Flow Through Motors
A byproduct of converting electrical power to mechanical work is heat. The only way to remove heat in electric machines is through heat transfer into the surrounding environment by either conduction, convection or radiation. The less heat that is generated by an electric motor, the less heat dissipation that is required to keep the temperature under the design limits.
In the application of downhole rotating tools, especially electric submersible pumps (ESPs), heat generation is further exacerbated by mechanical losses due to the friction of the motor rotor spinning in the pressured motor oil system that protects the electrical components of the motor. Therefore, for ESP applications, the torque delivered by the motor is directly limited by how much heat (electrical and mechanical) can be dissipated into the surface area of the motor housing.
Advantages of Permanent Magnet Motor Technology
Upwing Energy has applied some of the cooling topologies used in the medical and defense industries to downhole applications to minimize heat generation. Permanent magnet (PM) motors are an ideal motor technology because they generate much less heat due to their higher electromagnetic efficiency when compared to induction machines, which require an iso-induced magnetic field in the rotor. In addition, PM motors can operate with very large air/fluid gaps between the motor stator and rotor, minimizing fluid friction losses and allowing for the hermetic enclosure of the motor components.
For the Upwing Subsurface Compressor System™ (SCS), the motor section is completely sealed from the pressurized produced fluids and torque is transferred through the magnetic coupling. This topology eliminates the fluid friction losses between the motor rotor and pressurized produced fluids by over 95%, therefore cooling is only required for the electromagnetic losses in the stator.
Innovative Motor Topology for Liquid Pumping
For the Upwing Magnetic Drive System™ (MDS), the required horsepower and associated heat transfer are significantly higher than SCS due to the liquid pumping application (i.e. over 1,000 HP for offshore pumps). Upwing has leveraged its PM motor by providing significantly higher surface area for the production fluid to flow through and carry the heat away from the MDS. The fluid has multiple flow paths inside the motor (around and inside the motor rotor, as well as inside and outside of the stator) to come in direct contact with the sleeved and protected motor components to remove heat. This innovative motor topology for downhole rotating devices enables Upwing PM motors to dissipate three to five times more heat vs. conventional ESP motors. In addition to eliminating the oil-filled, temperature-limited motor chamber and providing universal PM capabilities, the Upwing motor delivers roughly five times the power density of conventional induction motors, which are utilized in ESP applications currently.