Operating and Maintenance Instructions
Preventative maintenance
1HSB435409-100 en1 3
2. Preventative maintenance
2.1 Circuit-breaker
2.1.1 Circuit-breaker service life
Assuming that the recommended inspection intervals have been adhered to and the
appropriate measures have been implemented, the LTB E circuit-breaker will have a
service life exceeding 30 years or 10,000 mechanical operations.
The following points will ensure a long service life:
1. Burning-off of the arcing contacts is limited.
2. Each breaking unit is equipped with a absorption agent with the service life
equivalent to that of the circuit-breaker.
3. Bearings in the space filled with gas are maintenance-free.
4. The seals have double sealing rings.
Generally speaking, there are only two reasons to open the breaking unit:
– if the number of short-circuits x short-circuit current (kA) is approaching
the curve in Figure 2-1
or...
– if the number of operations for line, reactor or capacitor switching, as well as
switching of the load current
1
has reached the level specified under the
heading “Inspection intervals” in the inspection chart.
Other reasons for opening the breaking unit are limited to mechanical
faults/incorrect adjustment of the drive system that may cause damage to
components inside the breaking unit.
N.B. Opening the breaking unit requires special instruction and may only be done
by trained and authorised personnel.
The curve that defines the permissible number of short-circuits can be expressed
approximately as:
for LTB 245E1: Σ n x I
2
= 20000
for LTB 420E2: Σ n x I
1.9
= 20000
where
n = number of short-circuits
I = short-circuit current, kA (RMS)
All short-circuit current levels can be included in the total of the number of short-
circuits x short-circuit current, for example for LTB 245E1, to the power of 2.
For example: LTB 245E1: 10x30
2
+20x20
2
+20x10
2
=19,000.
1. All normal service switched-off and -on load currents are not to be included into this
formula- they are considered only in calculation of total number of mechanical CLOSE /
OPEN operations.
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