TECHNOLOGY
• Use solid-wall metal conduit or race-
SOME MITIGATION
DEVICES FOR
IMPROVED POWER
QUALITY
• Uninterruptible
power supplies
• Motor-generators
• Surge suppressors
• Ferroresonant
transformers
• Filters
• Tap changing
transformers
• Ride through devices
• DC versus AC
controls
SCE’s power quality
specialists can help
you determine which
types of mitigation
devices are right for
your equipment.
FOR ADDITIONAL
INFORMATION, PLEASE
CONTACT US AT:
Southern California Edison
Power Quality Department
7951 Redwood Avenue
Fontana, CA 92336
800-POWERCO
www.scebiz.com
pwrqlity@sce.com
way, connected to form a continuous
electrical path from the panel to the
equipment.
• Include an insulated grounding conductor in the same conduit or raceway
with its associated circuit conductors.
• Provide a grounding system with
many interconnected paths. Consider
a signal reference grid for computer
rooms and assembly lines where
equipment is close together.
• If equipment wiring instructions do
not comply with the NEC, resolve this
with the manufacturer so that the
installation meets the NEC.
INSTALL MITIGATION EQUIPMENT
Once you have a well-designed wiring
and grounding system, there are a
number of devices that can be incorporated to further improve the power
quality in your facility. Even the best
wiring and grounding cannot protect your
equipment from all disturbances. Devices
are available to protect your equipment
from transients, to power your equip-
ment during sags, interruptions, and
outages, and to keep harmonic currents
under control. Including mitigation
equipment in the design of your facility’s
electrical system can prevent future power
quality problems and expenses.
POWER QUALITY GUIDELINES FOR DESIGN
AND CONSTRUCTION OF NEW FACILITIES
CONSULT WITH EXPERTS
SCE has a staff of specialists ready to
answer your power quality questions. At
SCE’s Customer Technology Application
Center (CTAC) in Irwindale, you can
attend power quality classes and see
demonstrations of many different mitigation devices.
Also, the Institute of Electrical and
Electronics Engineers, Inc. (IEEE) and
others have published several references that can help you “design in”
power quality. A list of guidelines can
be found in SCE’s “Power Quality
Handbook.” Specifically helpful is the
“IEEE Recommended Practice for
Powering and Grounding Electronic
Equipment,” (IEEE Emerald Book, Std.
1100-1999).
A CHECKLIST FOR POWER QUALITY DESIGN
❏ Do you know the types of power quality disturbances that your equipment can
withstand and the types of disturbances your equipment may create?
❏ Do your equipment specifications include requirements regarding power quality?
❏ Is the design team using current power quality design standards and guidelines?
❏ Does your electrical system design use dedicated, isolated branch circuits to
power sensitive and critical equipment?
❏ Have harmonic and inrush currents been considered in the sizing of conductors?
❏ Does the grounding system design meet the latest NEC requirements and include
additional features to improve equipment performance, such as a signal reference grid?
❏ Have discrepancies between vendor installation instructions and the NEC been
resolved, so that the system design meets the NEC requirements?
s an architect, engineer, electrical
contractor, developer, or business
owner, you may specify and
install many advanced power electronics and microprocessor-based systems.
Equipment such as electronic lighting
ballasts, variable speed drives, automated control systems, and networked
computers can significantly increase
productivity, process control, and
energy savings. This equipment also
places additional demands on the facility’s electrical system which must be
addressed by the design team.
A
Studies have shown that in a typical facility, approximately 80 percent of electronic
equipment failures associated with power
quality problems are due to wiring, grounding, or equipment interaction problems
within the facility itself.
The most economical way for the
design team to address power quality
problems is to prevent them from
occurring. Waiting to correct power
quality problems until after the design
of a facility is completed (or later)
could result in costly change orders,
retrofits, and production shutdowns.
A properly designed and constructed
electrical system will help you avoid
some common power quality problems
and allow you to profit from the many
benefits offered by today’s advanced
electronic equipment.
Questions?
For power quality consulting, or
troubleshooting, phone us at:
1-800-POWERCO or send an e-mail
to: pwrqlity@sce.com
❏ Does your design include appropriate power quality mitigation devices?
To learn more, call 1-800-336-CTAC to sign up for a
class at SCE’s Power Quality Demonstration Center.
313-0899
WHAT YOU CAN DO TO “DESIGN IN” POWER QUALITY
Your facility will probably experience a
variety of electrical disturbances, including voltage sags and swells, harmonics,
interruptions, transients, and electrical
noise. These disturbances are caused by
equipment in the facility, equipment in
nearby facilities, faults on the system,
and normal utility operations. Most
disturbances do not result in any equipment malfunctions and go unnoticed.
