Siemens SIRIUS 3RT Series System Manual page 174

SIRIUS 3RT2 contactors/contactor assemblies
2.7 Accessories
RC circuit with varistor
Varistors (voltage-dependent resistors) limit the maximum level of the overvoltage, as they
become conductive above a certain threshold voltage. Shower discharges occur up to that
level, in a similar way to those seen with the magnet coil without an RC circuit, but they do
not last as long overall. Unlike an RC element, varistors do not reduce the rate of the voltage
rise. Varistors can be used for DC- and AC-operated contactors.
Note
Varistors extend the contactor's OFF time by around 2 to 5 ms.
Figure 2-28
Voltage peaks still occur. They are truncated at around 400 V and do not last as long overall
(approximately 50 μs).
Note
Oscillogram is truncated; voltage drops to zero after around 3 ms.
174
RC circuit with varistor (AC/DC operation)
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03