Driving units of submersible pumps, so called "wet type motors", have been used to a large extent for many years.
Due to their simple construction, these motors can be manufactured in comparably small series. This enables end-user countries to set up their own production. This is not possible for canned, oil-filled, motors.
Unlike an oil filled motor, whose insulation would fail due to contact with moisture entering from without, the water filled unit will continue to operate.
There is also no danger of polluting water with oil.
The advantages of „wet type motors“ in comparison to canned motors are known all over the world and production of such motors is increasing steadily.
The application of this technology though, does not rest solely in the traditional field of submersible pumps.
Nowadays, „wet type motors“ are used more and more as driving units of special pumps, dredge boats, submarines, deep-sea research instruments etc.
The winding wires of „wet type motors“ are continually in contact with liquids that are more or less aggressive.
For this reason the extruded insulation of the winding wires has to be absolutely water tight and resistant to a number of different substances.
The dielectric properties of the insulation (dielectric strength, insulation resistance, dielectric losses), have to meet high standards that, of course, have to be fulfilled under the influence of moisture for long periods of time.