Transient Suppression Devices and Principles By Littelfuse

Transient Suppression Devices and Principles By Littelfuse
Transient Suppression Devices and Principles
Application Note
January 1998
Transient Suppression Devices
Diverting a transient can be accomplished with a
voltage-clamping type device or with a “crowbar” type
device. The designs of these two types, as well as their
operation and application, are different enough to warrant a
brief discussion of each in general terms. A more detailed
description will follow later in this section.
A voltage-clamping device is a component having a variable
impedance depending on the current flowing through the
device or on the voltage across its terminal. These devices
exhibit a nonlinear impedance characteristic that is, Ohm’s
law is applicable but the equation has a variable R. The
variation of the impedance is monotonic; in other words, it
does not contain discontinuities in contrast to the crowbar
device, which exhibits a turn-on action. The volt-ampere
characteristic of these clamping devices is somewhat
time-dependent, but they do not involve a time delay as do
the sparkover of a gap or the triggering of a thyristor.
With a voltage-clamping device, the circuit is essentially
unaffected by the presence of the device before and after the
transient for any steady-state voltage below the clamping
level. The voltage clamping action results from the increased
current drawn through the device as the voltage tends to
rise. If this current increase is greater than the voltage rise,
the impedance of the device is nonlinear (Figure 1). The
apparent “clamping” of the voltage results from the
increased voltage drop (IR) in the source impedance due to
the increased current. It should be clearly understood that
the device depends on the source impedance to produce the
clamping. One is seeing a voltage divider action at work,
where the ratio of the divider is not constant but changes.
However, if the source impedance is very low, then the ratio
is low. The suppressor cannot be effective with zero source
impedance (Figure 2) and works best when the voltage
divider action can be implemented.
10-102
NONLINEAR Z ( = 5)
0Ω
PE
DA
N
C
E
Z = 50
100
LI
N
EA
R
IM
Z = 10Ω
=
1Ω
10
Z
Attenuating a transient, that is, keeping it from propagating
away from its source or keeping it from impinging on a
sensitive load is accomplished with filters inserted in series
within a circuit. The filter, generally of the low-pass type,
attenuates the transient (high frequency) and allows the signal
or power flow (low-frequency) to continue undisturbed.
Z = 1Ω
1000
VOLTAGE (V)
There are two major categories of transient suppressors: a)
those that attenuate transients, thus preventing their
propagation into the sensitive circuit; and b) those that divert
transients away from sensitive loads and so limit the residual
voltages.
AN9768
1
0.01
0.1
1
10
100
1000
CURRENT (A)
V
LINEAR IMPEDANCE: I =
R
NONLINEAR IMPEDANCE (POWER LAW): I = KV
FIGURE 1. VOLTAGE/CURRENT CHARACTERISTIC FOR A
LINEAR 1Ω RESISTOR AND NONLINEAR
ZS
ZV
VOC
ZV
V ZV = ---------------------ZV + ZS
V OC
FIGURE 2A. VOLTAGE CLAMPING DEVICE
ZS
Z1
SCR
VZV
VOC
R1
FIGURE 2B. CROWBAR DEVICE
FIGURE 2. DIVISION OF VOLTAGE WITH VARIABLE
IMPEDANCE SUPPRESSOR
1-800-999-9445 or 1-847-824-1188 | Copyright
© Littelfuse, Inc. 1998
Application Note 9768
Crowbar-type devices involve a switching action, either the
breakdown of a gas between electrodes or the turn-on of a
thyristor, for example. After switching on, they offer a very
low impedance path which diverts the transient away from
the parallel-connected load.
These types of crowbar devices can have two limitations.
One is delay time, which could leave the load unprotected
during the initial transient rise. The second is that a power
current from the voltage source will follow the surge
discharge (called “follow-current” or “power-follow”). In AC
circuits, this power-follow current may not be cleared at a
natural current zero unless the device is designed to do so;
in DC circuits the clearing is even more uncertain. In some
cases, additional means must be provided to “open” the
crowbar.
Filters
The frequency components of a transient are several orders
of magnitude above the power frequency of an AC circuit
and, of course, a DC circuit. Therefore, an obvious solution is
to install a low-pass filter between the source of transients
and the sensitive load.
