CA2027288A1 - Series gapped metal oxide surge arrester - Google Patents
Series gapped metal oxide surge arresterInfo
- Publication number
- CA2027288A1 CA2027288A1 CA 2027288 CA2027288A CA2027288A1 CA 2027288 A1 CA2027288 A1 CA 2027288A1 CA 2027288 CA2027288 CA 2027288 CA 2027288 A CA2027288 A CA 2027288A CA 2027288 A1 CA2027288 A1 CA 2027288A1
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- Prior art keywords
- arrester
- gap
- voltage
- surge arrester
- disk
- Prior art date
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- Abandoned
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
- H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
- H01C7/12—Overvoltage protection resistors
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- Microelectronics & Electronic Packaging (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Thermistors And Varistors (AREA)
Abstract
ABSTRACT
A surge arrester is provided including highly non-linear metal oxide varistor disks in series with one or more resistively graded gap assemblies. The gap assemblies comprise a low exponent, non-linear silicon carbide resistive material in parallel with a spark gap. In this combination, the arrester voltage is shared between the gap assemblies and the MOV disks at normal steady-state system voltages. The arrester provides substantial improvements in temporary overvoltage performance and protection levels over conventional gapless MOV
arrester designs.
A surge arrester is provided including highly non-linear metal oxide varistor disks in series with one or more resistively graded gap assemblies. The gap assemblies comprise a low exponent, non-linear silicon carbide resistive material in parallel with a spark gap. In this combination, the arrester voltage is shared between the gap assemblies and the MOV disks at normal steady-state system voltages. The arrester provides substantial improvements in temporary overvoltage performance and protection levels over conventional gapless MOV
arrester designs.
Description
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SERIES GAPPED METAL OXIDE SURGE ARRESTER
The present invention relates in general to surge arresters for protecting electrical equipment from overvoltages. In particular to arresters having metal-oxide varistor elements, in series with a resistively graded gap assembly.
Power lines are periodically subjected to excessive overvoltage conditions, for example, when lightning strikes, when current limiting fuses operate, or when capacitors discharge. In these cases, it is necessary to protect critical and expensive equipment from these conditions by use of a surge arrester. The surge arrester is typically connected between the power line and ground, and when an overvoltage situation occurs, the arrester shunts the excess energy to ground through its terminals.
Surge arresters are usually one of two basic types. In both types of prior art arresters, the voltage-current relationship for nonlinear components is expressed as I=kEn where I is arrester current, k is a constant, E is ; arrester voltage, and n is the nonlinear exponent or coefficient. One type of the older gapped arrester uses low exponent nonlinear resistive elements in series with low exponent nonlinear graded gaps. Tha second type, a metal-oxide varistor (MOV) arrester, users only high .-' ,,, .: , ~
!
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exponent nonlinear elements of the metal-oxide variety and does not require series gap assemblies to operate properly.
The first type of arrester is shown in Fig. lA and is described in many previous patents such as ~.S. Patent Nos. 4,161,763 and 4,174,530. The series gapped silicon carbide ( SiC) arrester has been in use for many years, however, it has several inherent problems. In this configuration, the gaps are required to withstand full system voltage over the life of the arrester, and the nonlinear resistive elements are used only to limit current which in turn assists the gaps in turning off during a discharge operation. Since the gaps must withstand the full line to ground voltage, they are typically comprised of many parts, each of which withstand a portion of the voltage. This type of construction results in more consistent impulse or spark-over characteristics, however, it results in higher than desired impulse protective characteristics which is undesirable. Another inherent problem with this type of arrester is size and weight.
Yet another problem with this first type of arrester is that the high current discharge characteristic and the - power follow current levels are both controlled by the same . ~
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nonlinear elements. For lower high current discharge voltages, lower resistance of the silicon carbide elements is desired. For lower power follow currents, a higher resistance of the nonlinear silicon carbide elements is desired. Due to these diametrically opposed requirements of the same components, design compromises have resulted in less than desirable protective characteristics.
The second type of arrester commonly used is known as the gapless metal~oxide varistor, and is shown in Fig. 2. This arrester was developed to eliminate the undesirable impulse characteristic of the series gapped silicon carbide arrester. In this type of arrester, the nonlinear element eliminates the need for a series gap by remaining highly non-conductive at normal operating voltages. As the applied voltage is increased, the semiconductor gradually begins to conduct, without a disruptive discharge, as with the series gap type. This switch type characteristic enables the metal-oxide arrester to shunt all fundamental transient overvoltage energies to ground. The inherent problem with this type of arrester is that both breakdown voltage and high current discharge voltage are controlled by the same nonlinear elements. It is desirable to have higher breakdown voltages so that lower nondestructive transient overvoltages do not result in conduction. At the . .
. .
same time it is also desirable to have lower high current discharge voltages to provide better equipment protection.
Again, as in the series gapped silicone carbide arrester, two diametrically opposed requirements of the same component result in a compromise of characteristics. In some cases the discharge voltage capability is compromised, and in others, the temporary overvoltage capability is reduced.
