Alternator Synchronous Generator | Definition and Types of Alternator

An alternator is defined as:

An alternator is a machine which converts mechanical energy to electrical energy in the form of alternating current (at a specific voltage and frequency). Alternators are also known as synchronous generators.

History of Alternator

Michael Faraday and Hippolyte Pixii gave the very first concept of alternator. Michael Faraday designed a rotating rectangular turn of conductor inside a magnetic field to produce alternating current in the external static circuit. After that in the year of 1886 J.E.H. Gordon, designed and produced first prototype of useful model. After that, Lord Kelvin and Sebastian Ferranti designed a model of 100 to 300 Hz synchronous generator. Nikola Tesla in 1891, designed a commercially useful 15 KHz generator. After this year, poly phase alternators came into picture which can deliver currents to multiple phases.

Use of Alternator

The power for the electrical system of a modern vehicle gets produced from an alternator. In previous days, we used DC generators or dynamos for this purpose, but after the development of alternator, we replaced the DC dynamos by more robust and lightweight alternator. Although the electrical system of motor vehicles requires direct current, still an alternator along with diode rectifier instead of a DC generator is a better choice as the complicated commutation is absent in alternator. This particular type of generator used in the vehicle is known as an automotive alternator.

Another use of alternators is in diesel-electric locomotive. The engine of this locomotive is nothing but an alternator, driven by a diesel engine. The alternating current produced by this generator is converted to DC by integrated silicon diode rectifiers to feed all the DC traction motors. These DC traction motors drive the wheel of the locomotive.

We also use this machine in marine similar to a diesel-electric locomotive. We specially design the synchronous generator used in marine and navy with appropriate adaptations to the salt-water environment. The typical output level of a marine alternator is about 12 or 24 volt. In big marine sheep, more than one units are used to provide massive power. In this marine system, the energy produced by the alternator is first rectified then used for charging the engine starter battery and auxiliary supply battery of marine.

One of the primary uses of alternators is in the production of bulk ac power for commercial purposes. In thermal power plants, in hydel power plants, even in nuclear power plants, alternators only converts mechanical energy to electrical energy for supplying to the power system.

Types of Alternators

Alternators or synchronous generators can be classified in many ways depending upon their applications and designs.

The types of alternators include:

  • Automotive type – used in modern automobiles.
  • Diesel-electric locomotive type – used in diesel electric multiple units.
  • Marine type – used in marine applications.
  • Brushless type – used in electrical power generation plants as the main source of power.
  • Radio alternators – used for low brand radio frequency transmission.

We can categorize these AC generators (alternators) in many ways, but the two main categories depending on their design are:

  1. Salient Pole Type
  2. Smooth Cylindrical Type

Salient Pole Type

We use it as low and medium speed alternator. It has a large number of projecting poles having their cores bolted or dovetailed onto a heavy magnetic wheel of cast iron or steel of good magnetic quality.

Such generators get characterized by their large diameters and short axial lengths. These generators look like a big wheel. These are mainly used for low-speed turbine such as in hydel power plant.

Smooth Cylindrical Type

We use it for a steam turbine driven alternator. The rotor of this generator rotates at very high speed. The rotor consists of a smooth solid forged steel cylinder having certain numbers of slots milled out at intervals along the outer periphery for accommodating field coils.

These rotors are designed mostly for 2 poles or 4 poles turbo generator running at 36000 rpm or 1800 rpm respectively.

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