DC Motor vs. Three-Phase Induction Motor Components

Direct Current (DC) Motor Components

DC Motor Constitution

• Stator (Carcass or Inductor)

  The fixed part, also known as the carcass or inductor. Its function is to create the excitation magnetic field. It may use permanent magnets or electromagnets (spools located around ferromagnetic poles). The protruding poles are typically made of soft iron casing and are not in parallel.

• Rotor (Induced or Armature)

  The moving part of the motor. Its primary function is to provide torque to move the shaft and generate a counter-electromotive force (EMF) that opposes the initial current intensity traveling through the coil. The rotor creates a magnetic field that opposes the inductor's magnetic field. It consists of the induced coil wound around a slotted ferromagnetic core.

• Commutator Segments

  Each of the copper plates welded to the end of the induced coil, marking the start of the next segment. They are thin and designed for single coils.

• Collector

  This is the group of commutator segments, isolated from each other and placed on a shaft.

• Brushes

  These are fixed electrical contacts, one connected to the positive pole and one to the negative pole.

• Brush Holders

  Metal parts that hold the brushes. They press against the collector and supply current to the induced coils.

• Air Gap

  The gap between the rotor and the stator where the magnetic flux passes from one component to the other.

Three-Phase Asynchronous Induction Motor

Benefits of Asynchronous Motors

• Easy maintenance
• Cost-effective and simple design
• High starting torque
• Rated torque exceeds starting torque

Objective

To transform electrical current (AC) into mechanical energy.

Motor Constitution

• Stator

  The fixed part of the motor. Its mission is to create a rotating magnetic field. It is formed by a crown of slotted steel plates where three coils are introduced, phased 120 degrees apart.

• Rotor

  The moving part. Its mission is to interact with the stator's rotating magnetic field. The variable magnetic field induces a current in the rotor, which creates its own magnetic field that interacts with the stator's field, causing the rotor to spin.

Types of Rotors

1. Squirrel Cage Rotor

   Formed by a series of metallic conductors assembled in two metal crowns (rings) that are internally short-circuited. Ferromagnetic material sheets hold the assembly together.

2. Wound Rotor

   Composed of shunt-connected coils.

Functioning Principle

The three-phase AC circulating through the stator coils generates a rotating magnetic field. Currents are induced in the rotor conductors located within this rotating magnetic field, generating electromagnetic forces and an induced magnetic field. This induced magnetic field interacts with the stator's magnetic field, causing the rotor to turn. Note: The rotor speed never reaches the speed of the stator's rotating magnetic field (synchronous speed).