Electrical & Power
SPRING EDITION
Contents
3 — Do you know the vital requirements for standby power?
13 — Cummins Power Integration Center (PIC) Virtual Tour
14 — Your questions answered: Harmonics solutions for water
and wastewater applications
27 — Take an In-Depth Exploration into Cummins State-of-theArt Microgrid Testing Facility
32 — Your questions answered: Critical power: hospital
electrical systems
38 — Why decarbonization, ESG initiatives are a bigger priority
for building owners
41 — PODCAST: Brian Alessi on decarbonization strategies in
building design
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Do you know the vital requirements
for standby power?
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The ability to provide power to a building or load when utility power is lost
can be a critical need for a facility to support vital operations or building and
occupant safety
O
wners, architects, contractors and engineers tend to use the terms emergency/
backup/standby power interchangeably to indicate that during a utility power
outage, there is a need to have specific loads or even an entire structure’s power maintained for facility operation.
There are distinct differences in the requirements for legally required standby power
systems. The first step in designing a robust and code-compliant standby power system for a project is understanding the project requirements.
Legally required standby power system loads are generally described as loads, which
upon failure of the normal power source, could create hazards or hamper rescue or
fire-fighting operations.
Depending on the project, there may be a need for various types of loads to be served
by alternate power sources. These loads can include emergency loads that are loads
legally required by governmental agencies for the purposes essential for safety for
human life.
Legally required standby loads can also be present in a facility; these include loads
that could create hazards or hamper rescue or fire-fighting operations if power is lost.
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Do you know the vital requirements for standby power?
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Additionally, optional standby systems may be present that include loads that, when stopped, could
cause discomfort, serious interruption of the process
or damage to the product or process.
Lastly, there may be additional loads that do not
Figure 1: Sample project code analysis
summary that outlines pertinent
information for understanding
emergency and standby power
requirements. These are typically found
on the front pages of the architectural
or general project drawings. Courtesy:
Design Group Facility Solutions
neatly fall into one of the above categories, but are
still required based on an owner’s request to be supported by an alternate power system mainly for reasons of convenience, comfort or financial impact. These load types
could be considered optional standby loads.
There is some overlap between the various power systems above for the same load
type. These loads should be classified based on the occupancy of the space as well as
the function of the load. Additional clarification and guidance can be found in many of
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Do you know the vital requirements for standby power?
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the codes and standards required for
the proper design and construction of
a building.
Standby power codes and
standards
NFPA 70: National Electrical Code
(NEC) Articles 700, 701 and 702 provide directions as to the electrical
safety of the installation, operation and
maintenance of emergency, standby
and optional standby systems. That is
to say, the NEC dictates the technical
requirements for electrical installations
that include: commissioning, testing,
capacity and rating, transfer equipment requirements, wiring methods,
identification, etc.
These NEC articles provide guidance in general for the
emergency power supply systems (EPSS) themselves along
with other NEC code articles; other codes and standards
such as the International Building Code (IBC), the NFPA
101: Life Safety Code, the International Mechanical Code
Figure 2: Double-wall diesel
generator base-mounted
fuel tank rated for required
emergency power supply
systems class. Courtesy: Design
Group Facility Solutions
and International Fire Code (IFC), local building codes and
amendments, federal and military codes and standards, the Environmental Protection
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Do you know the vital requirements for standby power?
Agency, FM Global and other insurance company requirements, to name just a few,
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also have specific design criteria requirements.
These codes and standards provide further clarity on how loads within specific facilities
should be treated. While the NEC is the code that electrical engineers reference most
regularly, the designer or engineer cannot rely solely on the NEC for direction; in fact,
there are many other sources in which criteria for the proper application of alternate
power systems can be found.
NFPA 110: Standard for Emergency and Standby Power Systems defines the following:
“EPSS: A complete functioning emergency power supply system coupled to a system of conductors, disconnecting means and overcurrent protection devices, transfer
switches and all control, supervisory and support devices up to and including the load
terminals of the transfer equipment needed for the system to operate as a safe and
reliable source of power.”
The terms EPSS and standby power supply systems include but are not limited to:
• Emergency power systems.
• Alternate power systems.
• Standby power systems.
• Legally required standby systems.
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Do you know the vital requirements for standby power?
• Alternate power sources.
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NFPA 110 specifies the installation, performance, maintenance and test requirements
for EPSSs in terms of types, classes and levels for the categories above, therefore the
category terms used depend on the application involved. These types, classes and
levels are essential in helping to distinguish the proper classification of the alternate
power distribution system.
An EPSS class refers to the length of time required for an EPSS to provide power to a
load (duration the load can be served) without being refueled (NFPA 110 Table 4.1(a))
as well as the maximum time allowed for the load terminals of transfer equipment to
be without acceptable power (how quickly the load needs to receive power, (NFPA 110
Table 4.1(b)).
Further, NFPA 110 defines levels for EPSS equipment installation, performance and
maintenance requirements. A Level 1 system is where failure of the equipment to perform could result in loss of human life or serious injuries. A Level 2 system is where failure of the EPSS to perform is less critical to human life and safety. NFPA 110 Appendix
A is a reference to assist the designer in understanding the intent of what loads might
qualify as either Level 1 or Level 2.
