<s>
An	O
alternator	B-Algorithm
is	O
an	O
electrical	O
generator	O
that	O
converts	O
mechanical	O
energy	O
to	O
electrical	O
energy	O
in	O
the	O
form	O
of	O
alternating	O
current	O
.	O
</s>
<s>
For	O
reasons	O
of	O
cost	O
and	O
simplicity	O
,	O
most	O
alternators	B-Algorithm
use	O
a	O
rotating	O
magnetic	O
field	O
with	O
a	O
stationary	O
armature	O
.	O
</s>
<s>
Occasionally	O
,	O
a	O
linear	B-Algorithm
alternator	I-Algorithm
or	O
a	O
rotating	O
armature	O
with	O
a	O
stationary	O
magnetic	O
field	O
is	O
used	O
.	O
</s>
<s>
In	O
principle	O
,	O
any	O
AC	O
electrical	O
generator	O
can	O
be	O
called	O
an	O
alternator	B-Algorithm
,	O
but	O
usually	O
the	O
term	O
refers	O
to	O
small	O
rotating	O
machines	O
driven	O
by	O
automotive	O
and	O
other	O
internal	O
combustion	O
engines	O
.	O
</s>
<s>
An	O
alternator	B-Algorithm
that	O
uses	O
a	O
permanent	O
magnet	O
for	O
its	O
magnetic	O
field	O
is	O
called	O
a	O
magneto	B-Algorithm
.	O
</s>
<s>
Alternators	B-Algorithm
in	O
power	O
stations	O
driven	O
by	O
steam	O
turbines	O
are	O
called	O
turbo-alternators	B-Algorithm
.	O
</s>
<s>
Large	O
50	O
or	O
60Hz	O
three-phase	O
alternators	B-Algorithm
in	O
power	O
plants	O
generate	O
most	O
of	O
the	O
world	O
's	O
electric	O
power	O
,	O
which	O
is	O
distributed	O
by	O
electric	O
power	O
grids	O
.	O
</s>
<s>
Lord	O
Kelvin	O
and	O
Sebastian	O
Ferranti	O
also	O
developed	O
early	O
alternators	B-Algorithm
,	O
producing	O
frequencies	O
between	O
100	O
and	O
300	O
Hz	O
.	O
</s>
<s>
Some	O
,	O
such	O
as	O
Yablochkov	O
arc	O
lamps	O
introduced	O
in	O
1878	O
,	O
ran	O
better	O
on	O
alternating	O
current	O
,	O
and	O
the	O
development	O
of	O
these	O
early	O
AC	O
generating	O
systems	O
was	O
accompanied	O
by	O
the	O
first	O
use	O
of	O
the	O
word	O
"	O
alternator	B-Algorithm
"	O
.	O
</s>
<s>
The	O
introduction	O
of	O
transformers	B-Algorithm
in	O
the	O
mid-1880s	O
led	O
to	O
the	O
widespread	O
use	O
of	O
alternating	O
current	O
and	O
the	O
use	O
of	O
alternators	B-Algorithm
needed	O
to	O
produce	O
it	O
.	O
</s>
<s>
After	O
1891	O
,	O
polyphase	O
alternators	B-Algorithm
were	O
introduced	O
to	O
supply	O
currents	O
of	O
multiple	O
differing	O
phases	O
.	O
</s>
<s>
Later	O
alternators	B-Algorithm
were	O
designed	O
for	O
various	O
alternating	O
current	O
frequencies	O
between	O
sixteen	O
and	O
about	O
one	O
hundred	O
hertz	O
,	O
for	O
use	O
with	O
arc	O
lighting	O
,	O
incandescent	O
lighting	O
and	O
electric	O
motors	O
.	O
</s>
<s>
Specialized	O
radio	O
frequency	O
alternators	B-Algorithm
like	O
the	O
Alexanderson	O
alternator	B-Algorithm
were	O
developed	O
as	O
longwave	B-Algorithm
radio	I-Algorithm
transmitters	O
around	O
World	O
War	O
1	O
and	O
used	O
in	O
a	O
few	O
high	O
power	O
wireless	O
telegraphy	O
stations	O
before	O
vacuum	O
tube	O
transmitters	O
replaced	O
them	O
.	O
</s>
<s>
Since	O
the	O
currents	O
in	O
the	O
stator	O
windings	O
vary	O
in	O