The simplest form of filter is a capacitor placed across the
line. The impedance of the capacitor forms a voltage divider
with the source impedance, resulting in attenuation of the
transient at high frequencies. This simple approach may
have undesirable side effects, such as a) unwanted
resonances with inductive components located elsewhere in
the circuit leading to high peak voltages; b) high inrush
currents during switching, or, c) excessive reactive load on
the power system voltage. These undesirable effects can be
reduced by adding a series resistor hence, the very popular
use of RC snubbers and suppression networks. However,
the price of the added resistance is less effective clamping.
Beyond the simple RC network, conventional filters
comprising inductances and capacitors are widely used for
interference protection. As a bonus, they also offer an
effective transient protection, provided that the filter's frontend components can withstand the high voltage associated
with the transient.
There is a fundamental limitation in the use of capacitors
and filters for transient protection when the source of
transients in unknown. The capacitor response is indeed
nonlinear with frequency, but it is still a linear function
of current.
To design a protection scheme against random transients,
it is often necessary to make an assumption about the
characteristics of the impinging transient. If an error in the
source impedance or in the open-circuit voltage is made in
that assumption, the consequences for a linear suppressor
and a nonlinear suppressor are dramatically different as
demonstrated by the following comparison.
10-103
A Simplified Comparison Between
Protection with Linear and Nonlinear
Suppressor Devices
Assume an open-circuit voltage of 3000V (see Figure 2):
1. If the source impedance is ZS = 50Ω
With a suppressor impedance of ZV = 8Ω
The expected current is:
3000
1 = ---------------- = 51.7 A and V R = 8 × 51.7 = 414V
50 + 8
The maximum voltage appearing across the terminals of a
typical nonlinear V130LA20A varistor at 51.7A is 330V.
Note that:
Z S × I = 50 × 51.7 = 2586V
Z V × I = 8 × 51.7 = 414V
= 3000V
2. If the source impedance is only 5Ω (a 10:1 error in the assumption), the voltage across the same linear 8Ω suppressor is:
8
V R = 3000 ------------- = 1850V
5+8
However, the nonlinear varistor has a much lower
impedance; again, by iteration from the characteristic curve,
try 400V at 500A, which is correct for the V130LA20A; to
prove the correctness of our “educated guess” we
calculate I,
3000-400V
I=
5
= 520A
ZS x I = 5 x 520 = 2600V
400V
VC =
= 3000V
which justifies the “educated guess” of 500A in the circuit.
Summary
TABLE 1. 3000V “OPEN-CIRCUIT” TRANSIENT VOLTAGE
ASSUMED SOURCE IMPEDANCE
50Ω
PROTECTIVE DEVICE
5Ω
PROTECTIVE LEVEL ACHIEVED
Linear 8Ω
414V
1850V
Nonlinear Varistor
330V
400V
Similar calculations can be made, with similar conclusions,
for an assumed error in open-circuit voltage at a fixed source
impedance. In that case, the linear device is even more
sensitive to an error in the assumption. The calculations are
left for the interested reader to work out.
The example calculated in the simplified comparison
between protection with linear and nonlinear suppression
devices shows that a source impedance change from an
assumed 50Ω to 5Ω can produce a change of about 414V to
1850V for the protective voltage of a typical linear
suppressor. With a typical nonlinear suppressor, the
Application Note 9768
corresponding change is only 330V to 400V. In other words,
a variation of only 21% in the protective level achieved with a
nonlinear suppressor occurs for a 10 to 1 error in the
assumption made on the transient parameters, in contrast to
a 447% variation in the protective level with a linear
suppressor for the same error in assumption. Nonlinear
voltage-clamping devices give the lowest clamping voltage,
resulting in the best protection against transients.
Crowbar Devices
This category of suppressors, primarily gas tubes or carbonblock protectors, is widely used in the communication field
where power-follow current is less of a problem than in
power circuits. Another form of these suppressors is the
hybrid circuit which uses solid-state or MOV devices.
In effect, a crowbar device short-circuits a high voltage to
ground. This short will continue until the current is brought
to a low level. Because the voltage (arc or forward-drop)
during the discharge is held very low, substantial currents
can be carried by the suppressor without dissipating a
considerable amount of energy within it. This capability is a
major advantage.
Volt-Time Response - When the voltage rises across a spark
gap, no significant conduction can take place until transition
to the arc mode has occurred by avalanche breakdown of
the gas between the electrodes.
Power-Follow - The second characteristic is that a power
current from the steady-state voltage source will follow the
surge discharge (called “follow-current” or “power-follow”).
