Module 3 IoT Processing Topologies and Types

 Working principle of a DC generator:
 According to Faraday’s laws of electromagnetic induction, whenever a conductor is placed in a varying
magnetic field (OR a conductor is moved in a magnetic field), an emf (electromotive force) gets induced
in the conductor.
 The magnitude of induced emf can be calculated from the emf equation of dc generator.
 If the conductor is provided with the closed path, the induced current will circulate within the path.
 In a DC generator, field coils produce an electromagnetic field and the armature conductors are rotated
into the field.
 Thus, an electromagnetically induced emf is generated in the armature conductors.
 The direction of induced current is given by Fleming’s right hand rule.
 The two basic essential parts of an generator are
1) a magnetic field and
2) conductors which move inside that magnetic field.

 According to Fleming’s right hand rule, the direction of induced current changes whenever the direction
of motion of the conductor changes.
 Consider an armature rotating clockwise and a conductor at the left is moving upward.
 When the armature completes a half rotation, the direction of motion of that particular conductor will be
reversed to downward.
 Hence, the direction of current in every armature conductor will be alternating.
 But with a split ring commutator, connections of the armature conductors also gets reversed when the
current reversal occurs.
 We get unidirectional current at the terminals.

 DC Generator
 A dc generator is an electrical machine which converts mechanical energy into direct
current electricity.
 This energy conversion is based on the principle of production of dynamically induced
emf.
 A DC generator can be used as a DC motor without any constructional changes and
vice versa is also possible.
 Thus, a DC generator or a DC motor can be broadly termed as a DC machine

Yoke
 The outer frame of a generator or motor is called as yoke.
 Yoke is made up of cast iron or steel.
 Yoke provides mechanical strength for whole assembly of the generator (or motor).
 It also carries the magnetic flux produced by the poles.
Poles
 Poles are joined to the yoke with the help of screws or welding.
 Poles are to support field windings.
 Field winding is wound on poles and connected in series or parallel with armature winding or sometimes
separately.
Pole Shoe
 Pole shoe is an extended part of the pole which serves two purposes,
(1) to prevent field coils from slipping and
(2) to spread out the flux in air gap uniformly.

Field winding: wound on the poles with a definite direction.
 Usually made of copper.
 Field coils are former wound and placed on each pole and are connected in series.
 They are wound in such a way that, when energized, they form alternate North and South poles.

Armature
Armature core:
 Rotor of the machine.
 It is cylindrical in shape with slots to carry armature winding.
 The armature is built up of thin laminated circular steel disks for reducing eddy current losses
 It may be provided with air ducts for the axial air flow for cooling purposes.
 Armature is keyed to the shaft.
Armature winding:
 It is usually a former wound copper coil which rests in armature slots.
 The armature conductors are insulated from each other and also from the armature core.
 Armature winding can be wound by one of the two methods; lap winding or wave winding.
 Double layer lap or wave windings are generally used.
 A double layer winding means that each armature slot will carry two different coils.

 Commutator and brushes:
 Physical connection to the armature winding is made through a commutator-brush arrangement.
 The function of a commutator, in a dc generator, is to collect the current generated in armature
conductors.
 Whereas, in case of a dc motor, commutator helps in providing current to the armature conductors
 A commutator consists of a set of copper segments which are insulated from each other.
 The number of segments is equal to the number of armature coils.
 Each segment is connected to an armature coil .
 Commutator is keyed to the shaft.
 Brushes are usually made from carbon or graphite.
 They rest on commutator segments and slide on the segments when the commutator rotates keeping the
physical contact to collect or supply the current.

Types of Armature Winding
1. Lap Winding
2. Wave winding

 Conductor: It is the actual armature conductor which is under the influence of the magnetic field, placed
in the armature slot.
• Turn: The two conductors placed in different slots when connected together, forms a turn. While
describing armature winding the number of turns may be specified from which, the number of
conductors can be decided.
• Z = 2 × Number of turns
Coil: For simplicity of connections, the turns are grouped together to form a coil.
If coil contains only one turn it is called single turn coil while coil with more than one turn is called
multiturn coil.
Pole-pitch: The distance between the two adjacent poles is called a pole pitch. It is measured in terms
of number of slots. Thus total slots along the periphery of armature divided by the total number of
poles is called a pole pitch.
Pole pitch = Number of armature slots / P
If armature bore diameter is given then the pole pitch can be obtained as,
Pole pitch = π × Вore diameter / P
Thus expressing bore diameter in metres, the pole pitch in metres can be obtained.

 Separately Excited
 The field coils are energized from an independent exterior DC source in a separately excited type
generator.

Module 3 IoT Processing Topologies and Types

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