Modern Wind Turbine | Common AC Generator Types | Squirrel Cage Rotor Induction Generator

Invented by Nikola Tesla and Mikhail Dolivo-Dobrovolsky in the late 19th century, the Squirrel Cage Induction Machine can be successfully used as generator in small scale hydro applications. Simple, robust and compact, it is ranked as the most reliable type of electric generator, mainly due to the small number of components. The power and speed range are standardized, making the induction generator available as on-the-shelf component in the power range of up to several hundred kW.

01-squirrel cage induction generator-Induction motor works as generator-wind turbine

Small scale Wind stations uses several induction generator types:

  • SQIN – squirrel cage;

  • WRIN – wounded rotor, with brushes and slip-rings;

  • CEIN – capacitor excited.

If connected to the national grid (DOL, Y/D or with soft starter) it imposes a cvasi-constant speed operated turbine, proper for constant head and flow sites. If driven by reaction type turbines, as for efficiency reasons, variable head and flow conditions can be dealt by constant speed induction generators combined with adjustable stator guide vanes and rotor blades, or by variable speed induction generators combined with fixed stator guide and rotor blades. The second solution simplifies the mechanical equipment, but requires regenerative 4Q frequency converters, offering excellent results.

01-constant speed induction generators-adjustable stator guide vanes and rotor blades-variable speed induction generator

In island operated applications, the squirrel cage induction generator has to be excited through external capacitors. This configuration works up to 15 kW, at constant speed, thus external hydraulic or ballast load controllers have to be deployed.

Several constructive variants (1/3-phase, low or medium voltage, horizontal or vertical, open-drip proof, etc.) of induction generators are available.

01-15kw constant speed squirrel cage induction generator-excited by external capacitor

RT Prototyping | Rapid Tooling

An Application of Rapid prototyping is Rapid tooling, this an automatic fabrication of machine tools. Tooling is one of the most costly steps in the manufacturing process.

01-rapid tooling-RT Rapid prototyping-Mold making examples in rapid prototyping

Tools are often complex and need to be wear resistant for production. To meet these requirements, molds and dies are traditionally made by CNC machining, EDM or other methods. All traditional methods are expensive and time consuming; making rapid tooling prototyping the desired alternative. Many believe tooling and design cost may be cut by 50% to 70% by using rapid prototyping.

Rapid tooling is divided in two categories; indirect tooling and direct tooling.

Indirect Tooling

01-indirect tooling-Rapid tooling types

Most rapid tooling today is indirect tooling. Rapid prototyping parts are used as patterns for making molds and dies. These models can be in the following manufacturing processes.

  • Investment Casting

01-investment-casting of parts

Some rapid prototyping can be used as investment casting patterns. Patterns must retain size when heated and not crack during the finishing process.

  • Injection Modeling

01-injection moulding-plastic moulding

A Stereo lithography machine is used to make a match-plate pattern of the desired molding. To form this mold it is plated with metal material such as nickel; then reinforced with ceramic. The two halves are separated to remove the pattern, leaving a perfect model capable to producing thousands of injection models.

  • Sand Casting

01-Green_Sand-casting-the traditionla method of casting cylinder blocks

A rapid prototyping model is used as a pattern which sand mold or “casting” is built. (make the following link) Laminated Object Manufacturing (LOM) machines can be used for this process. A LOM model can produce nearly 100 sand molds.

  • Vacuum Casting

01-vacuum-casting-process-fundamentals of metal casting process

The oldest and simplest rapid tooling prototyping technique; a pattern is suspended in a vat of liquid silicon. When the material cures, the pattern may be removed. The silicon molds can produce 15 or more patterns.

Direct Tooling

01-direct tooling-types of rapid tooling

To make metal tooling direct from CAD file through rapid prototyping process; is the answer to every production engineers dream.

  • Rapid tool

A process which uses SLS to sinter  poly- coated steel pellets together to produce metal mold.

  • Laser Engineering Net Shaping (LENS) –          

01-laser engineering net shaping-LENS

A process that can create metal tools directly from a CAD file. This process is capable of using multiple materials, stainless steel, HSS, tungsten carbide as well as others. A laser beam melts the top layer of the part in areas where material is to be added until the part is complete. Unlike sintering, LENS does produce a solid metal part since the metal was melted.

  • Direct AIM

01-Direct AIM-investment casting parts-RTV Molding

Another technique provided by 3D Systems of Valencia, Ca. Stereo lithography produced cores are used with traditional metal molds for injection moldings from HDPE, Polystyrene, polypropylene and ABS.

  • LOM Composite

01-laminated object manufacturing-lom_process

A method of using ceramic composite material for Laminated Object Manufacturing.

  • Sand Molding

01-sand molding-shell-mold-casting

A rapid prototyping technique that constructs sand molds directly from a CAD file.