Datasheet

Solid-State Switching Devices for Resistive Loads
Solid-State Relays
General data
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Siemens IC 10 · 2011
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■ Overview
Solid-state relays
SIRIUS solid-state relays are suitable for surface mounting on
existing cooling surfaces. Mounting is quick and easy, involving
just two screws. The special technology of the power semicon-
ductor ensures there is excellent thermal contact with the heat
sink. Depending on the nature of the heat sink, the capacity
reaches up to 88 A on resistive loads.
The solid-state relays are available in three different versions:
• 3RF21 single-phase solid-state relay with a width of 22.5 mm
• 3RF20 single-phase solid-state relay with a width of 45 mm
• 3RF22 three-phase solid-state relay with a width of 45 mm
The 3RF21 and 3RF22 solid-state relays can be expanded with
various function modules to adapt them to individual
applications.
Version for resistive loads, "zero-point switching"
This standard version is often used for switching space heaters
on and off.
Version for inductive loads, "instantaneous switching"
In this version the solid-state relay is specifically matched to in-
ductive loads. Whether it is a matter of frequent actuation of the
valves in a filling plant or starting and stopping small operating
mechanisms in packet distribution systems, operation is carried
out safely and noiselessly.
Special "Low noise" version
Thanks to a special control circuit, this special version can be
used in public networks up to 16 A without any additional mea-
sures, such as interference suppressor filters. As a result, in
terms of emitted interference, it conforms to limit value curve
class B according to EN 60947-4-3.
Single-phase solid-state relays with a width of 22.5 mm
With its compact design and a width of just 22.5 mm, which stays
the same even at currents of up to 88 A, the 3RF21 solid-state
relay offers an ultra small footprint. The logical connection
method, with the power infeed from above and load connection
from below, ensures tidy installation in the control cabinet.
Single-phase solid-state relays with a width of 45 mm
The solid-state relays with a width of 45 mm provide for connec-
tion of the power supply lead and the load from above. This
makes it easy to replace existing solid-state relays in existing ar-
rangements. The connection of the control cable also saves
space in much the same way as the 22.5 mm design, as it is sim-
ply plugged on.
Three-phase solid-state relays with a width of 45 mm
With its compact design and a width of just 45 mm, which stays
the same even at currents of up to 55 A, the 3RF22 solid-state
relay offers an ultra small footprint. The logical connection
method, with the power infeed from above and load connection
from below, ensures tidy installation in the control cabinet.
The three-phase solid-state relays are available with
• two-phase control (suitable in particular for circuits without
connection to the neutral conductor) and
• three-phase control (suitable for star circuits with connection to
the neutral conductor or for applications in which the system
requires all phases to be switched)
Selection notes
When selecting solid-state relays, in addition to information
about the network, the load and the ambient conditions it is also
necessary to know details of the planned design. The solid-state
relays can only conform to their specific technical specifications
if they are mounted with appropriate care on an adequately di-
mensioned heat sink.
The following procedure is recommended:
• Determine the rated current of the load and the mains voltage
• Select the relay design and choose a solid-state relay with
higher rated current than the load
• Determine the thermal resistance of the proposed heat sink
• Check the correct relay size with the aid of the diagrams
You can find more information on the Internet at:
www.siemens.com/solid-state-switching-devices
© Siemens AG 2010