NFPA 110 provides excellent guidance in understanding the requirement when classifying the requirements of different types of emergency power supply systems, but how
does the designer know which components of a building or project are applicable to
these classifications? Start with the understanding of the project and its occupancy and
use classification in the applicable building code or standard.
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Do you know the vital requirements for standby power?
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Understanding power
system intent
The building code or standard for a
given municipality is dictated by the
authority having jurisdiction (AHJ). The
AHJ, whether that is the local building
department or other governmental
agency will determine the building
code that is applicable at the time of
design. The IBC is a common compliance requirement for many buildings.
The IBC defines the following terms:
“Emergency power system: A source of
automatic electric power of a required
capacity and duration to operate required life safety, fire alarm, detection
and ventilation systems in the event
of a power failure of the primary power. Emergency power
systems are required for electrical loads where interruption
of the primary power could result in the loss of human life
or serious injury.”
Figure 3: Exterior diesel
generator with base-mounted
fuel tank. Courtesy: Design
Group Facility Solutions
These systems are required to make power available within 10 seconds per NFPA 70
Section 700.12.
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Do you know the vital requirements for standby power?
“Standby power system: A source of automatic electric power of a required capacity
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and duration to operate required building, hazardous material or ventilation systems
in the event of a failure of the primary power. Standby power systems are required for
electrical loads where interruption of the primary power could create hazards or hamper rescue or fire-fighting operations.”
These systems are required to make power available within 60 seconds per NFPA 70
Section 701.12.
NEC Article 701.1, Informational Notes 4 and 5 further correlate the intent of standby
system loads as being loads that any interruption of could create a hazard or hamper
rescue or fire-fighting efforts and could result in loss of human life (Level 1) or less critical to human life and safety (Level 2).
Why standby power systems matter
Understanding the intent of the various codes and standards is interesting, but as designers, why should we care? We care because based on the types of loads, different
requirements are required for different load types including but not limited to: operation, location and installation.
For example, IBC Chapter 909.11 requires that for smoke control systems, the standby power source and its transfer switches shall be in a separate room from the normal
power transformers and switchgears.
NEC Article 701:
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Do you know the vital requirements for standby power?
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• Indicates a legally required standby system shall
have the load capacity calculated in accordance
with Parts I through IV of Article 220 or other approved method.
Figure 4: Dedicated transfer switches
for separate emergency power supply
systems loads. Courtesy: Design Group
Facility Solutions
• Dictates the design of the transfer equipment of the standby power system to include allowing the ability to bypass the transfer equipment and the requirement for
the transfer equipment to be electrically operated and mechanically held.
• Mandates signage at the service entrance identifying each legally required standby
power source.
• Defines the maximum time allowed for the legally required standby source to become available to support the required loads (60 seconds, or per NFPA 110, Type 60).
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Do you know the vital requirements for standby power?
• Defines the minimum operation time before refueling (two hours, or per NFPA 110,
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Class 2).
• Provides an approved list of alternate power sources that can be used for standby
power systems (some of which require AHJ approval). These include:
• Public gas system.
• Municipal water supply.
• Storage batteries.
• Generator sets.
• Stored energy power systems.
• Separate service.
• Connection ahead of the service disconnecting means.
• Microgrid systems.
• The standby power source should be carefully evaluated based on the loads supported and their purpose.
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Do you know the vital requirements for standby power?
It is important to understand that the NEC, IBC, NFPA 110 or other codes and stan-
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dards are to be used as a guide and minimal compliance standard only. It is impossible
for these documents to be comprehensive for every situation, so it is up to the design
professional with approval by the AHJ to determine the proper classification of the
electrical loads on each project while meeting the owner’s project goals.
It is the responsibility of the electrical designer to stay current with the understanding
of the ever-changing code requirements. The major building and construction codes
typically provide changes on a three-year code cycle. The requirements for standby
power systems are no exception.
Erika L. Bolger
Erika L. Bolger, PE, LEED AP, is a director at Design Group Facility Solutions and has
more than 30 years of consulting engineering experience.
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Cummins Power Integration Center (PIC) Virtual Tour
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
Cummins Power Integration Center (PIC)
Virtual Tour
Enjoy an exclusive look into the Cummins Power Integration
Center (PIC), located in Fridley, MN. Designed by Cummins
leading engineers and microgrid advisors, the PIC is one of the
largest and most configurable microgrid testing facilities in the
world. This virtual tour will provide an in-depth look into this
state-of-the-art facility and education on the basics of microgrids.
13
Your questions answered:
Harmonics solutions for water
and wastewater applications
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Technical recommendations for reducing harmonic distortion and
improving system capacity and improving system reliability while
evaluating installed costs.
P
roblems associated with harmonic distortion are well understood for many power
system applications; however, finding the right solution is challenging. Because of
the significant use of variable frequency drives in water and wastewater applications,
understanding the appropriate solutions for your application is important. There are at
least 10 different technologies and strategies to choose from, each with specific technical and economic advantages.
During a webcast on Sept. 12, presenters from Eaton Corporation provided technical
recommendations for reducing harmonic distortion and improving system capacity and
improving system reliability while evaluating installed costs.
Additional questions were answered by Dan Carnovale, Director, Eaton Experience
Centers, Eaton Corporation.
Question: For what size drive would you consider 18 pulse a good financial choice?
Answer: At about 150 HP or more, the cost of an 18-pulse drive is more cost effective
than a 6-pulse drive with additional filtering to compensate to an equivalent harmonic
level compared to the 18-pulse drive.
