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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007
Electrical Surge-Protection Devices for Industrial
Facilities—A Tutorial Review
Kostas Samaras, Member, IEEE, Chet Sandberg, Fellow, IEEE,
Chris J. Salmas, Member, IEEE, and Andreas Koulaxouzidis
Abstract—Industrial facilities are becoming more and more
dependent on computer control of their processes, and as a consequence, require an increase in cleanliness and reliability of
the electrical power supply system. Electromechanical subsystems are being replaced by electronic logic. Harmonic interference,
welding, variable speed drives, and other “in plant” noise have
reliable mitigation procedures. However, lightning and other
external sourced power disturbances rank high on the list of
“uncontrollable” events that have shut down facilities in recent
years. This paper provides an overview of the causes of power-line
surges and their consequences for an industrial plant. The relevant
international surge-protection standards will be briefly reviewed,
and their differences will be analyzed. Different technologies utilized in the implementation of various commercially available
surge-protection devices will be presented, followed by a comparative analysis. Finally, the latest trends and the most promising
technologies in surge-protection systems as well as their ability
to overcome the problems associated with conventional protection
devices will be overviewed, and experimental data based on field
trials are reported.
Index Terms—Lightning protection, overvoltage protection,
surge protection.
I. I NTRODUCTION
TERM “surge” is used to describe a transient overvoltT HE
age on a power line that has a duration of a few microseconds. A transient overvoltage can exceed the insulation rating
of electrical equipment causing degradation of insulation and
immediate damage to the equipment. Relatively low-amplitude
transient overvoltages applied repetitively on the equipment
will reduce its mean time before failure. The result will be
that equipment will have to be repaired more often, increasing
operating costs.
Every piece of electronic equipment found in an industrial
environment is subjected to power surges generated on the
utility grid either inside or outside of the plant and are transmitted to the equipment via incoming power lines. In order to
protect their equipment from surges, users are installing surgeprotection devices (SPDs) either at the main circuit breaker
for the equipment or the branch circuit breaker depending on
equipment ratings. There are several SPDs available, utilizing
different overvoltage-protection technologies and topologies.
The commercially available SPDs significantly differ in terms
of their surge handling capabilities and the level of protection
they provide. Field experience has revealed serious safety issues
related to the SPD operation, particularly during its end-of-life
situation.
Power surges can cause failure, permanent degradation, or
temporary malfunction of electronic devices and systems. The
development of an effective SPD is of paramount importance
to manufacturers and users of industrial electronic equipment.
Electrical surges have been studied since the 1960s [1]; however, during the last decade, the issue of surge protection for
electronic equipment is receiving more attention. Semiconductor
integrated circuits are much more vulnerable to failure by
overstresses compared to earlier electronic circuits.
Modern semiconductor technology has been widely used
in many industrial applications. Industrial control systems,
variable-speed drives (VSDs), electronic measurement and
process control systems are only a few examples where integrated circuits (electronic switches, power-line carriers, microcontrollers, memory chips, etc.) are now extensively used,
replacing older technologies. These systems provide a better
performance while offering additional features to the user. On
the other hand, these systems can be damaged from power
surges, causing partial or complete disruption of an industrial
process, eventually leading to increased maintenance costs and
loss of revenue due to discontinuation of the process. The
oil and gas industry is a heavy user of sensitive electronic
equipment; thus, the use of surge protection is of paramount
importance.
Almost all manufacturers of industrial-type SPDs use metal–
oxide
varistors (MOVs) in their design. MOVs are composed of
Paper PID-06-14, presented at the 2005 IEEE Petroleum and Chemical
Industry Technical Conference, Denver, CO, September 12–14, and approved a thin disk wafer of material (metal–oxide) that has a known
for publication in the IEEE T RANS ACTIONS ON I NDUSTRY APPLICAT IONS voltage breakdown characteristic. At low voltages, the MOV
by the Petroleum and Chemical Industry Committee of the IEEE Industry conducts very little current (microamperes). As the voltage
Applications Society. Manuscript submitted for review September 15, 2005 and
approaches breakdown, the MOV then begins to conduct current.
released for publication September 22, 2006.
At voltages slightly above the break down, large currents flow,
K.Samaras and A. Koulaxouzidis are with Raycap Corporation, 151 24
Athens, Greece (e-mail: [email protected]).
effectively clamping the output voltage. This clamping feature
C. Sandberg is with Shell E&P, Palo Alto, CA 94303 USA (e-mail:
allows the higher voltage levels to be shunted to ground,
[email protected]).
preventing overvoltages on equipment. Figs. 1 and 2 show the
C. J. Salmas is with the Schlumberger Edmonton Product Center, Edmonton,
voltage waveform before and after an ideal SPD.
AB T6B 2W9, Canada (e-mail: [email protected]).
Color versions of one or more of the figures in this paper are available online
at http:iieeexplore.ieee.org.
Digital Object Identifier 10.1 109/TIA.2006.887994
This paper describes in brief the power-line surges and their
impact on industrial facilities with concentration on gas and
0093-9994/$25.00 © 2007 IEEE
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
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Fig. 1. Voltage waveform before SPD.
