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ACDC > Dc Machines > Flashcards

Dc Machines Flashcards

1
Q

is a device which
converts mechanical energy into electrical
energy or vice versa.

A

ELECTRICAL MACHINES

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2
Q

– interaction of both magnetic and
electric field
– electromagnetic induction

A

BASIC Principles:
Electromagnetics

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3
Q

– are the fundamental
mechanism by which energy is converted from
one form to another in motors, generators, and
transformers.

A

Magnetic Fields

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4
Q

Four basic principles describe how magnetic fields are used in these devices:

A
  1. A current-carrying wire produces a
    magnetic field in the area around it.
  2. A time-changing magnetic field induces a voltage in a coil of wire if it passes
    through that coil. (This is the basis of
    Transformer Action).
  3. A current-carrying wire in the presence
    of a magnetic field has a force induced
    in it. (This is the basis of Motor Action)
  4. A moving wire in the presence of a
    magnetic field has a voltage induced in
    it. (This is the basis of Generator Action).
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5
Q

– the induced emf in a closed loop
equals to the negative of the time rate of
change of magnetic flux.

A

FARADAY’S Law

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6
Q

– The direction of any magnetic induction effect is such as to oppose the cause of the effect.

A

LENZ’S Law

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7
Q

– can work as generators, motors and
brakes

A

DC Machines

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8
Q

The machine is driven by a prime mover
(such as a steam turbine or a diesel engine)
with the mechanical power converted into
electrical power.

A

GENERATOR MODE

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9
Q

The machine is drives a mechanical load
with the electrical power supplied converted
into mechanical power.

A

MOTOR MODE

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10
Q

The machine decelerates on account of
the power supplied or dissipated by it and,
therefore, produces a mechanical braking
action.

A

Brake mode

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11
Q

Applications of DC Machines
DC Generators: 1-4

A
  1. early power systems (until late 1800’s)
  2. power sources for standalone systems
    (cellular & telephone towers)
  3. used to control speed and torque of
    motors used in lifts, cranes, trains,
  4. voltage regulators to make up for the
    voltage drop in DC distribution feeders
    such as railways.
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12
Q

Applications of DC Machines
DC Motors: 5-7

A
  1. commonly used in household (in toys,
    electric shaver, electric toothbrushes,
    printers, etc…)
  2. small DC motors are used as control
    devices
  3. medical equipment which needs small
    and precise of fluids such as a dialysis
    machine.
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13
Q

Applications of DC Machines
DC Motors: 8-10

A
  1. industrial uses (steel, rolling mill motors
    and railway traction motors)
    .
  2. power windows, car fans, starting motors in vehicles.
  3. as actuators and as speed and position
    sensing devices (tachogenerators for
    speed sensing and servomotors for
    positioning and tracing.
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14
Q
  • is an electrical machine which converts
    mechanical energy (input) into direct
    current electricity (output). This energy
    conversion is based on the principle of
    production of dynamically induced
    emf.
A

DC Generator

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15
Q
  • is a mechanical machine that drives the
    rotor of a DC generator
  • this machine will serve as an input to
    the armature of a generator.
A

Prime mover

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16
Q

• internal Combustion Engines (ICE)
➢either diesel or gasoline engine
• hydraulic turbines
• steam turbines

A

Prime movers for large DC generators

17
Q

• synchronous motors
• squirrel cage induction motors
• internal combustion engines.

A

Prime movers for small DC generators

18
Q

Three main parts of DC generator : MAC

A
  1. Magnetic field system
  2. Armature
  3. Commutator and brush gear
19
Q

Other parts of DC generator:
MPFABBS

A
  1. magnetic frame and yoke
  2. pole core and pole shoes
  3. field or exciting coils
  4. armature coils and windings
  5. brushes
  6. bearings
  7. shaft
20
Q
  • is the stationary or fixed part of the machine
  • it produces the main magnetic flux
A

MAGNETIC Field System

21
Q

MAGNETIC FIELD system Consists of: FPF

A
  1. frame or yoke
  2. pole core and pole shoes
  3. field or exciting coils.
22
Q

