Automation Direct Stellar SR55 Series, User Manual

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Appendix B: Soft Starter Application Considerations
Page B–5 Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
b.2 – R
ules foR
s
pecIfIc
A
pplIcATIoNs
b.2.1 – i
n
-d
elTa
o
peraTion
The SR55 control system allows the soft starter to be installed “in the delta” connections of
the motor, which can permit the use of a lower current rated unit. However, in this mode of
operation it is important that the soft starter is connected in accordance with the relevant
wiring diagram. The power-circuit wiring diagram in Chapter 2, “Electrical Installation” gives
detailed instructions for this configuration. If motor rotation is incorrect, the connections
should be changed as described in the diagram. It should be noted that six connections are
required between the motor and soft starter. The “Firing Mode” parameter must be set for
delta mode, which also disables iERS (Chapter 3: Configuration and Parameters). For SR55
soft starters, an in-line isolation contactor controlled by the soft starter MUST be used with the
In-Delta Firing Mode and motor connections.
b.2.2 – h
igh
-i
nerTia
l
oads
High-inertia loads, such as centrifugal and axial fans, grinders, flywheel presses, etc., may
require a larger size soft starter than the motor. For example, a 75kW [100 hp] starter may be
needed for a 55kW [75 hp] motor. This is necessary to allow for the extra heating effects of
the prolonged over-current on the soft starter thyristors during the extended starting time. If
very high-inertia loads are involved, then an analysis of the starting characteristics should be
made. This requires accurate data about the motor and the load:
• Complete motor data: Current, Voltage, Power, Speed, Rotor Inertia, Speed/Torque/Current
curves�
• Complete load data: Type of load, Speed, Inertia, Speed/Torque curve, Power absorbed or
Full-load Torque�
Consideration must also be given to thermal overload and fuse protection systems when
extended start times are involved. This is the case for heavy duty starting, as a standard
thermal overload will trip under these conditions. A heavy-duty start thermal overload or an
electronic overload with dual settings for start and run is recommended. Modern HRC motor
fuses will allow for some overload during the start, but the fuse curve, giving time/current
data, will give an indication of suitability for the particular application.
b.2.4 – r
esisTive
l
oads
AutomationDirect does not support the control of resistive loads with the SR55 Soft Starter.
b.2.5 – f
requenT
s
TarTing
High starting frequencies require careful consideration of the soft starter thermal capabilities.
In many cases a standard sized SR55 may be suitable, as start times are generally shorter for
this type of application. If this is not the case, then a larger soft starter may be required.
b.2.6 – o
pTimizing
Drives which operate for long periods of time at less than their rated capacity can benefit from
the energy saving function (iERS optimizing) of the SR55, which adjusts the thyristor triggering
to reduce the excitation losses of the motor. This feature will lower the running temperature
of the machine and help to extend its life. See Chapter 4, Principles of the Energy Saving Mode
(iERS).