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Your questions answered: Harmonics solutions for water and wastewater
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Question: Does PV generated power contain harmonics?
Answer: PV/solar inverters often have some voltage distortion from the converter, but
most are relatively low magnitude. The frequency of the harmonics are usually higher
orders from the pulse-width-modulated controls.
Question: How will harmonics affect natural cable or bus in electrical system?
Answer: 3rd harmonics accumulate on a 3 phase 4 wire system neutral. The 3rd harmonics on the neutral are additive (i.e., if you have 100A of 3rd harmonic on phase
A, 80A of 3rd harmonic on phase B and 90A of 3rd harmonic on phase C, you will see
270A of 3rd harmonic on the neutral). Coincidentally, if you have 100A of 60Hz on
phase A, phase B and phase C, you will have 0A of 60 Hz on the neutral because the 60
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Your questions answered: Harmonics solutions for water and wastewater
Hz currents are all 120 degrees apart while the 3rd (and odd multiples of 3rd, i.e., 9th,
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etc.) are all in phase and additive from each phase.
Question: Is split AC in home one example for voltage distortion?
Answer: Mini-split air conditioners in homes MAY be harmonic producing loads as
most of these units have a VFD and would produce harmonic currents.
Question: What mitigations can we do at the utilities transformers to solve the
harmonics?
Answer: At the secondary of the utility transformer, you can use many of the typical
harmonic solutions to reduce voltage distortion by offering a low-impedance path —
harmonic filters, active filter, pairs of phase shifting transformers, etc.
Question: In our thermography surveys, we have seen very hot 200F to 300F
filter/choke transformers connected to VFDs. Is this normal? Or does it just show
that the filter/choke is working hard to filter out the harmonics?
Answer: Line reactors are designed to run hot — some hotter than others. I would
check with the reactor vendor to see what they expect as “normal.” Reactors, like
transformers, have an X/R ratio that is the ratio of inductance to resistance, and the
higher the resistance, the more losses and the more heat.
Question: Is there useful information in the IEEE 519-1992 version that would
make it desirable to keep/get the 1992 version?
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Your questions answered: Harmonics solutions for water and wastewater
Answer: I personally don’t believe so. I’ve looked through it in detail, and most of it
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was things like notch depth and more theoretical/mathematical parts that aren’t really
relevant to solving the issue of harmonics for the general application. The newer standards get to the key points and summarize well what is important.
Question: With a passive filter that has a backup generator, the VFD cabinet
manufacturer will introduce a bypass contactor. Will that bypass during a generator, or just at a certain speed? How do you keep the PF from going leading at
low loads, any loads, and trip the generator?
Answer: With older UPSs, this was a very typical problem, and the passive filters were
shut down on the generators at 35% load. A fixed filter (drive dedicated filter with a
large capacitor) can be turned off with a contactor on the generator, but sometimes if
you need filtering on the generator, you can’t afford to have the filter off. At very light
loads, yes, turn off the filter, but at heavy loads, accommodations should be made and
tested/modeled to ensure proper operation. By the way, a generator can take a leading load but not too far leading.
Question: In the following chain of the power system model, what is the place
to tackle the harmonics: utilities substation … utilities switch … at the user yard
utilities transformers … at the user yard distribution center … at user yard load
(VFD, UPS, etc.)?
Answer: Great question. It depends on the goal of taking care of harmonics. If you
are trying to fix the problem at the PCC, filter/correct at the user distribution center or
higher. If PF correction is the issue, anywhere downstream of the utility will fix the PF,
but it may make it difficult to ensure you don’t overload the filter. For very high-voltage
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Your questions answered: Harmonics solutions for water and wastewater
distortion or capacity issues downstream, fix the problem at the load. I2R loss reduc-
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tion is about 1-4% for both PF correction and for harmonic mitigation, so you won’t get
a great payback but you can achieve some.
Question: I have recently seen a lot of installs of line filters in front of drives but
have no contactors to bring in the caps. The caps are in all of the time. Is this a
concern? There is a lot of wasted energy, but my concern is at lower speeds of
the drives. Is the filter really doing its job?
Answer: Having a cap/filter on at low speed can be an issue with leading PF and higher
voltage. I don’t think it will create too much of an issue with kW/losses, but the concern is
really just 60 Hz (overvoltage and PF). For drive dedicated filters, they often do have a dedicated contactor to remove the filter branch at very light loads, especially for larger units.
Question: Are there any unique considerations for current harmonics on ungrounded power systems?
Answer: Current harmonics follow a pattern positive sequence, negative sequence,
zero sequence — 1st (+), 2nd (-), 3rd (0), 4th(+), 5th (-), 6th (0), etc. In my experience, the
only issues I’ve seen that are different for ungrounded or HRG systems are higher order
zero sequence harmonics — i.e., maybe 39th, for example, that are capacitively coupled
through the natural capacitance of the power system and coupled in from the PWM output of drives. This can show up on some HRG systems as a false issue and can be coupled into other equipment. Use a scope with a good higher frequency FFT to analyze.
Question: When would you pick a 6-pulse drive with a line reactor over an AFE
drive? Is the performance the same?
