Whatever they are using, it is absolutely necessary.
The reason nobody has used high-power electrostatic motors is that they require high electric fields, which would cause the electric breakdown of air and of most fluids. In contrast, the normal electromagnetic motors use high magnetic fields, which do not cause the breakdown of air, so they do not need immersion in an insulating fluid.
It is likely that the fluid used by them is some kind of fluorinated hydrocarbon, as those have high breakdown fields. Therefore leaks from such a motor are undesirable, so it would be interesting to know how do they prevent leaks between the rotating axle and its bearing. Rotating seals can never be perfect, as the users of Wankel motors must be aware. The main reliability problem of the Wankel motors has also been the rotating seals.
I assume that nobody has tried before to make such motors because nobody has found a way to prevent the leaks until now.
Perhaps the motors are intended to work only with the axle pointing upwards, in which case gravity would prevent the leaks.
No seal is perfect, everything can deteriorate. Why would the seals need to rotate like a Wankel? I think this would be more like the end seals on traditional automotive transmissions. Leaks aren't really that common of a problem there.
There seems to be a lot of different dielectric fluid options. It seems flourinared hydrocarbons are increasingly being replaced by other options. It's possible their proprietary fluid is something else. It would surprise me if their fluid is highly flammable.
It seems to me that 'counter pumping' seals could work here, as is used on many automotive shaft work and with no contamination mechanism = no fail mode?
You could use a magnetic coupling to allow a true static seal. It's reasonably common in light-to-medium duty pumps for the same reasons around leakage, but there are limits on the transferable torque.
The reason nobody has used high-power electrostatic motors is that they require high electric fields, which would cause the electric breakdown of air and of most fluids. In contrast, the normal electromagnetic motors use high magnetic fields, which do not cause the breakdown of air, so they do not need immersion in an insulating fluid.
It is likely that the fluid used by them is some kind of fluorinated hydrocarbon, as those have high breakdown fields. Therefore leaks from such a motor are undesirable, so it would be interesting to know how do they prevent leaks between the rotating axle and its bearing. Rotating seals can never be perfect, as the users of Wankel motors must be aware. The main reliability problem of the Wankel motors has also been the rotating seals.
I assume that nobody has tried before to make such motors because nobody has found a way to prevent the leaks until now.
Perhaps the motors are intended to work only with the axle pointing upwards, in which case gravity would prevent the leaks.