Voltage-Clamping Devices
To perform the voltage limiting function, voltage-clamping
devices at the beginning of the section depend on their
nonlinear impedance in conjunction with the transient source
impedance. Three types of devices have been used: reverse
selenium rectifiers, avalanche (Zener) diodes and varistors
made of different materials, i.e., silicon carbide, zinc oxide,
etc. [1].
Selenium Cells - Selenium transient suppressors apply
the technology of selenium rectifiers in conjunction with a
special process allowing reverse breakdown current at highenergy levels without damage to the polycrystalline
structure. These cells are built by developing the rectifier
elements on the surface of a metal plate substrate which
gives them good thermal mass and energy dissipation
performance. Some of these have self-healing
characteristics which allows the device to survive energy
discharges in excess of the rated values for a limited number
of operations characteristics that are useful, if not “legal” in
the unsure world of voltage transients.
The selenium cells, however, do not have the clamping
ability of the more modern metal-oxide varistors or
avalanche diodes. Consequently, their field of application
has been considerably diminished.
10-104
Zener Diodes - Silicon rectifier technology, designed for
transient suppression, has improved the performance of
regulator-type Zener diodes. The major advantage of these
diodes is their very effective clamping, which comes closest
to an ideal constant voltage clamp.
Since the diode maintains the avalanche voltage across a
thin junction area during surge discharge, substantial heat is
generated in a small volume. The major limitation of this type
of device is its energy dissipation capability.
Silicon Carbide Varistors - Until the introduction of metaloxide varistors, the most common type of “varistor” was
made from specially processed silicon carbide. This material
was very successfully applied in high-power, high-voltage
surge arresters. However, the relatively low a values of this
material produce one of two results. Either the protective
level is too high for a device capable of withstanding line
voltage or, for a device producing an acceptable protective
level, excessive standby current would be drawn at normal
voltage if directly connected across the line. Therefore, a
series gap is required to block the normal voltage.
In lower voltage electronic circuits, silicon carbide varistors
have not been widely used because of the need for using a
series gap, which increases the total cost and reproduces
some of the characteristics of gaps described earlier.
However, this varistor has been used as a current-limiting
resistor to assist some gaps in clearing power-follow current.
Metal-Oxide Varistors - A varistor functions as a nonlinear
variable impedance. The relationship between the current in
the device, I, and the voltage across the terminals, V is
typically described by a power law: I = kV α. While more
accurate and more complete equations can be derived to
reflect the physics of the device, [2, 3] this definition will
suffice here. A more detailed discussion will be found in
Application Note AN9767, “Littelfuse Varistors - Basic
Properties, Terminology and Theory”.
The term α (alpha) in the equation represents the degree of
nonlinearity of the conduction. A linear resistance has an
α = 1. The higher the value of a, the better the clamp, which
explains why α is sometimes used as a figure of merit. Quite
naturally, varistor manufacturers are constantly striving for
higher alphas.
This family of transient voltage suppressors are made of
sintered metal oxides, primarily zinc oxide with suitable
additives. These varistors have α values considerably
greater than those of silicon carbide varistors, typically in the
range of an effective value of 15 to 30 measured over
several decades of surge current.
The high exponent values (α) of the metal-oxide varistors
have opened completely new fields of applications by
providing a sufficiently low protective level and a low standby
current. The opportunities for applications extend from lowpower electronics to the largest utility-type surge arresters.
Application Note 9768
Because of diversity of characteristics and nonstandardized
manufacturer specifications, transient suppressors are not
easy to compare. A graph (Figure 3) shows the relative voltampere characteristics of the four common devices that are
used in 120V AC circuits. A curve for a simple ohmic resistor
is included for comparison. It can be seen that as the alpha
factor increases, the curve's voltage-current slope becomes
less steep and approaches an almost constant voltage. High
alphas are desirable for clamping applications that require
operation over a wide range of currents.
It also is necessary to know the device energy-absorption
and peak-current capabilities when comparisons are made.
Table 2 includes other important parameters of commonly
used suppressors.
Standby Power - The power consumed by the suppressor
unit at normal line voltage is an important selection criterion.
Peak standby current is one factor that determines the
standby power of a suppressor. The standby power
dissipation depends also on the alpha characteristic of the
device.
