What Are AC and DC Generators?

A generator is a type of machine that converts mechanical energy into electrical energy which can either be in AC or DC form. As such, the major difference between an AC and DC generator is that each generates AC or DC electrical energy respectively. Before we dive into more distinguishing characteristics, we must outline how a generator produces electricity.

How Is Electricity Generated?

Electricity is generated using Faraday’s law of electromagnetic induction which states that a current or electromotive force is induced in a conductor when it is placed in a changing magnetic field. AC and DC generators apply this principle to generate electrical current. However, there are two distinct ways to vary the magnetic field acting on the conductors.

The magnetic field can be rotated around a stationary conductor, or the conductor can be spun within a stationary magnetic field. In either case, the magnetic field lines acting on the conductor change and induce an electric current in the conductor. Generators, in particular, take advantage of the method wherein the conductor spins inside a stationary magnetic field.

Meanwhile, the conductor is wound around a rectangular armature, and due to the fact that it rotates inside the generator, it is generally called the rotor. The magnetic field surrounding the rotor is either a permanent magnet or electromagnet energized by a separate DC supply that remains stationary; thus, it is called the stator of the generator.

As the rotor rotates inside a stationary magnetic field, the direction of the induced current changes through half rotation increments. That being said, the current produced inside the rotor is always AC. To supply the current from the rotor to the stator, slip ring and split ring commutators are utilized. These special devices help provide AC and DC supply to the circuit.

AC Generator

AC generators are specially-designed to generate alternating current (AC) with a frequency of 50 or 60 Hz. The current induced in the rotor is provided to the circuit via slip rings. The slip rings consist of two separate conducting rings affixed to the rotor’s terminals and supply current to the circuit through sliding contacts called brushes. When in operation, the brushes remain stationary, while the rings rotate within the rotor. The slip rings themselves are continuously providing the alternating current generated inside the rotor. Because the brushes slide across the rotor, there is no risk of short circuiting or sparking. It is worth noting that alternators are another type of generator that only generates AC electrical energy.

DC Generator

Also called dynamos, DC generators produce a pulsating direct current that does not change its direction. Within the rotor, the induced current is alternating in nature and is converted into DC with the help of a split ring commutator. The commutator provides the current from the rotor to the stationary circuit while maintaining the direction of the supplied current. The split ring is a ring-shaped conductor that is split in half so that there are two clearances between the rings. Each side of the conductor is connected to the terminals of the armature conductor, and two stationary brushes slide across it. Since the current in the rotor is AC, each half rotation changes the current direction in each half of the ring. With this in mind, the output current supplied via the stationary brushes stays in one direction. Unlike AC generators, the gap between the rings makes the brushes touch both halves simultaneously, causing short circuiting and sparking between them. Generally, this wears out the brushes rapidly and reduces the service life of the generator.


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