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2 Designing data center electrical distribution systems Designing efficient and reliable data center
electrical systems requires looking through the
eyes of the electrical engineerand the owner.
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cover story
ON THE COVER:
The photo depicts servers that are part of
a recently built data center on a university
campus. At the time the photo was taken, the
project was almost completed. The servers
are powered through busplugs in the busway
running under the ceiling. The cable trays are
dedicated solely to fiber-optic cable runs.
Courtesy: Jacobs Engineering
FEATURESManaging power
through networked
electrical systems
Engineers should consider thebenefits of networking electrical
systemsmonitoring and
controlling power, its usage, and
how it affects system reliability.
Integrating commercial
buildings, utilities with
the Smart GridKnowing where and how much
power is needed allows the Smart
Grid to adjust power distribution in
real time. The agility of matchingpower demand with power
production minimizes the amount
of power that generating facilities
must dump, and keeps base-
load plants running at minimum
capacity.
Mitigating arc
flash hazardsEngineers should know about
selecting the appropriate risk-
reducing strategies to help their
clients ensure compliance withNEC, NFPA 70E, and OSHA.
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Data centers are among the hottest
developments in the technologyworld. The growing needs of the
Internet of Things have forced the
biggest players in the computing world to
spend billions of dollars on new multi-
megawatt data centers. This boom in data
center construction is largely fueled by the
growing use of cloud services, which has
put a strain on server capacity (see Figure
1). Additionally, data centers are considered
mission critical when their operation is
of importance to organizations economicor functional needs. Even a disruption of
a few seconds in the operation of certain
types of mission critical data centers could
cost millions of dollars.
This article explores data center
design through the eyes of both the
owner and the electrical engineer. It also
discusses the key components of data
centers and touches on the codes and
standards that apply to data centers and
their components.
PRELIMINARY CONSIDERATIONS
Data centers, many having servers as their main compo-
nents, need electrical power to survive. It is, therefore, only
natural that any talk about building a data center should
begin with figuring out the electrical needs and how to
satisfy those needs.
Capacity:Before deciding anything else, the owner
must decide the capacity of the data center (in megawatts).
In previous planning efforts, it was common to use W/sq ft.
However, today it is more common to discuss kW per rack,
which may vary from 5 to 60 kW. This power concentration
per rack can also drive cooling system type and capacity,
which must be planned for in the capacity. The owner also
needs to consider future capacity.
Another big decision is to determine the level of
redundancy. Reliability is very important for data cen-
ters, and disruptions are costly. But the cost of building a
data center increases significantly with higher reliability.
Therefore, the owner should decide where to draw the
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Designing efficient and reliable data center electrical systems requires looking through the eyes
of the electrical engineerand the owner.
Designing data centerelectrical distribution systems
By Eduard Pacuku, PE, Jacobs, Philadelphia
Figure 1: Increasing demand for cloud services is putting a strain on
server capacity. This photo shows data center servers while they are being
configured and wired. All graphics courtesy: Jacobs Engineering
LEARNING OBJECTIVES
Understand the preliminaryconsiderations of designingdata center electrical distribu-tion systems.
Know how to design efficientdata centers that can also ac-commodate growth.
Identify the codes and stan-dards that apply to designingdata center electrical distribu-tion systems.
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CoverStory
line, and determine how much
risk is acceptable.
Auxiliary power:After the datacenter capacity is decided, the
facility power must be computed.
The facility power includes data
center heating and cooling. A
focus of recent years is to make the
facility (non-data) power as low
as possible to improve efficien-
cies and lower operating costs. To
address the efficiency of facility
power within a data center, the
term power usage effectiveness
(PUE) was coined. The closer tounity the PUE is, the smaller the
nonproducing faci lity power is.
Years ago, it was normal to ac-
count for the facility and cooling
load as being half of the total pow-
er delivered to the data centers.
That means that if a data center
had a capacity of 10 MW, the facil-
ity and cooling load also would be 10 MW, leading to a PUE
of 2. PUE equal to 2 is deemed to be average efficiency, but
not satisfactory to many data center owners. New technolo-
gies have pushed the PUE very close to unity.
Reliability and tiers:To classify data centers in terms of
reliability, the Uptime Institute created standards referred
to as Tiers (see Table 1). Data centers are classified in four
Tiers. Tier I data centers dont have a redundant electri-
cal distribution system, and their components dont have
redundant capacity. Tier II data centers differ from Tier I
data centers in that they have components with redundant
capacity. Tier III data centers have dual-powered IT equip-
ment and more than one distribution path to the servers.
Tier IV data centers have all the features that Tier III data
centers have. In addition, Tier IV data centers are fault
tolerant in that they have more than one electrical power
distribution path. Tier IV data centers have HVAC equip-
ment that is also dual powered and have storage capacity.
Determining which Tier to select depends on numerous
factors. Many organizations used to have large consoli-
dated data centers, which led to choosing a Tier III or Tier
IV system. Also, many organizations involved in finan-
cial industries choose Tier III and Tier IV systems. Other
organizations choose to have multiple data centers that can
handle data needs when another center goes down, leading
to an ability to use lower Tier systems.
Usage:Data centers are also categorized according totheir usage. These include data centers serving a private
domain, such as a corporation or
a government entity; data centers
serving a public domain, such asInternet providers; and multi-user
data centers.
Power distribution:Currently,
there is debate about what kind of
electrical power to use to feed data
centers. Should it be ac or dc? Each
has merits. Recently, dc power has
received increasing consideration
because data center computing
equipment uses dc power. Having
dc power distribution eliminates
the need for transformers andac-to-dc converters on the server
floor. Using dc also eliminates har-
monics because there is no switch-
ing of power. In addition, using dc
eliminates conversion steps, which
leads to higher efficiency (each
conversion step introduces losses),
thereby decreasing cost.
However, ac has been the dominating form of power
distribution for many years (see Figure 2). The benefits of
ac include readily available equipment, lower costs, and
easier maintenance (because the maintenance crews al-
ready know the equipment and the spare parts are readily
available). Historically, most ac power distr ibution systems
were designed at 208/120 V. The ever-evolving technolo-
gies have helped make the case for using higher ac voltages
at 400/415 V, and even 480 V because of the higher power
demands and efficiencies delivered by newer electrical
equipment.
PUE: Another important factor in data center design
and construction is PUE. The closer the PUE is to unity,
Figure 2: For many years, ac has been the dominating form
of data center power distribution as shown in this photo of
servers powered through overhead busways via busplugs.
Table 1: Uptime Institute tier systemClassification Description
Tier I Lack a redundant electrical system.
Have components without redundant capacity.
Tier II Have components with redundant capacity.
Tier III Maintain duel-powered IT equipment.
Have multiple distribution paths to the servers.
Tier IV
Have multiple distribution paths to the servers.
Have multiple electrical power distribution paths.
Have storage capacity and dual-powered HVAC equipment.
Table 1: Data centers are classified into one of four Tiers from lowest tohighest reliability.
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the better. A data center with PUE of 1.5 is considered the
middle line of efficiency. A PUE above that number shows
an inefficient data center; a data center with PUE below 1.5
is considered to be efficient. A data center with a PUE of
1.2 is considered to be very efficient. The most important
part of a data center is the IT equipment. If there were nosupporting (auxiliary) loads, the PUE would be 1. Because
the auxiliary loads are necessary, the PUE is always greater
than 1. The auxiliary loads include HVAC loads and small
electrical loads, such as lighting and receptacles.
