3RT1/3RH1 contactors
SIRIUS System Manual
3-74
GWA 4NEB 430 0999-02b
Varistor
Figure 3-56: Circuit with a varistor (AC/DC operation)
This is what happens when a coil is disconnected that is connected to a
varistor (voltage-dependent resistor):
Voltage peaks still occur. They are cut off at approximately 400 V and have a
shorter overall duration (approximately 50 microseconds).
(Note: The oscillogram is cut off, and the voltage is reduced to zero after
approximately 3 ms.)
A varistor is suitable for AC and DC operation.
The off-delay of the contactor is extended by approximately 2 to 5 ms.
RC element
Figure 3-57: Circuit with an RC element (AC/DC operation)
This is what happens when a coil is disconnected that is connected to an RC
element:
The amplitude and rate of rise of the switching overvoltage are reduced by
the capacitor. Showering arcs no longer occur. The voltage swings briefly to
400 V and then slowly drops down. This represents ideal damping.
Disadvantage: The component is larger and generally more expensive.
RC elements are suitable for AC and DC operation.
Only a minimal off-delay occurs (under 1 ms).
Circuit with a varistor
AC/DC o
eration
0
20
200
U
Sp
[V]
0
t [
µ
s]
U
Sp
Circuit with an RC element
AC/DC o
eration
0
5
200
U
Sp
[V]
t [ms]0
U
Sp
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