Occasionally, disturbances affect equipment, resulting in lost production time
and damaged equipment. Simple wiring
and grounding techniques can reduce your
vulnerability to many disturbances.
AN INTEGRATED APPROACH TO
FACILITY ELECTRICAL DESIGN
Designing an electrical system to meet
the current National Electrical Code
(NEC) requirements will not ensure
that the power quality requirements of
your equipment are met. The NEC
describes the minimum wiring and
grounding requirements necessary for
safety, but does not specifically address
power quality.
The following information should
help you bridge the gap between the
NEC requirements and the power quality
requirements of your equipment.
KNOW YOUR EQUIPMENT
In addition to the rated voltage and
power demand, equipment vendors
should be able to provide information
regarding the ability of their equipment to tolerate power quality disturbances. (See the “ITIC curve” in SCE’s
Power Quality Handbook). Vendors
should also be able to provide you with
information on the sorts of disturbances their equipment may create. For
example, many laser printers draw current in short “bursts,” which can result
in light flicker and may affect other
office and process equipment.
SPECIFY YOUR REQUIREMENTS
Some customers include power quality
requirements in their specifications for
new equipment. This practice helps
them avoid introducing equipment into
their facilities that may cause, or be
susceptible to, electrical disturbances.
This also places some responsibility on
the manufacturer to deliver equipment
that can function in the customer’s
facility without modification.
SEPARATE SENSITIVE EQUIPMENT
Once you have a good understanding of
the equipment requirements and how
one piece of equipment may affect others, you can design the facility’s electrical distribution system to minimize
problems. One beneficial practice is to use
dedicated, isolated branch circuits to
power sensitive and critical equipment.
This helps prevent electrical interference problems between different pieces
of equipment. Physical isolation keeps
disturbances in one circuit from being
magnetically coupled into other nearby
circuits.
Equipment can be grouped together
on feeders if it all has similar power
quality requirements and will not
interfere with other equipment in the
group. This also will make it easier and
more economical to install power quality
equipment in the future, such as an
uninterruptible power supply (UPS), if
required. For example, a single UPS
might be installed at a subpanel to protect all desktop personal computers, but
not the office lighting.
CONSIDER LOAD CHARACTERISTICS
WHEN SIZING CONDUCTORS
GROUND EQUIPMENT FOR SAFETY
AND PERFORMANCE
It is important to consider more than
just the steady-state current drawn by
the equipment when sizing conductors.
Some equipment, such as transformers
and motors, draw large inrush currents
when being energized, resulting in voltage drops that may affect other equipment sharing the same conductors.
Improper grounding within the facility is
the most common cause of power quality
problems. A properly engineered and
installed grounding system improves
safety and equipment performance.
Other equipment, such as motor
drives, electronic lighting ballasts, computers, and control systems draw harmonic currents. Harmonic currents can
cause overheating in transformers and
conductors and can cause thermal overcurrent devices, like fuses, to operate.
Harmonic currents also result in voltage distortion. This distortion can, in
turn, affect other equipment, causing
overheating in motors for example.
When a three-phase, four-wire system
serves a large number of harmonic-producing loads, the current in the neutral
conductor can be significantly higher
than any of the individual phase currents. In systems serving a large number
of harmonic-producing loads, it is recommended that the neutral conductor have an
ampacity equal to twice that of the phase
conductors. Each single-phase branch
circuit should also have its own neutral
conductor extending back to its upstream panel. This will reduce voltage
drop and distortion.
In general, all conductors should be sized
to minimize the impedance between the
source and the load, as much as practical.
One method of reducing the conductor
impedance is to use two or more conductors for each phase. This practice is
allowed by the NEC and is especially
beneficial where harmonic currents are
present. The increased surface area of
the multiple conductors will reduce
the circuit’s impedance to harmonic
currents and reduce the harmonic
voltage distortion.
The grounding system improves safety
for both equipment and personnel by
providing a low impedance path for
ground fault current, and equalizing
“touch potentials” between adjacent
pieces of equipment. The NEC grounding requirements are designed to provide these safety benefits.
A well designed grounding system will
also help ensure the proper operation of
electronic equipment. This includes computer networks, security systems, and
any other systems that must reliably
send and receive electrical signals in
order to perform their function. A good
grounding system will help prevent communication problems and data loss by establishing a common ground reference
throughout the facility for interconnected
electronic equipment.
Some specific steps can be taken during the design and installation of the
grounding system to ensure both safety
and equipment performance.
• Start with a system that meets the
latest NEC grounding requirements.
Most grounding problems result from
grounding practices that do not meet
the NEC requirements.
