Download LIGHTNING THEORY – Explanations

IEEE PES SPDC Working Group 3.6.13
Smart Grid SPD Whitepaper
DRAFT 5/10/2011
Smart Grid SPD Whitepaper Outline and Writing Assignments
Update 11/18/2010
Section
Number
1.0
2.0
2.1
2.2
2.3
Section
Topic
Introduction and Purpose of paper
Smart Grid
Overview of Smart Grid – include comm.,
low voltage and high voltage topics
Smart Grid and Communications
Importance of Surge Protection for Smart
Grid
2.4
Smart Grid SPD related case studies
3.0
3.1
Electrical disturbances and surges
Internally generated disturbances
3.2
Lightning disturbances
3.3
Other line-side disturbances – include cap
banks, switching, etc.
Surge Protection
Overview of surge protection devices
4.0
4.1
4.2
5.0
Application of various SPDs for different
types of surges
Assessment process to determine proper
surge protection for different facilities and
equipment
Interaction of loads with different SPDs –
include C62.48 and C62.72
Existing standards and resources
5.1
5.2
SPD Related Standards
Additional Resources
4.3
4.4
Assignment
Matt Wakeham
----Al Martin
Al Martin
Sarah Beadle
Ray Hill, Don
Parker
----Ron Hotchkiss,
James Moellmann
Joe Koepfinger,
James Moellmann
Ray Hill
----Andi Haa
Section
Complete
Yes
--Yes
Yes
Yes
NEMA
paper
Yes
YES
Yes
NEMA
paper
Ken Brown, Andi
Haa
Doug Dorr
Paul Saa, Lou
Farquhar
John Caskey, Andi
Haa
John Caskey
John Caskey, Andi
Haa
Yes
Yes
Yes
Yes
1.0 Introduction and Purpose
The intent of this paper is to outline how surge protective devices play an integral part in
improving the operability and reliability of the Smart Grid. This document focuses on
surge protective devices that operate on systems up to 1000 V AC or 1500 V DC.
Applications include connection to ac power equipment, as well as data and signalling
circuits for control, monitoring and communication. The selection and application of
surge protective devices based on transient exposure levels are discussed.
2.0 Smart Grid
2.1 Overview of Smart Grid
The basic concept of Smart Grid is to add monitoring, analysis, control, and
communication capabilities to the national electrical delivery system to maximize the
throughput of the system while reducing the energy consumption. The Smart Grid will
allow utilities to move electricity around the system as efficiency and economically as
possible. It will also allow the homeowner and business to use electricity as economically
as possible.
Creating a secure, connected, and interoperable Smart Grid is a top national priority. Title
XIII (Smart Grid) of The Energy Independence and Security Act of 2007 requests that the
National Institute of Standards and Technology (NIST) develop a Smart Grid
Interoperability Roadmap and also coordinate the development of Smart Grid
Interoperability standards. NIST released the first issue of the Roadmap in January 2010.
The Roadmap summarizes the current state of Smart Grid–related standards and
identifies gaps in standards that need to be addressed. The Roadmap also includes a list of
standard-related tasks that need to be completed to ensure the interoperability of Smart
Grid.
The United States Department of Energy (DOE) is also tasked with helping the nation
deploy Smart Grid and through its effort on the Modern Grid Initiative identified the
following characteristics for Smart Grid:




Enable consumer participation
Accommodate generation and storage
Enable new products and services
Provide power quality



Optimize asset utilization
Anticipate and respond to system disturbances
Operate against physical and cyber attacks
2.2 Smart Grid and Communications
Much has been written about the protection of equipment connected to Smart Grid AC
power [see for example www.NEMASURGE.com], but little has been said about
protection of Smart Grid communications. Protection of communication links is
important, because Smart Grid operation depends on two-way communications between
the power utility and the customer to enable the control of power flow to the customer.
Control may be as simple as providing the customer with frequent updates about the cost
of the power he is using; or it may involve the use of the home [or building] network for
the actual control of equipment within the customer’s premises, to minimize usage during
peak power demand from the grid.
Communication may occur over a wireless link, over the power lines, or via a wired or
fiber-optic telecommunications service such as cable or phone. However implemented,
this communications link needs to be interfaced to the home network. Generally this
interface is implemented by a box called a gateway, which is located where the
communications service enters the structure. A prevalent myth is that if this gateway is
served by a fiber optic or wireless connection, it is immune from damage by lightning.
2.3 Importance of Surge Protection for Smart Grid
Three key aspects of Smart Grid point to an increased need for surge protection:
1. Addition of electronically based monitoring, analysis, control and communication
equipment. – Surge protection is required to protect this electronic equipment
from damage due to voltage transients.
2. Increase in utilities moving electricity around the system from multiple new
sources such as wind, solar, cogeneration and other sources – This increased level
of switching of electrical sources can lead to increased levels of switching
transients that can damage electrical and electronic loads.
3. Increase in residential, commercial and industrial use of energy management
systems and distributed generation cause more switching of loads and generation
sources with in the premise; thereby increasing the need for point-of-use
protection inside the premise.
The addition of electronically based monitoring, analysis, control and communication
equipment can result in equipment being susceptible to disruption or damage caused by
surges and transients. This is due to the fact that this type of electronically-based
monitoring, analysis control and communication equipment is fraught with
semiconductors in close proximity to one another and to the system. Surge protection is
required to protect this electronic equipment from damage due to voltage transients.
In addition to the complexity of the system as shown above, the increase in utilities
moving/switching electricity around the system from multiple new alternative energy
sources such as wind, solar, cogeneration creates its own set of power quality challenges.
This increased level of switching of electrical sources can lead to increased levels of
transients that can damage electrical and electronic loads.
The utilization of solar and wind power present unique problems. The nature of solar
power is intermittent and the effect of this on capacitor banks and regulators is just now
being studied. In fact it has been pointed out that if a system is balanced to accommodate
the solar load, a stray cloud can destroy that balance.
Due to their height and typical location wind turbines are exposed to both direct &
indirect lightning strikes. The resulting induced transient surges will directly impinge on
power & signal leads and usually damage equipment including signal, communication
lines and the primary distribution panel. The results of direct lightning strikes on a wind
turbine have been well documented in technical papers published throughout the world.
According to some sources, a wind turbine is at least 3 times more likely to be damage by
indirect lighting than direct lightning.
Generators in large, modern wind turbines generally produce electricity at 690 volts. A
transformer located next to the turbine, or inside the turbine tower, converts the
electricity to high voltage (usually 10-30 kilovolts).
Inverters are key components in these systems. Their function is to convert the DC power
generated by the solar panels or wind turbine into usable AC power that is synchronized
with the grid power on a grid tie system or power that is used directly to power the
electrical system in a stand alone or battery storage system.
Inverters, however, are loaded with sensitive electronics. Their purpose, among other
things, is to synchronize the AC power to be in phase with the grid supplied power.
Obviously this is a critical function and failure of these inverters is unacceptable as the
energy generation system relies on this to function properly.