Fig. 2. Voltage waveform after an ideal SPD.
oil facilities. It provides an overview of the commercially
available surge-protection technologies designed for industrial
applications, emphasizing their principle of operation followed
by a comparative analysis among different technologies. A
brief description of the relevant international standards is also
provided. Some representative examples of hardware failure
due to surges as well as SPD failures will be described. Finally,
the latest technologies in SPDs and their advantages compared
to conventional protection devices will be overviewed, and the
data collected from field trials are provided.
II. C AUSES OF P OWER- L INE S URGES
Power surges and transient overvoltages are due to the sudden change in the electrical conditions of a circuit and the
release of large amounts of energy stored in the inductance and
capacitance elements of the system. Sources of power surges
can be external or internal to the facility. External sources of
transient overvoltages can be [1] the following:
1) lightning;
2) switching (on/off) of capacitor banks, for power coefficient correction;
3) power-line disconnection and reconnection;
4) transformer switching on/off;
5) electrostatic discharges;
6) power utility load switching;
7) poor quality of power transmission and distribution grids.
Internal surges are caused by the operation of the following
devices:
1)
2)
3)
4)
circuit breakers or fuses;
electric motors, i.e., elevators;
air conditioners;
VSDs generators.Fig. 3. Simplified relationships between voltage,
duration, rate of change, and their effects on equipment.
III. I NTERNATIONAL SPD STANDARDS O VERVIEW
In this section, we briefly describe the standards which are
applicable to the evaluation of SPD performance and safety.
The following aspects are covered in general:
1) location of the SPD installation, classification according
to the estimated surge exposure level at a particular
location, and the surge withstand capability of the device;
2) determination of the voltage and current waveforms to be
used for testing;
3) recommendation of the test equipment and the test
procedures;
4) safety of SPDs.
Every SPD must be tested according to the recommendations
of the following standards.
IEEE C62.41.1-2002—This standard forms a guide on the
surge environment in low-voltage ac power circuits. The surges
considered in this standard do not exceed one half cycle of the
normal mains waveform (fundamental frequency) in duration
[2]. They can be periodic or random events and can appear
in any combination of line, neutral, or grounding conductors.
Their amplitude, durations, or rates of change can be sufficient
to cause equipment damage or operational upset, as presented in
the general diagram shown in Fig. 3. While SPDs acting primarily
on the amplitude of the voltage or current are often applied to
divert the damaging surges, the upsetting surges might require
other remedies, as for example, voltage regulators.
This standard also includes a comprehensive reference list
of documents supporting the fundamental concepts adopted
by the standard. Finally, the standard extensively presents the
limitations and resulting assumptions or simplifications made
to develop a definition of a representative generic environment.
IEEE C62.41.2-2002—This standard describes the concept
of the location categories and determines the test waveforms
and amplitudes of the voltage and current that best approximate
power-line surges at each location category [3].
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007
E QUAT IONS
FOR
TABLE I
S T ANDARD S URGE T EST W AVEFORMS
Fig. 4. Combination wave open-circuit voltage.
According to the location category concept, Location
Category A applies to the parts of the installation at some
distance from the service entrance—the main distribution panel
of an electrical installation of a building. Location Category C
applies to the external part of a structure. Location Category B
extends between Location Categories C and A. Because the
reality of surge propagation is a continuous situation, separating
the categories by sharp conceptual boundaries would be an
arbitrary and debatable process. Instead, the concept of location
categories recognizes the existence of transition bands that
connect the categories by overlapping.
Three representative surge waveforms are described in this
standard. These are the “Combination Wave,” the “100-kHz
Ring Wave,” and the “10-/1000-us Long Wave” which are
briefly described here. The mathematical equations for the
combination wave and the ring wave are given in Table I.
Combination wave—The combination wave is delivered by
a generator that can apply a 1.2-/50-us voltage across an open
circuit and an 8-/20-us current wave into a short circuit. The
exact waveform that is delivered is determined by the generator
and impedance of the SPD under test. A plot of the nominal
open-circuit voltage is shown in Fig. 4, and a plot of the nominal
short-circuit current is shown in Fig. 5. The open-circuit voltage
waveform has a front time equal to 1.2 us and duration equal
to 50 u s. The front time is defined as 1 . 67 x ( t 90 - t 30 ) ,
where t90 and t 30 are the times of the 90% and the 30%
amplitudes on the leading edge of the waveform. The duration
is defined as the time between the virtual origin and the 50%
amplitude point of the tail. The virtual origin is the point where
the straight line between the 30% and 90% points on the leading
edge of the waveform intersects the V = 0 line.
Fig. 5. Combination wave short-circuit current.
Fig. 6. 100-kHz ring wave voltage waveform.
The short-circuit current waveform has a front time of 8 us
and duration of 20 us. The front time in this case is defined as
t
t
whe re
an d t
1 . 25 x ( 90 - 10)
10 are times of the 90% and
t 90
10% points on the leading edge of the waveform.