50
ER
ST
LU
C
OR
OR
IST
DE
VAR
O
E
I
S
R D TELFU
NE
LIT
ZE
20
α = 35
10
5
NIUM
1" SELE
2
1
SILICON CARBIDE
0.5
α = 25
α=8
α=4
0.2
0.1
96
98
100
102
104
106
108
110
PERCENT OF RATED VOLTAGE
FIGURE 4. CHANGES IN STANDBY POWER ARE
CONSIDERABLY GREATER WHEN THE
SUPPRESSOR'S ALPHA IS HIGH
I)
Typical volt-time curves of a gas discharge device are shown
in Figure 5 indicating an initial high clamping voltage. The
gas-discharge suppressor turns on when the transient pulse
exceeds the impulse sparkover voltage. Two representative
surge rates 1kV/µs and 20kV/µs are shown in Figure 5.
When a surge voltage is applied, the device turns on at
some point within the indicated limits. At 20kV/µs, the
discharge unit will sparkover between 600V and 2500V. At
1kV/µs, it will sparkover between 390V and 1500V.
1
2
3
4 5
8 10
LITTELFUSE VARISTOR
(20mm DIA.)
(α > 25)
20
30 40 50
80 100
300
INSTANTANEOUS CURRENT (A)
FIGURE 3. V-I CHARACTERISTIC OF FOUR TRANSIENT
SUPPRESSOR DEVICE
The amount of standby power that a circuit can tolerate may
be the deciding factor in the choice of a suppressor. Though
high-alpha devices have low standby power at the nominal
design voltage, a small line-voltage rise would cause a
10-105
200
10-9
MINIM
/µs
SILICON POWER
TRANSIENT SUPPRESSOR
(ZENER) (α ≅ 35)
MA
X
1kV
200
1000
800
600
500
400
300
/µs
300
2000
20kV
SELENIUM 2.54cm
(1") SQ (α ≅ 8)
500
400
APPLIED VOLTAGE (V)
ES
IS
1000
800
100
6000
5000
4000
3000
TO
R
(α
≡
SILICON CARBIDE VARISTOR
(α ≈ 5)
R
INSTANTANEOUS VOLTAGE (V)
As an example, a selenium suppressor in Table 2 can have a
12mA peak standby current and an alpha of 8 (Figure 3).
Therefore, it has a standby power dissipation of about 0.5W
on a 120VRMS line (170V peak). A zener-diode suppressor
has standby power dissipation of less than a milliwatt. And a
silicon-carbide varistor, in a 0.75” diameter disc, has standby
power in the 200mW range. High standby power in the lower
alpha devices is necessary to achieve a reasonable
clamping voltage at higher currents.
dramatic increase in the standby power. Figure 4 shows that
for a zener-diode suppressor, a 10% increase above rated
voltage increases the standby power dissipation above its
rating by a factor of 30. But for a low-alpha device, such as
silicon carbide, the standby power increases by only 1.5
times.
STANDBY POWER DISSIPATION (PER UNIT)
Transient Suppressors Compared
10-8
10-7
IM
UM
VO
LT
AG
E
UM V
OLTA
GE
9.5mm OD, 230V
GAS-DISCHARGE SUPPRESSOR
10-6
10-5
10-4
10-3
SHORT-TIME SURGE RESPONSE (S)
FIGURE 5. IMPULSE BREAKOVER OF A GAS-DISCHARGE
DEVICE DEPENDS UPON THE RATE OF
VOLTAGE RISE AS WELL AS THE ABSOLUTE
VOLTAGE LEVEL
Application Note 9768
TABLE 2. CHARACTERISTICS AND FEATURES OF TRANSIENT VOLTAGE SUPPRESSOR TECHNOLOGY
V-I CHARACTERISTICS
V
DEVICE
TYPE
LEAKAGE
FOLLOW
ON I
CLAMPING
VOLTAGE
ENERGY
CAPABILITY
Ideal Device
Zero
To
Low
No
Low
High
Zinc Oxide
Varistor
Low
No
Moderate To
Low
Zener
Low
No
Crowbar
(Zener - SCR
Combination)
Low
Spark
Gap
Zero
CLAMPING VOLTAGE
RESPONSE
TIME
COST
Low
Or
High
Fast
Low
High
Moderate
To
High
Fast
Low
Low
Low
Low
Fast
High
Yes
(Latching
Holding I)
Low
Medium
Low
Fast
Moderate
Yes
High
Ignition
Voltage
High
Low
Slow
Low
To
High
High
Low
Moderate
Moderate
CAPACITANCE
WORKING VOLTAGE
TRANSIENT CURRENT I
V
WORKING
VOLTAGE
I
V
MAX I LIMIT
WORKING
VOLTAGE
I
V
PEAK VOLTAGE
(IGNITION)
WORKING
VOLTAGE
I
V
PEAK VOLTAGE
(IGNITION)
WORKING
VOLTAGE
Low Clamp
I
V
Triggered
Spark
Gap
PEAK VOLTAGE
(IGNITION)
Zero
Yes
WORKING
VOLTAGE
Lower
Ignition
Voltage
Low
Clamp
I
V
Selenium
Very
High
No
Moderate
To
High
Moderate
To
High
High
Fast
High
Silicon
Carbide
Varistor
High
No
High
High
High
Fast
Low
WORKING
VOLTAGE
I
V
WORKING
VOLTAGE
I
10-106
Application Note 9768
The gas discharge device is useful for high current surges
and it is often advantageous to provide another suppression
device in a combination that allows the added suppressor to
protect against the high initial impulse. Several hybrid
combinations with a varistor or avalanche diode are
possible.