ELECTRICAL DESIGN
After the owner decides on the above considerations, the
work of the design professionals begins, especially for the
electrical engineers. Electrical engineers have to come
up with a design that is efficient, has enough capacity for
future growth, and avoids unnecessary frills.
Power distribution elements:There are many parts toelectrical power distribution. It starts with utility trans-
formers, which in large data centers are owned by the data
centers owner. After the power is stepped down from the
utility transmission voltage to the distribution level, it goes
through distribution switchgear that redirects power to
where it is needed. Typically, the power must be stepped
down again, more often than not, via substation transform-
ers and through more than one path. The standby power,
usually present in todays data centers, is often introduced
at this level, bringing with it the automatic transfer switch
equipment. From the ATS, the power goes to the servers
(often via a UPS system), where it switches from ac to dc
power to be used by the servers. The next layer of distribu-
tion includes switchboards and panelboards that feed the
auxil iary load, HVAC loads, and regular house loads. Power
monitoring systems could also be employed at this point,which could provide very important information on how
different pieces of equipment are working and how power
is being used.
Going through so many pieces of equipment requires
meticulous work. The design professional must be mind-
ful of the cost of equipment and cables and also the losses
introduced by each piece of equipment. Having so many
pieces of electrical and mechanical equipment means that
the engineer also must be mindful of many codes and
regulations associated with these designs.
Relevant codes:The relevant codes for data center de-
sign professionals include ANSI/TIA-942-2005: Telecommu-nications Infrastructure Standard for Data Centers, NFPA
70: National Electrical Code, and ASHRAE: Standard 90.1:
Energy Standard for Buildings Except Low-Rise Residen-
tial Buildings. Other very important codes include Inter-
national Building Code, International Mechanical Code,
International Plumbing Code, International Fire Code,
International Fuel Gas Code, International Energy Conser-
vation Code, NFPA 72: National Fire Alarm and Signaling
Code, and NFPA 90A: Standard for the Installation of Air-
Conditioning and Ventilation Systems.
Depending on the size of the data
center and the type of building host-
ing it, other codes such as NFPA 13:
Standard for Installation of Sprinkler
Systems, NFPA 30: Flammable and
Combustible Liquids Code, NFPA 10:
Standard for Portable Fire Ext inguish-
ers, NFPA 101: Life Safety Code, NFPA
110: Standard for Emergency and
Standby Systems, NFPA 780: Standard
for Installation of Lightning Systems,
and NFPA 20: Standard for Installation
of Stationary Pumps for Fire Protection
may apply.
Utility service:As with any other
project, designers start by considering
the utility service. Because of the impor-
tance of reliability, owners must engage
early on with the utility company to dis-
cuss the service. Depending on the size
of the data center, the service options
include a separate dedicated utility line
or an existing, very reliable line.
The electrical designer, in close col-
laboration with the owner, must decidehow many layers of equipment will be
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Figure 3: This one-line diagram of a typical data center shows the tie breaker on the primary side of
the transformers. However, locating the tie breakers on the secondary side is just as effective. Thetie breaker makes it possible to have two sources of normal power.
Typical data center diagram
ATS ATS
To load To load
Generator farm
Transformer Transformer
Utility line Utility line
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there. The more equipment introduced, the more points of
failure are present. In mission critical facilities, it is impor-
tant to avoid single points of failure.
The utility service will most likely be medium voltage.
Depending on the size and location of the data center,
the service could be between 13.8 and 345 kV. The nextstep is to step down the voltage to a level usable for the
servers. Most data center IT equipment works with dual
voltage, 100 to 120 Vac and 200 to 240 Vac. The higher
voltage208 or 240 Vincreases efficiency, thereby low-
ering losses. Having servers powered at 415 Vac further
increases data center efficiency, making for a better PUE.
If the designer decides to use the higher voltage, 415 V,
the auxil iary mechanical load would then be at 480 V.
This means that autotransformers must be used to take
the power from 415 to 480 V.
At what point does one decide to convert the medium
voltage to low voltage (below 600 V)? The answer to thisquestion depends on the size of the data center and the
distance from the service drop. If the data center is part
of a campus, the data center can be quite far from the
service drop. If that is the case, it is preferable to distribute
the electrical power at a voltage level as high as possible,
typical ly 13.8 kV. If the service voltage is higher than 13.8
kV, the first transformation will be at the service entrance,
stepping down the voltage from whatever the utility volt-
age is to 13.8 kV. This power is delivered to the data center
where the second transformation takes place, stepping the
voltage down to 480 or 415 V.
Redundancy: What sets data centers apart is the level
of redundancy. But everything comes at a price. The
more layers of redundancy that are added, the more
expensive construction of the data center becomes.
Granted, having a data center blackout (or brownout) is
very expensive as well.
The servers, by design, come with two power sup-
ply options. In addition, they are backed up by batteries.
Therefore, there are two different normal power supplies to
each server. That means that the servers would be served
from two different substations. To be fully redundant,
the substations need to be fed from two different utility
lines. In the best-case scenario, the utility lines have a tie
between them at some point in the electrical distribution
system, and each utility line has enough capacity to carry
the entire load of the data center. This scenario describes a
fully redundant, normal power data center (see Figure 3).
The normal power redundancy is very important, but it
is not enough by itself. The normal power is often backed
up by a standby system. The standby system is generally
composed of generators, which could be diesel, natural
gas, or a hybrid. Diesel generators are the preferred type of
generation because they are reliable machines and can be
easily maintained. Depending on the type of building thedata center is housed in, the generators may or may not be
part of the life safety system. Nevertheless, the generators
are usually set to be ready to back up the power system
very quickly, usually in 10 to 30 sec. The time depends on
how long the server backup batteries can last.
FINAL THOUGHTS
Although designing a data centers electrical distribution
system may seem straightforward, there are inherent chal-
lenges. The electrical engineer must:
Work closely with the owner to determine current and
future data center capacity.
Work with the owner to decide which data center Tier
would be appropriate for the clients needs.
Work closely with the owner to determine the level of
redundancy.
Design a system simple enough to be easy to operate,
but one that is also robust.
Eliminate single points of failure.
Design a very efficient system with the goal of achiev-
ing a PUE under 1.5.
Apply the relevant industry codes and regulations.
Designing data centers is complex (see Figure 4). Build-
ing data centers is very expensive, as is their operation and
maintenance. Continuous collaboration with the owner is
extremely importantmore so than in any other type of
project. The successful completion and implementation of
the design depends on that collaboration.
ABOUT THE AUTHOR
Eduard Pacuku is electrical project engineer at Jacobs, where
he spends the majority of his time designing electrical dis-
tribution systems for universities (including laboratories),
health care facilities, and data centers.
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Figure 4: Although data center design can be complex, the completed
project can be efficient, reliable, and robust if designed well.
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Networked Electrical Systems
I
n the ever-changing world of technology,
at times it seems that marketing a new
technology requires either creating newwords or stringing old words into new
phrases to make it sound new and cutting-
edge, or perhaps just confuse the consumer
altogether. In fact, its hard to imagine a
profession that uses more buzzwords and
acronyms than the field of engineering and
construction. When it comes to networking
of electrical systems and power management,
there is no shortage of this trendy lingo: digital energy
networks that monitor distributed energy resources
tied to the virtual power plants, or the detailed en-
ergy survey (DES) for the energy conservation measure
(ECM) and its interface with the building management
system (BMS)shall I go on? But what does it all mean as
it relates to the networking of systems and overall power
management?
