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PUREPOWER/

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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.

PUBLICATION SERVICES

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LLC. All rights reserved. Editorial offices are located at 1111 W. 22nd Street, Suite 250,

Oak Brook, IL 60523. Phone 630-571-4070.

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

CoverStory 2

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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

CoverStory 4

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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



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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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.



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.

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Network interface

Lightingcontrols Plug loads

Motors

Transfer switches



12/32


13/32

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14/32

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



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


17/32

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18/32

16


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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.


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


19/32

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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The past decadehas seen dramatic

advances in automationsystems and smart

devices.-Kevin Krause,Affiliated Engineers Inc.


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18


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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


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


21/32

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26/32

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

Arc Flash Mitigation 24


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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



26

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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

Arc Flash Mitigation



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

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