The question becomes, how do we address these issues? Solar panel installations require
surge protection to protect the costly inverters that can fail during lightning storms. Wind
Turbines require surge protection to protect their voltage regulators and motor driven
generators. It has been found that there is a substantial quantity of voltage spikes and
disturbances related to unstable wind conditions. Wind gusts can burst from 0 to 60 mph
in less than one minute causing voltage spikes on the power grid.
Surge Protective Devices (SPDs) should be utilized protect the inverters utilized in these
systems, on both the output (AC) and input (DC) to protect the sensitive internal
electronics. Along with protecting this equipment, the customer equipment must also be
protected at each facility location. Surges and spikes can be internally or externally
generated and only a solid protection system will ensure the most effective power quality
system possible. Surge Protective Devices are a necessary part of the commercial,
industrial and residential power distribution system landscape. Whether incorporating a
surge panel, a surge strip or a full three-tiered system including a panel, sub-panel and
point of use device, surge protection provides valuable down line protection from damage
due to surges on the power lines. As you will find many positive changes have occurred
within the industry and as a result end users are receiving improved protection at a better
value.
2.3 Smart Grid Related Case Studies
3.0 Electrical Disturbances and Surges
Surges, or transients, are brief overvoltage spikes or disturbances on a power waveform
that can damage, degrade, or destroy electronic equipment within any home, commercial
building, or manufacturing facility. Transients can reach amplitudes of tens of thousands
of volts. Surges are measured in microseconds.
The presence of sensitive electronic equipment such as computers, answering machines,
microwaves, and other microprocessor-based equipment is growing exponentially in
virtually every aspect of life. Surges can cause damage resulting in equipment loss or
damage and lost A common source for surges generated inside a building is devices that
switch power on and off. This can be anything from a simple thermostat switch operating
a heating element to a switch-mode power supply found on many devices. Transients can
originate from inside or outside a facility, and it is estimated that 60 – 80% of surges are
internally generated within a facility.
3.1 Internally Generated Disturbances
Surges produced by sources internal to the power system come from a variety of sources.
Most often, internally-generated surges are produced during some type of switching
activity whether they are considered a normal, abnormal, intentional, or unintentional
activity. From Clause 4.3 of IEEE Std. C62.41.1TM-2002 [1]:
Generally, any switching operation, fault initiation, interruption, etc. in an
electrical installation is followed by a transient phenomenon in which
overvoltages can occur. The sudden change in the system can initiate damped
oscillations with high frequencies (determined by the resonant frequencies of the
network), until the system is again stabilized to its new steady state. The
magnitude of the switching overvoltages depends on many parameters, such as
the type of circuit, the kind of switching operation (closing, opening, restriking),
the loads, and the type of switching device or fuse.
The standard goes on to detail specific information regarding the expected waveform,
amplitude, and frequency of oscillation associated with these internally-generated surges.
Specific sources and activities that lead to internally-generated surges are described
below cited from [2].
Examples of sources of switching surges that are considered normal events or operations
follow.
Contactor, relay, and breaker operations. Unless inherently or otherwise protected,
contactors, relays, and breakers (or other overcurrent circuit protective devices) can often
produce switching surges that have complex waveforms and amplitudes that are several
times greater than the nominal system voltage [1]. This phenomenon occurs due to the
arcing that often occurs across the output contacts of the contactor, relay or breaker. In
inductive-capacitive circuits, the switching arc is often unstable. This scenario can cause
the current to interrupt and re-strike several times before opening the circuit properly [3].
The action of the arc forming between the contacts generates a switching surge that has a
ringing voltage waveform.
Switching of capacitor banks. Capacitor banks are commonly used for operations as
power factor correction within many electrical systems. Further, these capacitor banks are
often switched into and out of the electrical system depending on the characteristics of
the loads that are currently connected to the electrical system. The switching action can
create ringing, voltage transients that are as high as four times the nominal voltage. This
phenomenon is detailed in [1].
Discharge of inductive devices. Another common source of switching transients is the
discharge of inductive devices. This can include the discharge of energy stored in fault
current limiters, transformers, reactors and motors [1], [3]. These devices store energy
while completing their action. When this type of load is switched off the energy stored in
the device can be released into the electrical system. The signature of the switching
transient is formed by the inductance and capacitance of the circuit and the system.
Starting and stopping of loads. In a similar fashion to that described above in the
discharge of inductive devices, starting and stopping loads often creates a voltage
transient [1], [3]. Further, the larger the load, the larger the transient tends to be. As an
example, this happens frequently when voltage fluctuates at the startup of a motor
producing a voltage surge.
Fault or arc initiation. Another common source of switching transients that are from
normal and intended sources includes devices that create an intentional fault or arc as part
of their operation. A prime example of this type of source is an arc welder [3]. In the
author’s experience, this source of surges often provides dramatic effects. Once, when
monitoring a circuit intended to measure the frequency of occurrence of switching and
ringing surges, over 1,000 surges where recorded in a period of roughly 10 minutes. This
monitoring coincided with a time when a neighboring facility was operating an arc
welder intermittently over that same time period. Similar experiences have occurred
during the operation of metal grinding equipment.
In contrast, other sources of switching surges are created by abnormal operations. These
sources of switching surges are sometimes intentionally activated but typically are due to
an undesired or unintended event, such as a fault. Other sources grouped with abnormal
operations include actions from faulty equipment or wiring. The intended or corrective
reaction of the electrical system to abnormal events can also produce surges [1].
Even though these scenarios are undesired or unintended, they are also common.
Examples of sources of switching surges that are considered abnormal events or
operations follow.
Arcing faults and arcing ground faults. Often, arcing faults or arcing ground faults occur
due to an instance of insulation breakdown, either in electrical system wiring or in motor
winding insulation, for example. Much like the action of a contactor or relay as described
previously, the arc associated with an arcing fault can generate surges that interact with
the inductance and capacitance of the system. Further, in ungrounded systems, where
many arcing ground faults occur, the stray capacitance of the system allows the surge
amplitude to rise to 2 or 3 times the peak voltage. During conditions of resonance, the
amplitudes can be much greater [3].
Fault clearing. The reaction of the electrical system to a fault is typically to clear the
fault through the opening of a fuse or circuit breaker. Current-limiting fuses or fast-acting
circuit breakers can leave inductive energy trapped in the circuit upstream. If no lowimpedance path is offered to lessen the stored energy, high voltages are generated. The
resultant voltage surge appears in parallel with the loads where the fault is being cleared
[1], [3].
Power system recovery. As part of the action of trying to clear a fault from the electrical
system, the system may be re-closed. This re-closing of the electrical system can produce
voltage surges of amplitudes that approach twice the nominal voltage and are of longer
durations [1]. Although, these occurrences are often considered outside the scope of a
“surge” (often considered a swell) [3], they are noteworthy nonetheless.
Loose connections. Another unintended source of switching surges is loose connections –
more specifically, the arcing that can occur due to loose connections [3]. The switching
surges generated by this condition may be similar to that described above for contactor
and relay operations and arcing faults. Further, this situation is not only a source of
switching transients but also a concern with heat buildup and intermittent or incorrect
operation of connected equipment.