In recent years, billions of dollars have been spent by
electrical utility companies on Smart Grid technologies.
A Smart Grid consists of two-way digital communications
between energy users (facilit ies) and the utilitys network
operation center. Capturing this smart technology concept
and filtering it much further in to the facility (down to the
end-use device) opens up opportunities to better manage
overall power, ranging anywhere from an individual facil-
ity to a large campus system. BMS have been around for
decades, providing the ability to monitor and control HVAC
components, and more recently, the BMS may integrate fire,
security, and lighting control systems. However, programs
such as demand response and other energy management
curr icula have created a strong motivation to fully integrate
what traditional BMS systems have left out. Additional
components, such as power generation equipment, UPS,
power switching equipment, and other metered loads now
want to be part of the same smart system. One of the latest
buzz phrases to describe this facility trend is networkedelectrical systems. This concept of a networked electri-
cal system not only includes the electrical
system that delivers the electricity, but also
encompasses the components that use theelectricity.
THE FACILITY
MANAGERS STRUGGLE
Energy is a major operating expense for
most organizations and, according to
EnergyStar.gov, can represent 30% of
a typical commercial office buildings
operational costs (see Figure 1). However, managing energy
usage can be a daunting task. The facility manager is often
fighting mounting pressure to lower costs while energy
prices are on the rise. Additionally, the reliability of that
energy supply is declining. The expectation that facility
managers do more with less presents a challenge even for
the seasoned and highly qualified facility managers. The
paradigm is that the workforce responsible for overseeing
these complex energy systems continues to age. Accord-
ing to the International Facility Management Association
(IFMA), in 2011 the average age of a facil ity manager was
49. And according to the Sloan Center on Aging and Work,
it is expected that more than 50% of facility management
personnel will retire within the next 10 years. The good
news is that in 2011, IFMA also reported that more young
people are entering facility management with 9% age 34 or
younger. This is up 2% from 4 years prior. However, at that
rate, a one-for-one replacement will not be possible, which
presents a challenge for the design engineer and end user
alike. As codes continue to rapidly change and energy costs
continue to rise, the engineer is charged with providing
a workable design solution for managing a facility. At the
same time, the facility manager is responsible for operating
the systems as they were intended with less overall man-
power. The need for a connected and monitored system
where usage can be tracked and controlled from a central
location exists in any facility where power is critical. Facili-ties such as health care, commercial, industrial manufac-
Engineers should consider the benefits of networking electrical systemsmonitoring and controlling power,
its usage, and how it affects system reliability.
Managing powerthrough networked electrical systems
By Danna Jensen, PE, LEED AP BD+C, ccrd partners, Dallas
LEARNING OBJECTIVES
Understand the importance ofmeasurement and verification.
Know the available monitoringsolutions.
Identify the criteria for inte-grating electrical networkingsolutions into facility electricaldistribution systems.
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Networked Electrical Systems
turing, governmental, data centers, and higher education
are perfect candidates for this technology. Large campus-
type facilities are particularly good candidates because
they have multiple buildings to monitor. A migration to a
centralized management system could be the solution.
MEASUREMENT AND VERIFICATION
There are several aspects of networking electrical systems
that must be considered. Step No. 1 is to correlate the
popular management statement as it relates to energy: You
cant manage what you dont measure. Understanding
what drives energy usage is the first key to managing it.
Interpreting the data and recognizing what to do with them
is the next step in successfully implementing changes in
the system to provide the desired end result.
The industry term measurement
and verification (M&V) is a process
for quantifying savings determinedby an energy conservation measure.
Although M&V continues to be an
evolving art, various standards and
protocols demonstrate best practices. One of the most
popular is the U.S. Green Building Council LEED rating
system. LEED specifically references the International
Performance Measurement and Verification Protocol
(IPMVP) Volume III: Concepts and Options for Deter-
mining Energy Savings in New Construct ion. Another
popular reference is ASHRAE Guideline 14: Measurement
of Energy and Demand Savings.
The IPMVP Volume III protocol states that it was devel-
oped to provide a concise description of the best practice
techniques for verifying the energy performance of new
construction projects. The objective is to provide clear
guidance to professionals seeking to verify energy and de-
mand savings at either component- or whole-building level
in new construction.
ASHRAE Guideline 14 was developed to provide guide-
lines for reliably measuring
energy and demand savings
of commercial equipment.
Using the available
guidelines is an appro-
priate starting point for
the engineer to design a
solution that provides the
facility manager with the
proper tools to manage
energy in the facility. These
guidelines suggest various
starting points based on
the level of M&V desired,
including performing a DES
and planning specific ECMsto include in the design.
Prior to implementation, however, it is important to assess
the end users needs and capabilities when selecting the
appropriate monitoring approach.
MONITORING SOLUTIONS
Some monitoring solutions may be as simple as monitoringthe main power service and a few of the high-level distri-
bution feeders. This rather simple system allows the facility
manager to monitor the overall power quality and correct it
at a system level. This type of monitoring has been around
for quite some time; however, this type of approach is not
exactly a networked solution. A fully networked electri-
cal system incorporates a much broader range of system
components including those that generate energy as well
as use it (see Figure 2). Tracking provides the ability not
only to monitor a system, but also to
implement a control strategy to man-
age the energy usage and quantify theresults. For example, an office building
facility manager may want to monitor
the plug loads at individual workstations
to understand and chart usage. Tracking these data may
reveal that an excessive amount of power is being used
when the building is normally unoccupied, perhaps due to
tenants inadvertently leaving computers or miscellaneous
equipment on overnight. With this information, the facility
manager is armed with the appropriate data to implement
a building policy or perhaps install automatic switching
devices to minimize usage.
As previously mentioned, BMS have the ability to
monitor and control HVAC components and other systems
encompassed by the electrical systems. Many systems and
their associated controls communicate through a common
protocol, such as Modbus, BACnet, or LonWorks. How-
ever, incorporating additional system components tends to
consist of various manufacturers and models that provide a
wide range of assets and communication protocols. This is
one of the greatest challeng-
es in integrating systems,
but as the trend continues, a
growing number of compa-
nies such as Blue Pillar in
Indiana and Power Assure
in California are emerging
in an attempt to provide
a truly networked electri-
cal system. The network
solutions developed by such
companies are claiming
they are easier than ever to
both integrate into new con-
struction as well as retrofit
into existing facil ities. Thepotential energy savings
Figure 1: Energy represents 30% of a typical office buildings operating
costs and is a propertys single largest operating expense, according toEnergyStar.gov. All graphics courtesy: ccrd partners
Typical office building operating expenses
Energy usage
70%
30%
Other operating costs
You cant manage whatyou dont measure.
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and anticipated return on investment (ROI) renders theclaims worthy of exploration.
Fully networked electrical systems are migrating
together all aspects of energy consumption and genera-
tion (see Figure 3). The monitored infrastructure may
include anything from chil lers, air handling equipment,
fuel systems, pumps, switchgear, light ing, and plug loads,
to engine generators, UPSs, thermal storage, cogeneration,
and other equipment. The goal is that anything that uses
energy can be monitored and controlled from a single
location while anything that generates and stores energy
can be monitored and controlled to properly support
the energy usage as efficiently as possible. The system
network collects the information and provides the facility
manager with the appropriate data to make informed and
timely decisions. Some specific examples of the benefits
a facility may realize from a fully networked system are
detailed in the following sections.