The hybrid arrester, according to the present invention, is a combination of both prior arts. A low exponent, nonlinear, resistively graded, gap assembly is used in series with metal-oxide disks. This combination of parts results in significant and unexDected characteristic improvements. In this new type of arrester, no performance characteristics are compromised due to multiple conflicting requirements for the same component. During steady state operation, the gap assembly and disks share the voltage stress. During discharge conditions, only the disks are in the circuit after the series gaps spark over. In this new arrester, it is very important to properly match the steady state, 60 HZ impedance of the gap assembly and metal-oxide disks to achieve the proper voltage distribution.
Furthermore, it is important to proportionally match the exponents of the gap and disk to achieve desired temporary overvoltage performance. It is also important to insure :
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that "the gap front-of-wave discharge voltage is less than the disk discharge voltage.
Accordingly, it is the object of this invention to provide several improvements in performance over both prior arts.
The hybrid arrester provides higher temporary overvoltage capability than the typical gapless metal-oxide arrester, at no loss in discharge voltage performance. This results in more dependable power system operation and fewer component failures.
Another objective of this invention is to provide improved e~ternal cGntamination performance, over the gapped silicone carbide arrester. A buildup of dirt, salt, and-or foreign materials, etc., on the 0xternal surface of a series gapped arrester can cause an imbalance in the voltage distribution and premature sparkover. Improved performance in the hybrid arrester is a result of using fewer gaps than in prior art, and having a higher capacitive grading current during steady state operation.
Yet another object of the hybrid arrester is to provide lower discharge voltage characteristics. In this case, the present invention is superior to both prior arts.
t ~ ~j A further objective of this arrester is to provide a smaller package. This is achieved by the fact that the gap assembly is not required to dissipate any energy, and can be smaller and lighter than equal voltage rated MOV
material.
Yet another objective of the hybrid arrester is to provide, lower impulse protective characteristics. This is achieved by using fewer gaps than the SiC gapped arrester and fewer disks than the ungapped metal-oxide arrester.
lo A further additional object of the hybrid arrester is to provide a lower cost assembly. This is achieved by replacing relatively more expensive metal-oxide disks with lower cost gap and resistor ring assemblies.
Yet another object of this invention is to provide superior thermal stability characteristics. Due to gap assembly insensitivity to temperature, as the hybrid arrester temperature raisas for whatever reason, the gap assembly simply assumes a higher proportion of the arraster voltage. This increase in gap assembly voltage reduces the requirements on the disk which is more temperature sensitive.
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Fig. lA is an elevation view, partly in cross Section, of a prior art, series gapped silicon carbide arrester.
Figs. lB and lc depict enlarged views of certain components of the prior art series gapped silicon carbide arrester of Fig. lA.
Fig. 2 is an elevation view, partly in cross section, of a prior art, gapless metal-oxide arrester.
Fig. 3A is an elevation view, partly in cross-section showing the preferred embodiment of the present invention.
Figs. 3B and 3C depict enlarged views of certain components of the surge arrester of Fig. 3A.
Fig. 4A is an elevation view, partly in cross section of alternate embodiment of the surge arrester of Fig. 3A.
Fig. 4B depicts an enlarged view of certain components of the surge arrester shown in Fig. 4A.
Fig. 4C depicts an enlarged view of certain components of the surge arrester shown in Fig. 4B.
Fig. 5 is an exploded, cutaway view of nonlinear, resistivity graded gap assembly.
Fig. 6 is a graphic representation of the voltage distribution between the gap assembly and disks.
Fig. 7 is a graphic representation of the VI characteristic curve for prior art and present invention.
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Fig. 8A-8F are graphic representations of impulse and 60 Hz response of the prior art arresters of Figs. lA and 2 and the present invention.
Fig. 9 is an electrical schematic of the present invention.
Prior Art A prior art source arrester can be seen in Fig. lA wherein the arrester 10 consists of a porcelain housing ll having an upper terminal cap 12 and a lower terminal cap isolator 13. Arrester lO further contains within housing ll valve blocks 14 generally consisting of low exponent, silicon carbide material, connected electrically in series. Valve block 14 commonly has a metal electrode 14A attached to top and bottom, and an insulating collar 14B intimate-y attached on the circumference as shown in Fig. lC. Also contained within housing 11 are series gap assemblies consisting of lower cupped electrode 16, upper dimpled electrode 17 and mating nonlinear, low exponent silicon carbide ring 18, best shown in Fig. lB. Cupped electrode 16 and dimpled electrode 17 provide a simple spark gap l9 which is electrically in series with valve blocks 14, and electrically in parallel with ring 18.
Referring again to Fig. lA, a plurality of series gap assemblies 15 is arranged electrically in series to make up . - . . . : .
a full gap assembly 24. 20Also contained in housing 11 is spacer 20 and spring 21 connected electrically in series with valve blocks 14 and gap assembly 24.
