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I searched about this, but couldn't find any helpful explanations. All it says is that magnetic field is generated by either permanent magnets or electromagnets. In both cases, how does the exciter generator start, so that it creates magnetic field according to physics, (e.g. Lorentz law, or another) ?

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  • $\begingroup$ Hi, I'm having problems understand your question! Is this about the DC motor-generators? What do you mean by exciter? $\endgroup$ – Sam Farjamirad Dec 22 '18 at 21:40
  • $\begingroup$ I am new to the subject, that might be the reason. I guess the ones with permanent magnets are DC, and electromagnets are AC. I want to understand how exciter generators actually work, so that the AC or DC powered generator can start. Simply, I want to learn the principle of exciter generators (how they get started, and how they excite) $\endgroup$ – Vyun Dec 22 '18 at 23:10
  • $\begingroup$ The excitation winding is a part of stator in DC machines which produce the constant magnetic field, every conductor carrying current generates a magnetic field around itself that's how an electromagnets works a very very simplified version. But i don't understand where the problem lies? How AC induction or DC-machines works are actually the very comprehensive theory, i'm afraid i can't explain it here, because i don't know how much you know about electromagnetism, but if you have still question about specific type of AC or DC machines i would glad to help, sure others try to collaborate. $\endgroup$ – Sam Farjamirad Dec 22 '18 at 23:16
  • $\begingroup$ So, all generators actually initially produce AC current? In principle, if what generator is transforming mechanical energy to electrical energy, I just do not understand what role the exciter generator takes. $\endgroup$ – Vyun Dec 24 '18 at 22:34
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There are two ways that exciter generators start, so they can then spin up the excitation current to start a larger generator.

The easy way is to use permanent magnets in the exciter generator. As soon as it begins to turn, it will generate the current to get the main generator going.

The tricky way is to rely on the fact that the iron in the armature and rotor of a generator usually retains a small amount of magnetic field even when the generator is shut down. When you start spinning this kind of generator, that residual field allows the generator to make its own excitation current and the generator will then start itself.

The self-starting principle using residual magnetism is commonly used in small gasoline engine powered AC generators.

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  • $\begingroup$ So, we start it manually and literally mechanically the permanent magnet types? But, I guess for that (and I guess that is DC), we need brushes, since they cannot induce emf? Then how do the AC and DC ones difference in that sense. I mean, if the starting principle is the same (self-starting) how do we exactly get an AC (sine wave) generator? Is it because the magnets start to sping with chemical energy (gasoline)? If so, another question, how exactly do we start it? (What do we do to make it start working)? $\endgroup$ – Vyun Dec 24 '18 at 14:18
  • $\begingroup$ Many questions here. Why not first have a look at wikipedia entries for generator, exctitation current, self exciting generator? $\endgroup$ – niels nielsen Dec 24 '18 at 20:21

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