Ensure optimum operation:When a facilitys energy
infrastructure is properly designed and commissioned,
optimum operating ranges are established based on un-
controllable factors such as weather, occupant load, etc.
Over time, the optimum setpoints tend to shift for any
number of reasons. The networked system diagnostics
may be set to alert the facility manager when equipment
is not operating at its optimum setpoint or using more
power than anticipated so that correct ive action may be
implemented. Examples include leaking valves, faulty
economizer damper controls, and manual overrides.
Improve reliability and power quality:Dirty power
is the buzz phrase given to electrical anomalies that exist
in a facility. Anomalies such as surges, sags, spikes, and
transients can wreak havoc on sensitive equipment if not
properly managed. Dirty power originates both outside and
within a facility. For example, lightning, utility switching,
and faults on the utility distribution system can affect thequality of power before it reaches the facility. Daily fluctua-
tions inside the facility, suchas harmonics produced by nonlinear loads and cyclical
equipment with frequent on/off switching, affect the power
quality from within. Monitoring of incoming power as well
as individual end users, such as computers and motors,
assists in identifying sources of dirty power. This allows
the operator to take corrective action to improve the power
quality, therefore avoiding critical damage on sensitive
equipment and improving the overall reliability.
Prevent premature equipment failure: Monitoring
large motors and HVAC equipment creates a predictive
maintenance program by identifying when the equipment
performance begins to fall below preset levels or other
unexpected anomalies occur. For example, if a pump with
a constant load starts trending toward increased electri-
cal usage over time, the networked system identifies this
tendency. It can provide an alarm for the facility manager
to investigate potential causes, such as increased bearing
friction or restrictions in the piping. This early detection
system is a predictive maintenance system that may be
used to schedule preventive maintenance. Preventive main-
tenance leads to overall reduced downtime before major
equipment damage occurs.
Reduce overall energy costs:Monitoring total energy us-
age to determine exact historical values will identify ways
to turn the network into a cost savings program. The data
assists the facility manager in determining the optimum
time to operate the on-site generating equipment or other
energy storage devices to reduce peak demand loads. This
also yields improved reliability by providing the capability
to operate on-site equipment with known load parameters
to ride through both temporary and extended utility out-
ages. Note that the use of on-site diesel-fired engine gen-
erators for nonemergency applications triggers additional
requirements from a regulatory standpoint, such as the U.S.
Environmental Protection Agency (EPA) regulations thatthe designer must consider.
9PUREPOWER//
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Figure 2: Advanced, fully networked electrical systems incorporate a much broader range of system components
than former simple monitoring systems.
LEGEND:
*DPM = digital power meter
*MVFS = medium voltage feeder switch
*MVPCB = medium voltage power circuit breaker
Basic Advanced
Switchboardmains and feeders
Controlautomation
Generatingequipment
Network interface
Lightingcontrols Plug loads
Motors
Transfer switches
Networked Electrical Systems
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2013 Caterpillar All rights reserved. CAT, CATERPILLAR, their respectiv e logos, Caterpillar Yellow, the Power Edge trade dress as well as corporate and product identity used herein, are trademarks of Caterpillar and may not beused without permission. www.cat.com www.caterpillar.com
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Q: Integration of facilities varied electrical and mechan-
ical systems into building automation systems (BAS)
is becoming more prevalent. How is your firm meeting
this need?
Chris Edward:Design for the new Gateway Building at
Oberlin College in Ohio was recently completed by our
Indianapolis and Quad Cities offices. This mixed-use hotel,
retail, and office building is pursuing LEED Platinum. It
required a highly customized BAS to be coordinated and
specified (see Figure 1). A geothermal field serves radiant
heating and cooling throughout the building and is assisted
by automated natural ventilation and window shading. The
lighting control system provides 0 to 10 Vdc daylighting
feedback and scheduling access, while power monitoring,
fire alarm, and access control systems integrate with the
BAS. The college provides for all buildings on campus to
display energy and water performance on a Web portal toencourage efficiency by the users.
KJWW often uses the BAS as a common platform in these
high-performance buildings to automate building control
functions and to bring viewable information together for
the owners benefit.
Kevin Krause: Building operations are simultaneously
challenged by the increasing complexity of integrated
systems and financial and human resource limitations.
Systems integration and analytics are a means of doing
more with less.
As a global standard-setting biomedical research center,
the 300,000-sq-ft Wisconsin Institutes for Discovery (WID)
at the University of Wisconsin-Madison represents state-of-
the-art and state-of-the-future strategies for implementing
and benefiting from system-integration-based analytics.
The building technologies required to meet the unique
goals of the project were necessarily advanced and often
inherently complex, compared to most commercial build-
ing systems. The multifaceted nature of the architecturalspaces required tailored solutions for systems, such as
Smart Grid Roundtable 12
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Knowing where and how much power is needed allows the Smart Grid to adjust power distribution in real time. The
agility of matching power demand with power production minimizes the amount of power that generating facilities
must dump, and keeps base-load plants running at minimum capacity. This article explores the relationship between
utilities, the Smart Grid, and commercial buildings through the consulting engineers eyes.
Integrating commercial buildings,utilities with the Smart Grid
By Jack Smith, Managing Editor
and Amara Rozgus, Editor in Chief
Figure 1: A sophisticated BAS at the projected LEED Platinum
Gateway Building assists Oberlin College in its commitment to
environmental sustainability. Courtesy: Solomon Cordwell Buenz
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Smart Grid Roundtable
HVAC, lighting, life safety,
access control, and scientific
processes. This high degree to
which systems were custom-
ized to various spaces created a
demand for specific control andautomation technologies. This
took the form of an intelligent
building architecture.
Interfaces throughout the
open ground floor of the WID
building draw from the systems
integration architecture to docu-
ment building performance and
resource use, providing informa-
tional content to the general pub-
lic and impacting the behavior of
building occupants.
Q:How has the relationship
between utilities, the Smart
Grid, and commercial buildings
changed in recent years, and
what should engineers expect
to see in the near future?
Steven Collier:Most buildings
have traditionally been passive
consumers of electric power and
energy generated by some 7,000
utility-owned power plants, and
delivered to them through high-
voltage transmission lines and
local distribution systems. Now,
however, buildings are becoming an important component
of the grid itself as they increasingly deploy their own
generation, storage, and energy management systems. They
are doing this for a variety of reasons including economy,
reliability, security, sustainability, and independence.
And, perhaps most importantly, they do it to maximize
the benefits for themselves, not to help their util ity solve
its problems. This trend will not only continue but it will
accelerate. Smart buildings will not just be served by the
Smart Grid, they will become an integral part of it.
John Cooper:Traditionally, commercial buildings man-
aged their energy largely independently of their electric
utility grid, focused primarily on minimizing their electric-
ity bill via conservation, energy efficiency, and minimizing
usage during high-cost periods. Starting in the 1980s, elec-
tric utilities began to offer financial incentives to custom-
ers who would allow them to control some portion of their
load to maximize operating economy and defer the need tobuild expensive new generators. Over the past decade, util-
ities more aggressively sought
to engage customers in demand
response programs wherein
customers would change when
they used electricity to mitigate
utilities growing problemswith grid economy, reliability,
and sustainability. Commercial
building owner/operators are
becoming increasingly less satis-
fied with the economy, reliabil-
ity, security, service quality, and
sustainability of the legacy grid.