Electrical connection is made to power lines by means of upper cap 12 and upper terminal 22. Electrical connection is made to ground by means of lower cap assembly 13 and ground terminal 23. Since valve blocks 14, and series connected rings 18 are continuously connected to the power system, a small amount of current flows constantly to ground. The high resistance, low exponent rings control the current magnitude to a level just required to maintain an even voltage drop across the gap assemblies during all external contamination conditions. This is known as grading current. The steady state impedance of gap assembly 24 is typically on the order of megohms whereas the typical resistance of the valve blocks 14 is ohms. As a result of this ratio, essentially all terminal voltage is stressed across gap assembly 24 during steady state conditions. Upon the occurrence of an overvoltage condition between terminals 22 and 23, the voltage is initially stressed in total across the gap assembly 24 until it reaches a level high enough to break down the gaps 19. This initial voltage level is known as the front-of-wave discharge voltage, and is the most undesirable feature o~ the series gapped silicon carbide _ g _ r.~ J ' ~ ~J
prior art arrester. Once the gaps 19 have sparked over, the system overvoltage is then stressed across the plurality of valve blocks 14. Valve blocks 14 then provide a low impedance path for excess system energies to be shunted to ground through terminals 22 and 23. The voltage current relationship of both ring 18 and block 1~ is predicted by the formula I=kE K is very high for ring 18, and n very low. For block 14, K is very low and n is approximately 4-5, similar to ring 18.
The second prior art surge arrester 30 can be seen in Fig. 2. Most of the basic components of arrester 10 and 30 are similar except for the internal active parts. The active components of arrester 10 are comprised of valve blocks 14 and gap assembly 15. The active components of arrester 30 are comprised of metal-oxide disks 31 only.
Disk 31 commonly has metallic electrodes 31A attached to top and bottom, and insulating collar 31B intimately attached to the circumference as shown in Fig. 3C.
Referring again to Fig. 2, MOV disks 31 are connected electrically in series, and provide the function of shunting overvoltage energies to ground through means of caps 12 and 13, and terminals 22 and 23. MOV disks 31 require no initial high front-of-wave sparkover to go into conduction as in arrester 10. Instead, as the applied voltage across terminals 22 and 23 increases, the MOV disks 31 simply become more conductive until they appear like a very low impedance resistor. The impedance follows the form I=KEn. For this type of arrester, n is in the range of 25 at system voltages, and is reduced to 5-10 at higher currents.
Present Invention The arrester configuration according to the preferred embodiment of this invention is shown in Figs. 3A-3C. Most parts are identical to those described in Figs. lA and 2.
However, the unique combination of gap assembly 33 and metal oxide disk 31 have resulted in a different mode of operation of each, and unexpected and vastly improved characteristics over both prior arts. Hybrid arrester 32 comprises metal-oxide disks 31 connected electrically in series with a gap-ring assembly 33. The operation of the hybrid arrester 32 is as follows: During steady state operation, a portion of the system voltage is impressed across both disks 31 and gap assembly 33. This is only the case when the low exponent ring 18 impedance is matched proportionally with the high exponent disk 31. As an overvoltage condition initiates, the current through arrester 32 begins to increase. Since ring 18 has a lower exponent than disk 31, voltage rises across ring 18 at a faster rate than that across disk 31. This shift in voltage is graphically displayed in Fig. 6.
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It can be observed in Fig. 6 that as the arrester voltage is increased, the gap voltage increases at a faster rate than the disk voltage. This change in voltage distribution is caused by differences in the nonlinear exponent of the ring and disk. This shift in voltage distribution toward the gap gives the hybrid arrester vastly improved temporary overvoltage capabilities with no compromise in discharge voltage.
In the initial sparkover of assembly 33, gap 19 exhibits, a front-of-wave (FOW) discharge voltage. However, because of the fact that only a few gaps are used relative to prior art, the peak level of the FOW voltage is low enough not to be of any concern. This is graphically shown in Fig. 8C in which the aberration on the rise of voltage trace is a result of gap breakdown, and is lower than the longer time discharge voltage.
Once gap assembly 33 sparks over, arrester 32 discharge characteristics are controlled by disks 31. Since fewer disks are used in the hybrid arrester than in prior art arrester 30 of Fig. 2, the resulting discharge voltage is lower over the entire current range. This is graphically shown in Fig. 7.
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To further elucidate the benefits of this preferred embodiment, Figs. 8D, 8E and 8F compare the power follow current characteristics of aforementioned arresters. It can be seen that SiC arresters 10 allow for considerable power follow, current, gapless arresters 30 allow no power follow current, and hybrid arresters 3~ can be designed for any level from 0-lOOO's of amps. This flexibility in design allows for many other gap assembly designs other than the one shown.
Another embodiment of the hybrid arrester is shown in Figs. 4A-4C. There are two differences in this embodiment. The first is that assembly 35 has electrode 36 which has dimples or raised portions only on the side facing ring 18. Also at least one assembly 35 is on each side of disk 31. By doing this, the gap assemblies can be better utilized as heat sinks during surge duty. This separation also distributes the heat generating components along the length of the housing 11 which also serves as a heat sink.
