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Basic of Alternators

 Basic of Alternators

  • Is defined that is capable of converts mechanical energy to electrical energy by electromagnetic induction is like an electrical generator, generator is a word with a combination of two words alternating and generator and alternator is distinguish between DC and AC generator.
  •  There some difference between DC generator and alternator in the connection to an external circuit the first one is connected by the commutator and the second connect by slip rings.
 By Number of Phases
  •  The electrical system In the aircraft use a three-phase alternator, we classification alternator by number of the phase of output voltage, the AC generator can have a single phase, two phase, three-phase, and more.
  By Armature or Field Rotation
  •  We can also, classification by type of rotor and stator used is excited two types of alternators the revolving field type and the revolving armature type :
 The revolving armature type:

  • this is work to the DC generator and have rotated armature is rotate through a stable magnetic field and type is found in the low power rating, the EMF generated in the armature and convert to unidirectional voltage through commutator but the AC generator is applying unchanged to the load through slip rings.
 The revolving field type:
  • Is have a rotor that has rotating field winding and stator have stationary armature winding, this stationary the armature has an advantage is can connect simply to the load without sliding contact in the circuit, and also the rotating armature is requiring brushes and slip rings and is can conduct the load current from the armature to external circuit.
 Single-Phase Alternator
  •  This type exists in many applications is can be delivered a pulsating power, The stator has 4 polar groups space around the stator frame of the alternator. And The rotor has 4 poles, the EMF generates from armature is alternating this sort of winding can use on alternator as on DC generator forms a single circuit generates output voltage and have stator can be made the number on winding in series on this alternator.
 Two-Phase Alternator
  • is have two or more single-phase winding space symmetric around the stator and there is also two single-phase winding space physically of the alternator, is induced by 90 degrees of phase the voltage induced the other and winding is separate from each other when we have some winding is cut  by  maximum flux the other cut by no flux all of this descript alternator with two-phase
 Three-Phase Alternator
  •  Is more existing in aircraft alternators is have three single-phase winding spaced and the voltage induced in any winding is 120 degrees out of phase with the voltage in the rest winding.

 Delta Connection :
  •  With this connection three phase stator connected end to end in this circuit and the line currents per phase currents are equal to the vector sum and the voltage is the same to phase voltage and when the load is balance the current per line is equal 1.73 times the phase current.
 Method of Excitation the alternator on aircraft
  •  The excitation of alternators used on the aircraft can be affected by following these steps:
  •   In the system, we have in some aircrafts system combine by DC generator fixed on the same shaft with AC generator, to variation this system is depending on the type of alternator use DC from the battery for excitation and then self-excited for alternator.
  •  Is depending on residual magnetism for initial AC voltage increase to rectification and transformation from the AC system OF this stuff.

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