As a result, as Steve observed,
they are putting in their own
energy production, storage, and
management systems.
Edward:Were approaching the
point where commercial build-
ings are starting to have a need
to communicate directly with
the utility grid. Utility compa-
nies have been using Smart Grid
technologies to modernize their
systems and provide greater
reliability, often with the use of
grants or agreements with their
local regulators. We are still
moving toward a system of dy-
namic or real-time pricing where
utilities and independent system
operators will see the benefit of
charging consumers based on
the actual cost of generation throughout the day. When
commercial buildings start seeing a high cost of energy at
peak usage times, there will be an incentive for two-way
communication with Smart Grids to avoid high costs, and
the relationship with the utility will change. The trend
toward this type of relationship has started in some parts
of the country and will likely expand as energy codes and
state regulators adopt related requirements.
Krause: The two primary drivers for all concerned parties
to embrace with respect to Smart Grid implementation re-
late directly to improved distribution system reliability and
enhanced power delivery efficiency. The improved electri-
cal reliability is derived from the significantly improved
communication directly from consumer meters that can
alert utilities of outages, low voltage, and poor power quali-
ty on an individual consumer basis. Such system anomalies
can readily be identified and isolated via utility supervisory
control and data acquisition (SCADA) systems, thus limit-ing the overall outage exposure to the rest of the distribu-
STEVEN COLLIER, director,
Smart Grid Strategies,
Milsoft Utility Solutions,
Abilene, Texas
CHRIS EDWARD, PE;electrical engineer; KJWW;
Indianapolis
JOHN COOPER,business
development manager,
Business Transformation
Services, Siemens Power
Technologies International,
Schenectady, N.Y.
KEVIN KRAUSE, PE, LEEDAP; principal; Affiliated
Engineers Inc., Madison,
Wis.
Meet our Smart Gridroundtable participants
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tion system. As the digital metering equipment continues
to evolve along with the communication systems, overall
improved system stability and reliability will result.
The system efficiency essentially is related to demand-
side controls implemented within the consumers own fa-
cilities. Smart Grids allow consumers to monitor their own
demand levels and establish internal controls to diminish
their own demand and energy consumption. Whether it
is time-of-day automated controls or the education of em-
ployees regarding manual switching of electrical loads, the
consumer has the impetus to institute these policies and
obtain the subsequent economic benefit. The utilities real-
ize improved load factors, which allow existing distribution
systems to operate more efficiently and preclude the need
to increase capital expenditures by not requiring more
power generation or more transmission lines and their as-
sociated substations.
These two elements are key to the success of the Smart
Grid concept and can be realized almost immediately
with the benefits being shared by the consumer and the
utility alike.
Q:How are BAS being impacted by the Smart Grid
developments?
Collier:Perhaps the better question is how are BAS im-
pacting Smart Grid developments? I think that in many
ways, the entire Smart Grid discussion has the cart before
the horse, so to speak. The electric uti lity industry in
general thinks of Smart Grid measures primari ly as a way
of preserving and prolonging the legacy grid. They think
of customer engagement as being important primarily sothat customers will reduce their demands on an increas-
ingly frail legacy grid. Meanwhile, technology (energy,
electronics, telecommunications, and information) is
making it possible for customers and an ever-growing
industry of nonutility providers (dis-intermediaries) to
simply leap-frog the legacy grid to an entirely new model.
Customers will always act in their own best interests.
They are not going to be interested in developing expertise,
exerting effort, or incurring expense for the benefit of their
electric utility.
Cooper:Commercial buildings enjoy steadily expand-
ing options not available historically, well beyond what
traditional building management systemseven emerg-
ing BAStypically provide. These include on-site power
production and storage, selling power back to the grid,
multiple-site resource dispatch optimization, and sophisti-
cated energy management systems. In fact, as technologies
continue to improve and emerge, and these trends progress
over the next few years, commercial buildings will have
the potential to use BAS integrated with distributed energy
resources (DER), such as on-site generators, fuel cells, or
solar/photovoltaic, to become prosumers, producing as
well as consuming energy, not to mention their ability to
store either thermal energy, or electricity in batteries.
With this newfound capacity, we can begin to speak
of buildings, like the grid, as evolving to become smart
buildings, with a wide range of power options, from net
zero (operating independently of the grid, as a building mi-
crogrid or a nanogrid) to power positive (acting as distrib-
uted power plants or storage units with excess production
capacity) to grid integrated (coordinating energy con-
sumption, storage, and production with gr id operations).Engineers can expect microgrid control technologies to find
14
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Figure 2: NREL technicians work in the Energy Systems Integration Lab within ESIF. The research conducted there addresses technical readiness, performance
characterization, and testing of hydrogen-based and other energy storage systems for optimal production and efficient use. Courtesy: Dennis Schroeder, NREL
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their way into this smaller realm of integrated, indepen-
dent, commercial building nanogrids. What remains to be
seen is the emerging business relationship between com-
mercial building owners and the utilities that serve them.
Q:Describe the various Smart Grid-ready solutionsyouve integrated into BAS of buildings and facilities and
their challenges and opportunities.
Collier:Our software
solutions are for elec-
tric utility engineer-
ing and operations,
and so our custom-
ers have historically
been electric utilities
and their professional
service providers, notretail consumers. It is
interesting, however,
that in recent years,
as more commercial
and industrial sites
(and their nonutility
providers) have begun
to own and operate
their own independent
distribution systems or
microgrid or nanogrid,
they are beginning to purchase and use similar software.
Cooper:My company offers a complete spectrum of
products, solutions, and services for the protection,
automation, planning, monitoring, and diagnosis of grid
infrastructure, as well as a complete suite of building
management services for the commercial and industrial
sectors. Our suite of Smart Grid applications integrate
with smart meter infrastructures, distr ibuted generation,
and BAS solutions, thus al lowing utilities and aggrega-
tors to enable Smart Grid offerings that fully leverage
distributed energy resources. Siemens Building Technolo-
gies provides energy services to the commercial sector.
For example, Gamma building control provides intelligent
solutions and services to maximize energy efficiency
and comfort in buildings. Anticipating ever-greater grid
integration with commercial buildings, Siemens has
developed integrated load management (ILM) technology
that merges distributed energy management systems with
demand response management systems to provide grid
operators and building owners with visibility and dis-
patch capability of a wide variety of edge resourcesfrom
edge power to edge storage devices to curtailable loads.
Siemens has three companies in particular activelyengaging in BAS and Smart Grid integration. PTI offers
business transformation and solution engineering ser-
vices based on Compass methodology, which integrates
business processes, business capabilities, and aspira-
tions with innovative technologies to guide util ities
and businesses into a new, more holistic and integrated
energy business model. Pace Global offers a customportfolio of strategic and tactical services for utilities,
commercial, and industrial customers, including inte-
grated resource planning, r isk-based capital allocation
strategy, energy data
management services,
energy efficiency
assessments, and
strategic sourcing pro-
grams, with a growing
focus on DER and mi-
crogrids. The eMeters
EnergyIP solution isa flexible, scalable
meter data manage-
ment (MDM) platform
that has the most
large-scale, mass-
market deployments
in the utility indus-
try, and has become
the standard MDM
solution. Also, eMeter
recently released
Energy Engage Mobile, its first mobile-web application
that brings energy consumption information direct ly to
the consumers fingertips, helping uti lities connect with
their customers.
