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Electric operability in high-pressure liquid environment

Live endurance experiments with power components and complete high voltage, high power converter modules in liquid pressurized environments have concluded that all electrical characteristics for the most critical components such as the power semiconductors, IGBT driver electronics and power capacitors are very well maintained under pressure, at least up to 300 bar (3000 m sea depth). Indeed, voltage and current waveforms are close to unaffected by pressure, indicating high stability for the electric functionality and operability. The positive outcome is in line with the conclusions from previous research at SINTEF on pressure tolerant power electronics. However PressPack has extended the validity for the conclusions to also represent components with the highest voltage rating presently available on the market, such as 6.5 kV IGBT power modules. The high voltage, high power converter modules that have been demonstrated represent building blocks for multi-megawatt medium and high voltage converters for applications such as motor drives and high voltage power conversion systems (HVDC)

The main conclusions from the power component and power circuit investigations in liquid pressurized environment up to 300 bar, can briefly be summarized as follows:

  • Power semiconductors with drivers
    • All electrical characteristics as well as mechanical ruggedness are well maintained
    • The termination area for the silicon chips is vulnerable for fibers and other particles. The chip and substrate interface need to be protected from direct contact with liquids by a material with the sufficient mechanical and electrical properties.
    • Humidity control is important. By time humidity will penetrate the complete converter environment, including critical locations. Then either hermetically sealed components encapsulations are required, or the complete converter filling liquid need to have humidity control
  • MPP (Metallized polypropylene) capacitors and ceramic capacitors
    • All electrical characteristics, such as capacitance and tan δ are well maintained
    • The mechanical durability such as the film interconnection to the termination layers is maintained.
  • MPP-film capacitors
    • Even though traces from the surrounding liquid are found inside the film roll, there are no indications of deterioration of the film metallization like erosion.
    • The major concern is that the important self-healing mechanism of the metalized PP-film seems to be negatively affected by the high pressure.
    • Continuing experiments applying reduced DC-voltage was in operation for a significant longer period compared to those resulting in failure.
    • This is taken as an indication that high pressure operability of PP-film capacitors could be feasible provided significant derating of operating voltage
  • Magnetic core materials for inductors and transformers
    • Iron wound cores, Amorphous wound cores, Ferrite cores, Nanoperm, Arnold powder cores have been subject to live operation in liquid pressurized environment, while mapping coercive force, saturation flux density, relative permeability
    • Even though they are all more or less affected by pressure, they all seem to be possible candidates for operation under high pressure, provided that proper design considerations are taken care of.
  • Transducers and sensors assumed to be located in the high pressure power circuit environment
    • A current transducer test object, representing advanced monitoring electronics, maintained all functionalities and specified accuracies.
    • Temperature and humidity sensors maintained all their specified functionalities