Lightning induced oscillatory surges. Although not truly due to switching or from an
internal source, the resultant surges of lightning induced oscillatory surges on system
wiring have very similar characteristics of switching surges. As described in [4], [5],
oscillatory surges with very similar waveshapes and effects as switching surges can be
coupled or induced into wiring when incoming conductors are subjected to surges with
the characteristic waveform of lightning. Further, to augment the effects of this action,
the oscillatory surges were found to produce reflections within the wiring system which
increased the amplitude of the surge voltages as they propagated.
Fig. 1 illustrates an example waveform of oscillatory (switching).
Fig. 1. Example ring wave surge voltage waveform (switching surge) [6]
Coupling of Electrical Surges
Another effect of internal (and external surges) on the electrical system is their impact on
other related and unrelated systems such as control and communication systems. The
coupling of electrical surges occurs when energy generated by a lightning or switching
surge is transferred to another system. This can occur due to the mutual resistance,
capacitance and/or inductance of the circuits [3]. For example, if a communication circuit
is physically near a power circuit and the power circuit is subjected to a surge, the
mechanisms of inductive coupling through magnetic flux can cause surge energy to be
deposited onto the communication circuit. This is similar to the effect of magnetic
transformer coupling. Similar surge coupling effects are possible through capacitive
coupling as well. These conducted or coupled surges can cause damage to many types of
equipment. For additional information on and a further explanation of this topic refer to
[3].
Surges that exist on the electrical system are often coupled onto nearby communication
systems or coupled to these systems via multi-port/multi-service loads or even SPDs [1],
[3]. These coupled or even direct, as in the case of lightning, events are often damaging
to communication equipment or even the physical cabling, connectors and interfaces.
Further, it is important to understand that surges are not only coupled from the power
conductors to communication or control conductors - the reverse is also true. A surge
propagating on communication or control circuits can also couple to power circuits as
well. It is a common mistake for one to assume that since a power related component in a
multi-service device has failed that a surge must have originated on the incoming power.
Of course, the opposite is also true. The failed component may have simply provided a
low impedance path for the surge to take – regardless of the original source. Further
discussion of this topic is available in [1].
Currently, the IEEE PES Surge Protective Devices Committee Working Groups 3.6.4 and
3.6.6 are working to expand the understanding of the sources, waveforms, amplitudes,
impact, and methods of mitigation of internally-generated surges.
[1]
[2]
[3]
[4]
[5]
[6]
IEEE Guide on the Surge Environment in Low-Voltage (1000 V and Less) AC Power Circuits, IEEE Standard C62.41.1TM2002
Hotchkiss, R.W.; , "Application of low-voltage SPDs: approach of the IEEE," Transmission and Distribution Conference and
Exposition, 2008. T&D. IEEE/PES, vol., no., pp.1-8, 21-24 April 2008 doi: 10.1109/TDC.2008.4517147
URL: http://ieeexplore.ieee.org/stamp/ stamp.jsp?tp=&arnumber=4517147&isnumber=4517029
IEEE Guide on Interactions Between Power System Disturbances and Surge-Protective Devices, IEEE Standard C62.48-2005
Martzloff, F.D., Pellegrini, G., “Real, realistic ring waves for surge testing”, Ninth International Zurich Symposium on
Electromagnetic Compatibility, 1991
Martzloff, F.D.; "Coupling, propagation, and side effects of surges in an industrial building wiring system," Industry
Applications, IEEE Transactions on , vol.26, no.2, pp.193-203, Mar/Apr 1990 doi: 10.1109/28.54243
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp =&arnumber=54243&isnumber=1948
IEEE Recommended Practice on Characterization of Surges in Low-Voltage (1000 V and less) AC Power Circuits, IEEE
Standard C62.41.2TM-2002
3.2 Lightning Disturbances
INTRODUCTION
The implementation of the NIST Roadmap report of 2010 indicates that the SMART
GRID is that it is going to be more communication intensivei than what is currently
required for the operation of the GRID. In IEEE Standards 1547 the term Area Electric
Power System (Area EPS) has been used to describe the part of the Smart Grid external
to that of the end user. The source of the energy supplied by the Area EPS is normally
obtained from large capacity fossil fueled generation, nuclear generating and hydro
generating facilities. In the future, we will see substantial integration of distributed
generation and energy storage facilities into the Grid supplied by Local EPS. This
integration will produce additional exposure to the Grid from environmental threats like
lightning. So, it is important to understand the theory of this threat and the mitigation
technique that should be addressed.
Lightning has intrigued man for thousand of years, but gaining a complete understanding
of this natural phenomenon continues to this day. In 1967, the Franklin Institute produced
a Special Issue on Lightning Research which was edited by Dr. Eugene W. Boehne and
Dr. R.H Golde. IEC Technical Committee 81, in conjunction with CIGRE, continues to
develop standards for defining the magnitude and shape of test waveshapes to be used to
test lightning protective systems and equipment survivability from the threat of lightning.
The availability and dependability of the electric power system, the communications
system and information exchanged can be impacted unless due consideration is given to
protection of these systems from both direct and induced lightning generated surge
voltage and surge current. The degree of lightning protection is based heavily upon the
application of probability techniques. A significant consideration in arriving at the degree
of lightning protection relates to the severity and frequency of lightning and the correct
application of earthing and bonding. Not all facilities require or need to have the same
degree of lightning protection Figure 1 shows the frequency of lightning exposure in the
USAii.
Figure 1 Number of Thunder Storm Day in the USA
The Smart Grid will result in the deployment and use of intelligent electronic equipment
in all of the sub domains of the electric power system and the public and private
communication sub domains. Unlike use of similar equipment in Substations and Control
Centers, the Smart equipment will be installed on distribution circuits where the
environment is much harsher and there less controlled environment.
It will be subjected to impulse voltages and current stresses from both direct strokes and
induced voltages from lightning strokes that are near and remote from the power and
communication facilities. It is important that the manufacturers of equipment have a clear
understanding of the surge environment threats and that they disclose the withstand levels
of their equipment capability to the threat of lightning and other voltage surges created by
switches/breakers operation switching loads and fault current interruption. Overvoltages
cause deterioration of the equipment insulation systems, its components and upset of
electronic functions. Because overvoltage causes equipment insulation systems to age, it
is going to be critical that those operating the Smart Grid be aware of the exposure
history of the Smart Grid equipment.
LIGHTNING THEORY – Generaliii
Over the last 300 years, there has been considerable pool of knowledge developed on the
phenomena of lightning.
In 1773 Benjamin Franklin published his observations regarding the function of a
Lightning conductor in Poor Richard Almanac. He observed that there was a similarity
between a lightning discharge and an electric arc. There was a belief at the time that a
lightning conductor (lightning Rod) had the ability to discharge the electric charge in a
cloud. He noted two years later that the prime purpose of a lightning conductor was to
provide a path for the lighting current.
