surge suppressor voltage limit

On Sep 21, 1:00 pm, snipped-for-privacy@ipal.net wrote:

Doubling a varistor's voltage does nothing to double its surge energy handling abilities. That energy number is more related to current - not voltage. Voltage is a symptom of that current. Increasing a varistor's voltage mean a varistor absorbs more energy which means the varistor fails (degrades) faster.
Protector does not work by absorbing surges. It works by acting more like wire during a surge. A protector that absorbs less energy is more effective and lasts longer.
How does a varistor absorb less energy? Increase its joules rating.
Doubling voltage is about getting a varistor to absorb no energy - conduct near zero current during normal operation. For example, a 185 volt varistor for 120 VAC operation will conduct 800 volts during a more destructive surges. Increase varistor voltage to 370 volts for 240 VAC operation and that varistor may conduct at 1500 volts. The resulting higher voltage for same current means the varistor absorbs more energy during that surge which is not desirable. See varistor manufacturer datasheets for V-I charts.
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Hi Tom
Regarding your comments, varistor do not conduct voltage, they conduct current, the voltage is the resistance produce by the flow of current through the device.
As I have said previously manufacturers sell there power strips using the Energy rating as a mean of trying to say their unit is better than the competitor, as it has a high energy rating whereas in real life this makes no difference to the actual protection they provide to the connected equipment, as it is the clamping voltage that makes the difference.
MOV only fail in a correctly designed power strip if they are subject to repeated high energy surges, this is rarely true in real life conditions.
Try reading the MOV manufacturers literature it explains the basic principles of how an MOV works, see http://www.littelfuse.com/design/appliterature/appnotes.html?WhichApp=6
BillB
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On Sep 22, 4:40 pm, snipped-for-privacy@nospam.tesco.net wrote:

Correct about a surge; it is current. References to conducting voltage are a misnomer used only to explain a concept - not an accurate engineering term.
In North America, joules must be listed per safety standards. Meanwhile, many protectors only use 1/3rd and never more than 2/3rd of their joules when doing protection. Number of joules actually used may be even lower depending on what surge is where. IOW joules number on a power strip protector really provides no useful information for engineering purposes - at best only provides a ballpark absolute maximum that will never be achieved. Joules is a number that must be published per North American standards.
Many also see the word 'joules'; then assume those joules will absorb all of a surge. Again, a conclusion based only on assumptions; not based in learning what joules actually measure.
Surges are current - as stated by both authors. Voltage is only a symptom of that current. A surge properly diverted (by a protectors or other methods) means a massive current creates 'near to zero' voltage.
Another way to reduce voltage during a surge? Increase varistor joules. More joules means less voltage and less energy gets absorbed. A concept that many have difficulty grasping.
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| On Sep 22, 4:40 pm, snipped-for-privacy@nospam.tesco.net wrote: |> Regarding your comments, varistor do not conduct voltage, they conduct |> current, the voltage is the resistance produce by the flow of current |> through the device. |> As I have said previously manufacturers sell there power strips using the |> Energy rating as a mean of trying to say their unit is better than the |> competitor, ... | | Correct about a surge; it is current. References to conducting | voltage are a misnomer used only to explain a concept - not an | accurate engineering term. | | In North America, joules must be listed per safety standards. | Meanwhile, many protectors only use 1/3rd and never more than 2/3rd of | their joules when doing protection. Number of joules actually used | may be even lower depending on what surge is where. IOW joules number | on a power strip protector really provides no useful information for | engineering purposes - at best only provides a ballpark absolute | maximum that will never be achieved. Joules is a number that must be | published per North American standards.
The clamping voltage would be more useful. But it would help to also know the clamped impedance (should be very very low, but it would not be zero).
| Many also see the word 'joules'; then assume those joules will absorb | all of a surge. Again, a conclusion based only on assumptions; not | based in learning what joules actually measure. | | Surges are current - as stated by both authors. Voltage is only a | symptom of that current. A surge properly diverted (by a protectors | or other methods) means a massive current creates 'near to zero' | voltage.
Right. And we want that voltage drop to be below the supply voltage so the surge is not any greater.
| Another way to reduce voltage during a surge? Increase varistor | joules. More joules means less voltage and less energy gets | absorbed. A concept that many have difficulty grasping.
Joules _is_ energy. So that doesn't make sense UNLESS you are saying that a higher joules RATING has a lower impedance, and that results in a lower voltage drop when conducting.
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On Sep 23, 1:38 am, snipped-for-privacy@ipal.net wrote:

