Rotor and Stator in Pump Motors

The stator–rotor system is the heart of the electric motor that drives submersible and surface pumps, transforming electrical energy into mechanical energy.

The stator, the fixed part, consists of a stack of silicon steel laminations with low magnetic losses, insulated from each other to reduce eddy currents. The windings, usually made of enameled copper wire (thermal class F or H), ensure high conductivity and thermal resistance; in some low-cost versions, enameled aluminum may be used. After insertion, the windings are vacuum impregnated with epoxy resins or insulating varnishes, improving electrical insulation, mechanical strength, and thermal performance. In submersible motors, the stator may be completely encapsulated in resin or immersed in dielectric oil, ensuring total insulation, moisture protection, and efficient cooling.

The rotor, the rotating part connected to the shaft, can be manufactured in different configurations:

• Squirrel-cage rotor: built with silicon steel laminations, with slots filled by die-cast aluminum bars (or copper bars in high-efficiency motors). These bars are short-circuited by end rings of the same material. The die-casting process ensures high mechanical robustness and dimensional accuracy.
• Wound rotor (less common in pumps): conductors are insulated copper wires connected to slip rings, used in applications requiring precise control of starting torque.
• Permanent magnet rotor (PM rotor): integrates high-energy permanent magnets (NdFeB, SmCo, or ferrite), which provide a constant magnetic field without rotor losses. Combined with a conventionally wound stator, this forms a Permanent Magnet Synchronous Motor (PMSM). These motors achieve higher efficiency, greater torque density, and better dynamic response, especially when paired with frequency converters (VFDs).

The shaft, integrated with the rotor, is usually made of alloy or stainless steel, with optional protective sleeves in corrosion-resistant materials (hardened stainless steel, duplex, tungsten carbide, or silicon carbide). In certain applications (e.g., hot water circulators), shafts can be made of ceramic (aluminum oxide – Al₂O₃) to provide corrosion resistance, quiet operation, and dimensional stability at high temperatures.

Main Materials

• Stator (core):
  • Laminations in silicon steel (Fe-Si), low-loss magnetic grade.
• Rotor (core and cage):
  • Laminations in silicon steel.
  • Bars and short-circuit rings in die-cast aluminum (standard) or die-cast copper (high efficiency).
  • In PMSMs: permanent magnets made of NdFeB, SmCo, or ferrite.
• Windings:
  • Enameled copper wire (thermal class F or H).
  • In low-cost versions: enameled aluminum wire.
• Insulation:
  • Epoxy resins or insulating varnishes (vacuum impregnation).
  • Slot liners or insulating tapes in mica, Nomex, or polyester.
  • In submersible motors: special resins or dielectric oil for insulation and cooling.