Electrode 36 and ring 18 combine to form preionizing gap 37. The height of ring 18 is approximately .25 inches and the diameter is approximately 1.5 inches. The height and diameter can be varied by a fraction of .5 to 4 to improve characteristics or just to match the other parts. When the dimensions of ring 18 is changed, electrode 16 and 36 must be similarly changed.
The preionization gap is approximately .007 inches and is formed by a second surface 50 of ring 18 and electrode 36 has raised portions 40 and depressed portions 42 which alternate. For example, raised portion 40 in Fig. 5 would form a preionizing gap, 37 with the ring above and depressed portion 42 would form a preionizing gap with the ring below. Preionizing gap spacing can also be increased or decreased .5 to 4 times for different design requirements. Preionization gap 37 generates ions that disperse throughout gap 19, and provide more consistent sparkover when the voltage stress is increased across gap 19. The size of gap 19 can vary from .010" to 1.00"
depending on the desired break down voltage. In general gap 19 cannot be thicker than ring 1~.
Fig. 5 provides a perspective view of gaD assembly IJ3.
For improved performance of gap assembly 33, conductive electrode 18A is attached to both faces of ring 18. These conductive electrodes may be applied in various manner, such as arc sprayed or flame sprayed and may be of suitable conductive material such as aluminum or copper. Conductive electrode may cover all or part of the ring face. Fig. 9 is the electrical schematic of the preferred embodiment 32 s ~
of Fig. 3A. As depicted in Fig. 9, Rg represents the resistance of gap assembly 33 while Cg represents its capcitance. Sg represents the sparkover voltage of gap 19 of assembly 33. Similarly, Rd represents the resistance of MOV disk 31 and Cd repr~sents its capacitance. According to the present invention, surge arrester 32 may have the following values:
R~noe . Cg 0-1000 pF
~ 1-20 Mn Sg 1500-3000 V r~s Cd 100-2000 pF
10~
In most preferred embodiment, the components of arrester 32 may be described as follows:
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Cg 50-90 pF
SERIES GAPPED METAL OXIDE SURGE ARRESTER
The present invention relates in general to surge arresters for protecting electrical equipment from overvoltages. In particular to arresters having metal-oxide varistor elements, in series with a resistively graded gap assembly.
Power lines are periodically subjected to excessive overvoltage conditions, for example, when lightning strikes, when current limiting fuses operate, or when capacitors discharge. In these cases, it is necessary to protect critical and expensive equipment from these conditions by use of a surge arrester. The surge arrester is typically connected between the power line and ground, and when an overvoltage situation occurs, the arrester shunts the excess energy to ground through its terminals.
Surge arresters are usually one of two basic types. In both types of prior art arresters, the voltage-current relationship for nonlinear components is expressed as I=kEn where I is arrester current, k is a constant, E is ; arrester voltage, and n is the nonlinear exponent or coefficient. One type of the older gapped arrester uses low exponent nonlinear resistive elements in series with low exponent nonlinear graded gaps. Tha second type, a metal-oxide varistor (MOV) arrester, users only high .-' ,,, .: , ~
!
j r~ ~ ' J ~ ~
exponent nonlinear elements of the metal-oxide variety and does not require series gap assemblies to operate properly.
The first type of arrester is shown in Fig. lA and is described in many previous patents such as ~.S. Patent Nos. 4,161,763 and 4,174,530. The series gapped silicon carbide ( SiC) arrester has been in use for many years, however, it has several inherent problems. In this configuration, the gaps are required to withstand full system voltage over the life of the arrester, and the nonlinear resistive elements are used only to limit current which in turn assists the gaps in turning off during a discharge operation. Since the gaps must withstand the full line to ground voltage, they are typically comprised of many parts, each of which withstand a portion of the voltage. This type of construction results in more consistent impulse or spark-over characteristics, however, it results in higher than desired impulse protective characteristics which is undesirable. Another inherent problem with this type of arrester is size and weight.
Yet another problem with this first type of arrester is that the high current discharge characteristic and the - power follow current levels are both controlled by the same . ~
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nonlinear elements. For lower high current discharge voltages, lower resistance of the silicon carbide elements is desired. For lower power follow currents, a higher resistance of the nonlinear silicon carbide elements is desired. Due to these diametrically opposed requirements of the same components, design compromises have resulted in less than desirable protective characteristics.
The second type of arrester commonly used is known as the gapless metal~oxide varistor, and is shown in Fig. 2. This arrester was developed to eliminate the undesirable impulse characteristic of the series gapped silicon carbide arrester. In this type of arrester, the nonlinear element eliminates the need for a series gap by remaining highly non-conductive at normal operating voltages. As the applied voltage is increased, the semiconductor gradually begins to conduct, without a disruptive discharge, as with the series gap type. This switch type characteristic enables the metal-oxide arrester to shunt all fundamental transient overvoltage energies to ground. The inherent problem with this type of arrester is that both breakdown voltage and high current discharge voltage are controlled by the same nonlinear elements. It is desirable to have higher breakdown voltages so that lower nondestructive transient overvoltages do not result in conduction. At the . .
. .
same time it is also desirable to have lower high current discharge voltages to provide better equipment protection.