Phil - you keep having this problem. Joules is energy. Does that mean varistors work by absorbing the surge? Of course not. A benchmark statement. More joules means less voltage and less energy gets absorbed by the varistor. A concept that so many have diffculty grasping, in part, because assumptions replace learning. Learn what joules measure before posting your assumptions.
Do the work. Learn from varistor datasheets. It's not difficult. Once you learn how varistors work, then this becomes obvious. More joules means the protector absorbs less surge energy - which is desireable in protectors. For better protection, we want varistors to absorb less energy. This is accomplished by increasing the joules.
That becomes obvious even on the V-I charts. Those datasheet V-I charts were referenced repeatedly. Did you review them yet? Then it becomes obvious: increasing joules means less energy gets absorbed.
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w_tom wrote:

. From previous threads, w_ seems to have the idea that high joule ratings magically reduce the actual clamp voltage.
In fact, high joule ratings come with high surge current ratings. Comparing a high joule MOV with a lower joule MOV (with the same nominal clamp voltage) at the same surge currents, the high rated one will be operating at a lower percentage of its rated surge current. The current density through the MOV will be correspondingly lower. That produces a lower actual clamp voltage. There is no magic involved. And the difference isn't that great.
High current/joule rated MOVs are used because they give long life. The joule rating for a MOV is a single event rating. As the individual energy hits on a MOV become a smaller percentage of the rating, the cumulative energy rating of a MOV goes up rapidly (not linearly).
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Thanks Bud I agree
BillB
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Thanks Tom
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| On Sep 23, 1:38?am, snipped-for-privacy@ipal.net wrote: |>> ?Another way to reduce voltage during a surge? ?Increase varistor |>> joules. ?More joules means less voltage and less energy gets |>> absorbed. ?A concept that many have difficulty grasping. |> |> Joules _is_ energy. ?So that doesn't make sense UNLESS you are saying that a |> higher joules RATING has a lower impedance, and that results in a lower voltage |> drop when conducting. | | Phil - you keep having this problem. Joules is energy. Does that | mean varistors work by absorbing the surge? Of course not. A
The operational aspect of the MOV is to pass the current between wires. But in so doing it _does_ absorb/dissipate energy.
| benchmark statement. More joules means less voltage and less energy | gets absorbed by the varistor. A concept that so many have diffculty | grasping, in part, because assumptions replace learning. Learn what | joules measure before posting your assumptions.
But this wording is contradictory and therefore cannot be used to render any using engineering meaning.
Joules measure energy. That is exactly what it means. So a statement that says more joules is less energy is no basis for anything meaningful.
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On Sep 24, 2:17 am, snipped-for-privacy@ipal.net wrote:

