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5 1
When inspecting
an
arc
chute
,
look for the
following :
4
.
Cleaning Arc Shields
.
Cleaning
methods for the first
two types of
dirt
are
obvious
as mentioned above
.
Particular
1
.
Broken
or Cracked Ceramic Parts
,
Small
pieces broken from the ceramics
,
or
small cracks
are not
important
.
But
large
breaks and particularly cracks
ex
-
tending from the inverted V slot in the
interrupter plates
out to
the edge
of the
plate
or to
the
top may interfere
with
top
performance
of the
interrupter
.
Hence
if
more
than
one or two
broken
or badly
cracked plates
are
apparent
,
renewal of
the ceramic stack is indicated
.
attention should be paid
to
any dirt
on
the plastic
surfaces
below the ceramic
arc
shield
.
Wipe
clean if possible
.
If
wiping will
not remove
the dirt
,
clean with
sand paper to
remove
all
traces
of carbon
or
metallic deposit
.
On breakers which
receive thousands of
operations
at
low and
medium interrupted
currents ,
tightly ad
-
hering dirt may
accumulate on the ceramic
arc
shields sufficiently
to
impair
proper
interrupting
performance
.
These
arc
shields
are
of
a very
hard material and a
hard non
-
conducting abrasive is
necessary
for cleaning
.
The best
and easiest way
to clean
them is by sand blasting
,
NOT
SHOT BLASTING
,
if a
sand blasting
outfit
is available
.
Next best is
a
flexible
abrasive disc on
an
electric drill with
medium
grain aluminum oxide discs
.
2
.
Erosion of
Ceramics
.
When
an
arc
strikes
a
ceramic
part in the
arc
chutes
,
the surface of
the ceramic
will
be
melted
slightly
.
When
solidified
again
,
the surface will have
a
glazed
whitish
appearance
.
At low
and
medium
current
,
this effect is very
slight
.
Hoever
,
large
current arcs
repeated many
times may
boil
away
appreciable
amounts
of
the
ceramic
.
When
the width of
the slot
at
its upper
or narrow
end ( originally 1
/
16
inch
)
has
been eroded
to
twice its original
size ,
(
about 1
/
8 inch
)
,
the
ceramic
stack
assembly
should
be replaced
.
The ceramic
arc
shields may appear
dirty and
yet
have
sufficient
dielectric
strength
.
may be used
as
a guide
in determining
when this complete
or
major
cleaning
operation is required
,
should withstand 15 KV
,
60 cycle
for
one
minute between the
front
and
rear arc
horns
.
Also the dirty
surface of
the ceramic
near
the
contacts
should withstand in the
order of 5 to 10 KV per inch when
test
prods
are
placed directly
on the ceramic
surface
.
there should be no luminous display
.
The following insulation
test
The
arc
chutes
3
.
Dirt
in
Arc Chute
.
In service the
arc
chute assembly will become dirty from
three
causes
.
First
,
dust
deposited
from
the air which
can
readily
be blown
out
of
the chute with a
dry compressed
air
stream
.
Second
,
loose
soot
deposited
on
the inside
surfaces of
the
arc
chute in
the
lower
portions
near
the
contacts
which
may be removed by wiping with cloths free
of grease or metallic
particles
.
Third
,
very
tightly adhering deposits
from the
arc gases on
the ceramic
arc
shields
near
the
contacts
.
These
deposits
from
the
metal vapors boiled
out
of
the
contacts
and
arc
horns
,
may accumulate
to a
harm
-
ful
amount
in breakers
which receive
many
operations
at
low
or
medium in
-
terrupted
currents
.
When
test
voltage
is
applied
,
LUBRICATION
The
most
reliable
performance
on
both
the stored
energy
and solenoid
mechanism
can
be obtained
by
lubrication
.
All parts
which
require it
are
lubricated with
"
molly
"
(
molybdenum polysulphide
)
Westinghouse
You
should
lubricate
some
items
at
the regular
maintenance period
.
Other
parts
normally
should require lubrication only after
long
M
.
No
.
8577
-
3 when assembled
.
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