AC vs DC Generator
The electricity we use has two forms, one is Alternating and the other is Direct (means no change over time). The power supply of our homes has alternating current and voltages, but the power supply of an automobile has unchanging currents and voltages. Both forms have their own uses and the method of generating both are same, namely electromagnetic induction. The devices used to generate power are known as the generators, and DC and AC generators vary from each other, not by the principle of operation but by the mechanism they use to pass the generated current to the external circuitry.
More about AC Generators
Generators have two windings components, one is the armature, which generates the electricity through electromagnetic induction, and the other is the field component, which creates a static magnetic field. When the armature moves relative to the field, a current is induced due to the flux change around it. The current is known as the induced current and the voltage which drives it is known as electro-motive force. The repetitive relative motion required for this process is obtained by rotating one component relative to the other. The rotating part is called as the rotor, and the stationary part is called the stator. Either armature or the field can operate as the rotor, but mostly the field component is used in high voltage power generation, and the other component becomes the stator.
Flux varies with the relative position of the rotor and the stator, where magnetic flux attached to the armature varies gradually and changes polarity; this process is repeated due to rotation. Hence the output current also changes polarity from negative to positive, and to negative again, and the resulting waveform is a sinusoidal waveform. Because of this repetitive alteration in the polarity of the output, the current generated is called the Alternating Current.
AC generators are widely used for power generation, and they transform mechanical energy supplied by some source into electrical energy.
More about DC Generators
Slight change in the configuration of the contact terminals of the armature allows an output that does not change the polarity. Such a generator is known as a DC generator. The commutator is the additional component added to the armature contacts.
The output voltage of the generator becomes a sinusoidal waveform, because of the repetitive change of the polarities of the field relative to the armature. The commutator allows the change of the contact terminals of the armature to the external circuit. Brushes are attached to the armature contact terminals and slip rings are used to keep the electrical connection between the armature and the external circuit. When the polarity of the armature current changes, it is countered by changing the contact with the other slip ring, which allows the current to flow in the same direction.
Therefore, the current through the external circuit is a current which do not change the polarity with time, hence the name direct current. The current is time varying though and are seen as pulses. To counter this ripple effects voltage and current regulation must be done.
What is the difference between AC and DC Generators?
• Both generator types work on the same physical principle, but the way the current generating component is connected to the external circuit changes the way the current passes through the circuit.
• AC generators do not have commutators, but the DC generators have them to counter the effect of changing polarities.
• AC generators are used to generate very high voltages, while DC generators are used to generate relatively lower voltages.