Frame or yoke
- for small generators, it is made
of cast iron
- for large generators, it is made
of cast steel or rolled steel

A

Frame or yoke

23
Q

Purposes of frame or yoke

A
  • serves as mechanical support
    for the entire assembly
  • provides mechanical
    protection to the inner parts of
    the machine
  • provides a low reluctance path
    for the magnetic flux
  • for small generators, it is made
    of cast iron
  • for large generators, it is made
    of cast steel or rolled steel
    Purposes:
  • serves as mechanical support
    for the entire assembly
  • provides mechanical
    protection to the inner parts of
    the machine
  • provides a low reluctance path
    for the magnetic flux
24
Q
  • fixed to the magnetic frame
    or yoke by bolts
  • has a curved surface which
    are made of thin cast steel or
    wrought iron laminations
    which are riveted together
    under hydraulic pressure
  • poles are laminated to
    reduce Eddy current loSS.
A

Pole Core and Pole Shoes

25
Q
  • supports the field or exciting
    coils
  • spread out the magnetic flux
    over the armature periphery
    more uniformly
  • increases the cross-sectional
    area of the magnetic circuit,
    as a results, the reluctance of
    the magnetic path is reduced.
A

Pole Core and Pole Shoes
Purposes:

26
Q
  • placed over a pole core to
    produce a magnetic field
  • enameled copper wire is
    used for its construction
  • wound in the former and
    placed around the pole core
  • when direct current passes
    through the field winding, it
    magnetizes the poles, which
    turns produces the flux
A

Field or exciting coils

27
Q
  • the rotating part of
    the DC machine or
    DC generator
  • consists of a shaft
    upon which a
    laminated cylinder,
    called armature
    core is placed.
A

ARMATURE

28
Q
  • cylindrical or drumshaped and keyed to
    the rotating shaft
  • the outer periphery has
    groves or slots which
    accommodate the
    armature winding
  • is made of silicon steel
    material to reduce
    hysteresis loss
A

ARMATURE Core

29
Q
  • armature core is
    laminated with a
    stamping of about 0.3
    to 0.5 mm thickness to
    reduce Eddy current loss
  • each lamination is
    insulated from the other
    by a coating of varnish.
A

ARMATURE Core

30
Q
  • it houses the
    conductors in the
    slots
  • provides an easy
    path for the
    magnetic flux
A

ARMATURE Core
Purposes:

31
Q
  • the insulated conductors are
    placed in the slots of the
    armature core
  • conductors are wedged,
    and bands of steel wire
    wound around the core and
    are suitably connected
  • this conductor arrangement
    is called armature winding
  • The HEART of the DC
    machine
A

ARMATURE Windings

32
Q
  • a place where the conversions of
    power takes place
  • where mechanical power is
    converted into electrical power
A

ARMATURE Windings

33
Q

CLASSIFICATIONS of Armature Windings;

A
  1. LAP WINDING
  2. WAVE WINDING
34
Q

– rotates with the armature
– cylindrical in shape and is
made from a number of
wedge-shaped hard drawn
copper bars or segments
insulated from each other
and from the shaft
– the segments form a ring
around the shaft of the
armature
– each commutator segment
is connected to the ends of
the armature coil.

A

COMMUTATOR

35
Q

COMMUTATOR
Purposes:

A

– connects the rotating
armature conductors to
the stationary external
circuit through brushes
– converts the induced
alternating current in the
armature conductor into
the unidirectional current in
the external load circuit

36
Q

– carbon brushes are placed
or mounted on the
commutator
– with the help of two or more
brushes current is collected
from the armature winding
– is supported in a metal box
called brush box or brush
holder
– made of high-grade carbon
(conducting material)
– provides lubricating effect on
the commutator surface

A

BRUSHES

37
Q

– made of mild steel with
maximum breaking
strength
– Used to transfer
mechanical power from
or to the machine
– The rotating parts like the
armature core,
commutator, cooling
fans, etc… are keyed to
the shaft

A

SHAFT

38
Q

– are fitted in the end
housings
– reduce the friction
between the rotating
and stationary parts of
the machine
– made of high carbon
steel as it is a very hard
materials

A

BEARINGS

ACDC (2 decks)

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