100-kHz ring wave—This waveform is used to simulate
oscillatory phenomena related to direct lightning strikes. No
short-circuit current waveform is specified for the 100-kHz
ring wave. The peak short-circuit current amplitude is selected
according to the location category of the SPD. The waveform
of the 100-kHz ring wave is plotted in Fig. 6.
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
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ferent technologies and to select the most appropriate product
for a particular application.
Fig. 7. 10-/1000-µs long wave.
10-/1000-us long wave—The long duration of the 10-/
1000-us long wave plotted in Fig. 7 has a front time of 10 us
and duration of 1000 us. The long duration of this waveform
reduces the effect of wiring inductance of the power lines.
IEEE C62.45-2002—This standard focuses on test procedure
for SPDs used in low-voltage ac circuits, by applying the representative surge waveforms described previously. It provides
specifications of the test equipment, its calibration procedure,
and practical guidance on the way the test is performed [4].
The above three standards are widely known as the
“Trilogy” concerning the occurrence, characterization, and
testing of surges in low-voltage ac power circuits.
NEMA LS-1—This international standard provides a uniform
specification for evaluating the performance of SPDs for lowvoltage (less than 1000 Vrms) transient surge environment. The
document presents a comprehensive description of the
specification parameters like the maximum continuous operating voltage, the maximum surge current, and the clamping
voltage. It also provides the methodology of determining these
specification parameters [5].
IEC 61643-1—This part of IEC 61643 is applicable to
low-voltage SPD devices for surge protection against indirect
and direct effects of lightning or other transient overvoltages.
Performance characteristics and standard methods for testing
and ratings are established for these devices. According to the
standard, SPDs are divided into three classes depending on their
performance [6].
1) Class I devices are tested using a current waveform defined by its peak current value and the charge transferred
from the surge generator to the device under test. The
exact shape of the current waveform is not specified;
however, the 10-/350-us waveform is commonly used to
characterize class I products.
2) Class II and Class III devices are tested using the
1.2-/50–8-/20-us combination wave, as it is defined in
IEEE C62.41.2-2002. Devices tested at open-circuit voltage
and short-circuit current lower or equal to 20 and 10
kA, respectively, are characterized as Class III products.
Above these values, SPDs are characterized as Class II
products.
The above standards are widely used by manufacturers to
evaluate the performance of their SPDs. They also serve as
thereference tools to assist the users of the SPDs to compare dif-
Even though all the above standards are valid worldwide,
there is a preference depending on the geographic region. IEEE
standards are mostly used in the North-American region, while
Europe shows a preference to IEC standards. The reason behind
this is that different technologies of SPDs are accepted in these
two main market regions. The use of voltage switching-type
SPDs (also called “crowbar type” devices), like spark gaps
and gas tubes, are allowed to be used as low-voltage SPDs in
Europe. In North America on the other hand, voltage-limitingtype devices (varistors and diodes, also called “clamping-type”
devices) are only allowed to be used at the low-voltage service
entrance of sensitive electronic equipment. The North American
market has excluded “crowbar” devices from protecting sensitive
electronic equipment due to the proven harmful interference that
crowbar devices induce during their conducting stage on the
electronic equipment that they intend to protect.
When an SPD operates during a transient surge, high current
(tens or hundreds of kiloampere) is passing through the device
heading to ground. Even though the internal resistance of the
SPD is generally low during the conduction stage, it is still large
enough to generate large amount of thermal energy inside the
device. Catastrophic failure of SPDs can also occur as the result
of abnormal overvoltage. Abnormal overvoltages occur due to
faults in the power-line network. For example, loss of neutral
line, line-to-neutral short circuit, or primary to secondary fault
in a medium voltage transformer. All conditions described
above can lead to a catastrophic thermal breakdown of an SPD,
turning it into a potential hazard for personnel and equipment
in close proximity of the device. Some examples of catastrophic
SPD failures will be presented later in this paper.
The safety issues related to the use of SPD products are
addressed by Underwriters Laboratories (UL), an independent
safety organization. The standard related to SPD products is
the UL 1449 2nd edition. This standard recommends testing
procedures for both the mechanical and the electrical characteristics of the device. Every SPD is required to comply
with this standard. In 1998, the UL 1449 2nd edition standard
became effective with special provisions to address the “slow
burn” or “thermal runaway” failure mode of SPDs, responsible
for catastrophic events which could compromise the safety of
electrical installations. One of the key tests required by UL
1449 2nd edition is the limited current abnormal overvoltage
test. This test examines the end-of-life condition of the SPD
at relatively low short-circuit currents. During this test, the
rms voltage applied on the SPD terminals is regulated so that
a constant current of 5-A rms is passing through the device.
The test requires that the SPD withstands the heat generated
inside the device for 7 h without emitting fire or smoke [7]. The
majority of the SPDs include thermal disconnect mechanisms
to isolate the SPD from the power supply before the SPD is
damaged.
