Feature
Low-Voltage Switchgear Continues
Its Evolution
L
ow-voltage switchgear distributes power and protects equipment within
a facility’s electrical system. Power is distributed through low-voltage,
air circuit breakers and faults are sensed in the system. Then fault sensing equipment can open the necessary circuit breaker(s) to clear the fault and
maintain power to the rest of the facility.
Over the last few years, low-voltage switchgear has matured into an intelligent
power distribution solution by providing greater information about the system
operation. Features have been introduced improving overall system reliability
and performance.
Using draw-out circuit breakers and industry-related standards, low-voltage
switchgear first entered the electrical industry in the 1930s when circuit breakers
were manually- or solenoid-operated and employed electromechanical trips. The
next major advancement occurred in the mid-1950s when circuit breakers with
stored energy mechanisms were introduced. In the 1970s, technology began to
grow rapidly with the introduction of solid-state tripping devices. By the 1980s
digital-trip units were using root-mean-square (rms) sensing, which aids in accurate protection when harmonic content is present.
Along with evolving protection capabilities, the use of digital low-voltage
switchgear technology provided improved metering data and communications.
This allowed power management systems to link various individual components
into unified low-voltage solutions.
These communication protocols, born from relatively slow, twisted-pair communication mediums of individual devices, soon offered full information transfer
for one substation at hundreds of megabits per second. These communication
improvements are featured on the most advanced low-voltage switchgear solutions today.
Circuit breakers used in low-voltage switchgear also have evolved, providing
higher interruption capability in smaller physical envelopes, transitioning from
iron-frame circuit breakers to circuit breakers with a high dielectric, molded
enclosure.
www.netaworld.org by Jane Barber
GE
Choosing low-voltage
switchgear
Generally, low-voltage switchgear
is used in industrial and critical power
applications, while integrated switchboards are typically used in commercial applications.
Low-voltage switchgear has circuit
breakers that feed larger and more
severe duty loads than integrated
switchboards. Low-voltage switchgear
circuit breakers provide power to motor control centers, switchboards, or
large motors located in various sites
throughout a facility.
The low-voltage switchgear circuit breakers have more metering
and protection of the circuits than
the loads typically found on switchboards. This provides protection and
maintains continuity of service to as
much of the facility as possible. Also,
the industry standards for low-voltage
switchgear vary greatly from those that
apply to switchboards and integrated
switchboards.
Minimizing arc-flash hazards
Arc flash is the release of energy
produced by an electric arc with temperatures reaching 35,000 degrees
Fahrenheit. According to the NFPA,
each year more than 2,000 people are
treated in burn centers for severe arcflash injuries.
Summer 2009 NETA WORLD
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Since the ability to minimize arc-flash energy is crucial,
many features are now designed into low-voltage switchgear.
By using precautionary measures such as remote monitoring,
remote racking, and real-time alarms and diagnostics, end
users can reduce the risk of an arc-flash injury by minimizing
the need for an operator to be near live equipment.
Systems equipped with these features enable fault reports
and event logs based on accurate, system-wide information
before, during, and after an event for each breaker. Systems
offering off-site-monitoring capabilities give users a constant flow of information to help monitor a system and know
exactly when and where something needs to be repaired.
Intelligent communication
Low-voltage switchgear will continue to evolve and meet
the needs of users and various applications by leveraging
technological advancements. The increased awareness of arc
flash will continue to influence advancements in providing
fast protection while maintaining selectivity.
On the horizon are innovative approaches to keep operators away from live equipment for routine procedures such as
metering, opening and closing circuit breakers, and racking
circuit breakers in or out of their cells.
Since many facilities and sites are losing experienced electrical maintenance personnel, it is more important than ever
to have switchgear that is both easy to use and intelligent,
providing detailed information regarding the dynamics of
the system. With staff reductions, communication of power
system information is becoming vital, whether for gathering information for a single facility or multiple facilities in
various geographic locations.
Consequently, ease of communication and providing
information – not just data – will continue to evolve, as
will better integration of protection and control functions.
Over the past 70 years, low-voltage switchgear reduced
exposure to arc-flash hazards and increased reliability for
power distribution protection and monitoring. The ability
to protect and track power distribution from anywhere at
anytime is a key feature for optimum performance and increased arc-flash hazard reduction. While the advancement
in arc-flash prevention features improves user safety, it also
will improve productivity and reliability in the long run.
At some point there will be a technological leap to provide even faster interruption of faults, similar to vacuum
technology becoming applicable in medium-voltage equipment in the 1970s.
While low-voltage switchgear has matured, even more
promising solutions are ahead.
Checklist: What to look for in a lowvoltage switchgear solution
Make sure your low-voltage switchgear solution delivers
these features to help reduce arc-flash hazards and increase
flexibility and reliability:
Safety
• Use zone-based protection modes such as bus differential,
zone-selective interlocking and multisource ground fault
protection to provide fast and selective protection in the
event of an arc flash.
• Remote racking eliminates the need for users to face a
moving breaker during rack-in and rack-out.
• Remote HMI provides operators with easy access for
monitoring and control outside the arc-flash zone.
• Multiple protection setting groups allow for different
instantaneous and/or short time overcurrent settings to
change a circuit to minimum pickup and maximum speed
when personnel will be near energized equipment.
Flexibility
• Simplified design using architecture that significantly
reduces component counts and wiring to expedite installation and startup as well as reducing longer term
maintenance.
• Easily upgraded system capabilities, such as software
upgrades for added functionality, allowing the user to
decrease system downtime and increase productivity by
eliminating the need for new devices and wiring to be
installed.
Reliability
• Redundant protection and control systems provide continuity of service as well as the ability to make repairs
without downtime.
• Event log and alarms provide reports based on actual
system dynamics and user-set alarms, allowing for realtime monitoring to inform users of situations before
problems arise.
• In high resistance ground fault (HRGF) systems, HRGF
protection indicates the circuit breaker load where the
ground fault exists and also includes priority tripping in
the event of multiple ground faults. This provides fast, efficient detection as well as protection should two ground
faults (on different phases) occur at the same time.
Jane Barber is the Entellisys low-voltage switchgear product manager
for GE Consumer & Industrial’s electrical distribution business. In 25
years at GE, she has led the development and management of low- and
medium-voltage switchgear, protective relays, power-management systems and aftermarket products.
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NETA WORLD Summer 2009
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