WHAT YOU CAN DO TO “DESIGN IN” POWER QUALITY
Your facility will probably experience a
variety of electrical disturbances, including voltage sags and swells, harmonics,
interruptions, transients, and electrical
noise. These disturbances are caused by
equipment in the facility, equipment in
nearby facilities, faults on the system,
and normal utility operations. Most
disturbances do not result in any equipment malfunctions and go unnoticed.
Occasionally, disturbances affect equipment, resulting in lost production time
and damaged equipment. Simple wiring
and grounding techniques can reduce your
vulnerability to many disturbances.
AN INTEGRATED APPROACH TO
FACILITY ELECTRICAL DESIGN
Designing an electrical system to meet
the current National Electrical Code
(NEC) requirements will not ensure
that the power quality requirements of
your equipment are met. The NEC
describes the minimum wiring and
grounding requirements necessary for
safety, but does not specifically address
power quality.
The following information should
help you bridge the gap between the
NEC requirements and the power quality
requirements of your equipment.
KNOW YOUR EQUIPMENT
In addition to the rated voltage and
power demand, equipment vendors
should be able to provide information
regarding the ability of their equipment to tolerate power quality disturbances. (See the “ITIC curve” in SCE’s
Power Quality Handbook). Vendors
should also be able to provide you with
information on the sorts of disturbances their equipment may create. For
example, many laser printers draw current in short “bursts,” which can result
in light flicker and may affect other
office and process equipment.
SPECIFY YOUR REQUIREMENTS
Some customers include power quality
requirements in their specifications for
new equipment. This practice helps
them avoid introducing equipment into
their facilities that may cause, or be
susceptible to, electrical disturbances.
This also places some responsibility on
the manufacturer to deliver equipment
that can function in the customer’s
facility without modification.
SEPARATE SENSITIVE EQUIPMENT
Once you have a good understanding of
the equipment requirements and how
one piece of equipment may affect others, you can design the facility’s electrical distribution system to minimize
problems. One beneficial practice is to use
dedicated, isolated branch circuits to
power sensitive and critical equipment.
This helps prevent electrical interference problems between different pieces
of equipment. Physical isolation keeps
disturbances in one circuit from being
magnetically coupled into other nearby
circuits.
Equipment can be grouped together
on feeders if it all has similar power
quality requirements and will not
interfere with other equipment in the
group. This also will make it easier and
more economical to install power quality
equipment in the future, such as an
uninterruptible power supply (UPS), if
required. For example, a single UPS
might be installed at a subpanel to protect all desktop personal computers, but
not the office lighting.
CONSIDER LOAD CHARACTERISTICS
WHEN SIZING CONDUCTORS
GROUND EQUIPMENT FOR SAFETY
AND PERFORMANCE
It is important to consider more than
just the steady-state current drawn by
the equipment when sizing conductors.
Some equipment, such as transformers
and motors, draw large inrush currents
when being energized, resulting in voltage drops that may affect other equipment sharing the same conductors.
Improper grounding within the facility is
the most common cause of power quality
problems. A properly engineered and
installed grounding system improves
safety and equipment performance.
Other equipment, such as motor
drives, electronic lighting ballasts, computers, and control systems draw harmonic currents. Harmonic currents can
cause overheating in transformers and
conductors and can cause thermal overcurrent devices, like fuses, to operate.
Harmonic currents also result in voltage distortion. This distortion can, in
turn, affect other equipment, causing
overheating in motors for example.
When a three-phase, four-wire system
serves a large number of harmonic-producing loads, the current in the neutral
conductor can be significantly higher
than any of the individual phase currents. In systems serving a large number
of harmonic-producing loads, it is recommended that the neutral conductor have an
ampacity equal to twice that of the phase
conductors. Each single-phase branch
circuit should also have its own neutral
conductor extending back to its upstream panel. This will reduce voltage
drop and distortion.
In general, all conductors should be sized
to minimize the impedance between the
source and the load, as much as practical.
One method of reducing the conductor
impedance is to use two or more conductors for each phase. This practice is
allowed by the NEC and is especially
beneficial where harmonic currents are
present. The increased surface area of
the multiple conductors will reduce
the circuit’s impedance to harmonic
currents and reduce the harmonic
voltage distortion.
The grounding system improves safety
for both equipment and personnel by
providing a low impedance path for
ground fault current, and equalizing
“touch potentials” between adjacent
pieces of equipment. The NEC grounding requirements are designed to provide these safety benefits.
A well designed grounding system will
also help ensure the proper operation of
electronic equipment. This includes computer networks, security systems, and
any other systems that must reliably
send and receive electrical signals in
order to perform their function. A good
grounding system will help prevent communication problems and data loss by establishing a common ground reference
throughout the facility for interconnected
electronic equipment.
