Contact Maintenance; Arc Chute Removal & I Nspection - GE AKR-30 Series Maintenance Manual

SECTION 8-Contact Maintenance
Breakers subjected to frequent interruption of high cur­
rents may eventually requ ire replacement of their contacts.
The general rule for determining need of replacement is
the loss of one-half or more of the mass of the contact tip
material. Roughening or light pitting of the contact surface
does not indicate loss of abi lity to carry or interrupt cu rrent.
When contacts are replaced , they m ust be adjusted to
ensure that the proper amount of force is developed be­
tween the movable and stationary co ntacts when the
breaker is closed. This is called the "wipe" adjustment.
"Wipe" is the distance through which the stationary co n­
tacts move when the breaker closes. It is measured bet­
ween the point of contact on a stationary contact when the
breaker is open, and the position of the same point when
the breaker is closed . The actual wiping motion is greater
because the contacts over-travel . "Wiping" i mparts a slid­
ing or "scrubbing" action to the contacts .
The wipe adjustment i nfl uences proper arc transfer dur­
ing interruption of fault currents. "Transfer" of the arc is its
forced sequential movement from the intermediate con­
tacts to the arcing contacts to the arc runner and fi nally to
the arc qu encher where it is dissipated and extinguished. It
is reco m mended that contact wipe be checked periodically
during normal mai ntenance i nspections.
CAUTION:
BEFORE DOING ANY OF THE FOL­
L O WI N G C O N TA C T A DJ U S TMENT AND RE­
PLA CEMENT WO R K,
CONNEC T THE CLOSING SPRING FROM THE
MECHANISM CAM SHAFT AS DESCRIBED UN­
DER SLO W CLOSING THE BREAKER, SECTION
7.4
MECHANICA L L Y DIS­
8 . 1 ARC C H UTE R E M OVAL
A N D I N S P ECTIO N
Th ere are two types of arc ch ute const ru cti on used
on the 800 thru 2000 ampere breakers. They are the
ceramic type shown in Fig. 5 and the m o lded type
shown in Fig . 6. The c eram ic type uses a two piece
porcelain frame to enclose its internal parts. The molded
type uses a one piece, glass-fil led polyester frame.
Arc ch utes should not be interchanged between
frame sizes or i nterru pting ratings.
The arc chutes are held i n p lace by retainers se­
c u red by bolts through the mechan ism frame. The
cera m i c type uses two retainers and the m olded type
uses o n ly one.
To remove the arc c hutes:
1 . Loosen and back off the retai ner bolt locking nut
from the mechanism frame. They do n ot h ave to be
removed .
2 . Loosen the retainer bolts until the retainer(s) can
be removed .
3. With the retai ner(s) removed , l ift the arc ch utes
off for inspecti on.
I n spect each arc ch ute for excessive b u rn i n g and
eros ion of the arc plates and arc runner. Also look for
fract u res, d amage to the l iner material used in the
molded arc chute and d amage to the insu lation
m aterial used i n both arc chutes. Check for any
m issing parts.
To in stall the arc ch utes:
1 . Replace the arc ch utes over each pole u n it .
2 . Locate t h e retainer(s).
3. Tighten the retainer bolts until the arc chutes are
secu re. There may be some side to side m otion of the
arc ch utes, but there must not be any front to back
m otio n . Torq u e the retainer bolts to 30 i n - l bs for the
molded type arc ch utes and 60 to 1 00 i n - l bs for the
ceram ic type. Do not over tig hten .
4 . Tig hten the lockn uts agai nst the mechanism
frame with 1 50 to 1 7 5 i n - l bs torque.
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