UL 1449 2nd edition also evaluates the end-of-life condition
of the SPDs when exposed to high short-circuit currents. This
test is known as the short-circuit current abnormal overvoltage
test. During this test, the overvoltage is applied on the SPD
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007
for 7 h. The short-circuit current is not limited; therefore, the
full available short-circuit current can pass through the SPD
device. The test is considered successful if the SPD becomes
disconnected from the ac supply by an overcurrent disconnection
device, preventing a catastrophic failure of the SPD.
In 2005, UL revised this standard after receiving reports
on catastrophic failure of UL listed or recognized SPD products.
The revised version of UL 1449 2nd edition standard becomes
effective in February 2007. This revised standard extends the
current range of the abnormal overvoltage testing to include
not only the low short-circuit current range (up to 5 A) and
the high short-circuit current range (from 25000 up to 200 000
A), but also to include intermediate short-circuit currents (100,
500, and 1000 A). All UL listed or recognized SPDs sold in the
market must meet these revised safety requirements of the new
UL 1449 2nd edition standard.
IV. O VERVIEW OF SPD T ECHNOLOGIES
A. SPD Technologies
There are three basic types of components: the gas discharge
tube (GDT), the silicon avalanche diode (SAD), and the
MOV. These components have significant differences in terms
of the principle of operation, the performance characteristics,
and the ability to handle high transient currents. In this
section, we present the main advantages and disadvantages of
each of the above technologies with particular focus on
their suitability as surge protectors for low-voltage industrial
control systems.
The GDT uses specially designed electrodes fitted inside
a tube filled with one or more gases under pressure. They
are rugged, relatively inexpensive, and have a small shunt
capacitance; therefore, they do not limit the bandwidth of highfrequency circuits as much as other nonlinear components.
However, there are three major drawbacks that prohibit their
use in low-voltage industrial applications involving sensitive
equipment.
1) They can be slow to conduct. The conduction threshold
depends on the rate of change of the transient voltage,
which is usually in the order of several hundreds of volts.
This level of protection is inadequate to prevent damage
in sensitive electronic systems like VSDs.
2) In some situations, they are difficult to turn off after the
transient has ended. This phenomenon is described as the
follow current. The presence of follow current results in
temporary disconnection of the power to the equipment
to be protected for as long as the follow current lasts.
3) The spark, which is developed between the electrodes in
a GDT, is a violent effect. When the GDT switches from
the insulating state to the conduction state, the high value
of dI/dt can cause problems to the equipment close to
the GDT.
SADs are semiconductor devices that can respond rapidly to
a transient voltage surge. They clamp the transient overvoltage
at a relatively low residual voltage. On the other hand, they
suffer from low energy withstand capability. To overcome this
problem, SPD manufacturers combine several SAD components in order to equally share the energy of a surge event within
the rated parameters of the SAD device. However, installations
in locations, where frequent as well as high energy transients
occur, have revealed the inability of SAD-type SPDs to withstand high energy transients without failing, while effectively
protecting the equipment.
MOV-type surge suppressors can withstand high transient
surges, at the same time maintaining sufficiently low clamping
voltages to protect the equipment. For this reason, MOV-based
SPD systems are considered to be the most effective protection
technology for industrial applications.
There are two types of MOV-based SPDs available for
industrial environments. The first one utilizes a combination of parallel MOVs, while the second type uses a single
MOV disk.
The first type uses commercial-type small-diameter MOVs,
which are primarily designed to protect individual electronic
PCBs. Individual commercial-type MOVs do not have the
required energy handling capability to protect an electronic
equipment from intense surges. They typically consist of an
MOV disk with a diameter of up to 20 mm coated with resin
to prevent moisture ingress, which deteriorates the performance
and shortens the life of the product. To overcome this problem,
several MOVs are connected in parallel to increase the surge
current capacity of the SPD. The vast majority of SPD manufacturers are using parallel MOV technology. The differences
between all these products are mainly focused on the diameter
and the number of the MOVs and the casing. They are designed
to be installed in power distribution panels (DIN-rail mounted
devices), or as a stand-alone permanently connected SPD
device.
The application of these devices for protection of industrial
equipment revealed several problems regarding their performance and safety which will be described in Section V.
The second type of surge protection is based on the use of a
single MOV disk capable of adequately handling the energy of
the surge event. This is achieved by utilizing an industrial grade
MOV material and by increasing the disk diameter to 80 mm.
Resin coating has been replaced with an aluminum housing
which also acts as a heat sink to the MOV. This type of SPD
technology will be described in detail in Section VI.
B. Modes of Protection
A typical single phase configuration of the power service
includes one phase wire and one neutral wire, which sometimes
is grounded at the service entrance of an installation. There are
three modes of protection.
1) Line-to-neutral (L-N)—An SPD module installed between
the line and the neutral protects the equipment from surges
originated mainly from disturbances generated on the
distribution grid. It can be caused by capacitor bank
switching, operation of transfer switches, or by the switching
on/off of nearby equipment (air conditioners, elevators,
motors, generators, etc.).