step	O
with	O
the	O
position	O
of	O
the	O
rotor	O
,	O
an	O
alternator	B-Algorithm
is	O
a	O
synchronous	O
generator	O
.	O
</s>
<s>
Automotive	O
alternators	B-Algorithm
use	O
a	O
rotor	O
winding	O
which	O
allows	O
control	O
of	O
the	O
alternator	B-Algorithm
's	O
generated	O
voltage	O
by	O
varying	O
the	O
current	O
in	O
the	O
rotor	O
field	O
winding	O
.	O
</s>
<s>
Alternators	B-Algorithm
used	O
in	O
central	O
power	O
stations	O
also	O
control	O
the	O
field	O
current	O
to	O
regulate	O
reactive	O
power	O
and	O
to	O
help	O
stabilize	O
the	O
power	O
system	O
against	O
the	O
effects	O
of	O
momentary	O
faults	O
.	O
</s>
<s>
The	O
output	O
frequency	O
of	O
an	O
alternator	B-Algorithm
depends	O
on	O
the	O
number	O
of	O
poles	O
and	O
the	O
rotational	O
speed	O
.	O
</s>
<s>
Alternators	B-Algorithm
may	O
be	O
classified	O
by	O
method	O
of	O
excitation	O
,	O
number	O
of	O
phases	O
,	O
the	O
type	O
of	O
rotation	O
,	O
cooling	O
method	O
,	O
and	O
their	O
application	O
.	O
</s>
<s>
There	O
are	O
two	O
main	O
ways	O
to	O
produce	O
the	O
magnetic	O
field	O
used	O
in	O
the	O
alternators	B-Algorithm
,	O
by	O
using	O
permanent	O
magnets	O
which	O
create	O
their	O
own	O
persistent	O
magnetic	O
field	O
or	O
by	O
using	O
field	O
coils	O
.	O
</s>
<s>
The	O
alternators	B-Algorithm
that	O
use	O
permanent	O
magnets	O
are	O
specifically	O
called	O
magnetos	B-Algorithm
.	O
</s>
<s>
In	O
other	O
alternators	B-Algorithm
,	O
wound	O
field	O
coils	O
form	O
an	O
electromagnet	O
to	O
produce	O
the	O
rotating	O
magnetic	O
field	O
.	O
</s>
<s>
A	O
device	O
that	O
uses	O
permanent	O
magnets	O
to	O
produce	O
alternating	O
current	O
is	O
called	O
a	O
permanent	O
magnet	O
alternator	B-Algorithm
(	O
PMA	O
)	O
.	O
</s>
<s>
This	O
method	O
of	O
excitation	O
consists	O
of	O
a	O
smaller	O
direct-current	O
(	O
DC	O
)	O
generator	O
fixed	O
on	O
the	O
same	O
shaft	O
with	O
the	O
alternator	B-Algorithm
.	O
</s>
<s>
The	O
DC	O
generator	O
generates	O
a	O
small	O
amount	O
of	O
electricity	O
just	O
enough	O
to	O
excite	O
the	O
field	O
coils	O
of	O
the	O
connected	O
alternator	B-Algorithm
to	O
generate	O
electricity	O
.	O
</s>
<s>
A	O
variation	O
of	O
this	O
system	O
is	O
a	O
type	O
of	O
alternator	B-Algorithm
which	O
uses	O
direct	O
current	O
from	O
a	O
battery	B-Algorithm
for	O
initial	O
excitation	O
upon	O
start-up	O
,	O
after	O
which	O
the	O
alternator	B-Algorithm
becomes	O
self-excited	O
.	O
</s>
<s>
This	O
voltage	O
is	O
used	O
to	O
excite	O
the	O
field	O
coils	O
for	O
the	O
alternator	B-Algorithm
to	O
generate	O
stronger	O
voltage	O
as	O
part	O
of	O
its	O
build	O
up	O
process	O
.	O
</s>
<s>
After	O
the	O
initial	O
AC	O
voltage	O
buildup	O
,	O
the	O
field	O
is	O
supplied	O
with	O
rectified	B-Algorithm
voltage	I-Algorithm
from	O
the	O
alternator	B-Algorithm
.	O
</s>
<s>
A	O
brushless	O
alternator	B-Algorithm
is	O
composed	O
of	O
two	O
alternators	B-Algorithm
built	O
