3RT1/3RH1 contactors
SIRIUS System Manual
GWA 4NEB 430 0999-02b
3-73
3 3RT1/3RH1 contactors
3.4.6 Surge suppression
When contactor coils are disconnected, overvoltage occurs (inductive load).
Voltage peaks of up to 4 kV with a rate of rise in voltage of 1 kV/ms can
result (showering arcs).
The consequences of this are:
• Heavy contact erosion and thus premature wearing of the contacts that
switch the coil
• Unwanted signals can occur that may cause false signals in electronic
controllers.
All contactor coils, therefore, should be damped against switching overvolt-
ages, particularly when working with electronic controllers.
Oscillograms
The following oscillograms illustrate the behavior at disconnection of contac-
tor coils with and without overvoltage damping:
Unused coil
Figure 3-55: Disconnecting an unused contactor coil
Oscillogram of a disconnection of the coil of an auxiliary contactor. The coil
is not used:
Showering arcs can be clearly seen (voltage peaks of up to approximately
4 kV). After the disconnection procedure has been started, showering arcs
occur for approximately 250 microseconds, and after that the oscillation is
merely damped.
Disconnection of an unused contactor coil
0
100
1000
3000
U
Sp
[V]
50
t [
µ
s]
U
Sp
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