Types of DC machines
DC machines are the electro-mechanical energy converters, which work from a dc source and generate mechanical power or convert mechanical power into a dc power. These machines can be broadly classified into two typ on the basis of their magnetic structure.
These are types of dc machines, these are two types
1. Homo polar machines
2. Hetropolar machines
1. Homo polar Machines
Even though the magnetic poles occur in pairs, the homo polar generator are arranged in such a manner that they always move under one polarity. Either North Pole or south pole could be used for this purpose. Since the conductor encounter, the magnetic plus the same formality everywhere it is called a home polar generator. A cylindrical smarted geometry is chosen. The conductor can be situated on the surface of the rotor with one slip ring and each of the conductors. A symbol instructor where there is only one cylindrical conductor with ring burses situated at the ends. The excitation coil produce a field which enter the inner member from outside all along the periphery the conductor thus see only one pole polarity or the flux directed in one sense. A study voltage now appear across the brushes.. it any give of rotation.
The polarity of the induce voltage can be reversed by reversing either excitation or the direction of rotation but not both. The voltage induce would be very low but such machine can supply the current of very large amplitude. Such source are used some application like pulse current and MHD generator, liquid metal pumps or plasma rockets the steady field can also be produced using of permanent magnet of ring shape which is radically magnetize. If higher voltage is required one force to connect many conductor in series. this series is connection has to be done externally. Many conductor must situated on the rotating structure each connected to a pair of sleep ring.
The voltage drop at the brushes become very significant at this level bringing down the efficiency of the power conversation. Even though homo polar machine are DC generator in a strict sense that the generate steady voltages. They are not quit useful for day-to-day use. A more practical converter can be found in a dc machine family called “hetero-polar” machines.
2. Hetro-polar DC machine
In the case of a hetro-polar generator, the induced EMF in a conductor goes through a cycle in voltage as it passes under north and South Pole polarity alternate. The induced EMF in the conductor therefore is not a constant but alternates in magnitude . For a constant velocity of sweep the induced e.m.f is directly proportional to the flux density under which it is moving .if the flux density variation is sinusoidal in space, then a sine wave voltage is generated. This principle is used in the ac generators; our aim is to get a steady dc voltage at the terminals of the winding and hots the shape of the EMF in the conductors. This is achieved by employing an external element, which is called a commutator, with winding.
hence these are main types of dc machines if you find incorrect in above please comment below.