To understand the threat of lightning upon the electric power system it is helpful to
understand the nature of lightning. Mr. Franklin observed that lightning was similar to a
arcing of a spark gap. He projected two theories related to the use of a pointed rod that
was connected by a conductor to earth.
a) The rod prevented lightning from striking the structure on which is was mounted by
gradually discharging the cloud
b) The rod was a path to earth for discharging the cloud. However he and other
researchers were inclined to believe that the Franklin Lightning Rod repelled lightning.
This was considered by many at that time to be the more rational function of the lightning
rod. In a letter written in 1775 by Frankliniv he acknowledges these two concepts and
noted that the rod’s prime purpose was to provide a conductive path for the lightning
stroke current.
This same theory was also prevalent in Europe as observed by Abbe’ Nolletv.
NUMBER OF POINTS NEEDED TO DISCHARGE A LIGHTNING CLOUDS
There have been several products that are based on the supposition that if there are
sufficient number of points that it is possible to protect a structure by developing arrays
of sharp points. A calculation was done by R. H. Golde to determine the number of
pointed rods that would be needed to discharge a typical lightning cloud. He used the
following assumptionsvi





voltage front-of-wave rate-of-rise
vertical conductor (mast)
Icontinue_discharge
the charge Q dissipated in av. flash
average rate of flashes estimated
= 20kV/m
= 15.2 m
= 5 µA
= 30 coulombs
= 2/min.
This calculation indicated that 6000 poinst would be required per ½ acre. The calculation
was used to confirm the theory that a few Franklin rods on a building are not going to
discharge a cloud.
Worldwide Charge Exchange
There is a constant exchange of current between the stormy areas of the earth and the
clear weather areas. This phenomenon is shown in the Figure 2 The cumulative value of
this DC current is in the area of 1200A to 2000A.
World Current
Stormy
Weather
Fair
Weather
Approx. 1200 to
2000A
Continuous Interchange of Cloud Charge
I
Figure 2 World Currents
When the transfer of the charge is not occurring fast enough there may be a build-up
charge in the cloud. This may be accompanied by the formation of ice crystals, at subzero temperatures in the lower part of the cloud that can result in charge stratification.
Lightning Flash Formation and Stroke Current
Seen in Figure 3 is what is generally believed to represent a typical storm cloud.
Interchange of Cloud Charge with Structure
2.5 to 10 miles
T < 0 deg C
Stroke Current
5 kA to >100 kA
plus many flashes
Approx 6 miles
Critical breakdown of air
is in the range of 300 kV to 500 kV / m
At 100 kA striking distance is approx.
100 m
Figure 3 Formation & Stroke Current
For current to flow, there has to be a conductive path, as was concluded by Franklin. In
this figure there is a Lightning strike to the steeple. It is assumed that the steeple is
protected by a Franklin rod that is properly earthed. The conductive path is created by a
dielectric breakdown of the atmosphere as is shown in Figure NNN.
Threat of Induced voltage in Structures with Lightning Protective Systems
Consideration of the effectiveness of lightning protective system has to take into
consideration the proximity of other conductive paths inside the building. The stroke
current can induce voltages (coupling voltages) into those conductors that are in close
proximity of the down conductor of the lightning protective system. If these conductors
have close paths circulating current will be generated by the coupling voltage. If the
conductor is a power system neutral conductor or a communication system metallic
shield that is earthed this provides an inducted current path to earth and may include loop
currents that involve equipment inside the structure.
If there are power and communication lines entering this building that
have their components connected to earth via the power system
neutral or by an earthing path in the communication circuit, then there
are many direct and indirect paths to earth for the lighting stroke
current flows. Even if a structure does not have a lightning protective
system installed, there are other air terminals on most residential and
small commercial buildings such as sewage vents, antennas, flag
poles, etc.
Figure 4 Stroke Current, Conductor Path & Induced Current
Where equipment is located inside the building that has both power and communications
inputs the inducted voltages in the building wiring can result in voltage stresses due to
lightning flashes that generate surges on one or both domainsvii. This has been known to
occur and can damage to the connected equipment unless properly protected.
The voltages stress imposed on the components and the current forced through them is a
function of impulse impedance of the secondary wiring, and the connected loads. The
lighting stroke acts like a constant current source more than like a constant voltage source
for this condition.
The relationship between the stroke current in the lightning down conductor and the
voltage induced in an internal conductive loop can be calculated knowing the value of the
induced voltages, and the coupling impedance.
 L1 * L2 is called the mutual inductance between the two conductors,
The Voltage Uind is determined as a function of the peak magnitude of the front of
the lightning current value and the time to peak. The time to peak is usually
measured between 10% and 90% of the peak value of the lightning current wave
shape. This value would present the voltage induced in conductor “b” by
M
12
lightning current in conductor “a” is given by U ind  M 12 * di A
dt
Figure 4 shows the magnetic coupling created by lightning discharge current flow
in the earthing conductor. This induces a voltage into and conductor inside he
structure located in vicinity of the lightning earthing conductor. The magnitude of
the induced voltage is reduced as the inverse natural log of the distance between
the lightning protective system earthing conduct and the nearby conductor.
LIGHTNING THEORY – Instrumentation and Records
From the earliest time man sought ways to record lighting so it could be studied.
Negative Impulse
Positive Impulse
Figure 5 Lichtenberg
like figures
Recording were made as early as 1777. The desire to learn more about lightning was
hampered by the lack of an easy recording mechanism until the advent of photographic
film
Many theories were developed regarding how lightning flashes are created and the
magnitude and waveshape of the voltages and current related to the lightning flash and
stroke current. The degree of investigation was dependent upon the maturity of the
instrumentation. The instrumentation, up until the 20th Century was very crude.
Early work in recording discharge current from a pointed was done by Georg Christoph
Lichtenberg, who discovered that it was possible to create branching figures when
discharging an impulse current into an insulated material covered with a dust mixture and
then pressed in a paper over the figures. The figures created were known as Lichtenberg
figures. An example of such figures is shown in the above figures. Another technique
involved the use of thermal links to measure current and energy. Around 1920 use was
made of a Klydonograph to record lightning stroke current. This device and a Boys
camera use photograph film to record the Lichtenburg figures.
The Klydonograph which is shown in Figure 6was composed of a round electrode that
was placed in contact with photograph film
or plate to record the lightning voltage
impulse. In 1925, magnetic links and
calibrated spark gaps were used for
recording the magnitude of the lightning
current. This device was used for many
years to make measurement of not only
lightning parameters, but to make
measurement of surges that occurred due the
switching operation of such devices as a
large electric arc furnace.
Figure 6 Klydonograph
The invention of the trigger oscilloscope equipped with a high speed trigger camera made
it possible to gather more information about lightning.
LIGHTNING THEORY – Explanations
Figure 7 Development of Up-ward Channel of a Negative Stroke Current
Figure 7 was one of the tools that were developed based on observation of lightning by
the use of cameras with photograph films. The first figure on the left show a channel
being created as the electric charge between the cloud and the earth starts to exceed the
dielectric strength of the air. The next five frames show the path further on in its
development. Finally in frame F the path is completed and back stroke discharge of
charge from the earth to the cloud begins to occur. By the time at Frame H is reached
(19s) the conductive column is completed.