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
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Fig. 9. Exploded multiple-MOV-based SPD module.
Fig. 8. Multiple-MOV-based SPD.
2) Neutral-to-ground (N-G)—It protects from surges developed between the neutral conductor and the ground.
3) Line-to-ground (L-G)—It protects from surges developed
between the line and the ground.
It is essential that an SPD protects from all the above modes.
In a typical three phase WYE configuration system, which
includes three line wires and one neutral wire, the SPD must
provide seven modes of protection: three for L-N, one for N-G,
and three for L-G.
V. E XISTING P ROBLEMS W ITH SPD D EVICES
A. Poor Design and Assumptions in Design
It is a common practice in the surge-protection industry to
install protection devices in parallel to achieve a higher rating
than just one device. A typical example of a conventional SPD
using parallel MOV technology is shown in Fig. 8. This practice
applies whatever the technology is in use. It is also commonly
assumed that the surge performance of a number of devices
is a simple multiplication of the performance of an individual
device. This is not the case both electrically and mechanically
[1]. Even semiconductor devices fabricated on the same slice
vary in performance due to the minor defects and/or impurities
in the lattice of the semiconductor material.
Differences in mechanical design can lead to one individual
MOV always having to handle more current than its neighbors.
As a rule, an electrical transient takes the shortest most conductive path, and when it goes around the corners, it exerts
forces on the current carrying conductors (Lorentz forces). The
net result is that for large transient currents, such as those
produced by lightning, SPDs often explode as a result of these
forces and energies dissipated in one device rather than the
many. An example is shown in Fig. 9. This picture was taken
from an actual installation. This device shows a catastrophic
failure even though it has been tested to comply with UL
1449 2nd edition. Another example of catastrophic failure is
given in Fig. 10.
Several SPD designs exist that attempt to achieve equal path
lengths for the devices placed in parallel. These designs do lead
to an increased resistance to transient events but tend to suffer
from longer events as the characteristics of the devices are
affected by temperature and by no means do all the devices in
Fig. 10. SPD internal fire.
one of these designs have the same ability to dissipate thermal
energy equally.
B. Fusing
Thermal fuses are known to have reliability issues and age
over a period of a few years usually accentuated by thermal
cycling. Conventional and thermal fuses also suffer aging from
mechanical shock. Mechanical shock can be delivered during
operation of the SPD by the transients. Martzloff [8] showed
that fuses are progressively weakened by transient currents. In
other words, the reliability of the protector is reduced as a result
of including a device that is present to protect the protector or
present to protect you from the protector. Obviously, when a
fuse opens, the protector is rendered totally ineffective, leaving
the equipment unprotected to subsequent surges.
C. Emission of Smoke and Fire
The photograph in Fig. 11 shows an SPD that has suffered
a varistor fire. The SPD modules are protected by 30-A fast
blow fuses. These fuses were intact and still providing power
to the unit. Investigation showed that the cause of the fire
was thermal runaway of the surge protector modules inside
the SPD. No raised system voltages were detected, and it is
believed that the device was wrongly sized for its exposure to
transients in a high lightning area and simply wore out from
overstress. Consider that a 30-A fuse can carry 20 A for a
considerable time, certainly greater than 1000 h, and during this
time on a 120-V system, 2400 W could be dissipated inside the
individual SPD.
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IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007
Fig. 12. Protection of VSD equipment using conventional SPD technologies.
VII. A PPLICATION OF SPD S IN VSD S FOR U SE W ITH
E LECTRICAL S UBMERSIBLE P UMPS (ESP S )
Fig. 11. SPD internal fire.
VI. INTEGRATION OF SPDS
There are two methodologies that can be employed to protect
industrial equipment. One method is to connect the SPD external
to a power distribution panel. This method of installation does
not provide a sufficient level of protection to the equipment at
high surge currents, as will be explained in the next section. The
second method is to integrate the SPD devices within
panelboards, switchboards, switchgear, motor control centers,
VSDs, or other electrical equipment. Integration of SPD
devices ensures the lowest clamping voltage, thus the highest
level of protection to the equipment.
Important items to consider in the selection of SPDs for an
integrated application are the following.
1) The location of the SPD should achieve the best electrical
connection with respect to the phase, neutral, and ground
buses in the electrical distribution equipment to effectively suppress the transient overvoltages to a voltage
level which is lower than the immunity level of the
equipment. The use of long lead wires as well as wire
bending should ideally be eliminated.
2) An SPD must be compatible with the available shortcircuit current of the power distribution system and have
the appropriate ratings and listings.
The system design engineers must ensure that the SPDs have
been listed as UL recognized components and have successfully
passed all the safety tests described in the UL 1449 2nd edition
standard, including the recent changes effective February 2007,
before approving the SPDs for integration. In particular, it is
essential that when SPDs are to be integrated into an industrial
system, the SPD must sustain the available fault current of the
power system for a period of at least three complete cycles of
the sinusoidal current waveform without a catastrophic failure.