Comparison of Zener Diode and Littelfuse
Varistor Transient Suppressors
At 1ms, the two devices are almost the same. At 2µs the
varistor is almost 10 times greater, 7kW for the P6KE 6.8
Zener vs 60kW for the varistor V8ZA2.
Clamping Voltage
Clamping voltage is an important feature of a transient
suppressor. Zener diode type devices have lower clamping
voltages than varistors. Because these protective devices
are connected in parallel with the device or system to be
protected, a lower clamping voltage can be advantageous in
certain applications.
VOLTAGE
The gas discharge device may experience follow-current. As
the AC voltage passes through zero at the end of every half
cycle the arc will extinguish, but if the electrodes are hot and
the gas is ionized, it may reignite on the next cycle.
Depending on the power source, this current may be
sufficient to cause damage to the electrodes. The follow
current can be reduced by placing a limiting resistor in series
with the device, or, selecting a GDT specifically designed for
this application with a high follow-current threshold.
Transient suppressors have to be optimized to absorb large
amounts of power or energy in a short time duration:
nanoseconds, microseconds, or milliseconds in some
instances.
Electrical energy is transformed into heat and has to be
distributed instantaneously throughout the device. Transient
thermal impedance is much more important than steady
state thermal impedance, as it keeps peak junction
temperature to a minimum. In other words, heat should be
instantly and evenly distributed throughout the device.
The varistor meets these requirements: an extremely reliable
device with large overload capability. Zener diodes dissipate
electrical energy into heat in the depletion region of the die,
resulting in high peak temperature.
Figure 6 shows Peak Pulse Power vs Pulse width for the
V8ZA2 and the P6KE 6.8, the same devices compared for
leakage current.
200
60kW
50
10kW
600W
V8
ZEN
ZA
ER P
21
6KE
0m
6.8
7kW
m
POWER kW
20
10
5
2
DE
3.5kW
1
VIC
E
0.5
0.2
0.1
100ns 200
1µs 2
ZENER
CURRENT
Peak Pulse Power
100
VARISTOR
10µs 20
100µs
PULSE TIME
FIGURE 6. PEAK PULSE POWER vs PULSE TIME
10-107
1000µs
FIGURE 7. CHARACTERISTICS OF ZENER AND VARISTOR
Speed of Response
Response times of less than 1ps are sometimes claimed for
zener diodes, but these claims are not supported by data in
practical applications. For the varistor, measurements were
made down to 500ps with a voltage rise time (dv/dt) of 1
million volts per microsecond. These measurements are
described in Application Note AN9767. Another
consideration is the lead effect. Detailed information on the
lead effect can be found further in this section and in
Application Note AN9773. In summary, both devices are fast
enough to respond to real world transient events.
Leakage Current
Leakage current can be an area of misconception when
comparing a varistor and zener diode, for example. Figure 8
shows a P6KE 6.8 and a V8ZA2, both recommended by their
manufacturers for protection of integrated circuits having 5V
supply voltages.
Application Note 9768
Failure Mode
The zener diode leakage is about 100 times higher at 5V
than the varistor, 200µA vs less than 2µA, in this example.
Varistors subjected to energy levels beyond specified ratings
may be damaged. Varistors fail in the short circuit mode.
Subjected to high enough energy, however, they may
physically rupture or explode, resulting in an open circuit
condition. These types of failures are quite rare for properly
selected devices because of the large peak pulse
capabilities inherent in varistors.
100µA PER VERTICAL DIV.
1V PER HORIZONTAL DIV.
Zeners can fail either short or open. If the die is connected
by a wire, it can act as a fuse, disconnecting the device and
resulting in an Open circuit. Designers must analyze which
failure mode, open or short, is preferred for their circuits.
