mapua ee153 q1 sir chua

8/14/2019 MAPUA EE153 Q1 SIR CHUA

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DYNAMO

1. FUNCTIONAL VIEW

GENERATOR – a rotating machine converting mechanical energy

into electrical energy.

MOTOR – a rotating machine for converting electrical energy

into mechanical energy.

2. STRUCTURAL POINT OF VIEW

Dynamo- is a rotating machine which functions by producing a

relative motion between electrical conductors and a magnetic field.

ESSENTIAL PARTS OF A DC MACHINE

1. Magnetic frame or field yoke

Serves as a return path for all the circulating magnetic flux that

passes from the field poles to the armature.

Made of cast iron, cast steel, or rolled steel. Acts as mechanical support for the poles and also for the end

pieces which carry the bearings.

2. Pole cores and pole shoes

The pole core holds the pole windings coils (field coils). It serves

as magnetic path for the magnetic field pole produced by the

field coils.

Pole shoes spread out the flux in the air gap reducing the

reluctance of the magnetic path. It also supports the field coils.

Made of thin lamination of highly magnetic steel alloy.3. Pole coils or field coils

When current is passed through the field coils, they electro

magnetize the poles which produce the necessary flux that is

cut by revolving armature conductors.

4. Armature core

Serves as a support for the winding conductors that pass

through the magnetic field.

Provides as path for the magnetic flux through the armature

from North Pole to South Pole.

5. Armature windings or conductor

The winding wherein the voltage is induced electromagnetically.

Placed in the armature slots, which are lined with tough

insulating material. This slot insulation is folded over above the

armature conductors and is secure in place by special hand

wooden or fiber wedge.

6. Commutator Provide electrical connection between the rotating armature

coils and the stationary eternal circuit.

As the armature rotates, it performs a switching action,

reversing the electrical connections between the outside lines

and each armature coil voltages add together and result in a dc

output viltage.

7. Brushes

Collect the current from the commutator.

Normally made of carbon or carbon graphite or a copper filledcarbon mixture.

MAGNETIC CIRCUIT OF A DC MACHINE

1. Field Poles

2. Field Yoke

3. Air Gap

The space between the armature and the pole shoes (from top

of teeth to pole face).

4. Armature Core

ELECTRICAL CIRCUIT OF A DC MACHINE

1. Field Pole windings

2. Armature windings

3. Commutator

4. Brushes

SLOT PITCH/SLOT SPAN (Sp)



Distance from center of one slot to center of adjacent slot

measured on the armature.

POLE PITCH

6 slots

The periphery of the armature divided by the number of poles

of the generator between two adjacent poles.

CONDUCTOR

The length of the wire lying in the magnetic field and in which

the emf is induced.

COIL OR WINDING ELEMENT

Two conductors along with their end connections constitute

one coil or winding element.a. SINGLE-TURN COIL

A single turn coil will have two conductors.

b. MULTI-TURN COIL

A multi-turn coil may have many conductors per coil side. The

group of wires or conductors constituting a coil side of a multi-

turn coil is wrapped with a tape as a unit and is placed in the

armature slot.

COIL SPAN OR COIL PITCH (Ys)

4 slots

It is the distance, measured in terms of armature slots (or

armature conductors) between two sides of a coil.

It is the periphery of the armature spanned by the two sides of

a coil.

a. FULL-PITCHED

The coil span or the coil-pitch is equal to the pole pitch. In this

case, the coil sides lie under opposite poles, hence the induced

emf will be maximum.

b. FRACTIONAL-PITCHED

If the coil-span is less than the pole-pitch, then the winding is

fractional-pitched. The total emf round the coil, which is the

vector sum of the two coil sides, is less compared to the full-

pitched.

PITCH OF A WINDING (Y)

It is the distance round the armature between two successive

conductors, which are directly connected together.

It is the distance between the beginnings of two consecutive

turns.

BACK PITCH (Yb)

It is the distance, measured in terms of the armature

conductors, which a coil advances on the back of the armature.