Again, as in the series gapped silicone carbide arrester, two diametrically opposed requirements of the same component result in a compromise of characteristics. In some cases the discharge voltage capability is compromised, and in others, the temporary overvoltage capability is reduced.
The hybrid arrester, according to the present invention, is a combination of both prior arts. A low exponent, nonlinear, resistively graded, gap assembly is used in series with metal-oxide disks. This combination of parts results in significant and unexDected characteristic improvements. In this new type of arrester, no performance characteristics are compromised due to multiple conflicting requirements for the same component. During steady state operation, the gap assembly and disks share the voltage stress. During discharge conditions, only the disks are in the circuit after the series gaps spark over. In this new arrester, it is very important to properly match the steady state, 60 HZ impedance of the gap assembly and metal-oxide disks to achieve the proper voltage distribution.
Furthermore, it is important to proportionally match the exponents of the gap and disk to achieve desired temporary overvoltage performance. It is also important to insure :
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that "the gap front-of-wave discharge voltage is less than the disk discharge voltage.
Accordingly, it is the object of this invention to provide several improvements in performance over both prior arts.
The hybrid arrester provides higher temporary overvoltage capability than the typical gapless metal-oxide arrester, at no loss in discharge voltage performance. This results in more dependable power system operation and fewer component failures.
Another objective of this invention is to provide improved e~ternal cGntamination performance, over the gapped silicone carbide arrester. A buildup of dirt, salt, and-or foreign materials, etc., on the 0xternal surface of a series gapped arrester can cause an imbalance in the voltage distribution and premature sparkover. Improved performance in the hybrid arrester is a result of using fewer gaps than in prior art, and having a higher capacitive grading current during steady state operation.
Yet another object of the hybrid arrester is to provide lower discharge voltage characteristics. In this case, the present invention is superior to both prior arts.
t ~ ~j A further objective of this arrester is to provide a smaller package. This is achieved by the fact that the gap assembly is not required to dissipate any energy, and can be smaller and lighter than equal voltage rated MOV
material.
Yet another objective of the hybrid arrester is to provide, lower impulse protective characteristics. This is achieved by using fewer gaps than the SiC gapped arrester and fewer disks than the ungapped metal-oxide arrester.
lo A further additional object of the hybrid arrester is to provide a lower cost assembly. This is achieved by replacing relatively more expensive metal-oxide disks with lower cost gap and resistor ring assemblies.
Yet another object of this invention is to provide superior thermal stability characteristics. Due to gap assembly insensitivity to temperature, as the hybrid arrester temperature raisas for whatever reason, the gap assembly simply assumes a higher proportion of the arraster voltage. This increase in gap assembly voltage reduces the requirements on the disk which is more temperature sensitive.
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Fig. lA is an elevation view, partly in cross Section, of a prior art, series gapped silicon carbide arrester.
Figs. lB and lc depict enlarged views of certain components of the prior art series gapped silicon carbide arrester of Fig. lA.
Fig. 2 is an elevation view, partly in cross section, of a prior art, gapless metal-oxide arrester.
Fig. 3A is an elevation view, partly in cross-section showing the preferred embodiment of the present invention.
Figs. 3B and 3C depict enlarged views of certain components of the surge arrester of Fig. 3A.
Fig. 4A is an elevation view, partly in cross section of alternate embodiment of the surge arrester of Fig. 3A.
Fig. 4B depicts an enlarged view of certain components of the surge arrester shown in Fig. 4A.
Fig. 4C depicts an enlarged view of certain components of the surge arrester shown in Fig. 4B.
Fig. 5 is an exploded, cutaway view of nonlinear, resistivity graded gap assembly.
Fig. 6 is a graphic representation of the voltage distribution between the gap assembly and disks.
Fig. 7 is a graphic representation of the VI characteristic curve for prior art and present invention.
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Fig. 8A-8F are graphic representations of impulse and 60 Hz response of the prior art arresters of Figs. lA and 2 and the present invention.
Fig. 9 is an electrical schematic of the present invention.
Prior Art A prior art source arrester can be seen in Fig. lA wherein the arrester 10 consists of a porcelain housing ll having an upper terminal cap 12 and a lower terminal cap isolator 13. Arrester lO further contains within housing ll valve blocks 14 generally consisting of low exponent, silicon carbide material, connected electrically in series. Valve block 14 commonly has a metal electrode 14A attached to top and bottom, and an insulating collar 14B intimate-y attached on the circumference as shown in Fig. lC. Also contained within housing 11 are series gap assemblies consisting of lower cupped electrode 16, upper dimpled electrode 17 and mating nonlinear, low exponent silicon carbide ring 18, best shown in Fig. lB. Cupped electrode 16 and dimpled electrode 17 provide a simple spark gap l9 which is electrically in series with valve blocks 14, and electrically in parallel with ring 18.
Referring again to Fig. lA, a plurality of series gap assemblies 15 is arranged electrically in series to make up . - . . . : .
a full gap assembly 24. 20Also contained in housing 11 is spacer 20 and spring 21 connected electrically in series with valve blocks 14 and gap assembly 24.