Since this information was develop work by Vladimir A. Rakov, Thottappillil and Marti
Uman resulted in the discovery of what is called the M component current. It occurs
some distance from the main channel of the return stroke current and is conducting
charge in the opposite direction.
Figure 8 Development of a Lightning Stroke
Current
This picture provides considerable information about the nature of lighting. Captured in
this picture are the downward leaders from the charged cloud showing scintillation that
occurs as the charge exceeds the dielectric strength of the atmosphere.
The much brighter line shows the results of the first formation of a conductive channel of
ionized gases that allow the charge to be transferred either form the earth to the cloud or
the transfer of the charge from the cloud to the earth. This photo is not taken with a time
sequence shutter. Today high speed cameras maybe use to record more detail that mirrors
the information given in Figure 7
Trigger Lightning Investigation the dispersion of lightning stroke current in
a Simulated House equipment surge protection
Since lighting randomly occurs in the real world, some researchers, like Franklin, need to
the have some control over the data acquisition process. One such facility was designed
and built as a joint outdoor lightning research laboratory that used triggered lightning.
Construction was jointly funded by the Electric Power Research Institute (EPRI) and
Power Technology Inc. (PTI) in 1993. It is now known as the International Center for
Lightning Research and Testing (ICRLT) and is operated by the University of Florida.
One of the main discoveries as a result of the research conducted at this facility was the
discovery of the M component of the lightning stroke current. The electrostatic field
associated with the M current is a time derivative of the M current. This M current, when
it flows is located a few meters distance from the main channel of the stroke return
current. It is a downward progressive wave which is the opposite of the Stroke current
flow.viii It has been found that the M field is relatively insensitive to the change in
distance from the main channel. It ranges in 1.5 kV/m at 30 m to 0.4 kV/m at 500m. This
discovery has been useful in the development of a more accurate models of lightning.
The Camp Blanding site also contains a typical distribution system consisting of
padmounted transformers and simulated house. Two tests were conduct by initiating
lightning strikes to the simulated house as shown in the Figure 9.
4 ohms
A7
X1
V1
6 ohms
X3
A8
V2
A6
A3
A1
A2
1500 ohms
X1
A5
X2
A4
550 ohms
A9
Padmount Transformer
P
V3
X2
A10
V4
X3
To underground cable
to terminal pole
V5
A13
A11
A15
A12
N
A14
250 ohms
Lightning Flash to
Simulated House
and Current Distribution
Figure 9 Electric On-Line of Instrumentation for Lightning study of
Simulated House and the Associate Distribution System
Triggered Lightning Tests were conducted to assess the distribution paths that the
lightning stroke current might take during a lightning flash to the simulated house located
at Camp Blanding, Florida. All of the instrumentation was specially designed to measure
impulse currents and voltages. The path flows of the currents are time dependent due to
the inductive and capacitive values of the various current paths. What is picture here is a
composite of the current flows. The lightning flash is shown striking the lighting Mast on
the building in the upper left hand area of this diagram. As can be seen there is current
flow in each of the two ground rods, which on the front of the wave is controlled by the
inductance and capacitance of the earth. The front of the lightning current waveshape was
very steep, cresting in less than a 0.1µs. The current initially tried to flow into the two
ground rods, but immediately stops. It is believed that the initial flow of current, which
had a magnitude close to that of the stroke current, was related to charging of the earth
capacitance. The current in the earthing rods (grounding rods) cease to flow until after the
crest of the stroke current waveshape. During that short period of zero current in the
earthing rods the current attempts to flow back on the power system neutral to the
distribution transformer neutral earthing point.
Then as the rate-of-change of the stroke current decreases on the tail of the stroke current,
the associated value of the inductive impedance decrease. There was a redistribution of
current flows in all of the neutral paths sharing the lightning stroke current in accordance
with the time varying impedance of the paths to earth.
STANDARD CURRENT AND VOLTAGE WAVESHAPES USED FOR
SIMULATING THE WITHSTAND LEVEL OF EQUIPMENT SUBJECTED
TO LIGHTNING
This still needs to be developed further, but it will cover two current
waveshapes and one voltage waveshape. I intend to discuss a technique used
to determine the lightning stroke current on distribution circuits. It may be at
the distribution level that the duration of the stroke current is more important
than the magnitude of the stroke current. It was found during some tests at
Camp Blanding that the current through the surge arrester had a longer time
of discharge than that of the initiating stroke.
I also have some information regarding the transfer of a lightning surge
through a distribution transformer that I might include if it is of any interest.
The intent is to show the difference between the IEC approach to the
selection of the 10/350 current waveshape to represent a severed
environment than is done in the US where a 8/20 current waveshape
predominates. In a Smart Grid installation, both low voltage power and
communication are going to co-habituate with the intelligent electronic
devices installed on utility poles or underground vaults. Our experience in
this area has shown that some control and switching equipment, when
installed on HV (> 15kV phase to phase), may have to take into
consideration the greater exposure this equipment has to lightning than that
of similar substation equipment.
25 April 2011
+++++++++++++++++++++++++++++++++++++++++++++++++
Communication may occur over a wireless link, over the power lines, or via a
wired or fiber-optic telecommunications service such as cable or phone.
However implemented, this communications link needs to be interfaced to the
home network. Generally this interface is implemented by a box called a
gateway, which is located where the communications service enters the
structure. A prevalent myth is that if this gateway is served by a fiber optic or
wireless connection, it is immune from damage by lightning.
Gateway
Ethernet
Communications
service
Service
Entrance
AC Power
Bond wire
Figure 1. A typical home network consisting of electronic equipment connected
to a gateway via an Ethernet link.
To see why damage to the gateway can be independent of the communications
service, consider the common case of a home network that runs ethernet over
cat 5 cable, an example of which is shown in Figure 1. Referring to Figure 1,
note that the National Electric Code [NEC] requires both the gateway and the AC
power neutral to be grounded; and also requires that there be a bond wire
between the grounds. The bond wire may be short if, as is common, the AC
power service and the communications service are located together. But the
bond wire can be long, if the AC power entry and the gateway are located in
different places, as shown in Figure 1. In this latter case, a lightning strike to the
AC power can create a high potential difference between the AC power ground
and the gateway ground, which can result in equipment damage. Here is how it
can happen.
For the purpose of illustration, Figure 2 shows a simplified version of Figure 1.
Here the equipment is referenced on the AC side to ground at point A (via the
branch circuit neutral and ground), but on the signal side, to point B. Direct or
induced current due to a lightning strike to the AC power will seek a ground,
either directly at A, or via the bond wire to the ground at B, or a combination of
these two.
Current flowing into the ground at A will create a ground potential rise [GPR] with
respect to B. For the case of a uniform resistive earth, the ground potential GP
of the earth at a distance r from the point where a lightning strike enters the
ground is given by1
Gateway
Ethernet
Equipment
Communications
service
Service
Entrance
V1
AC Power
Lightning
current
V1
A
Bond wire
V2
B
Figure 2. Simplified home network
GP 
I
2  r
(1)
Where ρ is the resistivity of the earth [generally being a function of distance,
angle, and depth], and I is the lightning current.