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Your questions answered: Harmonics solutions for water and wastewater
Answer: A 6-pulse drive with a 5% reactor will be about 30-40% ITHD at a high load
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level. An active front end drive may have less than 5% ITHD across loading but may
have some high frequency coupled in, but the bigger concern is that it may cost 2X the
other drive. In systems that have a lot of drives and smaller drives, usually, 6-pulse with
other filtering (maybe even an AHF) will be the best cost-effective solution. Also, if
redundancy is used for drives, this is even more the case.
Question: Does active filtering consume a significant amount of power?
Answer: No, for passive filters. In fact, filtering, if done right, can reduce the I2R losses and reduce your kW consumption. However, for active filtering, because of the AC/
DC/AC conversion, yes, filtering can add a few kW losses depending on the size of the
unit. That said, active filters are mostly used for harmonics with PF as a secondary benefit, while passive filters are usually used for PF correction first and to achieve a slight
harmonic benefit without risk of resonance.
Question: How can a I tell if harmonics are too high during design phase if the
VFDs or computer power supplies are unknown?
Answer: With experience and measurements of similar systems. The good news about
harmonics is that they are relatively predictable, and models reflect well the real world if
they are done correctly. For example, you can measure the ITHD from an existing site for a
50 HP drive and get 35%, but in another site get 42% — the difference could be loading of
the drive or the source impedance (i.e., drive running at 90% speed versus 70% speed or
upstream transformer 300 kVA versus 750 kVA). I would be most careful of over-assuming
harmonic currents on a model costing you much more money than necessary.
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Your questions answered: Harmonics solutions for water and wastewater
Question: Can you clarify the difference between I1 and Il?
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Answer: I1 is the fundamental current (i.e., 60 Hz or 50 Hz) right now for instantaneous
measurements — IL is used only for the TDD calculation and is determined at the
maximum demand (for example, 15-minute window) during a previous month/year, etc.
Since the maximum value for IL is usually higher, TDD is usually lower. The numerator is
usually taken as a “high average” value of harmonic current.
Question: Do underutilized transformers also contribute to harmonics?
Answer: Very low levels of 2nd, 3rd, 4th harmonics show up on the FFT of a transformer
(primary) because the magnetizing branch requires these. However, it is almost always
there in the background but it is only noticeable when the transformer is lightly loaded.
Question: What are the best options for controlling harmonics generated by EC
Motors?
Answer: EC motors usually have VERY high THD because they often don’t use line
reactors — typical numbers may be 80% ITHD. The first step may be a 5% reactor, and
then the rest of the solutions are all the same for EC motors versus drives (filters, phase
shifting, etc.).
Question: Do triplen harmonics only occur in single-phase loads?
Answer: Yes, triplen harmonics only appear for three-phase systems with single-phase
loads. HOWEVER, you can have 3rd harmonic currents that aren’t actually triplen harmonics flowing between phases. An example is SCR heaters connected L-L on a 480V
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Your questions answered: Harmonics solutions for water and wastewater
system. You will have significant 3rd, 5th, 7th, etc. flowing out one phase and back an-
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other (not on the neutral). Triplens are considered triplen when they are on each phase
to and from a single-phase load and flow back together (in phase) on the neutral.
Question: You had mentioned that overheating equipment for a small period of
time may not be bad. Are there situations where harmonics could cause overheating to cycle (in other words, the equipment gets hot, then cools, then gets
hot again)? Should we be concerned for situations such as this?
Answer: Certainly cycling of heating is bad for electrical equipment (depends on how
long and the insulation type, etc.). The other concern I should have mentioned is that
short-term harmonics may cause a single failure or issue even if they are only there for
a few cycles or seconds — like a soft start that creates very high ITHD during startup or
harmonic current during transformer inrush. This may excite resonance with capacitors,
for example.
Question: What were the changes from IEEE 519 2014 to 2022?
Answer: The only major change was around DERs (distributed energy resources). The
new standard states that if you have DERs and the combined site rated generation is >
10% of the annual average load demand, you must apply current limits from a standard
with an applicable scope such as IEEE Std 1547 or IEEE Std 2800, otherwise, apply the
limits of IEEE 519 (for < 10%).
Question: Is it better for the utility to use a delta-wye transformer?
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Your questions answered: Harmonics solutions for water and wastewater
Answer: In general, yes, for harmonics. You can circulate 3rd in the delta, but it doesn’t
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benefit the end user as far as that goes. In general, harmonic reduction from transformers is only seen upstream of the transformer. The only exception to this is downstream
harmonics are affected by the impedance of the transformer and would be reduced
throughout the system (i.e., not allowed to flow or choked like a line reactor), but for
the winding type of any transformer, it doesn’t really affect the downstream harmonics.
Question: What is the effect of network MVA capacity (PCC)?
Answer: MVA capacity simply acts like an impedance, and the lower the MVA, the
higher the impedance. Therefore, smaller harmonic loads affect the voltage distortion
more on a weak source or lower MVA system. An easy way to think about it is if you put
a 30 HP drive on a 30 kVA transformer and measured the downstream voltage distortion, you would get pretty high voltage distortion compared to that same 30 HP drive
on a 3 MVA transformer — light load on a big transformer is not noticeable from a
harmonic standpoint.
Question: For motor protection, on which side of the drive should the CT and PT
be installed?
Answer: The drive will have motor protection programming built in, and generally you
don’t need external CTs like you would on a normal motor protector. But if it did require external CTs, it would be on the output because the drive decouples the motor
from the source at the DC link.
