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  • By the way, even in the Britannica the principle by which an EMF is induced in the conductor of a synchronous generator with closed magnetic fields is not indicated; there is only a statement of the result.

    Electric generator | Types, Uses & Advantages | Britannica


    Rotor


    elementary synchronous generator

    An elementary synchronous generator is shown in cross section in Figure 2. The central shaft of the rotor is coupled to the mechanical prime mover. The magnetic field is produced by conductors, or coils, wound into slots cut in the surface of the cylindrical iron rotor. This set of coils, connected in series, is thus known as the field winding. The position of the field coils is such that the outwardly directed or radial component of the magnetic field produced in the air gap to the stator is approximately sinusoidally distributed around the periphery of the rotor. In Figure 2, the field density in the air gap is maximum outward at the top, maximum inward at the bottom, and zero at the two sides, approximating a sinusoidal distribution.
    Stator

    The stator of the elementary generator in Figure 2 consists of a cylindrical ring made of iron to provide an easy path for the magnetic flux. In this case, the stator contains only one coil, the two sides being accommodated in slots in the iron and the ends being connected together by curved conductors around the stator periphery. The coil normally consists of a number of turns.

    When the rotor is rotated, a voltage is induced in the stator coil. At any instant, the magnitude of the voltage is proportional to the rate at which the magnetic field encircled by the coil is changing with time—i.e.,the rate at which the magnetic field is passing the two sides of the coil. The voltage will therefore be maximum in one direction when the rotor has turned 90° from the position shown in Figure 2 and will be maximum in the opposite direction 180° later. The waveform of the voltage will be approximately of the sine form shown in Figure 1.



    I made my own drawing which is exactly consistent with the maximum EMF with a three-phase winding and an implicitly polar magnetic rotor.

    480452977_9226741477409199_1244883750594752467_n.jpg?_nc_cat=103&ccb=1-7&_nc_sid=bd9a62&_nc_ohc=4C5fZtzzN8oQ7kNvgH9qPo4&_nc_zt=23&_nc_ht=scontent-iad3-2.xx&_nc_gid=fZ79WcEDj4_MyBqCKKc-aw&oh=00_AYH7Pxe3WIHgknznnljXs5BA-BR_HpXctxTo calculate the maximum EMF in a three-phase generator, you need to use this position. By the way, one of my friends asked his acquaintances in Israel to perform a registration of the maximum EMF depending on the rotor position on very good equipment. Unfortunately, these results were not provided to me for review, although I was the initiator of such a study. They wanted to prove me wrong. I wonder why they refused?
    Attached Files
    Last edited by Rakarskiy; 03-17-2025, 08:09 AM.

    Comment


    • Rakarskiy,
      Change subject somewhat.

      Your red and blue dynamo model isn't a very good design. It appears that half of the armature turns are ineffective. Therefore 250 instead of 500 should be used in the generated voltage calculation.

      Polish_20250317_075325923.png
      The upper two coil segments indicated with blue circle/dot are enclosed by the main magnetic circuit, or anapole, passing through A & B on the rotor, whereas the lower two, blue circles with cross, are not inside the main flux loop.

      Except for the single line in your FEMM connecting the bottom of the stator. If there is a flux linkage there, it will render the lower armature copper (circles with cross) counterproductive.

      Poor design.
      bi

      Comment


      • This illustrative model of an alternator is inefficient, but it is a model that shows students a real example of an alternator with a core. In a real armature, there are two windows (two focuses) or in a real turbo generator, both magnetic anapoles also participate with maximum generation efficiency.

        Comment


        • Originally posted by Rakarskiy View Post
          ...