The lightning current can usually be calculated or estimated2. However the
resistivity is generally a complicated function of the soil conditions at the site.
The important point is that GP is roughly inversely proportional to the distance
from where the lightning strikes.
S. Sekioka, K. Aiba, S. Okabe, “Lightning Overvoltages on Low Voltage Circuit Caused by Ground
Potential Rise,” www.ipst.org/techpapers/2007/ipst_2007/papers_IPST2007/Session23/197.pdf
2
R. B. Anderson and A. J. Eriksson, “Lightning parameters for engineering applications,” Electra No. 69,
pp. 65-102, March, 1980.
1
As an example of the potential difference that can arise between points A and B
in Figure 2 due to GPR, assume a moderately strong lightning surge of 3000 A3
on the AC power line and a separation of points A and B of 10 m. Whitaker4 has
a map showing the soil resistivity in various parts of the United States. In the
high lightning areas the soil resistivity runs 100 – 1000 ohm-meters. So for this
example, assume 300 ohm-meters. If all 3000 A flows into the ground at A, then
these numbers give
GP = V1 –V2 = 14 kV.
(2)
Suppose instead that all the lightning current flows through the bond wire to the
ground at B. Assume the 3000 A lightning current surge of the previous example
has a 3 μs rise time, and assume the same 10 m separation of points A and B.
The bond wire has an inductance of about 1 µhy/m, so the surge current flowing
from A to B in the bond wire will develop an Ldi/dt potential of 9000 V.
The results of both calculations depend heavily on the assumptions made. But
the point is that with reasonable assumptions, the potential difference (V 1 –V2)
between point A and point B can be on the order of 10,000 V. Referring to
Figure 2, (V1 –V2) appears across the power supply of the gateway [whether it be
internal or external], and could break down the insulation in the power supply. It
could also break down the insulation of the Ethernet transformer in the gateway,
which in turn could cause failure of the equipment. A use case will illustrate how
these failures may have actually happened.
Consequences of a lightning surge: A use case
An actual use case [from a Web report on the result of an actual lightning strike]:
I have fiber-optic connection to the phone network. My network consists of a
router, 4 Desktops, a game console, and two 1gig switches. These devices are
protected by UPS and surge protectors. Last night we had a near hit from
lightning. No power disruption. However, my network and POTS phone (wired)
went down hard. The router had a red light until I rebooted it. After a reboot it
came up with no internet connection. None of my PCs could see each other on
the network. The Optical Network Terminator (ONT) power supply and the
Router were toast. I lost a host of NICs as well as several ports on the gig
3
R. L. Cohen, D. Dorr, J. Funke, C. Jensen, S. F. Waterer, How to Protect Your House and Its Contents
from Lightning. IEEE Guide for Surge Protection of Equipment Connected to AC Power and
Communication Circuits. IEEE Press, 2005.
4
J. C. Whitaker, AC Power Systems H.andbook. CRC Press, Taylor & Francis Group LLC, Boca Raton,
FL, 2007.
switches. The game console seems to be OK and the PC located in the room
with the router is fine. My LAN printer's NIC is toast and will not print.
ONT
Home ethernet
Router
V1
Fiber optic
from service
provider
V1
V2
V1
V1
V1
PS
V2
V2
Service
Entrance
AC Power
V2
Figure 3. Schematic of the use case
Figure 3 illustrates the situation for the gateway and the router. V1 and V2 are the
voltages created by the lightning strike. Any difference of potential (V1 - V2)
exceeding 2500 V would likely break down the insulation in the power supply.
Power follow could then destroy the power supply, which would account for the
observation in the use case.
Now consider the Ethernet connection between the ONT and the router. The
circuit for this connection is shown in Figure 4, where V1 and V2 are the surge
voltages due to the lightning surge. Referring to Figure 3, note that the voltage at
the ground reference for the router is V2, whereas the voltage reference at the
ground reference for the ONT is at V1.
ONT
Router
PHY
A
PHY
B
75
75
V2
1000 nF, 2 kV
1000 nF, 2 kV
V1
V1
V2
Figure 4. Schematic of the ethernet connection shown in Figure 3.
The equivalent circuit for Figure 4 is shown in Figure 5. The two grounds have a
potential difference between them of (V1 – V2). The points A and B are
essentially tied together, so the two equal impedances form a voltage divider,
causing a voltage (V1 – V2)/2 to appear at A and B.
A
(V1 – V2)/2
Z
B
Z
Z=
75
1000 nF, 2 kV
~
V1 – V2
Figure 5. Equivalent circuit for the Ethernet connection shown in Figure 4.
Applying the result shown in Figure 5 to Figure 6, (V1 – V2)/2 appears at points A
and B. If (V1 – V2)/2 is between 2500 V and 5000 V, the breakdown voltage of
the router transformer will be exceeded, flashover will occur, and the PHY circuit
will be damaged. But the ONT will be OK. So again there is a possible
explanation for the observation in the use case.
Router
Transformer insulation
is typically tested
to 5 kV peak (Verizon)
Transformer insulation
Is typically tested to
2500 Vpeak (IEEE 802.3xx)
ONT
(V1 – V2)/2
PHY
A
B
Z
0V
PHY
Z
~
(V1 – V2)
Figure 6. Ethernet equivalent surge circuit redrawn from Figure 4.
Observations
The smart grid depends on communication with the home network for its
operation. The home network is connected to the outside world by a gateway
which the NEC requires to have a ground. Depending on the distance between
this ground and the AC power ground, and how far away the lightning strike is,
the difference in potential at the two grounds can be high enough to cause
equipment damage, independent of the communications service to the gateway.
TIA TR41.7 is preparing a standard to address this case5. Recent studies by
Tokyo Electric Power6 reinforce the observations made here.
How to fix the problem
One way to prevent damage to the equipment is to put surge protection on the
communications ports. Much has been written about the design of surge
protectors. For more information on surge protection and protector design, see
references 7 and 87,8
3.3 Other Line-Side Disturbances
“Resistibility to Surges of Smart Grid Equipment Connected to either DC or 120/240 V Single Phase AC,
and Metallic Communication Line(s)”, In preparation. http://www.tiaonline.org/standards/catalog/.
6
T. Miyazaki, T. Ishii, and S. Okabe, “A Field Study of Lightning Surges Propagating Into Residences”,
IEEE Trans. ON EMC, Vol. 52, NO. 4, Nov. 2010.
7
ATIS-PEG-CD-01, ATIS Protection Engineers Group – CD Compilation (1999-2008), March 2009 (This
Document is available from the Alliance for Telecommunications Industry Solutions (ATIS)
<www.atis.org>)
8
Electrical coordination of primary and secondary surge protection for use in telecommunications circuits,
ANSI/ATIS 0600338-2004, Alliance for Telecommunications Industry Solutions, Washington, D.C., 2005
5
4.0 Surge Protection
A Surge Protective Device (SPD) is a device that protects electrical and electronic
equipment from the damaging effects of voltage transients. This protection is typically
accomplished by shunting surge current to ground, reducing the level of the harmful
voltage transient.
