One of the most important discovery in electromagnetism is the electromagnetic induction which led to the construction of generators which are used to produce electrical energy in power stations.
A generator is a device which converts mechanical energy to electrical energy that’s why it is also defined as an energy converter. It is a device that generates emf. There are two types of generators – AC generator and DC generator.
An AC generator does not have a commutator. AC stands for alternating current. Figure ac1 shows a schematic diagram of an AC generator and ac2 shows the variation of emf over a complete rotation.
Based on the figure, the different parts of the AC generator are external rotator, slip rings, brushes, external circuit, magnet, and a loop of wire. The loop of wire or conductor rotates in a magnetic field, which produces emf. The end’s slip rings connect the end of the loop to the external circuit. The induced emf produced by the rotation of the loop in the magnetic field is expressed mathematically as
\varepsilon = \varepsilon_m sin \omega_d t (1)
where \varepsilon is the induced emf;
\varepsilon_m is the amplitude of the emf, m means maximum;
\omega_d is the angular frequency which is equal to the angular speed of the loop as it rotates in the magnetic field; and
\omega_dt is the phase of the emf.
When the loop is part of a closed conducting path, the induced emf produces an alternating current along the path with the same angular frequency which is called as the driving angular frequency. This current can be represented by the mathematical equation below
i = I\sin(\omega_dt - \phi).
The DC generator has almost the same components as the AC generator. The only difference is that DC generator has a commutator. The commutator functions as the slip rings in the AC generator. In a DC generator, induced emf in the coil reverses only when the coil in in the vertical position. Because of this, the one brush will always be positive and the other is negative. Although the value of the of emf changes, its direction never changes, thus, producing a direct current in an external circuit. Figure dc1 shows a schematic diagram of a dc generator and dc2 shows the graph of the emf in the brushes.