Automation Direct Stellar SR55 Series, User Manual

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Page 4–7 Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
Chapter 4: Principles of iERS (intelligent Energy Recovery System)
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During start-up, the SR55 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 SR55 enters the ‘motor running’ stage. At this stage, if required,
the motor may also operate in ‘iERS Mode’. Entering this mode can be pre-set from the SR55
touchscreen and stored for automatic operation, which will suit the majority of applications
where it is required. This is the default operating mode for the SR55. It can also be toggled
on and off while running by using either the iERS button in the Advanced Settings of the
touchscreen, or through external circuitry connected to one of the programmable inputs and
controlled by the driven process.
‘iERS’ Intelligent Energy Recovery System will sense when at a level where we will gain no
benefits from Energy Saving, the SR55 will energize the bypass relays, and there will be no
losses from the motor controller.
Energy Saving will try to be active at all times and is fully automatic. The bypass relays will
only energize depending upon the measured thermal capabilities of the unit, percentage
loading of the motor, and the power factor, etc.
The bypass relays will open at 80% loading of the motor current set and enter the energy
saving mode. The relays will not re-energize until at least we are a level of 90% of the motor
current set, or we have surpassed the measured thermal capabilities of the unit, or the power
factor is close to full loading.
There should be even higher levels of energy saving, as when the motor is fully loaded the
relays will be energized and we will have no losses in the thyristors. We will therefore gain
maximum saving which is especially beneficial on typical cyclic loading applications such as
pump jacks, injection molding machines, mixers, saws, etc.
In iERS 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 SR55
(at full voltage when the motor enters its running stage with the iERS 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 SR55 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 iERS
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.