DC GENERATOR

WORKING PRINCIPLE • Energy can be converted form one form to another.

• It uses Faraday’s law of electromagnetic induction.• Whenever there is change in the magnetic flux

associated with conductor, an EMF is induced in it.

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Electrical Generato

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Electrical

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• The direction of induced e.m.f. (and hence current) is given by Fleming’s right hand rule

• As per Faraday's law of electromagnetic induction, whenever a conductor moves inside a magnetic field, there will be an induced current in it. If this conductor gets forcefully moved inside the magnetic field, there will be a relation between the direction of applied force, magnetic field and the current. This relation among these three directions is determined by Fleming Right Hand rule

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Simple Loop DC Generator• Consider a single turn loop ABCD rotating clockwise in a uniform

magnetic field with a constant speed as shown in Fig.(1.1). As the loop rotates, the flux linking the coil sides AB and CD changes continuously. Hence the e.m.f. induced in these coil sides also changes but the e.m.f. induced in one coil side adds to that induced in the other. E.M.F. generated in the loop is alternating one. It is because any coil side, say AB has e.m.f. in one direction when under the influence of N-pole and in the other direction when under the influence of S-pole.

• A DC Generator operates on the principle of dynamically induced emf.• To convert the alternating bidirectional alternating current into

unidirectional direct current split rings are used.• Split rings are cut into two half's called segment separated by insulated

sheet mica. The ring segments are also kept insulated from the central shaft and are connected to the ends of the coil and the carbon brushes.

• The action of split rings is called commutation

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• Yoke of DC Generator - yoke are made of cast iron – Yoke of DC generator serves two purposes • It holds the magnetic pole cores of the generator and acts as

cover of the generator.• It carries the magnetic field flux.

Construction of DC Generator

• Pole Cores and Pole Shoes of DC Generator- There are mainly two types of construction available.

• One: Solid pole care, where it made of a solid single piece of cast iron or cast steel.

• Two: Laminated pole core, where it made of numbers of thin, limitations of annealed steel which are riveted together.

• The pole core is fixed to the inner periphery of the yoke by means of bolts through the yoke and into the pole body.

• The pole shoes are so typically shaped, that, they spread out the magnetic flux in the air gap and reduce the reluctance of the magnetic path.

Construction of DC Generator

• Armature Core of DC Generator- The purpose of armature core is to hold the armature winding and provide low reluctance path for the flux through the armature from N pole to S pole. Although a DC generator provides direct current but induced current in the armature is alternating in nature. That is why, cylindrical or drum shaped armature core is build up of circular laminated sheet.

• Armature Winding of DC Generator - Armature winding are generally formed wound. These are first wound in the form of flat rectangular coils and are then pulled into their proper shape in a coil puller. Various conductors of the coils are insulated from each other. The conductors are placed in the armature slots, which are lined with tough insulating material.

Construction of DC Generator

• Commutator of DC Generator - The commutator plays a vital role in dc generator. It collects current from armature and sends it to the load as direct current. It actually takes alternating current from armature and converts it to direct current and then send it to external load.

• Brushes of DC Generator - The brushes are made of carbon. These are rectangular block shaped. The only function of these carbon brushes of DC generator is to collect current from commutator segments.

• Bearing of DC Generator - For small machine, ball bearing is used and for heavy duty dc generator, roller bearing is used

Construction of DC Generator