PKZM0/XTPR…BC1 motor-
protective circuit-breakers
30
01/11 MN03402003Z-DE/EN
Temperature compensation
Two parameters influence the deflection of the bimetallic
releases. There is for one the heat which is generated in
proportion to the current flow, and secondly, the influence of
the ambient air temperature. The influence of the ambient
air temperature is automatically compensated within a
temperature range from –5 to +40 °C by means of an addi-
tional current-free bimetallic release that continuously
corrects the tripping range.
Phase failure
The PKZM0/XTPR…BC1 motor-protective circuit-breakers
are phase sensitive. The deflecting action of all three bime-
tallic releases is directed towards a tripping bridge that
switches over a quick-break switch when the limit value is
reached. At the same time, all three bimetallic releases shift
the differential bridge. If the path of action of one of the
bimetallic releases is reduced due to a phase loss, the differ-
ential bridge is retarded and the distance is converted into
an additional tripping distance, which leads to an early trip-
ping.
Figure 3: Function of the phase sensitivity by means of trip-
ping and differential bridge
a Trip bridge
b Differential bridge
c Distance
d Differential travel
three-phase
overload
Normal error-
free operation
Failure of one phase
(two-phase load)
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