Edward:Current BAS have the programming flexibility to
bring in Smart Grid technologies if needed. This is a plat-
form that will be able to expand to accommodate addition-
al control functions to react and respond to data provided
by the Smart Grid when that option becomes more widely
available. A building can be set up to provide warning
or automation to reduce total load as part of a demand
response program or a dynamic pricing event.
Krause:An era of transformation is upon us, as nonrenew-
able fuels are joined by an array of newly viable energy
sources including photovoltaics, geosourcing, wind power,
biofuels, and hydrogen. AEIs history of engineering effi-
ciency into energy-intensive facilities focuses us on smarter
energy use and smart buildings. Advanced integration
and communication of systems via more complex and
developed BAS calls for a high level of technical dexter-
ity to wade through assessment of hard data and growing
technologies of Smart Grid, energy sources, sustainability,and communication protocols.
Smart Grid Roundtable
U.S. electricity meter installed base
%o
ftotalinstalledbase
Year
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
2 01 2 2 01 3 2 01 4 2 01 5 2 01 6 2 01 7 2 01 8 2 01 9 2 02 02 01 2 2 01 3 2 01 4 2 01 5 2 01 6 2 01 7 2 01 8 2 01 9 2 02 0
Noncommunicating
Communicating
Figure 3: This graph shows the U.S. electricity meter installed base for communicating
and noncommunicating starting in 2012 and projected through 2020. Courtesy: IHS
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One of AEIs recently completed projects is the U.S.
Dept. of Energys Energy Systems Integration Facility (ESIF)
at the National Renewable Energy Laboratory (NREL) in
Golden, Colo. NREL is the nations primary laboratory for
renewable energy and energy-efficient research, demon-
stration, and deployment of systems such as Smart Grids(see Figure 2). Electrical delivery infrastructures and their
subsequent communications are focuses of the ESIF.
AEI planned, designed, and engineered two key parts
of the ESIF to allow this development to commence: the
research electrical distribution bus (REDB) and the facility
SCADA system. The renewable energy sources discussed
above variously produce incongruent ac
and dc power. The REDB functions as
the ultimate power integration circuit to
support further industry development of
uniform conversion, metering, safeties,
and system communications.This is where BAS and SCADA sys-
tems play a vital role. New technologies
demand robust safety systems. The ESIF
SCADA system does just that and more.
The system marshals safety PLCs, and
central electric, water, and HVAC utilit ies,
to name a few. AEIs unique safety- and
data-integrity-driven SCADA solution deploys hardware-
independent software governing the array of function-
specific control systems that comprise a smart building/
Smart Grid.
Q:What trends are you seeing in Smart Grid/BAS
integration?
Cooper:There are four trends that stand out in this area,
each interrelated with the other.
Power purchase agreements (PPAs):Equipment vendors
and service providers have begun to offer PPAs to commer-
cial building owners, enabling them to locate on-site power
production in their facilities immediately on a service
basis, with no upfront capital investment.
Bypass:PPAs and disruptive decentralized energy
technologies help drive a second trend: local distribution
utility bypass. A logical progression of maturing distrib-
uted power systems and aggressive marketing by vendors,
bypass occurs when commercial customers purchase en-
ergy solutions from new market entrants without consult-
ing or considering their traditional utility providers. Bypass
represents a significant threat to the conventional utility
business and revenue model.
Nanogrids: The term nanogrid has entered our lexi-
con only recently, and the term remains i ll-defined. For
our purposes, lets consider a nanogrid to be a building-
based microgrid. When a BAS is integrated with multipleon-site power systems to significantly reduce dependence
on the grid, commercial building energy options expand
to include the potential for islanding: operating indepen-
dently of the grid.
Complete demand response (DR):Nanogrids may de-
velop into what could be called complete DR: the ability
for buildings to significantly cur tail grid consumptionon demand, enabling constant wide swings in energy
demand from the grid, from slight declines up to full
islanding. As it develops, this trend will require new at-
titudes and thinking about the potential of demand-side
activity.
As Siemens ILM is implemented, it will enable newly
capable local distribution utilities to
embrace decentralized technologies and
maturing consumer attitudes to stay
ahead of the trends mentioned above.
Instead of viewing new technologies as
disruptive, to be controlled and man-aged as a threat to the status quo, a util-
ity with an ILM will be able to embrace
an array of new technologies that bring
added value to consumers, certain of
their ability to manage the disruptions
to grid operations that accompany new
technologies. Commercial buildings
will enjoy a robust market of new energy services from a
growing number of providers, with integration to utility
operations becoming standard. ILM enables an accel-
eration of the convergence of Smart Grid and BAS by
enabling greater flexibility and control while preserving
core aspects of the utility business model.
Collier:I agree with John about off-the-grid buildings
emerging, grid-connected buildings operating their own
microgrid, and buildings isolating parts of their energy
systems into independent nanogrids. I am also seeing
nonutilities (e.g., Enernoc) aggregating commercial and
industrial (even residential) buildings for participation in
transactive energy markets. An aggregator with access to
a competitive retail market can sell aggregated generation
(and storage), as well as the ability to reduce demand and
energy consumption based on aggregating loads (i.e., a
virtual power plant).
Edward:The trend is that both Smart Grid and building
automation technologies are becoming more sophisticated
and closer to being able to communicate with each other
in a straightforward way. Utilit ies across the country have
been installing a large amount of smart meters capable of
being the link between the power company and consumer
(see Figure 3). Attention has been given by manufactur-
ers of appliances to developing smart refr igerators, ovens,
etc., that can respond to smart meter data, but this type ofintegration has been very limited in practice. When the in-
17
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Smart Grid Roundtable
The past decadehas seen dramatic
advances in automationsystems and smart
devices.-Kevin Krause,Affiliated Engineers Inc.
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stallation of smart metering is more uniform, I expect that
integration with BAS will become much more common.
Krause:While a significant amount of development of
renewable energy sources, efficient end-use appliances,
and other Smart Grid components (e.g., submetering) hasbeen completed, a common communication model tying
it all together is necessary for the success of the Smart
Grid. This model must al low for the reliable, secure, and
accurate information exchange between
these technologies and the control
systems of utilities and other electrical
service providers. An understanding of
sources and loads and how they interact
is critical to fostering communications
between them.
The most common types of building
loads, of course, include lighting andHVAC. Yet in todays world of emerging
energy sources and loads encompass-
ing wind, solar, and electrical vehicles,
the landscape of the energy grid, and
the very concept and framework of the
Smart Grid, continue to evolve. Many of
these new loads actual ly represent both
a sink and a source of electrical energy.
This presents both demand control
issues and safety issues for the operation of the electri-
cal gr id in terms of what the industry is accustomed to,
where power flow has typically been a one-way street.
Thus is the need for further standardization of measure-
ment and control.
To respond fully and most effectively to the need for
more sophisticated demand and supply monitoring and
control, certain aspects of electrical energy management
must be addressed. Increased monitoring and reporting
of actual demands and behaviors of the end users, as
well as further educating the end users on the amount
and pattern of their electrical usage, is essential. Without
this knowledge, electrical energy suppliers delivering to
the grid are at a marked disadvantage to meet demand or
adjust to greater fluctuations in demand due to optimized
facility operations or the variable nature of many of the
distributed renewable energy sources being intercon-
nected. With a more sophisticated Smart Grid, concurrent
data across users and generators will allow for additional
demand control, adjustment, or curtailment, with the goal
of changing behaviors of the end consumer.