Purpose of wire is pass the current between locations. But in so doing, wire _does_ absorb/dissipate energy. Both wires and MOVs do the same thing better when less energy is absorbed. Superior is when wires and MOVs divert/transfer/conduct more energy and absorb less energy.
How to make a protector absorb less energy during a surge? Increase its joules. More joules means less voltage and less energy gets absorbed by the varistor. A concept that so many have difficulty grasping, in part, because assumptions replace learning.
Again, the V-I charts are in the datasheets. These above concepts are obvious once numbers from V-I charts are grasped.
Many foolishly feel that a protector works by absorbing surges. They *know* this because protectors are rated in joules. If true, then more joules in a protector means the protector absorbs more joules. They *knew* by replacing facts and numbers with assumptions. More joules means less energy gets absorbed by a protector.
A protector that absorbs less energy is the superior protector. A protector's job is to divert / connect / shunt / bond /conduct that energy into earth where surges get absorbed / dissipated harmlessly. Not to block or absorb energy. The less energy a protector absorbs means even more energy gets absorbed / dissipated harmlessly in earth.
But again, many have been so enthralled by what is promoted in retail stores as to *know* a protector works by absorbing surges. Many, using assumption, have difficulty grasping what MOVs do. Forget what was promoted by retail salesmen. Learn from this V-I charts in datasheets. The better protector with more joules absorbs even less energy.
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| On Sep 24, 2:17 am, snipped-for-privacy@ipal.net wrote: |> The operational aspect of the MOV is to pass the current between wires. |> But in so doing it _does_ absorb/dissipate energy. | | Purpose of wire is pass the current between locations. But in so | doing, wire _does_ absorb/dissipate energy. Both wires and MOVs do | the same thing better when less energy is absorbed. Superior is when | wires and MOVs divert/transfer/conduct more energy and absorb less | energy.
Wires and MOVs pass current, not energy. Maybe this is the point of confusion.
If I am passing 5 amps over a wire, tell me how much energy that is in a exact numeric value of joules.
| How to make a protector absorb less energy during a surge? Increase | its joules. More joules means less voltage and less energy gets | absorbed by the varistor. A concept that so many have difficulty | grasping, in part, because assumptions replace learning.
Joules is energy. You want to INCREASE it to accomplish DECREASING it?
I think you are misunderstanding the difference between Joules and Amps.
| Many foolishly feel that a protector works by absorbing surges.
That actually is ONE way to make protectors. It, by itself, is not very effective because it generally is a one-time use. It is not a practical method for home and most business usage.
| They *know* this because protectors are rated in joules. If true, | then more joules in a protector means the protector absorbs more | joules. They *knew* by replacing facts and numbers with assumptions. | More joules means less energy gets absorbed by a protector.
The ratings are understood to mean the surge energy level that can be protected against. The term "absorb" might be misused (probably is). But this says nothing about what will be absorbed and/or diverted by any given protector.
| A protector that absorbs less energy is the superior protector. A | protector's job is to divert / connect / shunt / bond /conduct that | energy into earth where surges get absorbed / dissipated harmlessly. | Not to block or absorb energy. The less energy a protector absorbs | means even more energy gets absorbed / dissipated harmlessly in earth.
No.
Earth is not the only target for diversion.
A protector can suppress a differential surge by simply providing a path for it to reach its opposing voltage. No earth is involved. Making such a path operate at as low an impedance as possible makes such protection both more effective and more survivable (to live on to protect again).
A protector can protect against a common mode surge by spreading the surge across a zone of interconnected equipment. Low frequency common mode surges are more common (because the inductance of the path up to this point of use impedes the higher frequency components more), so equalization can be effective to keep damaging current levels from taking place on equipment interconnections.
| But again, many have been so enthralled by what is promoted in | retail stores as to *know* a protector works by absorbing surges.
I'm not going to add the topic of "consumer misunderstanding of what terms like absorb means, or consumer misunderstanding of how surge protectors do their job". It's quite clear to me that even _you_ do not understand all the things involved.
| Many, using assumption, have difficulty grasping what MOVs do. Forget | what was promoted by retail salesmen. Learn from this V-I charts in | datasheets. The better protector with more joules absorbs even less | energy.
What does "with more joules" mean to you? You seem to be misusing the term.
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On Mon, 22 Sep 2008 20:40:58 GMT snipped-for-privacy@nospam.tesco.net wrote:
| As I have said previously manufacturers sell there power strips using the | Energy rating as a mean of trying to say their unit is better than the | competitor, as it has a high energy rating whereas in real life this makes | no difference to the actual protection they provide to the connected | equipment, as it is the clamping voltage that makes the difference.
Unless the MOVs are destroyed and go open circuit before the surge is complete.
| MOV only fail in a correctly designed power strip if they are subject to | repeated high energy surges, this is rarely true in real life conditions.
Or a substantial available current sufficient to heat the MOV to the point of vaporization.
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On Sep 23, 1:31 am, snipped-for-privacy@ipal.net wrote:

If vaporization failure occurs, then a protector was grossly undersized and was a threat to human life. Vaporization is a complete violation of the manufacturer's "Absolute Maximum Ratings" which are located at the very top of every MOV datasheet. Varistor must fail only by degrading. MOVs must never get so hot as to vaporize. But vaporization gets the naive to recommend obscenely profitable and ineffective protectors.
An effective protector remains functional after a surge so that humans never even knows a surge existed.
Increasing varistor voltage is to make the MOV not conduct energy during normal operation. Varistor voltage is kept as low as possible so that MOV does not conduct during normal operation and absorbs minimal energy during a surge.
Also stated correctly before and restated again. So that a protector absorbs even less energy, increase its joules. Increased joules means a protector absorbs less energy during a surge; which is what we want from a better protector. This concept is difficult for those who know only by using assumption. This concept is obvious once numbers from MOV datasheets are learned. Increasing joules means the protector is better - absorbs less surge energy.
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Thanks again Tom
BillB
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| On Sep 23, 1:31 am, snipped-for-privacy@ipal.net wrote: |> Or a substantial available current sufficient to heat the MOV to the point of |> vaporization. | | If vaporization failure occurs, then a protector was grossly | undersized and was a threat to human life. Vaporization is a complete | violation of the manufacturer's "Absolute Maximum Ratings" which are | located at the very top of every MOV datasheet. Varistor must fail | only by degrading. MOVs must never get so hot as to vaporize. But | vaporization gets the naive to recommend obscenely profitable and | ineffective protectors.
I've seen the end results of a surge (I was not nearby when the surge actually took place, fortunately) that vaporized most of a (approximately) 250 kcmil cable. Are you going to tell me that any surge protector on the market that would fail to survive that is undersized?
| An effective protector remains functional after a surge so that | humans never even knows a surge existed.
There is a huge dynamic range of possible surges. The extreme surges are very rare, fortunately. But they are possible and they can vaporize things. No protection can be 100% perfect. Are you expecting 100% perfection?
| Increasing varistor voltage is to make the MOV not conduct energy | during normal operation. Varistor voltage is kept as low as possible | so that MOV does not conduct during normal operation and absorbs | minimal energy during a surge.
That's the right theory.
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| On Sep 21, 1:00 pm, snipped-for-privacy@ipal.net wrote: |> 1+2 = maybe the "experts" are right. | | Doubling a varistor's voltage does nothing to double its surge | energy handling abilities. That energy number is more related to | current - not voltage. Voltage is a symptom of that current. | Increasing a varistor's voltage mean a varistor absorbs more energy | which means the varistor fails (degrades) faster.
The surge energy handling is not the issue I am asking about.
The issue I am asking about is using double the supply voltage when the MOVs are doubled in their clamping voltage.
| Protector does not work by absorbing surges. It works by acting | more like wire during a surge. A protector that absorbs less energy | is more effective and lasts longer. | | How does a varistor absorb less energy? Increase its joules rating.
An increase of joules rating is MORE energy, not less.
| Doubling voltage is about getting a varistor to absorb no energy - | conduct near zero current during normal operation. For example, a 185 | volt varistor for 120 VAC operation will conduct 800 volts during a | more destructive surges. Increase varistor voltage to 370 volts for | 240 VAC operation and that varistor may conduct at 1500 volts. The | resulting higher voltage for same current means the varistor absorbs | more energy during that surge which is not desirable. See varistor | manufacturer datasheets for V-I charts.
What I have read is that the varistors used for 120VAC operation conduct at 330V and posts here have said that is 400V. I just verified that one of my surge suppressors lists 330V. The theory is, if they double that voltage to at least 660V, then these could be used on 240VAC circuits. Originally I was expecting to use German Schuko surge suppressor strips. These are designed for 230V or the full 220V-240V European range. Complications with this would be plugging in wall warts that have US plug prongs. Once it is mentioned that power strips in USA should have the voltage rating of MOVs doubled, that opens up the possibility of power strips that can run on 240V and have the right outlet type.
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snipped-for-privacy@nospam.tesco.net wrote:

