Automationdirect.com Stellar SR44, User Manual

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3.4.4 – Optimizing with the SR44 System
During start-up, the SR44 software uses a patented method to compute and store a reference value
for the power factor. When the motor has reached full speed and is driving the load at the
demanded torque, the SR44 enters the ‘motor running’ stage. At this stage, if required, the motor
may also operate in ‘Optimizing Mode’. Entering this mode can be pre-set from the SR44 keypad
and stored for automatic operation, which will suit the majority of applications where it is
required. This is the default operating mode for the SR44. It can also be toggled on and off while
running by using either the OPTIMIZE button on the keypad, or through external circuitry
connected to one of the programmable inputs and controlled by the driven process.
In this mode the reference power factor is continuously compared with the running power factor.
The software continuously uses this comparison to compute and adjust the firing point of the
thyristors in order to maintain the best power factor. This method of continuous control minimizes
wasted energy caused by overfluxing the motor. It also maintains the power factor at the most
appropriate value for every condition of load demand. This can produce a significant reduction in
the kVA demand.
This is an operating condition that may, at light or partial load conditions, provide the benefit of
energy saving and if selected, is continuous from the dwell period until a STOP command is
initiated or the mode is disabled. It should be noted that this function is inhibited by the software
if the current being drawn by the motor exceeds 80% of the set current of the SR44 (at full voltage
when the motor enters its running stage with the optimizing mode selected).
The method of power factor management described does not affect motor performance, nor does it
detract from the motor’s capability to respond to changes in load demand. This feature of the SR44
Soft Starter is a purely electrical function which has the effect of ensuring that the motor delivers
the torque demanded at all times, but allows it to draw only the precise amount of magnetizing
current required to support that torque output. Without this feature, the motor would draw the
maximum magnetizing current regardless of load. The optimizing function cannot improve the
power factor beyond what it would ordinarily be at full load, but it does make the optimum
improvement possible at any partial load.
NOTE: SR44 soft starters have been discontinued. Please consider SR55 soft starters as a replacements.
Chapter 3: Applications
SR44 Series Soft Starter User Manual
1st Ed, Rev B 07/31/2019