Q:What codes/standards are applicable to Smart Grid/
BAS integration?
Collier:Standards are the single greatest challenge torealizingmuch less maximizingthe benefits of the
Smart Grid and smart buildings. In general, there is little
or no integration or interoperability between and among
competing vendors of utility Smart Grid or commercial
smart buildings. Sometimes theres not even integration
or interoperability between and among different product
lines or vintages of products from the same vendor. Thiswill change, though, because it is so crucially impor-
tant to our quality of life, productivity of business, and
national security. We will eventually see what has been
called 3-D integration: every device,
every application, and every com-
munications system will seamlessly
integrate and interoperate with every
other oneseamlessly, out of the box,
mix-and-match. Just like every con-
sumer appliance works everywhere
on the electric grid. Just like every
connectible devices works everywhereon any Wi-Fi network. Just like Skype
works on every device that can access
the Internet. I firmly believe that this
will be accomplished by the conver-
gence of the Smart Grid and smart
buildings with the Internet of Things.
Cooper:The OpenADR (IEC/PAS 62746-
10-1) standard is increasingly evident
for integrating with BAS, gateway devices, and more
recently, cloud-based services that provide remote control
of commercial, industrial, and residential controllers/
devices. The ILM technology is designed to accommo-
date any devices in compliance with OpenADR 2.0. We
also support IEC 60870-5-104 for generic load control,
MultiSpeak for load control through advanced metering
infrastructure headends, as well as an extensible adapter
architecture. IEC 61850 specifies substation automation
and wil l provide guidance on the link between edge
devices and the substation. The worldwide KNX standard
is used by more than 250 manufacturers of products that
optimize the control of lighting, shading, heating, and
cooling in rooms and buildings. Siemens Gamma building
control KNX complies with EN 50090, and ISO/IEC 14543
for intelligent building networks.
Edward:Cal ifornias 2013 Building Energy Efficiency
Standards create the broadest requirements in the U.S. for
smart metering and demand response. The code describes
an energy management control system (EMCS) that, at a
minimum, must be able to automatically reduce lighting
power by 15%, and central ly shed HVAC load based on a
demand response signal from the utility. The EMCS is a
separate category of BAS that has the purpose of selective-
ly reducing building power demands. This equipment andsoftware can be stand-alone or part of an overall BAS. It
Smart Grid Roundtable
I think that thepassing of the legacy
grid means that
architects, engineers,
and operators will have
to fundamentally change
how they think about
building design.-Steven Collier, Milsof t Util ity So lutions
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Electricians and main-
tenance staff oftenwillingly work on
energized electrical
equipment to perform routine
maintenance, take measure-
ments, or eliminate downtime
of critical loads in the system.
Unfortunately, this creates a
very dangerous work environ-
ment that is prone to arc flash
incidents, which can result in
serious injury or even death.
While consulting engi-
neers are not responsible for
determining the process for
achieving an electrical ly safe
work condition as defined by
the National Fire Protection Association (NFPA), they
can assist in determining the appropriate personal
protective equipment (PPE) by
performing arc-flash calcula-
tions. While the appropriate
PPE should always be worn by
contractors or maintenance
staff while working on live
equipment, the reality of the
built environment is that there
are some situations when the
appropriate minimum PPE
may not be enough to prevent
serious injury, or when contractors and maintenance
staff are not wearing the appropriate PPE identified
for the task.
Although the most effective way to prevent inju-
ries is to deenergize and ground equipment, there are
various ways consulting engineers can reduce arc flashhazards by implementing mitigating strategies.
CALCULATING ARC
FLASH ENERGYAn arc flash occurs when
the energy that is normally
channeled into magnetic and
heating forces for a bolted fault
is released into the atmosphere
in the form of intense heat,
pressure, and light, which are
incredibly dangerous and can
result in the destruction of
equipment, fire, and serious
injury to electrical workers
and bystanders. The event can
result from contamination,
water or condensation com-
ing in contact with the system,
deterioration, or even faulty in-
stallations. However, electrical equipment that has been in-
stalled, inspected, operated, and maintained in accordance
with the National Electrical Code (NEC) and the manu-
facturers specifications is not likely to pose an arc flash
hazard under normal operating conditions. Unfortunately,
violent arc flash incidents are commonly results of human
error, such as dropping a tool into the system or pulling on
loose connections. Therefore, the purpose of an arc-flash
hazard analysis is to quantify the worst-case potential risk
to individuals working on live electrical equipment so that
the minimum proper PPE can be selected to protect the
workers from thermal burns.
In recent years, the increased awareness of the dangers
associated with working on live electrical equipment has
prompted our national consensus standards and govern-
ment agencies to invoke more stringent laws to ensure
worker safety. NFPA 70: National Electrical Code Section
110.16 states that all electrical equipment that may require
work to be performed while energized, be field or factorymarked to warn qualified persons of potential electric arc
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Engineers should know about selecting the appropriate risk-reducing strategies to help their
clients ensure compliance with NEC, NFPA 70E, and OSHA.
Mitigatingarc flash hazards
By Michael J. Mar, PE, LEED AP, and Robert K. Sandy,
Environmental Systems Design Inc., Chicago
EARNING OBJECTIVES
Know the codes and standardsat govern arc flash energy
culations.Know how to perform an arcsh hazard analysis.
Know the arc flash mitigatingsign strategies and how toplement them.
Figure 1: This is a typical arc flash label applied to distribu-tion equipment identifying the hazard category or danger level
associated with working on that equipment while it is energized.
Courtesy: Environmental Systems Design
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Arc Flash Mitigation
flash hazards. OSHA mandates compliance with the NEC
when implementing electrical regulations that address the
employer and employee in the workplace. OSHA, however,does not simply require a label that indicates the existence
of a potential risk, but further requires an employer to
assess the workplace to determine if arc flash and shock
hazards are present, inform its employees of the poten-
tial risks, and select and provide
the appropriate PPE required to
protect the affected employees
from the hazards identified in
the assessment. As part of this
assessment, OSHA recommends
that employers consult consensus
standards such as NFPA 70E:Standard for Electrical Safety
in the Workplace as a guide for
hazard analyses. While OSHA
does not specifically enforce
the contents of NFPA 70E, the
standard can be used by OSHA
as evidence that a hazard ex-
ists or that there is a means of
remediating the risk.
Engineering firms are often
contracted to perform an arc
flash hazard analysis to help
their clients ensure compliance
with NFPA 70E and OSHA. The
goal of the analysis is to pro-
vide warning or danger labels
that indicate the minimum PPE
required at that particular system
location (i.e., switchboard, panelboard,
motor control center, disconnect switch,
etc.) (see Figure 1). The engineer wil l typically use a power
system analysis software tool to calculate the incident ener-
gy: that which would be released during an arc flash event.
Depending on the type of facility, voltage class of the sys-
tem, and frequency of work to be performed on energized
equipment, engineering firms may be called upon not only
to report the findings of the arc flash hazard analysis, but
also to provide potential solutions for minimizing the risk
and reducing the available incident energy.
