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Instruction Book
Page 40
Figure 6-2 Vacuum interrupter showing contact erosion
indicator with breaker open (shown here for clarity pur-
poses only).
SOME DC HIGH POTENTIAL UNITS, OPERATING AS
UNFILTERED HALF-WAVE RECTIFIERS, ARE NOT
SUITABLE FOR USE TO TEST VACUUM INTER-
RUPTERS BECAUSE THE PEAK VOLTAGE
APPEARING ACROSS THE INTERRUPTERS CAN BE
SUBSTANTIALLY GREATER THAN THE VALUE
READ ON THE METER.
6-5 CONTACT EROSION (EXCEPT 3150A)
Since the contacts are contained inside the interrupter,
they remain clean and require no maintenance.
However, during high current interruptions there may be
a minimum amount of erosion from the contact surfaces.
Maximum permitted erosion is 3 mm. To determine con-
tact erosion, close the breaker and observe the vacuum
interrupter moving stem from the rear of the breaker. If
the mark on each stem is visible, erosion has not
reached maximum value thus indicating satisfactory con-
tact surface of the interrupter. If the mark is not visible,
the pole unit assembly must be replaced (Figures 6-2
and 6-3).
WARNING
Figure 6-3 Vacuum interrupter showing contact erosion
indicator with breaker closed (indicators are checked
only when breaker is closed).
6-5.1 CONTACT EROSION (3150A ONLY)
In order to determine if the contacts of a 3150 ampere
breaker have eroded to the extent that the interrupter
must be replaced, close the breaker and observe the
erosion mark on the right inside of the pole unit support
(Figure 6-4). Use the erosion gauge (supplied with the
breaker) to inspect the erosion level of the interrupter. If
the pointer portion of the erosion gauge is aligned or
above the erosion mark, the interrupter assembly must
be replaced (Figure 6-5).
6-5.2 CONTACT WIPE (ALL RATINGS)
The adequacy of contact wipe can also be determined
by simply observing the indicator on the drive rod
toward the front of the closed breaker. If the wipe is ade-
quate, the entire vertical portion of the indicator "T" will
be visible along with all or a portion of the horizontal part
of the indicator "T" (Figures 6-6 and 6-7). If none of the
horizontal portion shows with the breaker closed, the
wipe is not adequate, and the pole unit assembly must
be replaced.
IB131009EN
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