Functional Description
24 S811+ Soft Starter MN03900001E—November 2012
Functional Description
Power
The S811+ Soft Starter controls the voltage applied to a
three-phase induction motor in order to control the starting
torque and provide a smooth starting characteristic. Within
the soft starter are three power poles, each of which
includes a set of anti-parallel SCRs (thyristors) in parallel with
a contact. During a start, the conduction periods of the SCRs
are continuously adjusted to apply a gradually increasing
voltage to the motor, resulting in gradually increasing torque
and a smooth start. As the motor reaches its rated speed,
the power pole contacts are closed, bypassing the SCRs for
the most efficient operation.
Inline Connected Soft Starter (default)
Inside-the-Delta Connected Soft Starter
Note: For soft starters used in an Inside-the-Delta
application, use of a shunt trip breaker is highly
recommended. The S811+ may be configured to
actuate a shunt trip breaker on user selected Fault Trip
parameters.
For each start, the length of time the SCRs are conducting
current as well as the magnitude of that current determine
how hot the SCRs will get. Between successive starts the
SCRs must cool down to avoid exceeding their thermal
limits. Appendix D gives the S811+’s application ratings for
various starting conditions. Staying within these specified
limits will aid in avoiding over temperature trips.
Control
There is one (1) 12-position connector, one (1) screw
terminal connector, and one (1) RJ45 connector on the face
of the S811+ soft starter that are used for control circuit
functions:
1. 24 Vdc Control Inputs—Soft Starter Permissive, Start,
Reset, and Auxiliary Relay control functions.
2. Network Communications—ModBus connection
(native).
3. Digital Interface Module (DIM) or Control Interface
Module (CIM)—soft starter communication with a user
interface device.
Note: Do not apply 120 Vac to any Terminal Block
Control Input. 120 Vac will permanently destroy the
printed circuit board.
The software contained in the S811+ Soft Starter is the heart
of the product. This software allows you to control nearly
every aspect of the soft starter’s functionality. In this section,
various features and protection options are described.
Note: You will find a complete listing of these parameters in
Appendix A.
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