Siemens-Allis FC-10008, Instructions Manual

Page: 67 / 80

"AS FOUND" TESTS
Some users perform "As Found" Insulation tests
using a megger or "Doble" testing to give
an
"As Found"
value for future comparative indication of insulation change.
This is desirable for new circuit breakers if they
are
to be
stored for extended periods, and may absorb moisture and
contaminants. Contact resistance tests can also
be made
using a "Ductor."
Since wide variations
can
occur in insulation values
and contact resistance because of atmospheric conditions,
contamination and test equipment, discrete values cannot
be given. However, making and recording these tests on
new equipment, and at regular intervals will give a com·
paratlve indication of insulation and/or contact resistance
change. Maintaining a permanent record of these values
for each circuit breaker should be part of the Maintenance
Program.
PERIODIC I NSPECTION AND MAINTENANCE
Prior to performing any maintenance work, make
certain all control circuits are open, and that the breaker
has been completely withdrawn from the metal·clad unit.
CAUTION
Do
not work on the breaker or operating
mechanism while the breaker is
in
the closed
position.
Do
not work on
the
breaker
or
operator while the closing springs
are
charged.
1. Remove interphase barriers (refer to page
15,
Phase Barrier Assembly ) and clean them and all other
insulating surfaces with dry compressed air - a vacuum
cleaner, or clean lint free rags. Inspect for signs of corona,
tracking or thermal damage.
2. Tilt the arc chutes to expose the main contacts
(refer to page 17 and Figure 2A, Tilting Arc Chutes).
3. Contacts
Examine the contacts (Figure 11). The major function
of the air circuit breaker depends upon correct operation
of its contacts. This circuit breaker has three contacts on
each pole; mains, tertiary and arcing.
When closed,
practically the entire load current passes through the main
contacts. If the resistance of these contacts becomes high,
they will overheat. Increased contact resistance can be
caused by pitted contact surfaces, corrosion of contact
surfaces, or weakened contact spring pressure. This will
cause excessive current to be diverted through the arcing
·32·
contacts, with consequent overheating and burning. Verify
proper main contact pressure by checking penetration
(refer to page 20, Procedure B).
Tertiary contacts act intermediately between main
and arcing contacts upon contact separation. They assist
current transfer from the mains to arcing contacts.
On the magnetic blowout air circuit breaker, the arc
is quickly removed from the arcing contacts by magnetic
forces and transferred to arc runners in the arc chute (Fig·
ure
6). The arcing contacts
are
expendable and may
eventually bum enough to require replacement.
The main and arcing contacts
are
made of tungsten
alloy to resist deterioration due to arcing. If the surfaces
are
only roughened or slightly pitted, they can be smoothed
with crocus cloth or draw filed. Be careful not to remove
much material, as this would shorten the contact life. If
significant erosion has occurred, the arcing contact lead
must be checked and adjusted.
If they are badly · pitted or burned, they should be
replaced (refer to page 17).
The main contacts may be lubricated per Figure 21,
but DO NOT LUBRICATE TH E ARCING CONTACTS.
4. Transfer Tips:
The transfer tips (Item 1, Figure 110) serve
as
run­
ners for the arc to transfer from the stationary contacts (5).
Accumulated dirt or carbon should be wiped off with
crocus cloth or lint' free rags. The tungsten tip, which
resists erosion from the arc, should be replaced if brazed
joints are badly burned or the base plate and extension
piece are distorted. Adjustment procedure on page 20
should be followed when replacing the transfer tips.
5.
Disconnect Arm Hinge Joint
Contact pressure of the disconnect arm hinge joint
is established by spring pressure, and does not require ad­
justment. Hinge contacts may be inspected and maintained
as
follows (refer to
Figure
llB).
Remove discnn .. ect arms as a unit by removing cotter
pin ( 19), screw
(5),
nut ( 10) and spring (12). Carefully
inspect all contact surfaces in hinge joint. Silver washer
(6) and adjacent surfaces should be clean and free of
roughness or galling. Lubricate silver washer and mating
surfaces by applying Siemens-Allis electrical contact lubri·
cant, 15-171-370·002 sparingly. Reassemble hinge joint.
Tighten screw (5) and nut (10) so that cotter pin (19)
can
be reinstalled. Spring (12) and washer (6) must be
assembled in their original position to assure proper adjust­
ment. Replace badly pitted or bumed contacts before they
are damaged to such an extent to cause improper operation
of breaker.
www
. ElectricalPartManuals
. com