Question: For small motor, does 18-pulse drive avoid line reactors?
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Your questions answered: Harmonics solutions for water and wastewater
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Answer: 18 pulse on very small drives may not be cost effective, but if you do apply
an 18-pulse drive on any motor, they usually use an internal reactor as well to gain that
additional impedance benefit. In general, though, if you use 18 pulse, you don’t need
an additional line reactor.
Question: What’s a good “time span” that can cause issues with sensitive equipment?
Answer: The IEEE 519 standard, for 95th percentile of measurements (i.e., most of the
normal time), you would follow the tables directly in the IEEE 519. For short-term 10
minutes or less, you can exceed the tables as much as 1.5X, and for 3 seconds or less,
you can exceed the tables by as much as 2X.
Question: Can harmonics generated by one VFD have an effect on the other VFD
on the same power source bus?
Answer: It is possible that the drive itself can cause enough current distortion to make
the voltage in front of it distorted enough to cause issues, but it is very unlikely on a
1:1 basis without other drives or influences. In fact, you can put a 10% reactor in front
of a drive and cause a very distorted square wave voltage, but if you think about it, the
first thing you do in the drive is convert to DC so a square wave isn’t as big of a deal to
convert. If, however, the impedance is so high that the voltage has multiple zero crossings or other waveshape distortions that make it difficult for the diodes to convert the
voltage to DC, then the drive may misoperate.
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Your questions answered: Harmonics solutions for water and wastewater
Question: Can you explain why harmonics increase vibration on motor?
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Answer: Current harmonics follow a pattern positive sequence, negative sequence, zero
sequence — 1st (+), 2nd (-), 3rd (0), 4th(+), 5th (-), 6th (0), etc. Generally speaking, negative sequence harmonics cause vibrations in motors so if you have current harmonics
causing 2nd, 5th, etc. harmonic voltages, then these vibrations can result from the 60 Hz
pushing the motor forward and the negative sequence harmonics resisting that forward
motion, causing heat and vibration. Physical vibrations often oscillate at 2X the electrical
harmonic frequency — i.e., 5th harmonic would vibrate at 600 Hz or 2 X 300 Hz.
Question: Could you clarify the impact of line impedance on the reflected noises
and the net distortions?
Answer: Source impedance is in series with the harmonic currents generated by the
load. Pulling harmonic current through an impedance, by Ohm’s Law, will create a distorted voltage at the same frequency. Therefore, the higher the impedance, the more
the voltage distortion. A large transformer has a lower impedance than a small transformer (even if they are the same %Z) by the proportion of the kVA sizes. As far as the
effect of that impedance on how much current can be drawn through it, the higher the
impedance, the lower the amount of harmonic current the drive or other load is “allowed” to draw or “able” to draw through that impedance. We use the term “choke”
because the impedance/reactor/reactance essentially chokes out the current (like
squeezing a water hose) and doesn’t allow as much current to flow.
Question: What is the trending solution for reducing harmonics at the MV or utility-scale systems?
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Your questions answered: Harmonics solutions for water and wastewater
Answer: For MV systems, for a single drive, 24 pulse systems are the most typical solu-
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tion. For large systems with multiple sources of harmonics, either fixed, switched multistage filters (capacitor/inductor) are used or for very dynamic MV systems, static var
compensators (SVC) are used. They typically have a fixed reactor and switched capacitor in the form of harmonic filters switched with SCR’s.
Question: What’s your opinion on relaxing the VTHD from 5% to 8% in IEEE 519?
Wouldn’t this extend the harmonic influence to other industrial plants connected
to the utility?
Answer: I have seen systems that are good at 5, good at 8 and good at 15% VTHD, but
I’ve also seen systems that are problematic at 2.5% VTHD, so it starts with what does the
load like/see. As far as the neighbors, the IEEE 519 is only about the neighbors and not
about how you affect yourself. That said, yes, the influence of a lot of background VTHD
will potentially cause your system to have problems that it wouldn’t without them, but
that may be more arbitrary than specific. You still need to understand at what level your
equipment has problems if you can even determine that (which is hard to do).
Question: How does one model a system to determine if harmonics may be a
problem?
Answer: SKM, CYME and other programs model harmonic currents on a power system and predict harmonic voltage distortion and resonance issues. The way it is done
is that you model the impedances at 60 Hz and then “inject” harmonic loads either
as individual loads or groups of loads (VFDs, for example) at a downstream bus. Once
the model is complete, you run scenarios where the impedance of the power system is
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Your questions answered: Harmonics solutions for water and wastewater
dynamically changed by the frequency (i.e., starts at 60 Hz, then 120 Hz, then 180 Hz,
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etc.), and then the harmonic currents from the loads are pushed back up through those
impedances to calculate the associated voltage drop at that frequency. Once all of the
dynamic load flows are done, the RMS totals for current and voltage at each bus are
calculated and displayed. For variations in load, source impedance (changing to generator source, for example) or adding capacitors that may cause resonance, new cases
are done and compared to the base case. Then, you can apply filters, phase shifting or
other solutions and compare the VTHD and ITHD at every bus/branch.
Question: Don’t a lot of utilities use delta-wye transformers? Doesn’t that help
keep it off the utility?
