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The DC machine has three main

  •  The DC machine has three main

    • Field or excitation system, represented 
    • Armature, represented
    • Commutator, represented

     

    The field system is stationary in DC machines and the field winding is wound on salient poles. The field system produces the magnetization required for the machine and is called as the stator of the machine.

     

    The stator of a DC machine consists of 

     

    • Yoke or frame
    • Main poles
    • Interpoles
    • Field winding

     

     

    Yoke or frame

    Yoke or frame is the part of the magnetic circuit of the DC machine. It also provides mechanical support to the machine. The yoke need not be laminated as the field system is stationary.

     

    Main poles

    Main poles are designed to produce the main magnetic flux. It consists of pole core and pole shoe. The pole shoe has dual functionality, i.e., it

    1. Supports the field coils
    2. Spreads the flux in airgap

    As the cross-section of pole shoe is increased, it reduces the reluctance of the magnetic path. The complete pole is built of laminations of sheet steel and is bolted together. They are bolted through the yoke in to the pole body.

     

    Interpoles

    Interpoles are provided to improve commutation and thus they ensure sparkless operation of the machine. They are made of laminated low carbon steel in case of large machines. Solid low carbon steel poles are used in case of small machines. They are tapered or parallel sided. To avoid magnetic saturation at the root, they are tapered to have sufficient sectional area.

     

    Field winding

    It is of two types: main field winding and interpole winding.

     

    Main field winding

    The main field winding consists of field coils wound with round copper wires for small and medium size machines. Rectangular conductors are used for large size machines. They are form wound for the correct dimension. The former is removed and the wound coil is placed over the pole body. The field winding can be wound with both series and shunt coils. The series field coil has a larger cross-section and is placed below the shunt coil.

     

    Interpole winding

    Similar to main field winding, the interpole winding is also made of round or square strip wire in case of smaller machines and are made of rectangular strips in case of larger machines.

     

    Reference: Electrical DC Machine Design

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