FRONT PITCH (Yf)

It is the number of armature conductors or elements spanned

by a coil on the front (or commutator end of n armature).

It is the distance (in terms of armature conductors between the

second conductor of one coil and the first conductor of the next

coil which are connected together at the front.

COMMUTATOR PITCH (Yc)

It is the distance (measured in commutator bars or segments)

between the segments to which the two ends of a coil are

connected.

SINGLE-LAYER WINDING

It is that winding in which one conductor is placed in each

armature slot.

POLE ARC



Radial length of pole face

ONE LEADS OR FRONT END CONNECTION

Ends or leads that connect to the commutator bars.

TWO-LAYER WINDING

In this type of winding, there are two conductors or coil sides

per slot arranged in two layers. Usually, one side of every coil

lies on the upper half of one slot and the other side lies in the

lower half of some other slot at a distance of approximately one

pitch away.

LAP AND WAVE WINDINGS

These are the type of winding employed for drum type

armature. The difference between the two is merely due to thearrangement of the end connections at the front or

commutator end of the armature. The lap winding is also known

as multiple winding while for wave winding is also known as the

series winding.

RULES APPLIED TO BOTH TYPES OF WINDINGS:

1. The front pitch and the back pitch are each approximately equal to

the pole pitch i.e. windings should be full pitched. This results in

increased emf round coils.2. Both pitches should be odd otherwise it would be difficult to place

the coils properly on the armature. For example, if Yb and Yf were

both even, then all the coils sides and conductors would lie either in

the upper half of the slots or in the lower half. Hence, it would

become impossible for one side of the coil to lie in the upper half of

one slot and the other side on the lower half of some other slot.

3. The number of commutator segments is equal to the number of

slots or coils (or half the number of conductors) because the front

ends of conductors are joined to the segments in pairs.

4. The winding must close upon itself i.e. if we start from a given point

and more from one coil to another, then all conductors should be

traversed and we should reach a break or discontinuity in between.

TYPES OF GENERATOR:

1. SEPARATELY-EXCITED GENERATOR

Are those whose field magnets are energized from an

independent external source of dc current or it’s a winding also

called shunt field winding is connected to an outside source (a

battery or another dc generator). It is used for laboratory

experiment purpose where voltage, are likely to be varied.

2. SELF-EXCITED GENERATOR

Are those whose field magnets are energized by the current

produced by the generators themselves.

a. SHUNT-WOUND

The field windings are connected across or parallel with the

armature conductors and have the full voltage of the generator

applied across them. It is used for constant voltage application

like in electric welding.

b. SERIES-WOUND

In this case, the field windings are joined in series with the

armature conductors. As they carry full load current, they

consist of relatively few turns of thick wires. It is used for

constant current application like in series lighting.

c. COMPOUND-WOUND

It is the combination of a few series and a few shunt windings

and can either be short-shunt or long-shunt.

TYPES OF COMPOUND GENERATOR ACCORDING TO DIRECTION OF FLUX

1. CUMULATIVELY COMPOUNDED

The series field aiding the shunt field for supplying power and

lighting loads.

a. UNDER COMPOUNDED



o The full load terminal voltage is less than the no load

voltage. It is used when the load is near from the

generator.

b. FLAT COMPOUNDED

o The full load terminal is the same as the no load

voltage. It is used when the load is at medium distance

from the generator.c. OVER COMPOUNDED

o The full load terminal voltage is greater than the no load

voltage. It is used when the load is far from the

generator.

2. DIFFERENTIALLY COMPOUNDED

The direction of flux of the series field winding opposes the

direction of the flux of the shunt field winding. It is used for

electric welding.

PRIME MOVERS:

1. Hydraulic Turbines

2. Steam Turbine

3. Internal Combustion Engine

COMPENSATING WINDING

Connected in series with the armature.

Used to neutralize armature reaction.

INTERPOLE WINDING

Connected in series with the armature. Used for spark less

commutation.

DIVERTER RESISTANCE

Connected in parallel with the series field.

mapua ee153 q1 sir chua

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