Some specific steps can be taken during the design and installation of the
grounding system to ensure both safety
and equipment performance.
• Start with a system that meets the
latest NEC grounding requirements.
Most grounding problems result from
grounding practices that do not meet
the NEC requirements.
TECHNOLOGY
• Use solid-wall metal conduit or race-
SOME MITIGATION
DEVICES FOR
IMPROVED POWER
QUALITY
• Uninterruptible
power supplies
• Motor-generators
• Surge suppressors
• Ferroresonant
transformers
• Filters
• Tap changing
transformers
• Ride through devices
• DC versus AC
controls
SCE’s power quality
specialists can help
you determine which
types of mitigation
devices are right for
your equipment.
FOR ADDITIONAL
INFORMATION, PLEASE
CONTACT US AT:
Southern California Edison
Power Quality Department
7951 Redwood Avenue
Fontana, CA 92336
800-POWERCO
www.scebiz.com
pwrqlity@sce.com
way, connected to form a continuous
electrical path from the panel to the
equipment.
• Include an insulated grounding conductor in the same conduit or raceway
with its associated circuit conductors.
• Provide a grounding system with
many interconnected paths. Consider
a signal reference grid for computer
rooms and assembly lines where
equipment is close together.
• If equipment wiring instructions do
not comply with the NEC, resolve this
with the manufacturer so that the
installation meets the NEC.
INSTALL MITIGATION EQUIPMENT
Once you have a well-designed wiring
and grounding system, there are a
number of devices that can be incorporated to further improve the power
quality in your facility. Even the best
wiring and grounding cannot protect your
equipment from all disturbances. Devices
are available to protect your equipment
from transients, to power your equip-
ment during sags, interruptions, and
outages, and to keep harmonic currents
under control. Including mitigation
equipment in the design of your facility’s
electrical system can prevent future power
quality problems and expenses.
POWER QUALITY GUIDELINES FOR DESIGN
AND CONSTRUCTION OF NEW FACILITIES
CONSULT WITH EXPERTS
SCE has a staff of specialists ready to
answer your power quality questions. At
SCE’s Customer Technology Application
Center (CTAC) in Irwindale, you can
attend power quality classes and see
demonstrations of many different mitigation devices.
Also, the Institute of Electrical and
Electronics Engineers, Inc. (IEEE) and
others have published several references that can help you “design in”
power quality. A list of guidelines can
be found in SCE’s “Power Quality
Handbook.” Specifically helpful is the
“IEEE Recommended Practice for
Powering and Grounding Electronic
Equipment,” (IEEE Emerald Book, Std.
1100-1999).
A CHECKLIST FOR POWER QUALITY DESIGN
❏ Do you know the types of power quality disturbances that your equipment can
withstand and the types of disturbances your equipment may create?
❏ Do your equipment specifications include requirements regarding power quality?
❏ Is the design team using current power quality design standards and guidelines?
❏ Does your electrical system design use dedicated, isolated branch circuits to
power sensitive and critical equipment?
❏ Have harmonic and inrush currents been considered in the sizing of conductors?
❏ Does the grounding system design meet the latest NEC requirements and include
additional features to improve equipment performance, such as a signal reference grid?
❏ Have discrepancies between vendor installation instructions and the NEC been
resolved, so that the system design meets the NEC requirements?
s an architect, engineer, electrical
contractor, developer, or business
owner, you may specify and
install many advanced power electronics and microprocessor-based systems.
Equipment such as electronic lighting
ballasts, variable speed drives, automated control systems, and networked
computers can significantly increase
productivity, process control, and
energy savings. This equipment also
places additional demands on the facility’s electrical system which must be
addressed by the design team.
A
Studies have shown that in a typical facility, approximately 80 percent of electronic
equipment failures associated with power
quality problems are due to wiring, grounding, or equipment interaction problems
within the facility itself.
The most economical way for the
design team to address power quality
problems is to prevent them from
occurring. Waiting to correct power
quality problems until after the design
of a facility is completed (or later)
could result in costly change orders,
retrofits, and production shutdowns.
A properly designed and constructed
electrical system will help you avoid
some common power quality problems
and allow you to profit from the many
benefits offered by today’s advanced
electronic equipment.
Questions?
For power quality consulting, or
troubleshooting, phone us at:
1-800-POWERCO or send an e-mail
to: pwrqlity@sce.com
❏ Does your design include appropriate power quality mitigation devices?
To learn more, call 1-800-336-CTAC to sign up for a
class at SCE’s Power Quality Demonstration Center.
313-0899