This test is known as three-cycle testing. This test ensures that
the SPD will withstand a fault condition for sufficiently long
time to allow the upstream circuit breaker to disconnect and
clear the fault. Failure to comply with this test may result in
a catastrophic failure of the SPD before the operation of the
overcurrent protection device and constitute a safety hazard
for the personnel and the adjacent equipment. A typical available short-circuit current value for VSD industrial applications
is 65-kA rms symmetrical.
A. Problems With Conventional SPD Technologies
Electronic VSDs are extensively utilized by the oil industry
for the speed control of electric motors used in several steps of
the oil extraction process. VSDs are connected to the utility grid
and powered by a three-phase three-wire low-voltage system.
They include semiconductor components which are sensitive to
surges coming through the power wires. Many years of field
experience has shown that power surge is the most frequent
reason for VSD failures whether as a result of a serious transient
event or a multiple of events over time which compromises
the insulating levels of components. This results in a loss of
production, which results in increased maintenance costs and a
significant revenue loss.
To overcome this problem, VSD users have tried to protect
their equipment using conventional SPDs based on fused multiple
MOV technology. Fig. 12 shows the interconnection diagram of a
conventional SPD device installed in VSDs used to control
ESPs. The SPD, which is located outside the VSD cabinet, is
connected to the power wires via a fused three-wire power
cable.
Field application of this protection scheme has shown the
following problems.
1) Conventional SPDs are using fuses to disconnect the
device and protect it from fire or explosion. This unavoidably leaves the VSD unprotected to a subsequent surge
when fuses are blown.
2) Repetitive high energy surges may result in a catastrophic
failure of the SPD. An example is shown in Fig. 13.
3) The conventional SPD requires the use of leads and fusing
to connect in parallel to the line side of the breaker
and cannot be mounted inside the equipment due to
the catastrophic failure condition of the device in case
of a high energy event. The length of the leads adds
impedance to the circuit and increases the residual voltage.
The residual voltage is increased by L × (dI/dt) + I ×
R, where L is the self-inductance of the leads, dI/dt is
the rate of change of the surge current, and R is the
resistance of the lead wire. This results in residual voltages
that are higher than desired, potentially leading to
equipment damage. Assuming that the inductance of the
wire is 0.255 µH/m, its resistivity is 1 mΩ/m, then, for a
total conductor leads length of 1 m and for surge current
10 kA (8/20 waveform), the residual voltage is increased
by approximately 115 V.
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
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Fig. 15. Single-MOV protection modules installed “in-line” inside a 815-kVA
sine wave drive.
Fig. 13. Failure of conventional SPD.
Fig. 16. Protection of VSD equipment using single-MOV protection modules
installed “in-line.”
Fig. 14. Single-MOV-based SPD module.
B. Solution: Single MOV Technology
As part of the quality health safety and environment policies,
the upmost importance is placed on ensuring human health,
operational safety, and protection of equipment, hence the
push to evaluate an alternative SPD technology for the
protection of VSD from power surges. This technology is based
on the use of a single MOV disk capable of adequately
handling the energy of the surge event, while keeping at the
same time the residual voltage at a level lower than the
overvoltage immunity level of the equipment. This
technology has been widely used for the protection of critical
telecommunication and power utility equipment worldwide,
particularly in locations highly exposed to lightning surges.
This technology utilizes one industrial grade MOV disk
which is encapsulated into an aluminum casing which seals
the MOV from moisture and acts as a heat sink. The aluminum
electrodes contact the entire surface of the MOV providing an
even distribution of the surge current over the total area of the
MOV. This design, contrary to the majority of other SPD
technologies, does not incorporate a thermal disconnect
mechanism, and it is proven to comply the UL 1449 2nd
edition. The single MOV-based SPD is illustrated in Fig.
14.
Due to its robust construction and the absence of flammable
materials in its housing, this design enabled the installation of
the SPD inside the VSD cabinet, as shown in Fig. 15. Furthermore, the absence of fuse enables the “in-line” installation
of the SPDs. They are connected directly on the load side
of the breaker, eliminating the need for long lead wires. A
general diagram of the “in-line” connection is illustrated in
Fig. 16.
A key advantage of this innovative method of protection is
the ability to protect the equipment under any surge condition.
In the rare event of extremely high energy surges, the SPD
fails in a short-circuit mode, thus enabling the breaker to trip
and disconnect power from the equipment, thus protecting the
equipment from subsequent surges.
Laboratory tests have proven the ability of the single MOVbased SPD to handle extremely large amounts of thermal energy. The amount of energy that an SPD can handle is described
by its I2t parameter, which is measured to be greater than
500 MA2s for the device illustrated in Fig. 14.
VIII. E XPERIMENTAL RESULTS
In this paragraph, we report the results from experimental
testing done both in actual field installations as well as in the
laboratory environment. These results demonstrate the fundamental differences in performance between devices based on
different technologies.
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
Fig. 17. Power-line transient overvoltages measured in a 24-h period before
installing single-MOV-based SPD (Site A).
9
Fig. 18. Power-line surges measured in a 24-h period after installing the
single-MOV-based SPDs (Site A).