P6KE 6.8
V8ZA2
When a device fails during a transient, a short is preferred,
as it will provide a current path bypassing and will continue
to protect the sensitive components. On the other hand, if a
device fails open during a transient, the remaining energy
ends up in the sensitive components that were supposed to
be protected.
FIGURE 8. CHARACTERISTIC OF ZENER P6KE 6.8 vs
LITTELFUSE VARISTOR V8ZA2
The leakage current of a zener can be reduced by specifying
a higher voltage device.
Another consideration is a hybrid approach, making use of
the best features of both types of transient suppressors (See
Figure 10).
“Aging”
R
It has been stated that a varistor's V-I characteristic changes
every time high surge current or energy is subjected to it.
That is not the case.
As illustrated in Figure 9, the V-I characteristic initially
changed on some of the devices, but returned to within a few
percent of its original value after applying a second or third
pulse. To be conservative, peak pulse limits have been
established on data sheets. In many cases, these limits have
been exceeded many fold without harm to the device. This
does not mean that established limits should be exceeded,
but rather, viewed in perspective of the definition of a failed
device. A “failed” varistor device shows a ±10% change of
the V-I characteristic at the 1mA point.
VOLTS AT 1mA
8 x 20µs WAVE V31CP20
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
INPUT
ZENER
VARISTOR
L
INPUT
VARISTOR
ZENER
FIGURE 10. HYBRID PROTECTION USING VARISTORS,
ZENERS, R AND L
Capacitance
Depending on the application, transient suppressor
capacitance can be a very desirable or undesirable feature.
Varistors in comparison to zener diodes have a higher
capacitance. In DC circuits capacitance is desirable, the
larger the better. Decoupling capacitors are used on IC
supply voltage pins and can in many cases be replaced by
varistors, providing both the decoupling and transient
voltage clamping functions.
0
1
2
3
4
5
6
7
8
9
NUMBER OF PULSES
FIGURE 9. 250A PULSE WITHSTAND CAPABILITIES
10-108
10
The same is true for filter connectors where the varistor can
perform the dual functions of providing both filtering and
transient suppression.
There are circuits however, where capacitance is less
desirable, such as high frequency digital or some analog
circuits.
Application Note 9768
As a rule the source impedance of the signal and the
frequency as well as the capacitance of the transient
suppressor should be considered.
The current through CP is a function of dv/dt and the
distortion is a function of the signal's source impedance.
Each case must be evaluated individually to determine the
maximum allowable capacitance.
The structural characteristics of metal-oxide varistors
unavoidably result in an appreciable capacitance between
the device terminals, depending on area, thickness and
material processing. For the majority of power applications,
this capacitance can be of benefit. In high-frequency
applications, however, the effect must be taken into
consideration in the overall system design.
References
For Littelfuse documents available on the web, see
http://www.littelfuse.com/
[1] Sakshaug, E.C., J.S. Kresge and S.A. Miske, “A New
Concept in Station Arrester Design,” IEEE Trans.
PAS-96, No. 2, March-April 1977, pp. 647-656.
[2] Philipp, H.R. and L.M. Levinson, “Low Temperature
Electrical Studies in Metal Oxide Varistors - A Clue to
Conduction Mechanisms,” Journal of Applied Physics,
Vol. 48, April 1977, pp. 1621-1627.
[3] Philipp, H.R. and L.M. Levinson, “Zinc Oxide for
Transient Suppression,” IEEE Trans. PHP, December
1977.
[4] “Surge Arresters for Alternating Current Power Circuits,”
ANSI Standard C62.1, IEEE Standard 28.
[5] “Lightning Arresters. Part I: Nonlinear Resistor Type
Arresters for AC Systems,” IEC Recommendation
99-1,1970.
[6] Matsuoka, M., T. Masuyama and Y. Iida, “Supplementary
Journal of Japanese Society of Applied Physics,” Vol.
39, 1970, pp. 94-101.
[7] Harnden, J.D., F.D. Martzloff, W.G. Morris and F.B.
Golden, “Metal-Oxide Varistor: A New Way to Suppress
Transients,” Electronics, October 2, 1972.
[8] Martzloff, F.D., “The Development of a Guide on Surge
Voltages in Low - Voltage AC Power Circuits,” Report
81CRD047, General Electric, Schenectady, New York,
1981.
[9] Martzloff, F.D., “Varistor versus Environment: Winning
the Rematch,” Report 85CRD037, General Electric,
Schenectady, New York, May 1985.
10-109
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