Maintenance
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2013-03-28
7) Adjusting the contact stroke:
Due to erosion and mechanical deformation (compression) of the contacts, the
contact stroke increases and the contact force is reduced. In order to maintain
break-times within the specified tolerances, the increase in the stroke may not
be more than 2 mm. By unscrewing the eye bolt in the insulating operating rod
(48.), it is extended and the contact stroke is reduced corresponding to the ratio
of the pole gearing (approx. 1:2). The determination of the contact stroke is
done as a difference measurement at the movable contact pins of the vacuum
interrupters in the CLOSED and OPEN switching positions.
Nominal dimension of the contact stroke of the vacuum interrupters for the
various types of vacuum circuit-breakers:
Fig. 68
Nominal dimension
8) Adjusting the contact stroke and the synchronism:
With vacuum circuit-breakers with two vacuum interrupters arranged one over
the other, the synchronism of the two vacuum interrupters must be checked and
adjusted if necessary, before the contact stroke for each of the vacuum
interrupters is adjusted.
To check the synchronism the lengths of the charged contact pressure springs
are compared on the closed vacuum circuit-breaker. If the difference is more
than 2 mm, the synchronism must be adjusted as follows:
- Open the vacuum circuit-breaker and separate the operating rods from the
circuit-breaker shaft in the operating mechanism. The contacts of the
vacuum interrupters move here under the effect of the air pressure until
contacting the first vacuum interrupter. The second vacuum interrupter is
blocked as a result.
- Release the four bearing block screws on the pole gearing. The bearing
block assumes a new central position and is screwed back in at this new
position.
- Coupling of the operating rod with the circuit-breaker shaft in the operating
mechanism and another check of the synchronism.
Afterward, the contact stroke of both vacuum interrupters can be checked and
adjusted to the nominal dimension as per "Note 7".
9) Replacement of the vacuum interrupters may possibly be necessary earlier,
depending on the number of electrical openings.
Circuit-breaker type
Tube type
Nominal dimension in mm
3AH4 754/55
VS 30040/41
16 +0/-1
3AH4 756/57/66
VS 10047/48
11 +0/-1
3AH4 784
VS 30029/30
20 +0/-1
3AH4 785
VS 30040/41
20 +0/-1
3AH4 794
VS 36025 L
14.5 +0/-1