Maintenance Technology July 2017 - 12

PLANT PROFILE

project," Sagan said. "Without
making it overcomplicated, we
came up with a design that utilized
much more advanced components
and would achieve a safer system.
This is the safest medium-voltage
switchgear in any Mercedes-Benz
facility in the world."

Communication-assisted
protection and control

"That is a long time in the
arc-flash world, which means
that you could be severely
injured or even killed if you
are exposed to the energy
from that arc flash."
To overcome the timedelay problem with the main
breakers, Sagan again used
the high-speed fiber-optic
network communications.
"Because all of the relays
can communicate with each
other, the system is able
to distinguish between a
fault on one of the feeders
from a main bus fault. This
allows the main breakers
to trip much faster, thereby
reducing the arc-flash
hazard."

One of the main features that
makes switchgear so safe is the
communication-assisted protection and control scheme. Sagan
explained that all of the relays are
connected by a fiber-optic network
to an automation controller. The
automation controller is located
in an HMI (human-machine
interface) cabinet a safe distance
away from the switchgear. This
allows an operator to open or close
Expansion requires
circuit breakers from the HMI
new infrastructure
screen rather than operating a
The 1.2-million-sq.-ft. body
Top. Mercedes-Benz U.S. International Inc., produces more
control switch while standing right
shop expansion project
than 300,000 vehicles a year in Vance, AL.
in front of the breaker.
also required increasing
"If there is a fault or a problem with
the assembly and paint
the breaker when it is opened-like an Above. A 2N redundancy approach assures that power is
shops. Several loads were
always available for the assembly line and all other areas
arc-flash event-and you are standing
re-circuited to the new
at the Mercedes-Benz plant.
right in front of it, you are at risk of
M2 switchgear to free
being injured from the arc flash," he
up capacity on M1. New
sensors in its main bus section. In this
emphasized.
circuits were then installed
case, if a short circuit occurs upstream of
Another major component that
at M1 to feed the new body-shop
the feeder breaker, the relay transmits a
improves the safety of the M2 switchgear
expansion.
message through the fiber-optic network
is the arc-flash-detection system.
"By doing this, I was able to rebalance
to tell the main relay that an arc flash
This system uses 44 arc-flash sensors
the plant loads and maintain the full 2N
has been detected. This allows the main
embedded throughout the switchgear.
redundancy throughout the system,"
breaker to trip and extinguish the arc
Each relay has four sensors connected by
Sagan said. "We literally now have the
flash 10 times faster than is possible on
fiber-optic cables. If an arc flash occurs
ability to fail half the transformers in this
the M1 switchgear.
on the part of the circuit protected by a
plant and still run full production."
Most industrial plants rely on
specific relay, light is transmitted to the
Sagan explained that his experience
traditional time-current-coordination
relay from the sensors. This, along with
earlier in his career made him realize how
protection schemes for their mediumthe fault current detected by the relay,
important backup redundancy was for
voltage switchgear. In this type of scheme,
causes the relay to trip its circuit breaker
the power system.
relays on the main breakers have a time
extremely fast.
"Not only does this provide flexibility
delay to coordinate with downstream
"This is the fastest any relay can
for supporting production in the event
relays. This prevents the main breaker
detect and issue a trip command on any
of a failure, but it also allows us to shut
from tripping for a fault on one of the
Mercedes-Benz power system in the
down major parts of the system for
feeders and shutting down the whole bus.
world," said Sagan. "Because the relays are
maintenance," he said. "Instead of having
But, if the fault is on the main bus, the
able to trip circuit breakers in less than
to schedule maintenance blackouts, we
main breaker still has to trip.
7-milliseconds, the arc-flash energy is
simply transfer the load using the redun"The breaker may delay as much as
drastically reduced."
dancy. Then we can perform maintenance
one second before it trips," Sagan said.
Each feeder relay also has arc-flash
testing during the week on straight time,

12 |

MAINTENANCE TECHNOLOGY

JULY 2017



Table of Contents for the Digital Edition of Maintenance Technology July 2017

Editorial
Uptime
On The Floor
Powering Auto Production
Following The North Star
Flying Inspections
Untangle Compressed Air Misconceptions
Change Your Lubrication Mindset
HMI-Design Essentials For Today's SCADA Systems
SAP: Tips and Tricks
Cybersecurity Best Practices
Bearing Storage
Interpreting IP Code
Noisy Pumps
Move From Time- to Condition-Based Lubrication
CMMS Energizes Maintenance Efforts
Products
Ad Index
Showcase
Final Thought
Maintenance Technology July 2017 - 1
Maintenance Technology July 2017 - Cover1
Maintenance Technology July 2017 - Cover2
Maintenance Technology July 2017 - 1
Maintenance Technology July 2017 - 2
Maintenance Technology July 2017 - 3
Maintenance Technology July 2017 - Editorial
Maintenance Technology July 2017 - 5
Maintenance Technology July 2017 - Uptime
Maintenance Technology July 2017 - 7
Maintenance Technology July 2017 - On The Floor
Maintenance Technology July 2017 - 9
Maintenance Technology July 2017 - Powering Auto Production
Maintenance Technology July 2017 - 11
Maintenance Technology July 2017 - 12
Maintenance Technology July 2017 - 13
Maintenance Technology July 2017 - 14
Maintenance Technology July 2017 - Following The North Star
Maintenance Technology July 2017 - 16
Maintenance Technology July 2017 - 17
Maintenance Technology July 2017 - Flying Inspections
Maintenance Technology July 2017 - 19
Maintenance Technology July 2017 - 20
Maintenance Technology July 2017 - 21
Maintenance Technology July 2017 - Untangle Compressed Air Misconceptions
Maintenance Technology July 2017 - 23
Maintenance Technology July 2017 - 24
Maintenance Technology July 2017 - Change Your Lubrication Mindset
Maintenance Technology July 2017 - 26
Maintenance Technology July 2017 - HMI-Design Essentials For Today's SCADA Systems
Maintenance Technology July 2017 - 28
Maintenance Technology July 2017 - 29
Maintenance Technology July 2017 - SAP: Tips and Tricks
Maintenance Technology July 2017 - Cybersecurity Best Practices
Maintenance Technology July 2017 - Bearing Storage
Maintenance Technology July 2017 - Interpreting IP Code
Maintenance Technology July 2017 - Noisy Pumps
Maintenance Technology July 2017 - Move From Time- to Condition-Based Lubrication
Maintenance Technology July 2017 - 36
Maintenance Technology July 2017 - 37
Maintenance Technology July 2017 - 38
Maintenance Technology July 2017 - CMMS Energizes Maintenance Efforts
Maintenance Technology July 2017 - 40
Maintenance Technology July 2017 - 41
Maintenance Technology July 2017 - Products
Maintenance Technology July 2017 - 43
Maintenance Technology July 2017 - 44
Maintenance Technology July 2017 - 45
Maintenance Technology July 2017 - Ad Index
Maintenance Technology July 2017 - Showcase
Maintenance Technology July 2017 - Final Thought
Maintenance Technology July 2017 - Cover3
Maintenance Technology July 2017 - Cover4
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