MITIGATING DESIGN STRATEGIES
The calculated incident energy is proportional to the arcing
current and the time or duration an individual is exposed
to the arc, and inversely proportional to the distance of
the worker to the arc. Therefore, solutions for minimizingthe arc flash hazard focus on reducing the arcing cur-
rent, removing the individual from direct contact with
the source (increasing the distance from the arc), and
decreasing the t ime it takes for the overcurrent protectionto clear the anticipated fault. Consulting engineers can
influence these variables through the power distribution
scheme they choose, the electrical distribution equip-
ment they specify, and the relays/overcurrent protection
devices they select.
Reduced fault current:Even though incident energy
is direct ly proportional to fault current, a reduction in
fault current does not always correlate to reduced
incident energy. Thats because reduc-
ing fault current can result
in increased fault clearing
time, which, in turn, mayresult in higher incident
energy. However, there are
designs that can reduce the fault cur-
rent without increasing the incident
energy. For example, a source-spot
network power-distribution scheme
provides added redundancy but lends
itself to much higher fault currents
because the transformers are paral-
leled. Specifying a system in a main-
tie-main configuration without allowing the
sources to be paralleled can achieve similar redun-
dancy goals with much lower maximum fault current
levels. In addition, if space permits, specifying numerous
smaller transformers in l ieu of a larger transformer would
reduce the total amount of fault current on the distribu-
tion system.
Workers distance:In the past, contractors were
required to manually service draw-out power circuit
breakers with a hand crank that dangerously put the
operator in close proximity to the live electrical bus in
switchgear. Several manufacturers now offer a motor-
ized remote circuit-breaker racking device, which is an
effective method of increasing worker safety by allowing
a technician or contractor to service draw-out style power
circuit breakers outside the arc flash boundary. Increasing
the distance between operators and energized electr ical
equipment significantly diminishes their exposure to arc
flash events. Remote racking systems are available in avariety of styles, and are compatible with equipment from
Figure 2: Arc-resistant switchgear is designed
to direct the energy released from an arc flash
upward and away from personnel in front of the
equipment. Courtesy: General Electric
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Figure 3: This graph represents a time-current curve of a main-tie-main unit substation with 480 Vac chillers.
Note that the potential arc flash incident energy before applying zone-selective interlocking results in aCategory 3 hazard. Courtesy: Environmental Systems Design
most major switchgear manufacturers with no modifica-
tions to the switchgear or circuit breakers. Various systems
are available depending on the type of racking operation
and extraction mechanism.
Arc-resistant gear: This type of switchgear is de-
signed to contain an arc flash within the equipment,and redirect the release of energy away from the worker
and out of the switchgear (see Figure 2). To be consid-
ered arc resistant, the equipment must be tested to ANSI
C37.20.7 in addition to all other ANSI/IEEE standards
for low-voltage metal-enclosed switchgear, including UL
1558. Arc-resistant switchgear must be labeled indicating
that the gear has been certified in accordance with ANSI
C37.20.7. Furthermore, the equipment must be labeled
indicating the operating conditions required to maintain
the arc-resistant rating. Arc-resistant switchgear can be
specified to have the arc-resistant construction at the
front only, or at the front, back, and sides. Dependingon the type specified, additional features can be added,
such as arc-resistant design between adjacent compart-
ments or sections and arc resistant with the low-voltage
instrument compartment door open, to name a few. The
second label indicating the operating conditions is very
important to ensure the safety of the personnel. Per
NFPA 70E, operation, insertion, and removal of circuit
breakers, and ground and test devices from cubicles with
the door closed will carry a hazard risk category of zero.
Infrared windows: Preventive maintenance must be
performed to ensure equipment functions safely and
as intended. One of the most common and frequently
performed maintenance procedures is infrared thermalscans, which are completed to detect loose cable con-
nections so they can be properly torqued to prevent an
arc flash situation. These scans are typically performed
by opening a panel door/cover and then scanning these
connection points while the equipment is live, which is
necessary for obtaining accurate readings. This increased
chance of an arc flash when a door/cover is opened on
live equipment can be eliminated by specifying infrared
scanning windows. These windows contain a properly
placed crystal that allows thermal images to be obtained
without having to open doors or covers.
Arc clearing time: Because incident energy is directlyproportional to the duration an individual is exposed to
hazards, reducing the arc clearing t ime reduces the mag-
nitude of damage that can be imposed on an individual.
One way to accomplish this is by properly sizing the over-
current devices to match the maximum load. In many fa-
cilities, the measured load is much lower than the actual
peak load connected to a panel. Therefore, by installing
power meters on each feeder to
a panel and install ing adjustable
trips on feeder breakers, the trip
settings can be easily and safely
reduced to match the actual
loads to potentially clear an arc
fault faster.
In addition, providing mains
on equipment can potentially
reduce risk to personnel. Even
though arc flash calculations
typically include the line and
load side of equipment and
therefore the arc flash warning
label would still be the same
hazard category with mains in-
stalled, the fault can be cleared
much more quickly if it occurred
on the main bus. The reduction
in incident energy would be
noticed more for those panels
downstream with a source that
is located a long distance away.
Current-limiting fuses:
Both circuit breakers and fuses
deenergize the circuit during an
overcurrent situation. However,
implementing current-limitingfuses can reduce the magnitude
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and duration of a fault current
because they have the capability
to clear a fault in less than
cycle when operating in its cur-
rent-limiting range. These fuses
are also easier to coordinatewith upstream devices compared
to circuit breakersespecially in
the instantaneous region. In ad-
dition, arc flash energy calcula-
tions are performed based on the
assumption that the overcurrent
protection device will trip as in-
tended. However, circuit break-
ers may not trip if not properly
exercised and maintained. But
a fuse should still open and
clear a fault even if the switch-ing mechanism is not routinely
exercised. For current-limiting
fuses to be effective in reducing
the arc flash hazard, the estimat-
ed arcing fault current should
be within the current-limiting
range of the fuses current-time
characteristic.
Zone-selective interlocking/
differential relaying: A common
method for reducing an arc flash hazard is adjusting the
trip settings in a circuit breaker to clear the arcing cur-
rent more quickly. Unfortunately, the trade-off with this
approach is a reduction in the coordination of the system.
Selective coordination in power distribution systems is
good engineering practice that is also code-required for
life safety emergency systems and hospital facil ities. A
selectively coordinated system minimizes loss in rev-
enue and risks that can harm occupants by automatically
deenergizing the minimal portion of a power distribution
system when removing hazards caused by an abnormal
condition. To accomplish this task, an upstream overcur-
rent protective device must have a longer trip setting than
downstream overcurrent protective devices. However, this
reduced arc clearing time causes increased arc flash energy
(see Figure 3).
Maintaining selective coordination while reducing arc
flash energy can be achieved with zone selective inter-
locking (see Figure 4). With this scheme, a downstream
breaker closest to the fault condition sends a signal to the
upstream device to restrain from tripping instantaneously,
allowing this downstream device to trip instantaneously
to clear the hazard and minimize the outage. However, if
a fault occurred between the main and feeder device, the
main would trip instantaneously because this restraintsignal is not sent from the feeder breaker.
Similarly, differential relaying can be used to provide
this selective coordination and reduce the clearing times.
For example, a bus differential relaying scheme measures
the current entering a bus versus the current leaving a bus.
Therefore, if a fault occurs on the bus, the resulting unbal-
anced current would cause the main device to trip instan-
taneously to reduce the arc flash incident energy. These
two schemes are compliant options that meet a relatively
new addition t