Electrical connection is made to power lines by means of upper cap 12 and upper terminal 22. Electrical connection is made to ground by means of lower cap assembly 13 and ground terminal 23. Since valve blocks 14, and series connected rings 18 are continuously connected to the power system, a small amount of current flows constantly to ground. The high resistance, low exponent rings control the current magnitude to a level just required to maintain an even voltage drop across the gap assemblies during all external contamination conditions. This is known as grading current. The steady state impedance of gap assembly 24 is typically on the order of megohms whereas the typical resistance of the valve blocks 14 is ohms. As a result of this ratio, essentially all terminal voltage is stressed across gap assembly 24 during steady state conditions. Upon the occurrence of an overvoltage condition between terminals 22 and 23, the voltage is initially stressed in total across the gap assembly 24 until it reaches a level high enough to break down the gaps 19. This initial voltage level is known as the front-of-wave discharge voltage, and is the most undesirable feature o~ the series gapped silicon carbide _ g _ r.~ J ' ~ ~J
prior art arrester. Once the gaps 19 have sparked over, the system overvoltage is then stressed across the plurality of valve blocks 14. Valve blocks 14 then provide a low impedance path for excess system energies to be shunted to ground through terminals 22 and 23. The voltage current relationship of both ring 18 and block 1~ is predicted by the formula I=kE K is very high for ring 18, and n very low. For block 14, K is very low and n is approximately 4-5, similar to ring 18.
The second prior art surge arrester 30 can be seen in Fig. 2. Most of the basic components of arrester 10 and 30 are similar except for the internal active parts. The active components of arrester 10 are comprised of valve blocks 14 and gap assembly 15. The active components of arrester 30 are comprised of metal-oxide disks 31 only.
Disk 31 commonly has metallic electrodes 31A attached to top and bottom, and insulating collar 31B intimately attached to the circumference as shown in Fig. 3C.
Referring again to Fig. 2, MOV disks 31 are connected electrically in series, and provide the function of shunting overvoltage energies to ground through means of caps 12 and 13, and terminals 22 and 23. MOV disks 31 require no initial high front-of-wave sparkover to go into conduction as in arrester 10. Instead, as the applied voltage across terminals 22 and 23 increases, the MOV disks 31 simply become more conductive until they appear like a very low impedance resistor. The impedance follows the form I=KEn. For this type of arrester, n is in the range of 25 at system voltages, and is reduced to 5-10 at higher currents.
Present Invention The arrester configuration according to the preferred embodiment of this invention is shown in Figs. 3A-3C. Most parts are identical to those described in Figs. lA and 2.
However, the unique combination of gap assembly 33 and metal oxide disk 31 have resulted in a different mode of operation of each, and unexpected and vastly improved characteristics over both prior arts. Hybrid arrester 32 comprises metal-oxide disks 31 connected electrically in series with a gap-ring assembly 33. The operation of the hybrid arrester 32 is as follows: During steady state operation, a portion of the system voltage is impressed across both disks 31 and gap assembly 33. This is only the case when the low exponent ring 18 impedance is matched proportionally with the high exponent disk 31. As an overvoltage condition initiates, the current through arrester 32 begins to increase. Since ring 18 has a lower exponent than disk 31, voltage rises across ring 18 at a faster rate than that across disk 31. This shift in voltage is graphically displayed in Fig. 6.
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It can be observed in Fig. 6 that as the arrester voltage is increased, the gap voltage increases at a faster rate than the disk voltage. This change in voltage distribution is caused by differences in the nonlinear exponent of the ring and disk. This shift in voltage distribution toward the gap gives the hybrid arrester vastly improved temporary overvoltage capabilities with no compromise in discharge voltage.
In the initial sparkover of assembly 33, gap 19 exhibits, a front-of-wave (FOW) discharge voltage. However, because of the fact that only a few gaps are used relative to prior art, the peak level of the FOW voltage is low enough not to be of any concern. This is graphically shown in Fig. 8C in which the aberration on the rise of voltage trace is a result of gap breakdown, and is lower than the longer time discharge voltage.
Once gap assembly 33 sparks over, arrester 32 discharge characteristics are controlled by disks 31. Since fewer disks are used in the hybrid arrester than in prior art arrester 30 of Fig. 2, the resulting discharge voltage is lower over the entire current range. This is graphically shown in Fig. 7.
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To further elucidate the benefits of this preferred embodiment, Figs. 8D, 8E and 8F compare the power follow current characteristics of aforementioned arresters. It can be seen that SiC arresters 10 allow for considerable power follow, current, gapless arresters 30 allow no power follow current, and hybrid arresters 3~ can be designed for any level from 0-lOOO's of amps. This flexibility in design allows for many other gap assembly designs other than the one shown.
Another embodiment of the hybrid arrester is shown in Figs. 4A-4C. There are two differences in this embodiment. The first is that assembly 35 has electrode 36 which has dimples or raised portions only on the side facing ring 18. Also at least one assembly 35 is on each side of disk 31. By doing this, the gap assemblies can be better utilized as heat sinks during surge duty. This separation also distributes the heat generating components along the length of the housing 11 which also serves as a heat sink.