end-to-end	O
on	O
one	O
shaft	O
.	O
</s>
<s>
Until	O
1966	O
,	O
alternators	B-Algorithm
used	O
brushes	O
with	O
rotating	O
field	O
.	O
</s>
<s>
With	O
advancement	O
in	O
semiconductor	O
technology	O
,	O
brushless	O
alternators	B-Algorithm
are	O
possible	O
.	O
</s>
<s>
Smaller	O
brushless	O
alternators	B-Algorithm
may	O
look	O
like	O
one	O
unit	O
but	O
the	O
two	O
parts	O
are	O
readily	O
identifiable	O
on	O
the	O
large	O
versions	O
.	O
</s>
<s>
The	O
larger	O
of	O
the	O
two	O
sections	O
is	O
the	O
main	O
alternator	B-Algorithm
and	O
the	O
smaller	O
one	O
is	O
the	O
exciter	O
.	O
</s>
<s>
The	O
main	O
alternator	B-Algorithm
uses	O
the	O
opposite	O
configuration	O
with	O
a	O
rotating	O
field	O
and	O
stationary	O
armature	O
.	O
</s>
<s>
A	O
bridge	O
rectifier	B-Algorithm
,	O
called	O
the	O
rotating	O
rectifier	B-Algorithm
assembly	O
,	O
is	O
mounted	O
on	O
the	O
rotor	O
.	O
</s>
<s>
The	O
main	O
alternator	B-Algorithm
has	O
a	O
rotating	O
field	O
as	O
described	O
above	O
and	O
a	O
stationary	O
armature	O
(	O
power	O
generation	O
windings	O
)	O
.	O
</s>
<s>
This	O
output	O
is	O
rectified	O
by	O
a	O
rotating	O
rectifier	B-Algorithm
assembly	O
,	O
mounted	O
on	O
the	O
rotor	O
,	O
and	O
the	O
resultant	O
DC	O
supplies	O
the	O
rotating	O
field	O
of	O
the	O
main	O
alternator	B-Algorithm
and	O
hence	O
alternator	B-Algorithm
output	O
.	O
</s>
<s>
The	O
result	O
of	O
all	O
this	O
is	O
that	O
a	O
small	O
DC	O
exciter	O
current	O
indirectly	O
controls	O
the	O
output	O
of	O
the	O
main	O
alternator	B-Algorithm
.	O
</s>
<s>
Another	O
way	O
to	O
classify	O
alternators	B-Algorithm
is	O
by	O
the	O
number	O
of	O
phases	O
of	O
their	O
output	O
voltage	O
.	O
</s>
<s>
Three-phase	O
alternators	B-Algorithm
are	O
the	O
most	O
common	O
,	O
but	O
polyphase	O
alternators	B-Algorithm
can	O
be	O
two	O
phase	O
,	O
six	O
phase	O
,	O
or	O
more	O
.	O
</s>
<s>
The	O
revolving	O
part	O
of	O
alternators	B-Algorithm
can	O
be	O
the	O
armature	O
or	O
the	O
magnetic	O
field	O
.	O
</s>
<s>
Many	O
alternators	B-Algorithm
are	O
cooled	O
by	O
ambient	O
air	O
,	O
forced	O
through	O
the	O
enclosure	O
by	O
an	O
attached	O
fan	O
on	O
the	O
same	O
shaft	O
that	O
drives	O
the	O
alternator	B-Algorithm
.	O
</s>
<s>
In	O
vehicles	O
such	O
as	O
transit	O
buses	O
,	O
a	O
heavy	O
demand	O
on	O
the	O
electrical	O
system	O
may	O
require	O
a	O
large	O
alternator	B-Algorithm
to	O
be	O
oil-cooled	O
.	O
</s>
<s>
Expensive	O
automobiles	O
may	O
use	O
water-cooled	O
alternators	B-Algorithm
to	O
meet	O
high	O
electrical	O
system	O
demands	O
.	O
</s>
<s>
Alternators	B-Algorithm
are	O
used	O
in	O
modern	O
internal	O
combustion	O
engine	O
automobiles	O
to	O
charge	O
the	O
battery	B-Algorithm
and	O
to	O
power	O
the	O
electrical	O
system	O
when	O
its	O
engine	O
is	O
running	O
.	O
</s>
<s>
Until	O
the	O
1960s	O
,	O
automobiles	O
used	O
DC	O
dynamo	B-Language
generators	O
with	O
commutators	O
.	O
