Chapter 3: Applications
3.2.7 – Soft Stopping
Soft stopping can reduce positive surge pressures in pipelines on shutdown. It is necessary to
make sure that the ramp-down time is long enough to remove the energy from the fluid before the
firing of the thyristors is stopped. Otherwise the surge pressure may still be present. Soft stopping
can also be successfully applied to loads such as conveyer belt systems where sensitive items such
as bottles are being transported.
3.2.8 – Reversing Drives and Plug-braking
SR44 Soft Starters used in conjunction with contactor controlled reversing and plug-braked motors
show considerable benefits to the user by reducing mechanical and electrical stresses, particularly
when utilizing the current limited start feature. This type of application requires inserting a 150–
350 ms delay between the opening of one contactor and the closing of the other, to allow any
residual flux in the rotor to die away. When plug-braking, there should be some form of zero-
speed detection to stop the drive after braking has been completed, otherwise the drive may either
accelerate the motor in the reverse direction, or switch off before zero speed has been reached.
The SR44 has a dual parameter setting feature which is particularly useful in plug-braking, where
the braking settings need to be different from the normal starting ramp time and current limit level.
See section 2.4.4 and Figure 2.4.6 of the Electrical Installation chapter for details.
3.2.9 – Replacement of Fluid Couplings
Soft-starters can replace fluid couplings yielding benefits of higher efficiency running and lower
costs to the user. If the coupling is used to magnify the available breakaway torque, it may be
necessary to replace the installed motor with another of a larger size, or one with a high starting
torque characteristic before a soft starter can be employed.
3.2.10 – Two-speed Motor Applications
Two-speed motors, whether Dahlander-connected or with dual windings, can be soft-started at
each speed, provided that the start is initiated when the actual motor speed is less than the
synchronous speed for the winding selected. This is particularly important when changing from
high to low speeds. The SR44 has a dual setting feature, which allows different operating settings
for the high and low speeds, and the ability to switch rapidly between them.
3.2.11 – Multiple Motor Starting
See section 2.4.2 of the Electrical Installation chapter for details.
3.2.12 – Overhauling Loads
Certain applications can overspeed the motor as part of normal operation. Power then flows from
the motor to the power supply. It is important to disable Optimizing Mode during over-speed
conditions, and reinstate Optimizing during normal conditions. (External control is required to
disable and reinstate Optimizing Mode.)
3.2.13 – Application Table
The table on the following page shows many common motor applications that suit the SR44 Soft
Starter. It lists typical breakaway torque requirements as a percentage of motor full-load torque
(FLT). For the most satisfactory soft starter in a given application, the motor should have a full-
voltage locked-rotor-torque (LRT) that is at least twice the breakaway torque (e.g. for a
reciprocating compressor the FLT is normally in the region of 50% motor LRT.) As a general rule,
the higher the motor LRT is above the load breakaway torque, the greater the control over the
starting process.
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019
3–6
Summary of Contents for Stellar SR44
Page 1: ...STELLAR SR44 SOFT STARTER USER MANUAL SR44 M WO 1st Edition Revision B...
Page 2: ...BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019...
Page 6: ...SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019 w 4 BLANK PAGE...
Page 8: ...BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019...
Page 12: ...Table of Contents BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019 t 4...
Page 23: ...ELECTRICAL INSTALLATION 2 CHAPTER CHAPTER 2 2 CHAPTER BLANK PAGE 2 1c...
Page 75: ...KEYPAD MENU ITEMS AND PARAMETERS CHAPTER 5 CHAPTER CHAPTER 5 BLANK PAGE 5 5 1c...
Page 237: ...BLANK PAGE SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019...
Page 238: ...SR44 Series Soft Starter User Manual 1st Ed Rev B 07 31 2019...