Electrode 36 and ring 18 combine to form preionizing gap 37. The height of ring 18 is approximately .25 inches and the diameter is approximately 1.5 inches. The height and diameter can be varied by a fraction of .5 to 4 to improve characteristics or just to match the other parts. When the dimensions of ring 18 is changed, electrode 16 and 36 must be similarly changed.
The preionization gap is approximately .007 inches and is formed by a second surface 50 of ring 18 and electrode 36 has raised portions 40 and depressed portions 42 which alternate. For example, raised portion 40 in Fig. 5 would form a preionizing gap, 37 with the ring above and depressed portion 42 would form a preionizing gap with the ring below. Preionizing gap spacing can also be increased or decreased .5 to 4 times for different design requirements. Preionization gap 37 generates ions that disperse throughout gap 19, and provide more consistent sparkover when the voltage stress is increased across gap 19. The size of gap 19 can vary from .010" to 1.00"
depending on the desired break down voltage. In general gap 19 cannot be thicker than ring 1~.
Fig. 5 provides a perspective view of gaD assembly IJ3.
For improved performance of gap assembly 33, conductive electrode 18A is attached to both faces of ring 18. These conductive electrodes may be applied in various manner, such as arc sprayed or flame sprayed and may be of suitable conductive material such as aluminum or copper. Conductive electrode may cover all or part of the ring face. Fig. 9 is the electrical schematic of the preferred embodiment 32 s ~
of Fig. 3A. As depicted in Fig. 9, Rg represents the resistance of gap assembly 33 while Cg represents its capcitance. Sg represents the sparkover voltage of gap 19 of assembly 33. Similarly, Rd represents the resistance of MOV disk 31 and Cd repr~sents its capacitance. According to the present invention, surge arrester 32 may have the following values:
R~noe . Cg 0-1000 pF
~ 1-20 Mn Sg 1500-3000 V r~s Cd 100-2000 pF
10~
In most preferred embodiment, the components of arrester 32 may be described as follows:
~g~
Cg 50-90 pF
2.0-12 Nn Sg 2500 V rms Cd ~ 300-1000 pF
Rd 1-100 Mt~ --The ratios of the thickness of the gap assembly to the thickness of the disk can vary from .2 to 2. The ratio of the voltage across the gap asssmbly to the voltage across the disk can vary from .2 to 2. The ratio of the diameterof the gap assembly diameter to the diameter of the disk can vary from .5 to 2.
In the case where the thickness of the ring is the same as the thickness of the disk the ratio of the voltage across the ring or gap assembly to the voltage across the disk is in the range of .5 to 4. This applies to nominal voltages and above nominal voltages.
The voltage drop across the gap assembly at nominal operating voltage is 5% to 90% of the voltage drop across the arrester.
Although the surge arrester described in this invention is designed for protection of electrical equipment on power systems, it can be used in electronic systems, residential wiring, industrial circuits or any installation requiring surge protection. Further, although the invention has been depicted in Fig. 3~ and Fig. 4 as housed in a procelain housing, it may similarly be employed in polymer housed, under-oil or dead front surge arresters.
Rd 1-100 Mt~ --The ratios of the thickness of the gap assembly to the thickness of the disk can vary from .2 to 2. The ratio of the voltage across the gap asssmbly to the voltage across the disk can vary from .2 to 2. The ratio of the diameterof the gap assembly diameter to the diameter of the disk can vary from .5 to 2.
In the case where the thickness of the ring is the same as the thickness of the disk the ratio of the voltage across the ring or gap assembly to the voltage across the disk is in the range of .5 to 4. This applies to nominal voltages and above nominal voltages.
The voltage drop across the gap assembly at nominal operating voltage is 5% to 90% of the voltage drop across the arrester.
Although the surge arrester described in this invention is designed for protection of electrical equipment on power systems, it can be used in electronic systems, residential wiring, industrial circuits or any installation requiring surge protection. Further, although the invention has been depicted in Fig. 3~ and Fig. 4 as housed in a procelain housing, it may similarly be employed in polymer housed, under-oil or dead front surge arresters.
Claims (18)
1. A surge arrester comprising:
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear silicon carbide resistive ring in parallel with a gap, said gap further comprising;
a first electrode and a second electrode.
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear silicon carbide resistive ring in parallel with a gap, said gap further comprising;
a first electrode and a second electrode.
2. A surge arrester as in Claim 1 wherein said disk has a dielectric collar.
3. A surge arrester as in Claim 1 wherein said disk has conductive electrodes on a first face and a second face of said disk.
4. A surge arrester as in Claim I wherein said gap is .01 to 1 inch.
5. A surge arrester as in Claim 1 wherein said gap us .01 to 1 inch.
6 A surge arrester as in Claim 1 wherein the diameter of said disk and said gap assembly are approximately the same.
7. A surge arrester as in Claim 1 wherein the diameter of said gap assembly is 50% to 200% of the diameter of said disk.
8. A surge arrester as in Claim 1 wherein the voltage drop across said gap assembly at nominal operating voltage, is approximately 5% to 90% of the voltage drop across said arrester.