ANSI/UL 1449 is the Standard for Safety for Surge Protective devices. The 3rd Edition of
this standard became effective on September 29, 2009. The term Surge Protective Device
(SPD) is the most current term for devices that provide protection from voltage transients.
In the past, these devices have also been known as Transient Voltage Surge Suppressors
(TVSS) or Secondary Surge Arrestors (SSA). These terms TVSS and SSA became
obsolete with the implementation of ANSI/UL 1449.
SPDs can be connected in series or parallel with electrical and electronic loads that may
be damaged by voltage transients. In addition, SPDs are often connected in parallel to
electrical distribution equipment through out a facility to reduce the level of voltage
transients that can enter an electrical facility from sources that are external to the facility
and to reduce the level of voltage transients that may be generated inside an electrical
facility such as switching transients.
The basic operating principle of an SPD is that under nominal voltage, the SPD does not
draw any current and is electrically invisible to the electrical system. When a voltage
transient appears on the system, the SPD changes state from being very high impedance
and drawing little to no current, to a low impedance state where excess current is shunted
to ground and the SPD clamps the voltage transient to a level that can be managed by the
load.
4.2 Application of Various SPDs for Different Types of Surges
The components used in SPDs vary considerably. Here is a sampling of those
components:





Metal oxide varistor (MOV)
Silicon avalanche diode (SAD)
Gas tubes
LCR filters
TVSS (transient voltage surge suppressor) hybrid
4.3 Assessment Process to Determine Proper Surge Protection for Different
Facilities and Equipment
To provide consumers with a logical and methodical means for selecting electrical
transient disturbance protection, the American National Standards Institute (ANSI) and
Institute of Electrical and Electronics Engineers (IEEE) developed C62.41.1-2002 as an
electrical transient exposure level/surge severity categorization guideline.
By identifying the various levels of potential transient exposure in a given facility and
then specifying products developed in accordance with the ANSI/IEEE categories,
today's purchaser is assured of a cost-effective and reliable power quality environment.
IEEE
Category C
High




Large ampacity service entrance
Service entrance in high lightning area
Service entrance near utility substation
Service entrance on grid with other large
industrial users
IEEE
Category C/B
High-to-Medium


Lower ampacity service entrance
Service entrance remotely located from
utility power factor correction and grid
switching
High-lightning area distribution panels
feeding roof-top loads

IEEE
Category B
Medium





IEEE
Category B/A
Medium-to-Low





IEEE
Category A
Low



Large distribution panels
Non-service entrance distribution
switchboards
Heavy equipment located near
unprotected service entrance
Panels feeding variable speed drives
Non-service entrance motor control
centers utilizing drives, PLCs, soft-start
or electronic starters
Branch panels with heavy sensitive
equipment loads
Branch panels with combination of "dirty"
and sensitive loads
Branch panels without up-stream
protection
Busway feeding sensitive loads
Bus riser feeding multiple floors with
critical or sensitive loads
Branch panels with upstream protection
Branch panels with primarily sensitive
electronic loading
Branch panels deep within a facility
TABLE XX - ANSI/IEEE Exposure Level Categories
4.4 Interactions of Loads with Different SPDs
Different types of SPDs interact differently with the various types of power system
disturbances and their loads. By definition, SPDs incorporate at least one nonlinear
component for the diversion of surge current and/or the dissipation of surge energy.
Examples include metal oxide varisitors (MOVs), silicon avalanche diodes (SADs),
thyristors, and spark gaps.
Benefits of SPDs on Power System Disturbances (C62.48, 6.1): SPDs offer the greatest
benefit to downstream loads when the surge enters the system upstream of the SPD.
When installed correctly, SPDs can protect sensitive loads from the damaging effects of
transient overvoltages.
Partial loss of power with voltage-switching SPDs (C62.48, 6.2): Voltage switching
SPDs, such as spark gap or gas discharge tubes can reflect surges back towards the source
due to the rapid change in voltage from the firing voltage to the arc voltage. This low arc
voltage can also result in a significant reduction of system voltage similar to a power
interruption.
Interaction of SPDs with protective relaying systems (C62.72, 15.1): The momentary
voltage drops caused by voltage-switching SPDs may cause unintended nuisance
operation of protective relaying systems.
Surge current introduction into a facility (C62.48, 6.3): Surge current can be introduced
into a system when the MCOV of downstream MOV based SPD(s) is lower than
upstream the upstream SPD. This is dependent upon the impedance of both devices and
interconnecting wiring. In cases where an SPD is installed between phase or neutral and
ground at protected equipment, significant transient voltage can occur across the ground
conductor. This can create touch hazards if the protected equipment frame is not
referenced to system ground or high frequency impedance of the ground path is
significant.
Voltage oscillations caused by SPDs (C62.48, 6.4): Some studies have shown that
voltage oscillations can occur downstream of an operating SPD due to voltage reflection.
SPD failure mode effects on power systems (C62.48, 6.6): SPDs can fail to an open
circuit, a high-impedance condition, or a low impedance short-circuit condition. These
failures can result in surge voltages, undervoltages, short-circuit failures, follow-on
current, and loss of power to portions or all of the electrical distribution system. SPD
certification to UL 1449 largely minimizes such effects. Open circuit SPD failures have
no effect on the power system other than loss of protection. A high-impedance shortcircuit failure may draw a few amperes (not enough to clear overcurrent protection).
During this period of abnormal leakage current flow, the SPD provides no protection. If
the SPD does not employ proper overcurrent and thermal protection, this condition can
result in a smoke and/or fire hazard damaging surrounding equipment. A low-impedance
short-circuit failure could resemble any other short circuit or fault on a power system. A
voltage dip will occur during overcurrent device operation and a voltage surge can occur
following fault clearing. Spark gap type SPDs can cause substantial follow-on current.
The flow of follow-on current can result in reduced system voltage. A loss of power can
occur when a failed SPD causes upstream overcurrent protection to open, interrupting
power to downstream loads.
Interaction with ground fault protection systems (C62.72, 15.1): When failed, SPD
components connected N-G may introduce objectionable currents to the grounding
system, if not equipped with adequate safety disconnectors. Objectionable currents may
desensitize or disable ground fault protection systems. (Note that N-G is not protected by
external overcurrent protection, suggesting SPDs need adequate internal safety
disconnectors.)
Interaction of SPDs on other protective devices (C62.72, 15.3): Coordinated overcurrent
protection of SPDs may be desirable as there have been instances of uncoordinated
systems causing widespread unexpected power interruption due to an SPD failure.
Effects of SPD peripheral components on power systems (C62.48, 6.7): Some SPDs
contain capacitors for EMI/RFI noise attenuation which may interfere with intentional
signal transmission upon power system lines.