</s>
<s>
With	O
the	O
availability	O
of	O
affordable	O
silicon-diode	O
rectifiers	B-Algorithm
,	O
alternators	B-Algorithm
were	O
used	O
instead	O
.	O
</s>
<s>
In	O
later	O
diesel-electric	O
locomotives	O
and	O
diesel	O
electric	O
multiple	O
units	O
,	O
the	O
prime	O
mover	O
turns	O
an	O
alternator	B-Algorithm
which	O
provides	O
electricity	O
for	O
the	O
traction	O
motors	O
(	O
AC	O
or	O
DC	O
)	O
.	O
</s>
<s>
The	O
traction	O
alternator	B-Algorithm
usually	O
incorporates	O
integral	O
silicon	O
diode	O
rectifiers	B-Algorithm
to	O
provide	O
the	O
traction	O
motors	O
with	O
up	O
to	O
1,200	O
volts	O
DC	O
.	O
</s>
<s>
Marine	O
alternators	B-Algorithm
used	O
in	O
yachts	O
are	O
similar	O
to	O
automotive	O
alternators	B-Algorithm
,	O
with	O
appropriate	O
adaptations	O
to	O
the	O
salt-water	O
environment	O
.	O
</s>
<s>
Marine	O
alternators	B-Algorithm
are	O
designed	O
to	O
be	O
explosion	O
proof	O
(	O
ignition	O
protected	O
)	O
so	O
that	O
brush	O
sparking	O
will	O
not	O
ignite	O
explosive	O
gas	O
mixtures	O
in	O
an	O
engine	O
room	O
environment	O
.	O
</s>
<s>
Larger	O
marine	O
diesels	O
may	O
have	O
two	O
or	O
more	O
alternators	B-Algorithm
to	O
cope	O
with	O
the	O
heavy	O
electrical	O
demand	O
of	O
a	O
modern	O
yacht	O
.	O
</s>
<s>
On	O
single	O
alternator	B-Algorithm
circuits	O
,	O
the	O
power	O
may	O
be	O
split	O
between	O
the	O
engine	O
starting	O
battery	B-Algorithm
and	O
the	O
domestic	O
or	O
house	O
battery	B-Algorithm
(	O
or	O
batteries	O
)	O
by	O
use	O
of	O
a	O
split-charge	O
diode	O
(	O
battery	B-Algorithm
isolator	O
)	O
or	O
a	O
voltage-sensitive	O
relay	O
.	O
</s>
<s>
Due	O
to	O
the	O
high	O
cost	O
of	O
large	O
house	O
battery	B-Algorithm
banks	O
,	O
Marine	O
alternators	B-Algorithm
generally	O
use	O
external	O
regulators	O
.	O
</s>
<s>
Multistep	O
regulators	O
control	O
the	O
field	O
current	O
to	O
maximize	O
the	O
charging	O
effectiveness	O
(	O
time	O
to	O
charge	O
)	O
and	O
battery	B-Algorithm
life	O
.	O
</s>
<s>
Multistep	O
regulators	O
can	O
be	O
programmed	O
for	O
different	O
battery	B-Algorithm
types	O
.	O
</s>
<s>
Two	O
temperature	O
sensors	O
can	O
be	O
added	O
,	O
one	O
for	O
the	O
battery	B-Algorithm
to	O
adjust	O
charging	O
voltage	O
and	O
an	O
over-temperature	O
sensor	O
on	O
the	O
actual	O
alternator	B-Algorithm
to	O
protect	O
it	O
from	O
overheating	O
.	O
</s>
<s>
High	O
frequency	O
alternators	B-Algorithm
of	O
the	O
variable-reluctance	O
type	O
were	O
applied	O
commercially	O
to	O
radio	O
transmission	O
in	O
the	O
low-frequency	O
radio	O
bands	O
.	O
</s>
<s>
In	O
the	O
Alexanderson	O
alternator	B-Algorithm
,	O
both	O
the	O
field	O
winding	O
and	O
armature	O
winding	O
are	O
stationary	O
,	O
and	O
current	O
is	O
induced	O
in	O
the	O
armature	O
by	O
virtue	O
of	O
the	O
changing	O
magnetic	O
reluctance	O
of	O
the	O
rotor	O
(	O
which	O
has	O
no	O
windings	O
or	O
current	O
carrying	O
parts	O
)	O
.	O
</s>