          If we consider the components of the magnetic circuit and the EMF diagram, we see that the induction of electromagnetic force occurs when the cross-section in which the magnetic circuit is closed changes. Induction is induced only in the wire that is in the focus of the changing magnetic circuit. At the same time, with a complete closure in the minimum or maximum value, the cross-section in which the magnetic circuit is closed, the induction of EMF is not induced. The main element in this case is the change in the cross-section of the conducting circuit in which there is a closed source of constant magnetic field.
          Ф = Bm*S, where S = a*b changes
          [/QUOTE]

          Rakarskiy,
          Your latest example contradicts the above observation, doesn't it?
          bi

          image_26148.gif

          Comment


          • This does not contradict, because these are two different systems. In addition, if you simulate an armature with a current that creates its own magnetic field of the armature, then everything works according to the algorithm of magnetization and remagnetization of the armature during rotation. I have already made the appropriate modulation. Rotation at idle is different from rotation with a current in the armature winding. I will make a video with explanations and animation.

            463238777.gif75952967.gif

            As for the drawing that you tried to attach to the moving armature, in this case the algorithm of my previous slide will be executed, a classic simpler AC generator with a moving magnetic rotor.
            ​​​​​​In the video we will also analyze this option.

            155718493.jpg
            2023-11-09_085408.jpg?_x_tr_sl=en&_x_tr_tl=uk&_x_tr_hl=ru&_x_tr_pto=wapp.jpg
            Last edited by Rakarskiy; Yesterday, 01:16 PM.

            Comment


            • Originally posted by Rakarskiy View Post
              The main element in this case is the change in the cross-section of the conducting circuit in which there is a closed source of constant magnetic field.

              Ф = Bm*S, where S = a*b changes
              Why you refer to it as "main element"? It is nothing more than saliency There are salient pole dynamos and non-salient ones. But the main "element" is changing magnetic flux influencing armature conductor(s). Look it up.
              bi

              Reference:

              Subject entered to Google search: -saliency in generator design-

              AI generated

              In generator design, "saliency" refers to the presence of protruding poles (salient poles) on the rotor, which differ from the smooth, cylindrical rotors of non-salient machines, impacting performance and application suitability.

              Here's a more detailed explanation:
              What is Saliency?
              Definition:
              Saliency, in the context of electric machines, refers to the degree to which the rotor poles "stand out" or project beyond the general outline of the rotor surface.

              Salient Pole vs. Non-Salient Pole:
              Salient Pole: Features protruding poles (salient poles) attached to a magnetic wheel.
              Non-Salient Pole (Cylindrical/Turbo): Has a smooth, cylindrical rotor surface, often with slots for windings.

              Inductance Variation:
              Saliency is also characterized by a variation in inductance depending on the rotor position, also known as inductance saliency or magnetic saliency.

              Impact on Generator Design and Performance:
              Application:
              Salient pole rotors are commonly found in synchronous AC generators operating at lower speeds, such as those used in diesel engine generators and hydroelectric plants. Non-salient rotors are used in generators connected to high-speed prime movers like steam turbines.

              Torque and Load Angle:
              Saliency influences the torque characteristics of the generator. The effect of saliency caused by reluctance torque shows that the load angle during rated operation increases, and the pull-out torque is obtained at a power angle greater than 90 degrees.

              Overload Capability:
              For applications where overload capability is important, saliency must be considered, and the generator design adapted according to the behaviour at overload operation.

              Design Considerations:
              The design of salient-pole wound-rotor (inner rotor) synchronous generators involves considering the air-gap between pole shoes and the internal diameter of the stator.

              Saliency Ratio:
              The saliency ratio is the ratio between q- and d-axis inductances.

              Examples:
              Salient-pole, ferrite generator: Has lower maximum torque than an NdFeB generator and a larger voltage drop at high current.
              12/10 DC-VRM sensorless drive: Reconstructing saliency effect in a 12/10 DC Vernier Reluctance machine can achieve sensorless operation in zero/low-speed regions.
              https://youtu.be/YZlc8OIc4mw?si=IrLQDgDvSzUvpw3o
              Last edited by bistander; Today, 01:28 AM.

              Comment

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