A. Results From a Field Trial
For the purposes of this paper and in order to evaluate the
performance of the single MOV-based module versus conventional surge-protection modules, two installation sites of the
same type of VSD, with rich history of severe power surge
problems, were selected for the trial installation.
Site A: Protection of the VSD using the single-MOV-based
SPD device.
Site B: Protection of the VSD using a conventional parallel
MOV-based-SPD device.
The purpose of this field experiment was to record the level
and the amount of surges on the VSD (over a period of 24 h)
without protection and also after the installation of the protection devices to examine the efficiency of the protection devices
in alleviating those surges. Since the observation period was
rather limited, we have carefully selected two sites in an area
of the plant where several failures had been recorded in the
past. This selection maximizes the likelihood of recording a
significant amount of surges. Most of those surges are due
to switching and operations inside the plant and not due to
lightning. In both sites, the electrical configuration was identical, a three-wire 240-/415-V three-phase system. In the case
of Site A, three single-MOV modules were installed between
each of the three power lines and the ground/protected earth.
Fig. 15 illustrates the type of configuration used to connect
the SPDs on the load side of the VSD breaker. In Site B,
the parallel MOV-based TVSS system was installed externally
to the drive cabinet due to space limitations inside the drive.
A power-line monitoring device (Powertronics, PQR-2020)
was installed prior to the installation of the SPD modules.
The device was set to record every transient overvoltage with
a peak amplitude of at least 50 V higher than the nominal
line to ground voltage of 240 Vrms and a duration of at
least 05 /is. Therefore, the device was essentially recording
surges of amplitude higher than 290 V. The time and peak
amplitude of the overvoltages, recorded for a period of 24 h,
Fig. 19. Power-line transient overvoltages measured in a 24-h period before
installing conventional SPD (Site B).
are shown in Fig. 17, for Site A—prior to the installation
of the SPD. This diagram shows surges recorded on all
three phases of the system. Only the overvoltage level above
240 V is shown, i.e., for a point of this diagram with a
value of 100 V, the actual overvoltage corresponding to it
was 340 V. A significant number of surges have been
recorded having peak amplitude voltages up to 652 V. The
same monitoring setup was used after the installation of the
three single MOV SPDs, and measurements were recorded
for a period of 24 h again. The results are shown in Fig.
18, and as it is clear, the situation was drastically improved.
In Site B, we followed exactly the same procedure as above,
for Site A. Measurements were recorded before and after
the installation of the parallel MOV SPDs. The distribution
of the surges’ magnitude as a function of time, before and
after the installation of the SPD, is given in Figs. 19 and 20,
respectively.
Examining the results plotted in Figs. 17–20, it becomes
apparent that the protection of VSD from power-line surges is
absolutely necessary. The installation of the single MOV-based
SPD has drastically reduced the frequency that surges appear.
Furthermore, the peak amplitude of the surges has been reduced
to a maximum of 215 V, thus ensuring a sufficient protection of
SAMARAS et al.: ELECTRICAL SURGE-PROTECTION DEVICES FOR INDUSTRIAL FACILITIES—TUTORIAL REVIEW
Fig. 20. Power-line surges measured in a 24-h period after installing a
conventional parallel-MOV-based TVSS (Site B).
TABLE II
S URGE STATISTICS IN 24-h P ERIODS
the VSD. Table II summarizes the results obtained from sites A
and B. The use of the single MOV-based SPD reduced the total
number of surges encountered by the equipment in the 24-h test
period by 84%.
The parallel MOV-based device on the other hand failed to
provide a sufficient protection to the equipment. The average
peak amplitude of the surges was reduced only by 18.5%,
allowing the peak amplitude of eight surges to exceed 500 V
in the 24-h test period.
B. Laboratory Tests
In addition to the results from the field installation described
in the previous paragraph, we have conducted a series of
tests in a laboratory environment, using different surge waveforms. In those tests, we try to simulate the effects of aging
on SPDs. In several field installations, we have been
encountering situations where the protected equipment was
failing without failure of the SPDs. With the tests described below, we prove that certain devices demonstrate
a nonconsistent level of protection over time, i.e., when a
parallel-MOV device is exposed to consecutive surges, its
Fig. 21. Residual voltage and surge current through a parallel-MOV device
during successive strikes.
10
performance characteristics do not remain constant and deteriorate over time.
1) Residual Voltage: In the first test, a parallel-MOV device
was exposed to a series of surge events while monitoring
the residual voltage and the actual current through the device after every surge hit. Ten surges were applied to the
device, each of them having an amplitude of approximately
9 kA. The waveform used was the typical 8/20 waveform
as described in IEEE C62.41. Between successive surges,
we allowed for 1-min delay in order to allow the device
to cool down. The residual voltage and the current through
the device are plotted on the same graph in Fig. 21 for all
ten hits.
As shown in the above diagram, we have observed a significant change in the values of the residual voltage and the
let-through current as a function of time. The initial residual
voltage recorded during the first hit was 1484 V, while during
the tenth hit, the residual voltage was increased to 3335 V.
