# Generators Part I (NAVEDTRA 14177 through page 1-12)

 The AMOUNT of voltage generated depends on what 4 factors? 1) The strength of the magnetic field2) The angle at which the conductor cuts the magnetic field3) The speed at which the conductor is moved4) The length of the conductor within the magnetic field The POLARITY of the voltage depends on what 2 factors? 1) The direction of the magnetic lines of flux2) The direction of movement of the conductor What is the simplest elementary generator that can be built? An AC generator An elementary generator consists of a wire loop placed so that it can be rotated in a ____________ Stationary magnetic field.Note: This will produce an induced emf in the loop.  Sliding contacts (brushes) connect the loop to an external circuit load in order to pick up or use the induced emf. In the elementary AC generator, what is the armature? The loop of wire that rotates through the field To what are the ends of the armature loop connected? Slip rings In the elementary AC generator, what do the slip rings and brushes do? The slip rings rotate with the armature.  The brushes, usually made of carbon, with wires attached to them, ride against the rings.  The generated voltage appears across these brushes. In the elementary AC generator, what is the position of the armature loops at 0 degrees? And what is this position called? Perpendicular to the magnetic fieldThis position is called the neutral plane The elementary DC generator What replaces the slip rings of the AC generator? A commutatorNote: This is the main difference in construction of the DC generator vs. the AC generator What is the process of commutation? The commutator mechanically reverses the armature loop connections to the external circuit.  This occurs at the same instant that the polarity of the voltage in the armature loop reverses.  Through this process, the commutator changes the generated AC voltage to a pulsating DC voltage. How many commutator segments are required in a 2-coil generator? 4 Instead of the permanent magnets used in the elementary generator, what do nearly all practical generators use? Electromagnetic poles Of what do electromagnetic field poles consist? Coils of insulated copper wire wound on soft iron cores What are the 2 main advantages of using electromagnetic poles? 1) Increased field strength2) A means of controlling the strength of the fieldsNote: By varying the input voltage, the field strength is varied.  By varying the field strength, the output voltage of the generator can be controlled. Sparking between the brushes and the commutator is an indication of what? Improper commutation. What is the main cause of improper commutation? Improper brush placement The magnetic field produced by current in the armature of a DC generator affects the flux pattern and distorts the main field. This distortion causes a shift in the neutral plance, which affects commutation. What is this change in the neutral plane and the reaction of the magnetic field? Armature reaction In small generators, how are the effects of armature reaction reduced? By actually mechanically shifting the position of the brushes In larger generators, what 2 means are used to eliminate armature reaction? 1) Compensating windings2) Interpoles Of what do compensating windings consist? A series of coils embedded in slots in the pole faces.  These coils are connected in series with the armature. What is motor reaction? When a generator delivers current to a load, the armature current creates a magnetic force that opposes the rotation of the armature. What is the device that provides the turning force applied to the armature? The prime moverNote: The prime mover may be an electric motor, a gasoline engine, a steam turbine, or any other mechanical device that provides turning force. In DC generators, certain forces act to decrease the efficiency. These forces, as they affect the armature, are considered as losses and may be defined as follows: 1) I2R, or copper loss in the winding2) Eddy current loss in the core3) Hysteresis loss (a sort of magnetic friction) What causes copper losses? The power lost in the form of heat in the armature winding of a generator is known as copper loss.  Heat is generated any time current flows in a conductor.  Copper loss is an I2R loss, which increases as current increases. How do we minimize copper loss in armature windings? By using large diameter wire Authorloveofthesea83 ID258947 Card SetGenerators Part I (NAVEDTRA 14177 through page 1-12) DescriptionStudy for the AE3 exam in 2014 Updated2014-01-29T02:30:47Z Show Answers