World Grain - September 2024 - 62

MILLING OPERATIONS
Variable frequency drives (VFDs) may stop functioning
while lighting and computer displays may flicker.
PCs, PLCs, and other microprocessor-based equipment
may lose data or have data processing errors.
* Transients: Also known as a spike and like a swell,
a transient is a high-energy burst that lasts 1/60th of a
second or less where the voltage is higher than expected.
They range from a few volts to several thousand
volts (some can be 6 kV or higher) and are caused
by the sudden release of stored energy. Lightning or
static discharge are common causes of transients, but
they also can be the result of disconnecting heavy
loads. Transients can be extremely damaging to any
electronic equipment with a power supply, such as
computers or instrumentation. Transients can destroy
circuit boards and processors, resulting in memory
loss and data corruption. We often use surge protection
devices to protect computers from surges and
transients induced by lightning
* Harmonic Distortion: Harmonic distortion is a deviation
from or deformity of a normal, sinusoidal
waveform, or sine wave. Sometimes called " dirty " or
" noisy " electricity, it can be introduced by any non-linear
load within a facility, such as LED (Light Emitting
Diode) lighting, DC (Direct Current) power supplies,
VFDs (Variable Frequency Drives), welding machines,
rectifiers, inverters, electronic starters, switching
power supplies, discharge lamps. Unlike transients or
sags, harmonics can remain at a steady state within the
system. High harmonic distortion can cause multiple
problems, including overheating of equipment like
motors or wiring, reduced efficiency of machines, and
Power quality is not a line item
on the mill electrical bill, but
poor power quality has hidden
costs to the milling operation.
nuisance tripping. Over time, harmonics can shorten
the lifespan of equipment and reduce power capacity.
Ultimately, the damage to equipment can be costly and
cause unplanned shutdowns.
* Flicker Effect: The flicker effect is a flickering of lights
induced by rapid variations in voltage. These voltage
variations are caused by loads in which the power absorption
varies very quickly: arc furnaces, welding machines,
rolling machines, laser cutters. Flicker impacts
workplace safety and productivity.
Four-step solution
The Power Quality Blog (see page 63) provides detailed
background in the Industrial Power Quality Problems article
by A. El Mofty K. Youssef, Alexandria Electricity Company,
Alexandria, Egypt. They report four steps to solve power
quality, including investigation, determination, analysis and
prevention. Investigation of power quality issues begins with
data logs of problem issues. In this instance, three separated
logs of information are maintained and brought together for
analysis and identification of problem areas.
Their publication identifies standards applicable to power
PG&E flow chart
Is your equipment new?
No
Have there been any changes
or additions?
No
Can you correlate the
problem with other activity?
No
Can you correlate problem
to a utility activity?
Yes
Yes
No
yes
Yes
Can the problem be traced to the
software or hardware?
No
Is equipment sensitive to other
load on the same circuit?
No
Are the wiring and
ground correct?
Yes
Is the voltage at the equipment
within specifications?
Yes
Can you determine the type of
disturbance affecting the equipment?
No
yes
No
Yes
Correct the wiring and grounding
in accordance with NEC
Consult a power quality
specialist
Consult a power quality
specialist
Call your energy company
62
September 2024 / World Grain / World-Grain.com
yes
Change to a different circuit
yes
Call the manufacturer
PG&E
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World Grain - September 2024

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