This represents a variation of 125%, which is translated into
significantly reduced protection level offered to the equipment
which may have been connected downstream from the SPD. At
the same time, the current through the device was reduced to
approximately 8000 A—starting from 9000 A during the first
surge event.
In a similar test setup, we have exposed a single MOV
device to a series of 2000 surges of 8/20 waveform with
amplitude of approximately 20 kA. We allowed for a 1-min
delay between successive surges. We measured the let-through
voltage during the first surge, and it was found 810 V. We also
measured the let-through voltage during the last surge, and it
was found 822 V, showing a variation in its performance of
less than 1.5%.
2) Long-Duration Surges: As mentioned before, not all
surges happening in the field are following the typical
8/20 model which accurately describes short-term highintensity surge events mainly due to lightning. In reality and
in most industrial environments (especially in geographic areas
where lightning is not a major concern), surges are mainly
due to load switching, capacitor switching, etc. These surges
tend to have significantly lower intensity but at the same time
significantly larger duration. IEEE C62. 11 describes a waveform which is regarded as describing such events. This is a
11
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 43, NO.1, JANUARY/FEBRUARY 2007
voltage of the multiple MOV-based products.
IX. C OMPARISON OF M ULTIPLE MOV AND S INGLE MOV
SPD TECHNOLOGIES
In Section V of this paper, the drawbacks of conventional
multiple MOV-based low-voltage SPD devices were presented.
The idea of an SPD design based on the use of a single
MOV was developed a few years ago in order to overcome
those problems. The main advantages of this design compared to the multiple MOV-based devices are summarized
below.
Fig. 22. Measured residual voltages of single-MOV and multiple-MOV SPDs.
rectangular (square) waveform of duration 2 ms and magnitude
in the order of 500–1000 A. The occurrence of surges like
those in industrial environments is associated with what is known
as failure due to the accumulated events. The intensity of those
surges is not that high to cause an immediate failure of the
SPD as may have happened during a lightning strike, but they
do carry significant amounts of energy (due to their longer
duration) which cause degradation in the material of the SPD.
The result is that after a number of exposures to such events,
devices fail.
We have exposed a parallel MOV device to a number of
square waveform surges, and we have recorded its performance.
During the first surge at 913 A, we did not observe any
visible damage to the device. During the second 2-ms surge
at 931 A, the device emitted heavy smoke, but it did not
fail. During the third surge, the device got on fire and some
of the MOVs exploded/disintegrated—this is regarded as a
failure. The residual voltage measured during the first surge
was 700 V. During the second surge, the residual voltage was
1890 V, and during the third surge, it was measured at 3360 V,
a 380% degradation.
In a similar test setup, we have exposed a single MOV
device to a series of 250 square waveform surges of amplitude
1030 A. We allowed for a 1-min delay between successive
surges. We measured the let-through voltage during the first
surge, and it was found 335 V. We also measured the letthrough voltage during the last surge, and it was found 339 V.
No visible damage or smoke emission or fire was observed
during the test.
3) Slope Resistance: The comparison of slope resistance
for a single MOV and a parallel MOV device is shown in
Fig. 20. To obtain these measurements, the standard 8/20 surge
waveforms were used at the levels indicated on the graph.
In particular, the diagram shown in Fig. 22 is a plot of the
measured residual voltage as a function of the surge current
passing through the device, for single MOV and parallel MOV
SPDs. The graph shows that single MOV devices exhibit low
slope resistance which results in lower residual voltages at
intermediate and high surge currents compared to the residual
1) No need for thermal disconnect mechanism to protect
the SPD. This is due to the material and design of its
housing. The absence of a disconnect mechanism ensures
that the equipment will never be left unprotected during
a surge event. Furthermore, disconnect mechanisms are
responsible for increased residual voltage across the SPD
terminals.
2) The use of just one industrial grade epoxy free MOV
eliminates the problems related to multiple MOV designs
which were discussed in detail in Section V.
3) The metallic casing of the design as well as the absence of
flammable materials allows the device to dissipate large
amount of thermal energy, resulting in an increased surge
current capability.
X. CONCLUSION
In this paper, we have provided a tutorial overview of the
critical issue of overvoltage protection for industrial electronic
applications with primary focus on the Oil/Gas/Mining industries. We have presented the available technologies utilized
for the implementation of surge-protection systems, and we
have outlined their basic advantages and disadvantages. A detailed description and references to the international standards
are provided. Finally, we have described a new technological
concept currently under extended trials worldwide as well as
results from its application. Field trial results as well as measurements in lab environment are provided. Strong indications
exist to prove that this new technology can provide superior
performance and complete protection to critical industrial plants.
REFERENCES
[1] R. B. Standler, Protection of Electronic Circuits From Overvoltages.
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[3]IEEE Recommended Practice on Characterization of Surges in LowVoltage (1000 or Less) AC Power Circuits, IEEE C62.41.2-2002.
[4]IEEE Recommended Practice on Surge Testing for Equipment Connected
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