. Francois Martzloff was the US-NIST guru on surges with many published papers. From one of them: "The fact of the matter is that nowadays, most electronic appliances have an inherent immunity level of at least 600 V to 800 V, so that the clamping voltages of 330 V widely offered by [surge suppressor] manufacturers are really not necessary. Objective assessment of the situation leads to the conclusion that the 330 V clamping level, promoted by a few manufacturers, was encouraged by the promulgation of UL Std 1449, showing that voltage as the lowest in a series of possible clamping voltages for 120 V circuits. Thus was created the downward auction of "lower is better" notwithstanding the objections raised by several researchers and well-informed manufacturers. One of the consequences of this downward auction can be premature ageing of [surge suppressors] that are called upon to carry surge currents as the result of relatively low transient voltages that would not put equipment in jeopardy."
The paper dates back to 1995. Suppressors with very high ratings are now readily and cheaply available which may make the argument less relevant.
For the 250V world, one would have to know the immunity level. It may be closer to the normal voltage than in the US, making an increase in clamp voltage less practical. .

. Matching would be better. At least you should sequentially go through the paralleled MOVs, with some sharing along the way. Or can you drive one into failure (conduction at normal voltages) before the others are 'used up'?
How do manufacturers get ratings of 1000+J for a single MOV in a plug-in suppressor? Paralleling? There seem to be high rated single MOVs that can be used in service panel suppressors. .

. Another Martzloff paper looks at the energy absorption for a MOV at the end of a branch circuit. It is surprisingly small for 2 reasons: 1. At about 6000V (US) there is arc over from panel busses to enclosure(+neutral+ground+earthing system). After the arc is established, the voltage is hundreds of volts. That dumps most of the energy coming in on hot power wires to earth. (Receptacles (US) also arc-over at about 6kV.) 2. The impedance of branch circuit wiring for surges greatly limits the surge current, and thus energy, that can reach a MOV.
The maximum energy dissipated in the MOV was 35 Joules for a 10 meter branch circuit. In 13 of 15 cases it was 1 Joule or less. That was with surges source currents from 2,000 to 10,000A (the maximum likely for a home). Surprisingly, the highest energies were for some of the lower surge currents because the MOV could hold the service panel voltage below arc-over.
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| snipped-for-privacy@nospam.tesco.net wrote: |> |> I cannot see any valid reason for doubling the live to ground clamping |> voltage, it the same as saying why bother to fit surge suppression in the |> first place. The lower the clamping voltage the less likely it is to damage |> the connected equipment. | . | Francois Martzloff was the US-NIST guru on surges with many published | papers. From one of them: | "The fact of the matter is that nowadays, most electronic appliances | have an inherent immunity level of at least 600 V to 800 V, so that the | clamping voltages of 330 V widely offered by [surge suppressor] | manufacturers are really not necessary. Objective assessment of the | situation leads to the conclusion that the 330 V clamping level, | promoted by a few manufacturers, was encouraged by the promulgation of | UL Std 1449, showing that voltage as the lowest in a series of possible | clamping voltages for 120 V circuits. Thus was created the downward | auction of "lower is better" notwithstanding the objections raised by | several researchers and well-informed manufacturers. One of the | consequences of this downward auction can be premature ageing of [surge | suppressors] that are called upon to carry surge currents as the result | of relatively low transient voltages that would not put equipment in | jeopardy." | | The paper dates back to 1995. Suppressors with very high ratings are now | readily and cheaply available which may make the argument less relevant. | | For the 250V world, one would have to know the immunity level. It may be | closer to the normal voltage than in the US, making an increase in clamp | voltage less practical.
