Siemens SIRIUS 3RT - Page 299

Accessories
9.4 Surge suppressor
SIRIUS - SIRIUS 3RT Contactors/Contactor assemblies
Manual, 09/2017, A5E03656507120A/RS-AE/006
299
Switching overvoltage - surge suppressor
Overvoltages when switching off contactors (inductive load) can cause faults in electronic
devices (timing relays, PLCs, coupling modules) in the same network if the contactors are
used without the appropriate filters.
Table 9- 18 Switching overvoltage - surge suppressor
Description
Suitable
for
Limited to
Additional delay
Advantage
Disadvantage
Freewheel diode
DC Forward voltage
(U
D
= ~1 V)
Very high (6-9x)
• Non-critical
dimensioning
• Lowest induction
voltage
• Very simple and
reliable
• Low-cost
• Long drop-out
delay
• Short-circuit on
failure
Suppressor diode
AC/DC Breakdown
voltage (U
BR
)
Very low
• Non-critical
dimensioning
• Simple design
• Protected against
reverse polarity
• Short pick-up time
No attenuation below
the breakdown voltage
(U
BR
)
Diode
combination
DC Breakdown
voltage (U
BR
)
Very low
• Non-critical
dimensioning
• Simple design
• Short pick-up time
No attenuation below
the breakdown voltage
(U
BR
)
Varistor
AC/DC Varistor voltage
(U
Varistor
)
Very low
• Non-critical
dimensioning
• High energy
absorption
• Very simple design
No attenuation below
U
Varistor
RC element
AC/DC U
RC
Very low
• HF attenuation
through energy
storage
• Immediate shutdown
• Extremely suitable for
AC
• Exact dimensions
required
• Expensive