Answer: You can circulate 3rd in the delta on a delta-wye transformer, and that will
keep the 3rd, 9th, etc. harmonics from going back on the utility, but the positive and
negative sequence harmonics (5th, 7th, 11th, 13th, etc.) will go right through the transformer by the turns ratio and at the same percentage THD on the secondary and primary. In addition, that doesn’t really help you as a user, and it doesn’t guarantee compliance with IEEE 519. In general, harmonic reduction from transformers is only seen
upstream of the transformer (in this case, the only benefit would be triplens). Remember that current MUST flow in a loop, and harmonics DO NOT go to ground — they
flow out on phase A, for example, and back on B and C. So they go out into the utility
system only to return on the other phases, right through the transformer.
Gary Cohen
Gary Cohen is senior editor and product manager at CFE Media and Technology.
26
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I
n 2022, Cummins proudly celebrated the opening of a
new microgrid laboratory, the Power Integration Center
(PIC) at their campus in Fridley, MN. The PIC is one of the
largest and most configurable microgrid testing facilities
in the world. Regardless of your power system needs (hypothetical or planned), this marvel of a facility is built to
test those possibilities in a zero-risk environment.
Since its opening, the PIC’s team of engineers have hosted
hundreds of tours and simulated a myriad of testing scenarios in collaboration with customers and partners from
various markets. Today they’re pulling back the curtain and
providing all with an in-depth look into the facility.
Take an In-Depth Exploration into Cummins State-of-the-Art Microgrid
“This virtual tour is the most detailed look Cummins has provided of the PIC. With it,
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we’ll be able to demonstrate the capabilities of the facility to customers and partners
who can’t make the trip to Fridley and provide education about microgrids to a wider
audience,” said Corey Bergendahl, Engineering Manager for the PIC.
The four main components of the PIC include:
Outdoor Testing Pads
The largest part of the lab’s 20,000 square foot design (about four times the area of a
basketball court), the outdoor pads provide the dedicated space needed to test any
source or load that can be integrated into a microgrid (ex. Gensets, Battery Energy
Storage, Hydrogen Fuel Cells and Electrolyzers, EV Chargers, and more). The outdoor testing pads are comprised of:
• Five 500 kW Testing Pads
• Two 2000 kW Testing Pads
• Two 500 kW RLC Load Banks
Electrical Mezzanine
This area boasts several unique features including:
Utility Distribution Substation
• Step-Down transformer – 13.8 kV to 480 V
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Take an In-Depth Exploration into Cummins State-of-the-Art Microgrid
• Two 1 MW utility feeds
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• Distribution switchgear
Solar Inverter Testing (Photovoltaic/PV)
• 400 kW rooftop solar array
• 105 kW DC simulation power supply
• Programmable weather scenarios
Bi-Directional Inverter Testing (Battery Energy Storage/BESS)
• 120 kW battery simulator
• Emulates different battery chemistries and size capabilities
• Allows you to quickly adjust the state-of-charge for the virtual battery system
Main Switchgear Room
This room houses a 2 MW switchgear lineup that’s the primary working switchgear
utilized for customer simulations within the lab. The switchgear is separated into three
buses with tiebreakers in-between and a ring bus around the back allowing for the creation of multiple different power system topologies including:
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Take an In-Depth Exploration into Cummins State-of-the-Art Microgrid
• Isolated Bus
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• Common Bus
• Single Transfer Pair
• Dual Transfer Pair
• Main-Tie-Main
• Dual Transfer Pair with Tie
Engineering Control Room
The control room acts as the central
nervous system for the whole facility.
Signals from the sources, loads and
connections are brought together for
our team of engineers to conduct and
visualize the extensive testing needed
to evaluate solutions.
As governmental regulations change,
the cost of operations increases, inclement weather persists and power
grid instability runs rampant, the need for reliable and efficient microgrid solutions is
more prevalent than ever. The PIC is an answer to those needs and allows customers to
thoroughly test solutions with zero operational risk.
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Take an In-Depth Exploration into Cummins State-of-the-Art Microgrid
“The needs of our customers are
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ever evolving and there’s a heightened focus on dependable, flexible,
economically efficient microgrid solutions,” added Bergendahl. “The PIC is
our dedication to powering a cleaner
future. This facility allows us to lead
our customers through their decarbonization journeys, directly tying into our
own Destination Zero strategy.”
Designed by Cummins Power Systems team of leading engineers and microgrid advisors, the PIC is a collaborative space for engineers, customers, technicians, sales
members and microgrid enthusiasts to come together in the name of innovating for a
greener future.
For more information about the Cummins Power Integration Center (PIC), visit:
Power Integration Center | Cummins Inc.
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Your questions answered: Critical
power: hospital electrical systems
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The Sept. 15, 2016, “Critical Power: Backup power systems” webcast
presenters addressed questions not covered during the live event.
D
esigning hospital electrical systems is more demanding than for conventional
commercial buildings because the stakes are so high. When specifying electrical
distribution systems in hospitals, engineers must account for the facility’s size, flexibility
needs, medical equipment and procedure types, essential (emergency) power needs,
and safety requirements. They must design and coordinate electrical protection for all
branches and the equipment fed by them. In addition, they must consider whether to
apply isolated power systems.
The Sept. 15, 2016, “Critical Power: Backup power systems” webcast presenters addressed questions not covered during the live event. The presenters are:
• Danna Jensen, PE, LEED AP BD+C, vice president, ccrd, a WSP | Parsons
Brinckerhoff Co., Dallas
• Robert R. Jones Jr., PE, LEED AP, JBA Consulting Engineers, Las Vegas
Q: Describe some typical issues that the local authority having jurisdiction (AHJ)
wants corrected.
