Subscribe to daily Feed

Delivered by Google Feedburner...
Mechanical Engineering

Mechanical Engineering

posted 2 months 3 weeks ago

Alternator or Synchronous Generator

Definition of Alternator

The definition of alternator is hidden in the name of this machine itself. An alternator is such a machine which produces alternation electricity. It is a kind of generators which converts mechanical energy into alternating electrical energy. It is also known as synchronous generator.

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 electric 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 were come into picture which can deliver electric currents of multiple phases.

Use of Alternator

The power for electrical system of modern vehicles produces from alternator. In previous days, DC generators or dynamos were used for this purpose but after development of alternator, the dc dynamos are replaced by more robust and light weight alternator. Although the electrical system of motor vehicles generally requires direct electric current but still an alternator along with diode rectifier instead of a DC generator is better choice as the complicated commutation is absent here. This special type of generator which is used in vehicle is known as automotive alternator.

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

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

Types of Alternator

Alternators or synchronous generators can be classified in may ways depending upon their application and design.
According to application these machines are classified as-

Automotive type - used in modern automobile.

Diesel electric locomotive type - used in diesel electric multiple unit.

Marine type - used in marine.

Brush less type - used in electrical power generation plant as main source of power.

Radio alternators - used for low brand radio frequency transmission.

These ac generators can be divided in many ways but we will discuss now two main types of alternator categorized according to their design. These are-

Salient pole type
It is used 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 are characterized by their large diameters and short axial lengths. These generator are look like big wheel. These are mainly used for low speed turbine such as in hydral power plant.

Smooth cylindrical type
It is used for steam turbine driven alternator. The rotor of this generator rotates in very high speed. The rotor consists of a smooth solid forged steel cylinder having a number of slots milled out at intervals along the outer periphery for accommodation of field coils. These rotors are designed mostly for 2 pole or 4 pole turbo generator running at 36000 rpm or 1800 rpm respectively.

Like | 0 View | 81

Mechanical Engineering

posted 2 months 3 weeks ago
                Transmission is the mechanism which is used to transfer the power developed by engine to the wheels of an automobile.  The transmission system of an automobile includes clutch, gear box, propeller shaft axle and wheels, etc.

The term ‘Transmission’ is used for a device which is located between clutch and propeller shaft. It may be a gear box, an over drive or a torque converter, etc.


Clutch is used to engage or disengage the engine to the transmission or gear box.

When the clutch is in engaged position, the engine power or rotary motion of engine crankshaft is transmitted to gear box and then to wheels.

 When clutch is disengaged, the engine power does not reach to gear box (and to wheels) although engine is running.

Clutch is also used to allow shifting or changing of gears when vehicle is running.

 For shifting gears, clutch is first disengaged then gear is shifted and then clutch is engaged.

Clutch has to be disengaged to stop the vehicle and also at the time of idling.

Principle of the clutch:

                It operates on the principle of friction.

When two surfaces are brought in contact and are held against each other due to friction between them, they can be used to transmit power.

If one is rotated, then other also rotates.

 One surface is connected to engine and other to the transmission system of automobile

 Thus, clutch is nothing but a combination of two friction surfaces.



Like | 0 View | 122