Tech Briefs Magazine - August 2021 - MD-17

Conventional full voltage starting can
cause mechanical shock to the equipment
and the work in process when frequent
stopping and starting of a conveyor
system places stress on all mechanical
linkage.
Power Considerations
Conventional full voltage starting
can't control the acceleration and deceleration
rates of a machine, nor the
speed of the machine. Furthermore,
conventional full voltage starting can't
control the in-rush current that the
motor draws when it starts and typically
allows 600% of the rated motor current
during startup. As a result, the in-rush
can cause voltage dips and other power
disturbances.
Utilities establish their pricing based
on average power consumption. " Peak
demand " charges may occur when starting
large motors across the line (typically
a 15-minute penalty at higher than
agreed rate). Reduced energy consumption
is achieved when applying
drives on variable torque loads. Var -
iable Frequen cy Drives connect easily
to offsite programming portals and can
offer Ether net and Profinet connectivity
for running additions to a brownfield
installation.
Drives are also being integrated into
virtual systems and cloud databases
more often today. These are perhaps
hidden but very real cost-saving potentials
for a machine builder or end user.
Careful consideration should be given to
such factors when developing a new
machine or retrofit plan.
Depending on the application, a variable
torque or a constant torque inverter
is used. The torque needed to perform a
function increases as the speed increases
in variable torque. Constant torque
means that torque remains the same as
power increases. Variable torque is ap -
plied to pumps and fans, while constant
torque applies to everything else. In centrifugal
applications, like pumps and
fans, a reduction in speed results in a
proportional reduction in flow.
Energy savings can be monitored and
reduced through VFDs. In air systems, a
VFD replaces the contactor to control
flow or pressure and the outlet damper
is opened fully. The same procedure
applies to water systems, replacing the
contactor with a VFD and opening the
throttling valve fully.
An OEM must think about how to
build a machine that will work on any
kind of power system. When building a
piece of equipment, how would a low
harmonic solution be provided? Other
issues that should be considered include:
How hot is the plant? What kinds of contaminants
are in the atmosphere?
Both OEMs and end users need to
design for two types of systems -
grounded and ungrounded - and they
must consider the locally required electrical
standards. Drives can play a significant
role in this process. Being cognizant
of the options and available features on
the market today will benefit you and
your customers in trackable ways.
This article was written by Chad White,
Motion Control Business, Siemens Industrial,
Atlanta, GA. For more information, visit
http://info.hotims.com/79416-284.
Motion Design, August 2021
Free Info at http://info.hotims.com/79416-707
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Tech Briefs Magazine - August 2021

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