5.0 Existing Standards and Resources
5.1 SPD Related Standards
There are a number of industry standards that apply to surge protective devices (SPDs),
whether they are connected to the electrical system through a plug-in connection or hardwired connection to the facility wiring. Some of the most significant ones include: IEEE
C62.41.1-2002, IEEE C62.45-2002, IEEE C62.48-2005, ANSI/UL 1449-2006 Third
Edition, NFPA 70 (NEC® 2008) Article 285.
IEEE C62.41.1 (2002): Guide on the Surge Environment in Low-Voltage (1000V and less)
AC Power Circuits
This guide provides comprehensive information on surges and the environment in which they
occur. It describes the surge voltage, surge current, and temporary overvoltages (TOV)
environment in low-voltage (up to 1000V root mean square [RMS]) AC power circuits. It is a
reference for the second document, which describes the surge environment.
IEEE C62.41.2 (2002): Recommended Practice on Characterization of Surges in LowVoltage (1000 V and less) AC Power Circuits
This guide presents recommendations for selecting surge waveforms and the amplitudes of surge
voltages and currents used to evaluate equipment immunity and performance of SPDs. Its
recommendations are based on the location within a facility, power line impedance to the surge,
total wire length, proximity, and type of electrical loads, wiring quality, and more. The document
describes typical surge environments and does not specify a performance test. The waveforms
included in the document are meant as standardized waveforms that can be used to test
protective equipment.
IEEE C62.45: Recommended Practice on Surge Testing for Equipment Connected to LowVoltage (1000V and Less) AC Power Circuits
This guide focuses on surge testing procedures using simplified waveform representations
(described in IEEE C62.41.2) to obtain reliable measurements and enhance operator safety. This
guide provides background information that helps determine whether equipment or a circuit can
adequately withstand surges.
ANSI/UL 1449-2006 Third Edition: Standard for Transient Voltage Surge
Suppressors (SPDs)
This standard specifies the waveforms to be used in testing American-manufactured SPDs,
defines terminology related to SPD manufacture and test procedures, establishes proper labeling
for SPD products, and specifies required testing.
Previous versions of UL 1449 identified only two types of SPDs: permanently connected or cordconnected. The third edition of UL 1449 has combined all categories into a formal classification
and identified them as four different types, each of which has consistent testing and application
requirements.




Type 1 - A permanently connected SPD intended for installation between the secondary
of the service transformer and the line side of the service disconnect overcurrent device,
as well as the load side, including watt-hour meter socket enclosures and intended to be
installed without an external overcurrent protective device.
Type 2 - A permanently connected SPD intended for installation on the load side of the
service disconnect overcurrent device, including SPDs located at the branch panel.
Type 3 SPDs - Point of utilization SPDs, installed at a minimum conductor length of 10
meters (30 feet) from the electrical service panel; e.g. cord connected, direct plug-in,
receptacle type SPDs installed at the utilization equipment being protected. The distance
(10 meters) is exclusive of the conductors provided with or used to attach the SPD.
Type 4 SPDs Component SPDs, including discrete components as well as component
assemblies. Must be tested for the installed location, i.e. Type 1, Type 2, and Type 3.
In addition to the new categorization, ANSI/UL 1449-2006 Third Edition specifies that surge
suppression products formerly identified as Transient Voltage Surge Suppressor (TVSS) will be
called Surge Protective Devices (SPDs). It modified the Suppressed Voltage Rating (SVR) test
from 6kV, 500A to 6kV, 3,000A, which represents six times more surge current. And let-through
voltage is now termed the Voltage Protection Rating (VPR).
There's also a Nominal Discharge Current rating up to 20kA. This is part of the Voltage Protection
Rating test and is a measure of the SPD's endurance capability. Manufacturers will choose the
applicable rating and show the data on literature, specifications, and products.
National Electrical Code (NEC) and National Fire Protection Association (NFPA)
Developed by the NFPA, the NEC was established to address electrical safety in the workplace.
While the code is updated every three years, not all states and municipalities have adopted the
same version of the NEC.
Article 285
When UL and the American National Standards Institute (ANSI) adopted the Standard for Safety,
Surge Protective Devices, some changes were required to the NEC. In the 2008 revision of the
NEC, you'll now find the requirements for connecting all SPDs rated 1000V or less to the
electrical distribution system of a facility. The SPD's location ranges from secondary terminals of
the service transformer to end-use equipment.
The standard addresses surge protection to help electricians properly install hardwired SPDs. It
also provides guidelines for electrical inspectors to ensure proper safety and fault current
coordination where SPDs are installed.
Article 285.6
This requires every SPD to be marked with a short circuit current rating (SCCR). This rating must
be equal to or greater than the available fault current present at the point where the SPD is
installed on the system.
Article 285.6 consists of three sections:
 Specifications, introduction, and definitions
 Selection and application criteria
 Test and evaluation procedures
Article 285.23
This identifies the applicable installation locations for a Type 1 SPD. These are allowed to be
installed on the supply side or line side of a service disconnect.
Article 285.24
This identifies the application requirements and installation locations for a Type 2 SPD. These
SPDs are permitted to be installed on the load side of the service disconnect overcurrent device.
National Fire Protection Association (NFPA)—780 Lightning Protection Code
NFPA 780 addresses the protection requirements for ordinary structures, miscellaneous
structures, special occupancies, industrial operating environments, etc. It requires that devices
suitable for protecting the structure be installed on electric and telephone service entrances, and
on radio and television antenna lead-ins.
5.2 Additional Resources
There are many associations that can provide additional technical help that are listed
below. One option is the surge protection website provided by the National Electrical
Manufacturers Association (NEMA) Surge Protection Institute at
www.NEMASURGE.com. Another general guide is published by The National Institute
of Standards and Technology (NIST) entitled “Surges Happen” Special Publication
#960-6. Additional resources include:





Institute of Electronic and Electrical Engineers (IEEE)
National Electrical Manufacturers Association (NEMA)
National Fire Protection Agency (NFPA)
National Institute of Standards and Technology (NIST)
Underwriters Laboratories (UL)
i
National Institute of Science and Technology (NIST) Special Publication 1108 NIST Framework and
Roadmap for Smart Grid Interoperability Standards Release 1.0, January 2010 with Erratum.
Technical paper No 19, Cimatological Services Division , Weather Bureau,
September 1952
ii
R.H. Golde, The Electric Research Association, Leatherhead, Surry, England – “The
Lightning Conductor” , Special Issue – Journal of the Franklin Institute, Philadelphia,
Vol., 283 Number 6, p452.
iii
iv
ibid endnote 2
v
ibid endnote 2 pp 452-453
vi
ibid endnote Error! Bookmark not defined. p 453
IEEE Standard PC62.50™ Standard for Performance Criteria and Test Methods for
Plug-in (Portable) Multiservice (Multiport) Surge-Protective Devices for Equipment
Connected to a 120/240 V Single Phase Power Service and metallic conductive
communication line(s)
vii
Valadimir A. Rokov, Rejeev Thottappilllil and Martin A. Uman, Department of
Electrical Engineering, University of Florida , Gainesville, FL, Journal of Geophysical
Research, Vol. 100 No. D12, pp 25,701-25,710 December 20, 1995
viii