Danna Jensen: The inspectors tend to look for things that are regularly missed, or new
additions to the code. A list that I’ve assembled that are typically on the top of the list
for items written up during an inspection include:
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Your questions answered: Critical power: hospital electrical systems
• Battery lights in anesthetizing locations
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• Battery light, life-safety light, and receptacle at automatic transfer switch (ATS) and
generator locations
• Bond between the normal and critical panelboards in electrical rooms
• Patient care area receptacle testing (resistance, contact tension, and millivolt leakage).
Q: Can renewable energy sources be integrated with the essential electrical system?
Robert R. Jones Jr.: Possibly, but it may be cost-prohibitive. Renewable energy sources are not specifically listed as an acceptable source of power in NFPA 70: National
Electrical Code (NEC) Article 517, but battery systems are. A renewable energy source
could be used to charge the batteries. However, the demand and consumption requirements of a hospital would likely require a very large battery system. Batteries
currently require a lot of physical space and are expensive to maintain.
Q: Are there any additional considerations when using a natural gas genset versus a diesel genset for backup power?
Jensen: There are two main considerations for using natural gas versus diesel. First,
does your local authority consider natural gas as meeting the requirement for onsite
storage of fuel (this is a requirement in NFPA 110: Standard for Emergency and Standby Power Systems and the number of hours depends on your facility classification, but
typically not less than 24 hours). I have not found many jurisdictions that do.
33
Your questions answered: Critical power: hospital electrical systems
Second, is the natural gas generator capable of being up and running and all loads connect-
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ed to it within 10 seconds? This is a requirement of NFPA 110 for Level 1 systems (which a
hospital is classified as). Natural gas engines start slower than diesel and, depending on the
size of the engine, may have trouble getting to the required ratings within 10 seconds.
Q: Can mobile backup generators not on the premise still be deployed and used
to power a hospital during an emergency?
Jones: NEC Article 517 requires that a generator be located on the premises and sized to
support the essential electrical system (EES) demand. Nothing precludes the installation of
provisions to hook up a mobile generator in addition. Applications may include backup of
the permanently installed generator due to failure/maintenance or supply of nonessential
loads desired to maintain normal operations during an extended loss of utility.
Q: What is a good demand factor you would suggest to use in addition to the
NEC demand factors to keep generators sized well?
Jensen: The demand factors must be used per NEC. There are specific demand factors
that can be used for lighting and receptacles in a hospital (NFPA 70-T220.42), elevators
(NFPA 70-T620.14), diagnostic equipment (NFPA 70-517.73(A)(2), and so on. You must
collect historical data to use the demand calculations listed in NFPA 70-517.30(D). This
can be done by compiling a database as shown in the presentation, or by metering the
load on the transfer switches and using that data.
Q: Which branch should a nurse call system be connected to, life safety or critical?
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Your questions answered: Critical power: hospital electrical systems
Jones: Nurse call systems should be connected to the critical branch. Refer to NEC
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Article 517.33(A)(5).
Q: What about pharmacies? Do those fall under NFPA 99: Health Care Facilities Code?
Jensen: It depends on their license. Most are designed to fall under USP 797 (or the
newer version 800), however if they are not licensed under the hospital, they are not
required to follow NFPA 99. If not, they can even be classified as “B” occupancy since
there is not inpatient care provided.
Q: You indicated that 36 outlets are required in new operating rooms. Does that
mean 36 double-outlet receptacles?
Jones: The receptacles provided to satisfy NEC Article 517.19(C) may be any combination of single, duplex, or both.
Q: NEC Article 700 requires surge protection device (SPD) protection of all distribution equipment. Does this apply only to the life safety branch? Are SPDs
required for critical or equipment somewhere else in the code?
Jensen: Yes. The requirement for SPDs listed in NEC Article 700 applies only to the
life safety branch because both NEC Article 517 and NFPA 99 state that the life safety branch of the EES shall meet the requirements of article 700 (NFPA 70-517.26 and
NFPA 99-6.4.2.2.1.5). SPDs are not required for critical or equipment branches elsewhere in NFPA 99 or NFPA 70-517.
35
Your questions answered: Critical power: hospital electrical systems
Q: Are special insulation re-
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quirements for isolated power
THE WORLD IS READY
FOR RENEWABLES.
WE’LL MAKE SURE
YOU’RE READY TOO.
conductors still required?
Jones: It would be a best practice to design the isolated power system with components to
Distributed energy from the leader in power systems integration
minimize leakage current from
Discover reliable microgrid control at cummins.com
line to ground. NEC Article
517.160(A)(6) Fine Print Note 2,
which is explanatory only and
not actual code, suggests minimizing branch circuit conductor
length and the use of conductors
with insulation properties of less
than a 3.5 dielectric constant and
resistance greater than 20,000
meg-ohms at 60°F. Type XHHW
conductors are suggested over
the use of THHN/THWN.
Q: It is my understanding
that the separation of emergency circuits begins at the
transfer switch, not the up-
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Your questions answered: Critical power: hospital electrical systems
Jensen: The code does not distinguish one way or the other. However, it is inferred by
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the diagrams in the handbook and the wording in the text that the “branch” consists
of all wiring and feeders, including the upstream overcurrent protective device (OCPD),
which must be selectively coordinated. I also have run across many jurisdictions that
consider the branch to start at the first OCPD supplying the transfer switch.