If this recommendation by Martzloff is adopted, and "immunity level" is shifted to at least 660V and maybe up to 800V, it would seem that these devices can then be used on 240VAC (340V peak). Do you know of a reason they could not be so used (other than the benefit Martzloff is expecting for 120VAC uses would not all be realized on 240VAC circuits).
| Matching would be better. At least you should sequentially go through | the paralleled MOVs, with some sharing along the way. | Or can you drive one into failure (conduction at normal voltages) before | the others are 'used up'? | | How do manufacturers get ratings of 1000+J for a single MOV in a plug-in | suppressor? Paralleling? There seem to be high rated single MOVs that | can be used in service panel suppressors.
And they are probably more expensive than manufacturers want to put into their "cost driven market" absed plug-in suppressors.
One option I am considering is to use one of those whole house protectors and put it into a box and run the power cord through it. But I don't know if this is getting me the right kind of protection for point of use.
| Another Martzloff paper looks at the energy absorption for a MOV at the | end of a branch circuit. It is surprisingly small for 2 reasons: | 1. At about 6000V (US) there is arc over from panel busses to | enclosure(+neutral+ground+earthing system). After the arc is | established, the voltage is hundreds of volts. That dumps most of the | energy coming in on hot power wires to earth. (Receptacles (US) also | arc-over at about 6kV.) | 2. The impedance of branch circuit wiring for surges greatly limits the | surge current, and thus energy, that can reach a MOV.
That impedance is quite different for common mode (higher impedance) than for differential mode (lower impedance). In differential mode, there is an equal and opposite current channel in parallel, confining the magnetic field, and limiting the inductance. For mixed mode surges, the common mode will be impeded greatly, leaving differential mode.
I notice from videos of the 33kV surges that happened to homes in Harford county MD, severe damage levels was propogated into at least the inside breaker panels. If the arcing at the meter and the service cable does not completely quench the surge, and it gets to the panel and destroys that, then why not also go beyond and take out appliances? The question is just how much voltage reached each point. Arcs have a voltage drop, but they do also have impedance (inductance). So they cannot completely clear a differential surge. Clearly the arc at the meter did not clear the surge since there was more surge damage at the panel.
| The maximum energy dissipated in the MOV was 35 Joules for a 10 meter | branch circuit. In 13 of 15 cases it was 1 Joule or less. That was with | surges source currents from 2,000 to 10,000A (the maximum likely for a | home). Surprisingly, the highest energies were for some of the lower | surge currents because the MOV could hold the service panel voltage | below arc-over.
Is this maximum based on the value at the END of the circuit, or at the entrance to the home? I do know surges MUCH greater than 6000V can hit a home.
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snipped-for-privacy@ipal.net wrote:

