Nguyên lý máy phát điện tàu Generator

by **shipdesign** Thu Aug 28, 2008 4:44 pm

Generators

The Alternator

The synchronous machine consists essentially of (a) a field system
excited by direct current and (b) an armature. Almost invariably the
armature is the stationary member and the field system the rotating
member. The induced e.m.f. in the armature winding is a motionally
induced e.m.f. and its mode of production identical with that of the
D.C. machine. The only difference is that it is the magnetic field
which moves whereas the armature conductor is stationary.
As with a D.C. machine the e.m.f. induced in an individual armature
coil ia an alternating e.m.f. and consequently by bringing the winding
out to fixed terminals, the e.m.f. between these will be alternating
also. The complete fixed armature, that is magnetic core and windings,
is called the stator, and the rotating field system the rotor. The
general constructional features of a salient pole alternator are shown
below
Nguyên lý máy phát điện tàu Generator Gen1

Nguyên lý máy phát điện tàu Generator Gen1

As the field system rotates and carries its flux with it,
each portion of the stator core will experience reversals of
magnetisation, and therefore, as in a direct current machine, the core
has to be laminated. For ventilation purposes, a series of radial
ventilating ducts are provided. Since the field system rotates, its
exciting winding has to be fed by means of two slip rings, but as the
excitation voltage is low and the power taken by the field winding
small, these present no difficulties
A salient pole has one field coil per pole, very like a
D.C. machine. For the very high speeds of turbine driven alternators it
is necessary to adopt a cylindrical construction for the rotor and in
such a case the field winding has to be housed in a number of slots. A
simplified form shows the cross section of a four pole turbo alternator
, the dispostion of the rotor field of a turbo alternator rotor may be
as high as 40,000 ft per min or 200 metres per sec. The stresses due to
centrifugal force are exceedingly high. The rotors are thus made from
steel forging, or in some cases from thick steel discs bolted together.
high speed rotor

Nguyên lý máy phát điện tàu Generator GEN2

Nguyên lý máy phát điện tàu Generator GEN2

The axial length is normally considerably greater
than the diameter. Has the advantage of great strength and stiffness.
The exciting current is carried by bar type conductors in the groups of
slots shown below. All currents in one group are in the same direction
, those on the next group on the opposite direction. Flux produced is
distributed over surface approximately according to sine law.

Details of stationary armature alternators.

Nguyên lý máy phát điện tàu Generator GEN3

Nguyên lý máy phát điện tàu Generator GEN3

Armature stampings pressed out of sheets of special
magnetic iron or steel alloy. In the smaller sizes the stampings are
pressed out in compete rings Nguyên lý máy phát điện tàu Generator GEN4

Nguyên lý máy phát điện tàu Generator GEN4

Section through top stator of salient pole machine. The
armature core is built up of laminations which are held tightly
together by end clamping rings. Spacing strips inserted at intervals
leave ducts for cooling air to pass through. The air is driven through
by the fan action of the rotor and escapes via the apertures in the
cast iron supporting frame. Nguyên lý máy phát điện tàu Generator GEN5

Nguyên lý máy phát điện tàu Generator GEN5

Types of armature slot. The filled slot has round wires but it is common to have rectangular conductors to economise slot space. Nguyên lý máy phát điện tàu Generator GEN6

Nguyên lý máy phát điện tàu Generator GEN6

Sectional simplified diagram of a turbo alternator

The rotor is turned from a steel forging ans slotted to
carry the exciting windings the slots being arranged as shown above.
Because of the high running speed, alternators for large outputs have a
considerable axial length compared with rotor diameter. Nguyên lý máy phát điện tàu Generator GEN7

Nguyên lý máy phát điện tàu Generator GEN7

Layouts of A.C. generators

Conventional excitation scheme (Rotary)

Separately excited D.C. exciter (Out dated) Nguyên lý máy phát điện tàu Generator GEN8

Nguyên lý máy phát điện tàu Generator GEN8

Brushless excitation scheme using shaft mounted diodes (Rotary)

Indirect self excitation (Error) Nguyên lý máy phát điện tàu Generator GEN9

Comparison of the value required to control with a fixed
value. When the variable differs from a fixed reference value an
'error' exists and the function of the controlling medium is to restore
equilibrium e.g. if the voltage output falls on the brushless rotary
excited alternator the a.v.r. controls the exciter field to restore
equilibrium.

Modern compound scheme (static)

Direct self excited (Functional) Nguyên lý máy phát điện tàu Generator GEN10

Nguyên lý máy phát điện tàu Generator GEN10

Control of the voltage to a set value is achieved by the inherent characteristics of the machine. A compound wound d.c. generator with a level compound
characteristic has additional current in the series field under load
conditions. In the self excited compound alternator there is a constant
amount of excitation required for no load condition. Additional
excitation due to more current form the current transformers is
obtained in response to extra external demands

Recovery graphs for 'functional' and 'error' layouts

Nguyên lý máy phát điện tàu Generator GEN11

Nguyên lý máy phát điện tàu Generator GEN11

Shaft driven generating system

Methods of drive

Belt or chain driven
Direct coupling engaging the propeller shaft
Power taken from the main gearbox.
Power taken from the free end of the engine

With D.C. auxiliaries power can be taken by either a
chain or belt drive from the propulsion system with an A.V.R.
maintaining constant voltage.For A.C. systems methods used include the use of a D.C.
generator with an D.C./A.C. converter, or direct A.C. generation. With
the latter either a constant speed drive is required or a frequency
converter. With either method the revolutions at which the shaft
alternator can be used is limited. In this way direct drive systems
will generally be fitted in conjunction with a C.P. system which
maintains constant engine speed under full away conditions.

Advantages

Saving on fuel costs, allows efficient use of heavy rather than gas oil
reduced maintenance costs
Capital saving on reduced number of auxiliary sets
Reduced space and weight
Reduction in noise

Disadvantages

Power available for propulsion reduced
Capitol cost of plant
Auxiliaries required for manoeuvring,
although some medium speed plants are capable of manoeuvring with shaft
alternators and C.P. system
Complicated constant speed or frequency gear required with slow speed engines
copy right by marine engineering knowledge

by TuanKhanh Mon Apr 11, 2011 1:43 pm

híc.Bác toàn chơi tiếng anh thế này,ngồi dịch mệt quá.Nhưng thanks bác nhìu nhé,Em không phải dân đóng tàu,nhưng em thích cái này nên tham gia với mấy bác :x

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Nguyên lý máy phát điện tàu Generator

Nguyên lý máy phát điện tàu Generator

Re: Nguyên lý máy phát điện tàu Generator