Q: Nursing home and long-term care facilities require only two branches, correct?
Jones: NEC Article 517.41(A) contains the requirements for the EES in nursing homes
and limited care facilities. If the facility admits patients who may need to be sustained
with life support equipment or performs surgical treatment requiring general anesthesia,
an EES is required. The EES is comprised of the life safety branch and the critical branch.
Q: Are you allowed to shed the equipment branch to serve a fire pump?
Jensen: No. If your system is running as usual (meaning all designed engines are still
operational), then all of the required systems must be connected and operational as
well. This includes the automatically connected equipment branch. The only time load
shed is permitted is if the load is optional to begin with, or you lose an engine or other catastrophe in which additional measures must be taken to keep as many systems
operational as possible. Note however, when the fire pump is running and you have a
fire in the facility, unless you have an intricate smoke control system, you will likely have
a reduced load on the equipment branch b the air handling unit will de-energize upon
sensing smoke in its return detector at the unit.
Danna Jensen, PE, LEED AP BD+C, and Robert R. Jones Jr., PE, LEED AP
37
Why decarbonization, ESG
initiatives are a bigger priority
for building owners
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Decarbonization and ESG initiatives are a major focus for building owners and
their tenants, but getting them access to the right data remains a hurdle.
B
uilding owners and tenants are emphasizing decarbonization more than ever as
environmental, social and governance (ESG) initiatives are growing. They’re not
only gaining attention for helping the environment, but also because they can help the
bottom line. The need to save money and attract tenants is a big priority for building
owners since the COVID-19 pandemic. Tenancy is down and they need to find a way to
attract customers into their building.
In a panel discussion at AHR Expo 2024 at McCormick Place in Chicago, the discussion
on “The Future of Energy Management: ESG, Decarbonization, and Electrification”
focused on where things currently stand and where they’re headed down the road.
“Clients are looking for carbon savings,” said panel moderator Brad White, president
of SES Consulting. “Building owners are willing to spend money on decarbonizing
their buildings.”
Stephanie Poole, a senior decarbonization engineer at SES Consulting, agreed, and
noted the shift in emphasis.
“It used to be about energy efficiency. Now it’s about decarbonization and we’re working on some very complex projects.”
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Why decarbonization, ESG initiatives are a bigger priority for building owners
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She cited an example where a building owner that
didn’t have a net zero plan was at risk of losing a valuable tenant, which would have cost them a great deal of
money. So they reached out and developed a long-term
plan to keep their tenant. This is not a one-off, Poole
said. It’s happening more often as owners and compa-
Left to right: Leon Wurfel, founder,
Bueno; Lauren Scott, VP, marketing
and sustainability, Intelligent Spaces
Group at Acuity Brands; Stephanie
Poole, senior decarbonization
engineer at SES Consulting.
Courtesy: Chris Vavra, CFE Media
and Technology
nies shift their priorities and emphasis.
For panelist Leon Wurfel, the founder of Bueno Systems, the emphasis on building
standards is nothing new in his native Australia. The National Australian Built Environment Rating System (NABERS) has been in effect for years and is required for all new
buildings that are more than 1000 square meters and uses a rating system of 0 to 6
stars to help determine how energy-efficient buildings are.
He said the system has, “Created a huge amount of opportunity and commercial potential,” noting there was a bit of vanity involved among owners and it helped get buy-in.
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Why decarbonization, ESG initiatives are a bigger priority for building owners
Lauren Scott, VP, marketing and sustainability at Acuity Brands, noted there has been
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a similar push in Europe and it has helped push technology much further than because
there is an incentive in the form of penalties and falling behind in general.
Getting the right data to the right people
Decarbonization and ESG initiatives are only as good as the data being transmitted.
For many building owners, that remains a big hurdle.
“The number 1 thing is the quality of data,” Scott said. “Users need access to the right
information. Try and find the tools for that measuring and monitoring is key.” She added that there is a labor shortage in general and the companies might be hiring some
inexperienced to make sense of the data. This can be overcome with the right funding,
but it won’t matter if a quick return on investment (ROI) can’t be shown.
Wurfel agreed. “Operationalizing and managing is a challenge. It’s becoming more
important as companies rely on the data coming from a building management system
(BMS) and putting it into the ESG reporting. Maintaining data quality is important.”
Poole said many don’t even know what they have to begin with. “It’s alarming how
people don’t know what they have. No concept of what their systems are. That has
been the hardest piece. Is your data accurate? Do you know where your systems are?”
Have a good dashboard can help, but it depends on context. “Develop dashboards for
the right people,” Poole said. “For operators the dashboards will be more complex.
Ask each person what they want and make things easier.”
Chris Vavra
Chris Vavra is web content manager for CFE Media and Technology.
40
PODCAST:
Brian Alessi on decarbonization
strategies in building design
D
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ecarbonization is often a top priority for new building or retrofit projects, however understanding an owner’s priorities and restrictions can create difficulties in
implementing these strategies. Brian Alessi, the sustainability director for Henderson
Engineers, gives the audience tips for approaching these conversations and creating
building systems that are healthy, sustainable, and resilient.
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