9. A surge arrester as in Claim 1 wherein the voltage drop across said gap assembly at nominal operating voltage is approximately 15% to 45% of the voltage drop across said arrester.
10. A surge arrester as in Claim 1 wherein height of said gap assembly is .5 to 2 times the height of said disk.
11. A surge arrester comprising:
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear resistive ring, a first electrode, a second electrode, wherein the voltage drop across said arrester at nominal operating voltage is divided between said ring and said disk proportional to the thickness of said disk and said ring.
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear resistive ring, a first electrode, a second electrode, wherein the voltage drop across said arrester at nominal operating voltage is divided between said ring and said disk proportional to the thickness of said disk and said ring.
12. A surge arrester as in Claim 10 wherein said ring is silicon carbide.
13. A surge arrester comprising:
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear resistive ring, a first electrode, a second electrode.
wherein the voltage drop across said nonlinear resistive ring at nominal operating voltage is equal t the voltage drop across said disk on a per thickness basis.
at least one metal oxide varistor disk in series with;
at least one gap assembly, said gap assembly comprising;
a nonlinear resistive ring, a first electrode, a second electrode.
wherein the voltage drop across said nonlinear resistive ring at nominal operating voltage is equal t the voltage drop across said disk on a per thickness basis.
14 A surge arrester as in Claim 13 wherein the voltage drop across said ring at nominal operating voltage is .5 to 4 times the voltage drop across said disk on a per thickness basis.
15. A surge arrester as in Claim 13 wherein said ring is silicon carbide.
16. A surge arrester as in Claim 13 wherein the voltage drop across said gap assembly is 20% to 200% of the voltage drop across said disk.
17. A surge arrester as in Claim 13 wherein the voltage across said ring relative to the voltage across said disks is higher per thickness at voltages above said nominal operating voltage.
18. A surge arrester as in Claim 13 wherein the voltage across said gap assembly relative disks to the voltage across said disks is one-half to four times higher per thickness at voltages above said nominal operating voltage.
2086b/18-21
2086b/18-21
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US42006989A | 1989-10-11 | 1989-10-11 | |
| US07/420,069 | 1989-10-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2027288A1 true CA2027288A1 (en) | 1991-04-12 |
Family
ID=23664959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2027288 Abandoned CA2027288A1 (en) | 1989-10-11 | 1990-10-10 | Series gapped metal oxide surge arrester |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPH03208280A (en) |
| AU (1) | AU6369790A (en) |
| CA (1) | CA2027288A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102013109393A1 (en) | 2013-08-29 | 2015-03-05 | Epcos Ag | Surge arresters |
| CN113629683A (en) * | 2021-07-22 | 2021-11-09 | 西安交通大学 | Intelligent combined protection assembly with pulse arc pollution prevention structure for trigger type overvoltage protection gap |
| CN115083705A (en) * | 2022-06-21 | 2022-09-20 | 深圳可雷可科技股份有限公司 | Silicon carbide nonlinear resistor for de-excitation of generator |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9088153B2 (en) | 2012-09-26 | 2015-07-21 | Hubbell Incorporated | Series R-C graded gap assembly for MOV arrester |
| CN104091661A (en) * | 2014-06-12 | 2014-10-08 | 宜兴华源电工设备有限公司 | Dual lightning protection and explosion-proof composite post type insulator |
-
1990
- 1990-10-02 AU AU63697/90A patent/AU6369790A/en not_active Abandoned
- 1990-10-10 CA CA 2027288 patent/CA2027288A1/en not_active Abandoned
- 1990-10-11 JP JP2273120A patent/JPH03208280A/en active Pending
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102013109393A1 (en) | 2013-08-29 | 2015-03-05 | Epcos Ag | Surge arresters |
| US9627855B2 (en) | 2013-08-29 | 2017-04-18 | Epcos Ag | Surge arrester |
| CN113629683A (en) * | 2021-07-22 | 2021-11-09 | 西安交通大学 | Intelligent combined protection assembly with pulse arc pollution prevention structure for trigger type overvoltage protection gap |
| CN113629683B (en) * | 2021-07-22 | 2023-08-01 | 西安交通大学 | Intelligent combined protection assembly with trigger type overvoltage protection gap of pulse arc pollution prevention structure |
| CN115083705A (en) * | 2022-06-21 | 2022-09-20 | 深圳可雷可科技股份有限公司 | Silicon carbide nonlinear resistor for de-excitation of generator |
| CN115083705B (en) * | 2022-06-21 | 2023-03-24 | 深圳可雷可科技股份有限公司 | Silicon carbide nonlinear resistor for de-excitation of generator |
Also Published As
| Publication number | Publication date |
|---|---|
| AU6369790A (en) | 1991-04-18 |
| JPH03208280A (en) | 1991-09-11 |
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| Date | Code | Title | Description |
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