Automation Direct Stellar SR55 Series, User Manual

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Page 4–5 Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
Chapter 4: Principles of iERS (intelligent Energy Recovery System)
h
oW
m
uCh
e
nergy
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The amount of energy used by a squirrel-cage induction motor operating with a soft starter
in energy-optimizing (iERS) mode is shown in the following figure (Figure 4.5.1), for the same
duty cycle as Figure 4.1.2. By reducing the voltage when torque demand is below maximum,
the magnetizing current is proportioned to the torque current.
Compare Figure 4.5.1 (energy-optimizing) with Figure 4.1.2 (non-optimizing). (These graphical
representations are illustrative only and not to scale.) Arriving at any exact figure for the
energy cost saved requires each individual case to be examined in detail, taking into account
the motor rating, type, and any special characteristics such as load, load characteristics, duty
cycle, supply voltage, and the cost of electricity.
f
igure
4.5.1: e
nergy
s
avings
40 60 80 100 120 140 160
seconds
%
FLC
100
50
0
Current demand with Energy Saving in operation
Magnetizing current
Torque current
The calculations to cover all the likely or possible conditions would be laborious. An empirical
method for arriving at a usefully realistic estimate has been devised. Used with a proper sense
of engineering circumspection, the tables in the “Estimating Energy Savings” sub-section
allow a user to gain a reasonably close estimate of the savings to be achieved within the motor
by using the SR55 optimizing soft starter. The method does not include any additional savings
and benefits conferred by other sources, such as:
• reduction of heating losses in cabling because of the lower voltages;
• potential reduction of maximum demand charges;
• further energy savings and other benefits deriving from the soft-starting process itself;
• reduced total energy demand;
• reduced wear and tear;
• reduced maintenance and replacement costs