describe the principal, construction and working of an alternating current generator (dynamo) Long answer?
Answers
Working Principle
AC generator working principle is, these are commonly referred to as alternators which work on the principle of Faraday’s Law of Electromagnetic Induction. The movement of a conductor in a uniform magnetic field changes the magnetic flux linked with the coil, thus inducing an emf.
Working of AC Generator
The coil is rotated in the magnetic field to produce a strong magnetic field. As coil on one side moves up through the magnetic field, an emf is induced in one direction. As the rotation of the coil continues and this side of a coil moves down and another side of the coil moves up, an emf is induced in the reverse direction. Fleming’s right-hand rule is used to determine the direction of the induced emf. This process repeats for every cycle and the emf produced is of alternating type.
Consider a coil of rectangular shape with ‘N’ turns that rotates in a uniform magnetic field ‘B’ of an angular velocity ‘ω’. The angle between the magnetic field ‘B’ and normal to the coil at any time ‘t’ is given by, θ = ωt.
In this position, the magnetic flux is perpendicular to the plane of a coil and is given by B Cos ωt.
Construction of AC Generator
The simple AC generator has two main parts – Rotor and Stator. The rotor is a rotating component and the stationary part of a machine is a stator.
Stator
The stator is a stationary component that efficiently holds armature winding. The armature winding purpose is to carry current to the load and the load can be any external equipment that consumes electrical power. It consists of three main parts:
Stator Frame – It is an outer frame that is used to hold stator core as well as armature windings.
Stator Core – It is laminated with steel or iron to reduce eddy current losses. Slots are made on the interior part of a core to hold armature windings.
Armature Windings – Armature windings are wound on the slots of armature core.
Rotor
The rotor is a rotating part of an AC generator. It consists of magnetic field windings. DC supply is used to magnetize magnetic poles. Each end of magnetic field windings is attached to slip rings. This combination is connected to a common shaft on which the rotor rotates. The two types of the rotor are salient pole rotor and cylindrical pole rotor.
Salient Pole Rotor
The salient pole rotor type is shown in the figure below. In this type of rotor, the number of poles gets projected, known as salient poles with their bases pinned to the rotor can be observed. They are used in low and medium speed applications.
Cylindrical type rotors consist of an unruffled and robust cylinder with slots arranged on the outer surface of a cylinder. It is used in high-speed applications. The diagram of the cylindrical pole rotor is shown below.
AC generators are of two types. They are :-
Asynchronous Generators
Asynchronous generators are also known as induction generators. In this type of generator, slip helps the rotor to rotate. Rotor always attempts to match the synchronous speed of a stator but fails. If the rotor matches the synchronous speed of a stator, the relative velocity becomes zero, and hence the rotor experiences no torque. They are suitable to run wind turbines.
Synchronous Generators
The synchronous generator is a type of AC generator that rotates at a synchronous speed. It works on the principle of Faraday’s law of electromagnetic induction – an emf is induced when a coil rotates at a uniform magnetic field. They are mainly used in power plants to generate high voltages.
Applications
The applications of the ac generator mainly include generating power from windmills, hydro-electric dams, and many more.