DC Generator Components
State the operating principle of how a DC generator produces electricity.
- DC generators operate on the principle that when a coil of wire is rotated in a magnetic field, a voltage is induced in the coil.
- The amount of voltage induced in the coil is determined by the rate at which the coil is rotated in the magnetic field.
Identify the major parts of a DC generator and state their operating function.
- DC generators consist of field windings, an armature, a commutator, and brushes.
- Field windings are electromagnets used to produce the magnetic field in a generator. The magnetic field used in a generator can be produced by permanent magnets or electromagnets.
- An armature is the movable coil of wire in a generator that rotates through the magnetic field. A DC generator always has a rotating armature and a stationary field (field windings).
- A commutator is a ring made of segments that are insulated from one another. Each end of a coil of wire is connected to a segment. A voltage is induced in the coil whenever the coil cuts the magnetic lines of force of a magnetic field.
– A brush is the sliding contact that rides against the commutator segments or slip rings and is used to connect the armature to the external circuit. A DC generator is designed so that the brushes ride on the different segments of the commutator each time the current is zero. Therefore, the current in the external circuit (load) always flows in one direction; however, its magnitude varies continuously.
Explain the left-hand generator rule.
- The left-hand generator rule is the relationship between the current in a conductor and the magnetic field existing around the conductor.
- The left-hand generator rule states that with the thumb, index finger, and middle finger of the left hand set at right angles to each other, the index finger points in the direction of the magnetic field, the thumb points in the direction of the motion of the conductor, and the middle finger points in the direction of the induced current.
DC Generator Types
Explain the difference between a series-wound generator and a shunt-wound generator.
- A series-wound generator is a generator that has its field windings connected in series with the armature and the external circuit (load). In a series-wound generator, the field windings consist of a few turns of low-resistance wire because the load current flows through them.
- The output voltage of a series-wound generator may be controlled by a rheostat (variable resistor) connected in parallel with the field windings.
- A shunt-wound generator is a generator that has its field windings connected in parallel (shunt) with the armature and the external circuit (load). Because the field windings are connected in parallel with the load, the current through them is wasted as far as output is concerned. The field windings consist of many turns of high-resistance wire to keep the current flow through them low.
- The output voltage of a shunt-wound generator may be controlled by means of a rheostat connected in series with the shunt field.
Describe a compound-wound generator.
- A compound-wound generator is a generator that includes series and shunt field windings.
- In a compound-wound generator, the series field windings and shunt field windings are combined in a manner to take advantage of the characteristics of each.
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