical cable and use a subsea transformer to step-down to a voltage suitable for use by the subsea electric motors.
The subsea transformer components are often submerged in a transformer oil that is contained within a tank. However, the pass through points of the tank wall, such as for the electrical connections with the supply and load conductors, are potential sources of failure. In order to increase reliability, some subsea transformers have used a “tank-in-a-tank” arrangement that is schematically illustrated in
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
A subsea transformer is described that includes: a primary set of coil windings; a secondary set of coil windings; and a first sealed tank defined by a first tank wall that houses the primary and secondary sets of coil windings and a first dielectric oil which bathes the primary and secondary sets of coil windings. The first tank wall is configured for long-term deployment in a subsea environment. The transformer further includes a second sealed tank which houses a second dielectric oil and is positioned adjacent to the first sealed tank such that the first and second tanks share a portion of the first tank wall; a set of primary terminals mounted on the second tank connected to a first electrical conduction path to the primary set of coil windings and passing through the second tank, the shared portion of the first tank wall and into the first tank. The transformer further includes a set of secondary terminals mounted on the second tank, connected to a second electrical conduction path to the secondary set of coil windings and passing through the second tank, the shared portion of the first tank wall, and into the first tank.
According to some embodiments, the shared portion of the first tank wall is less than about 50% of the total surface area of the first tank, and the non-shared portion of the first tank wall is configured for direct contact with ambient seawater that provides cooling to the first dielectric oil. According to some embodiments, the shared portion of the first tank wall is less than about 30% of the total surface area of the first tank. The subsea transformer can remain operational when either (1) seawater leaks in to the second tank but no leak exists between the first and second tanks, or (2) when a leak exists between the first and second tanks but no seawater leaks into the second tank.
According to some embodiments, the transformer also includes: a first pressure compensator in fluid communication with the first tank and configured to balance internal pressure of the first tank with ambient seawater pressure and/or pressure within the second tank; and a second pressure compensator in fluid communication with the second tank and configured to balance internal pressure of the second tank with ambient seawater pressure. The first pressure compensator can be housed within the second tank.
According to some embodiments, instruments can be housed within the second tank, and a temperature sensor in the first tank can be used to measure temperature of the first dielectric oil. According to some embodiments, an integrated high resistance grounding system is housed within the first tank interconnected and configured to provide a high resistance ground path between a neutral node of the secondary windings and a ground. According to some other embodiments, a seawater based high resistance grounding system can be mounted to an exterior portion of the subsea transformer and exposed to ambient seawater.
The transformer can be configured to supply power to a subsea motor used for processing hydrocarbon-bearing fluids produced from a subterranean rock formation. The subsea motor can be used to drive subsea device such as a subsea pump, compressor or separator.
The subject disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the subject disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:
The particulars shown herein are by way of example, and for purposes of illustrative discussion of the embodiments of the subject disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details of the subject disclosure in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Further, like reference numbers and designations in the various drawings indicate like elements.
Known tank-in-a-tank designs, such as shown in
Due to the arrangement of the tanks as shown, the transformer is fault tolerant in that it remains fully operable if one of the tank barriers fails. According to some embodiments, a subsea transformer tank sealing system is provided that combines a single lower tank wall for the active parts with a double seal philosophy between seawater and all active parts and open connections. The single wall steel lower tank allows for enhanced cooling properties and the double seal philosophy provides redundancy. A single seal failure anywhere in the system will not cause an electrical system failure.
Referring again to
The upper tank 220 is filled with an environmental fluid (such as a dielectric oil), and houses the connection systems and instrumentation. Although upper tank 220 is filled with an environmental fluid, tank 220 is designed and qualified to tolerate seawater. According to some embodiments, the upper tank 220 includes a lower volume 380, which acts as a “swamp” that can collect a certain amount of seawater. If a leakage between upper tank 220 and the sea occurs, a small amount of environmental fluid will leak to sea, but system will be operational. If leakage between upper compartment and lower compartment occur, system will also be operational. Note that the system can remain operational even in some cases where a combination of failures in both barriers was to occur. If a relatively small leakage occurs between the sea and the upper tank 220, the seawater entering the upper tank 220 will collect in the “swamp” volume 380. In such cases the main volume of upper tank 220 remains oil-filled and the system can tolerate leakage between the upper tank 220 and lower tank 210.
Visible in
While the subject disclosure is described through the above embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while some embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the subject disclosure should not be viewed as limited except by the scope and spirit of the appended claims.
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