. You would have to add protection for any signal wires that run to the protected equipment (not difficult). .

. A MOV at the end of a branch circuit is differential mode.
If there was a common mode surge on the power, at the end of a branch circuit the return would be the power system ground, which is an adjacent conductor. .

. It was not a surge.
It is difficult-to-impossible to design practical protection for a power line cross.
Thanks for separating out .mpgs from this event [another thread]. (But I haven't downloaded them yet.) .

. "With surges *source* currents...." Most lightning produced surges act as current sources. The source current went to a panel which fed a branch circuit. One point of the explanation above is that there is arc-over at panel at about 6kV. The branch circuit sees a pulse over 6kV, the arc starts, the source voltage drops to hundreds of volts. (Except for some smaller surges where the MOV was able to keep the voltage at the panel below 6kV as I said above.)
The 'experiment' was actually run on simulation software which has been validated with physical experiments.
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| snipped-for-privacy@ipal.net wrote:
|> |> | Matching would be better. At least you should sequentially go through |> | the paralleled MOVs, with some sharing along the way. |> | Or can you drive one into failure (conduction at normal voltages) before |> | the others are 'used up'? |> | |> | How do manufacturers get ratings of 1000+J for a single MOV in a plug-in |> | suppressor? Paralleling? There seem to be high rated single MOVs that |> | can be used in service panel suppressors. |> |> One option I am considering is to use one of those whole house protectors |> and put it into a box and run the power cord through it. But I don't know |> if this is getting me the right kind of protection for point of use. | . | You would have to add protection for any signal wires that run to the | protected equipment (not difficult).
Of course. Right now I am doing that by means of wireless isolation. So there are no metallic signal wires involved. Everything will be in one zone, powered through one power supply path with the protection in place. If I end up needing signaling at higher data rates than wireless can do, then I will use optical.
|> | Another Martzloff paper looks at the energy absorption for a MOV at the |> | end of a branch circuit. It is surprisingly small for 2 reasons: |> | 1. At about 6000V (US) there is arc over from panel busses to |> | enclosure(+neutral+ground+earthing system). After the arc is |> | established, the voltage is hundreds of volts. That dumps most of the |> | energy coming in on hot power wires to earth. (Receptacles (US) also |> | arc-over at about 6kV.) |> | 2. The impedance of branch circuit wiring for surges greatly limits the |> | surge current, and thus energy, that can reach a MOV. |> |> That impedance is quite different for common mode (higher impedance) than |> for differential mode (lower impedance). In differential mode, there is |> an equal and opposite current channel in parallel, confining the magnetic |> field, and limiting the inductance. For mixed mode surges, the common mode |> will be impeded greatly, leaving differential mode. | . | A MOV at the end of a branch circuit is differential mode. | | If there was a common mode surge on the power, at the end of a branch | circuit the return would be the power system ground, which is an | adjacent conductor.
Unless the common mode is across ALL wires including the EGC. That is where w_tom thinks it has to go to earth. But in fact it can be reflected back up the circuit.
A surge that is arriving on one wire and not the other wire(s) is a mixed mode surge.
|> I notice from videos of the 33kV surges that happened to homes in Harford |> county MD, severe damage levels was propogated into at least the inside |> breaker panels. If the arcing at the meter and the service cable does not |> completely quench the surge, and it gets to the panel and destroys that, |> then why not also go beyond and take out appliances? The question is just |> how much voltage reached each point. Arcs have a voltage drop, but they |> do also have impedance (inductance). So they cannot completely clear a |> differential surge. Clearly the arc at the meter did not clear the surge |> since there was more surge damage at the panel. | . | It was not a surge.
So do you classify anything happening to utility equipment as NOT a surge?
| It is difficult-to-impossible to design practical protection for a power | line cross. | | Thanks for separating out .mpgs from this event [another thread]. (But I | haven't downloaded them yet.)
And yet these are things that do happen a lot, although not generally as spectacular as what happened in Harford county that one day. I remember reading about one such event when I was around 12 years old. Based on what I remember from that reading, it sounded like all conductors into the author's home were energized at the same polarity, or else the voltage was not as high. More often the crosses that happen are 7200 to 8000 volt lines dropping down onto lower wires, the 120/240 network, or even phone or cable wires. Then those make give the MV a new path to ground.
|> | The maximum energy dissipated in the MOV was 35 Joules for a 10 meter |> | branch circuit. In 13 of 15 cases it was 1 Joule or less. That was with |> | surges source currents from 2,000 to 10,000A (the maximum likely for a |> | home). Surprisingly, the highest energies were for some of the lower |> | surge currents because the MOV could hold the service panel voltage |> | below arc-over. |> |> Is this maximum based on the value at the END of the circuit, or at the |> entrance to the home? I do know surges MUCH greater than 6000V can hit |> a home. | . | "With surges *source* currents...." Most lightning produced surges act | as current sources. The source current went to a panel which fed a | branch circuit. One point of the explanation above is that there is | arc-over at panel at about 6kV. The branch circuit sees a pulse over | 6kV, the arc starts, the source voltage drops to hundreds of volts. | (Except for some smaller surges where the MOV was able to keep the | voltage at the panel below 6kV as I said above.)
I am also looking for ways I can protect against the very strong surges, from a direct hit of lightning onto the meter panel, to a "Harford count event". The latter case would be the most difficult (as you point out) because of the large current and continuing supply. A simple MOV would start conducting, but the supply from a 33kV line would very quickly vaporize that thing. An arc tube would likely protect more, but even it would be soon overcome.
But that is not the topic of THIS thread. It would make an interesting thread on its own. Maybe I'll ask that (again) some day (or you can, if you want).
One thing I do wonder about in the Harford event is how much internal arcing was happing in the transformers intended to step the 13/8kV down to 120/240 because of 33kV being applied. If you have a transformer designed to step 13.2kV (dual bushing) down to 120/240, what is the rated BIL? How high a voltage is it tested with?
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