kwired
Electron manager
- Location
- NE Nebraska
Gar is old enough to have invented lightning though
Discrepancy on electrical theory between credible sources. Especially surge arrestors
- Thread starter Jpflex
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ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Lightning is so chaotic, variable, and transitory that I don't think anyone can fully understand it.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
220908-1445 EDT
My previous two posts were to try to define a circuit you could use to analyze what an MOV does. You need actual real values for whatever your system is. You also need to consider the inductance, and possibly capacitance in the circuit as well. But in reality an MOV alone is not a real good limiter.
More complex circuits can do a much better job. For example something that goes from an insulator to a very low impedance, for example a spark or arc discharge that goes from a very high impedance to a very low voltage drop when triggered. A spark drop might be in the range of a few hundred volts to many thousands at moderate current levels, and if current increases to a higher level it will transition to an arc drop which might be in the 10s to a 100 or so V drop.
Also using a low pass filter will take the energy of a short high voltage pulse, and transition this energy into a lower voltage pulse but stretched out in time.
A combination of these various techniques can provide very good protection.
.
My previous two posts were to try to define a circuit you could use to analyze what an MOV does. You need actual real values for whatever your system is. You also need to consider the inductance, and possibly capacitance in the circuit as well. But in reality an MOV alone is not a real good limiter.
More complex circuits can do a much better job. For example something that goes from an insulator to a very low impedance, for example a spark or arc discharge that goes from a very high impedance to a very low voltage drop when triggered. A spark drop might be in the range of a few hundred volts to many thousands at moderate current levels, and if current increases to a higher level it will transition to an arc drop which might be in the 10s to a 100 or so V drop.
Also using a low pass filter will take the energy of a short high voltage pulse, and transition this energy into a lower voltage pulse but stretched out in time.
A combination of these various techniques can provide very good protection.
.
Jpflex
Electrician big leagues
- Location
- Victorville
- Occupation
- Electrician commercial and residential
When you mentioned adding 100 fuel injectors (parallel) they would eventually stop working and I assume you mean line voltage main positive B+ cable to ground cable B- will noticeably Drop such as when a starter high current draw causes a good batter to drop to a level at 10.5 volts (source)?
Jpflex
Electrician big leagues
- Location
- Victorville
- Occupation
- Electrician commercial and residential
I was referring to how line voltage line (Source) to return circuit can drop based on placement of surge protector placed in parallel to circuit load needing protection.
Observing high current draw from automotive starters I can now see that line source voltage can drop 12.65 volts to 10.5 or less on line source but this confuses laws of parallel circuits That all voltage remains constant in a parallel circuit UNLESS this new lower voltage is common to all parallel paths, which I think it is. For this reason automobiles used to bypass all available power to the starter during cranking event and restore power to rest of system after cranking ended and automobile started. Is this correct? Feedback welcome
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Usually after they do their job, they are "toast".
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
This is all you you need to know about SPDs
“You get what you pay for. More is better”
Mike Holt
“You get what you pay for. More is better”
Mike Holt
If you look at home theater type spd power strips, internally you would see MOV's but they have the series inductors first. And those have a rating like 4000 Joules (total energy, which hits very fast and then is gone).
The series inductors are non linear and drop voltage according to the speed of the rise time of the pulse, E = L di / dt. di / di is bigger when dt, the time slice, is very small. E does not drop much for 60 cycle sinewave but does drop a lot for fast transients several orders of magnitude faster than regular grid power.
The upstream line in a home, 100 ft. of #12 and some #16 SJT cord itself limits how much peak energy is delivered to the spd and drops voltage for the rest, E = IR or E = IZ.
Putting MOV's on the line in industrial plants with high current distribution and no series inductance. As soon as the total energy of the pulse is over the Joules rating, the MOV's are likely to go poof, which would be most applications of an MOV in an industrial control or power cabinet. Seen them mostly misapplied, even in cabinets with nearby line reactors. Likely if I checked the reactors would be parallel off the bus but serving a different load. So the MOV's end up being also parallel from the bus but then not series through some other load (they short to ground from the bus). Neither protects the other and the MOV's are likely to go poof. The line reactors are indestructible and could last many generations of equipment changes.
Seen them go poof and seen them installed as a gimmick, something they charge for but likely to go poof, exposed to industrial plant noise and everything. Which is why I'm pretty sure the (MOV spd) modules come with internal sacrificial fuses. Since they parallel with nothing downstream in series, the spd can go poof without notice by the rest of the system. Unless they make such a mess going poof in the cabinet that it causes some flashover at 480 onto the protected load. Then that goes poof also.
Internally built into the device, like a Meanwell industrial power supply, has something for spd on the front end. But without a series line reactor in front of the Meanwell, they go poof pretty easily. Adding another MOV spd from the same bus adjacent to, paralleled shorted to ground, is not really visualizing the entirety of the problem task at hand. Line reactor in front of the Meanwell would probably save many of them.
The series inductors are non linear and drop voltage according to the speed of the rise time of the pulse, E = L di / dt. di / di is bigger when dt, the time slice, is very small. E does not drop much for 60 cycle sinewave but does drop a lot for fast transients several orders of magnitude faster than regular grid power.
The upstream line in a home, 100 ft. of #12 and some #16 SJT cord itself limits how much peak energy is delivered to the spd and drops voltage for the rest, E = IR or E = IZ.
Putting MOV's on the line in industrial plants with high current distribution and no series inductance. As soon as the total energy of the pulse is over the Joules rating, the MOV's are likely to go poof, which would be most applications of an MOV in an industrial control or power cabinet. Seen them mostly misapplied, even in cabinets with nearby line reactors. Likely if I checked the reactors would be parallel off the bus but serving a different load. So the MOV's end up being also parallel from the bus but then not series through some other load (they short to ground from the bus). Neither protects the other and the MOV's are likely to go poof. The line reactors are indestructible and could last many generations of equipment changes.
Seen them go poof and seen them installed as a gimmick, something they charge for but likely to go poof, exposed to industrial plant noise and everything. Which is why I'm pretty sure the (MOV spd) modules come with internal sacrificial fuses. Since they parallel with nothing downstream in series, the spd can go poof without notice by the rest of the system. Unless they make such a mess going poof in the cabinet that it causes some flashover at 480 onto the protected load. Then that goes poof also.
Internally built into the device, like a Meanwell industrial power supply, has something for spd on the front end. But without a series line reactor in front of the Meanwell, they go poof pretty easily. Adding another MOV spd from the same bus adjacent to, paralleled shorted to ground, is not really visualizing the entirety of the problem task at hand. Line reactor in front of the Meanwell would probably save many of them.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
A car battery is a voltage source, but it's not an ideal voltage source. High current draw will pull down the voltage because of the internal resistance of the battery.
kwired
Electron manager
- Location
- NE Nebraska
The voltage drop in that case is across the source (battery) which is a series component of the complete circuit.
Yes the injectors in the example that has been used will see a lower voltage, but all of them will see the same lower voltage because they are in parallel to one another. Put a second battery in parallel to the first and you lessen the overall source resistance and will see a lesser voltage drop with the same loading conditions. Voltage across each source will measure the same in that situation.
kwired
Electron manager
- Location
- NE Nebraska
After a major surge event yes they very well might be. This typically is close by lightning events or maybe if POCO happens to have a higher voltage distribution line come into contact with a lower voltage line for whatever reason. It doesn't have to be directly onto your service drop either, seen cases where a transmission line dropped onto a MV distribution line and resulted in damages to customer equipment over wide area, and takes out customer surge protectors in addition to other items in that event.
A major benefit of of using them is they will handle many many lesser surges like from POCO switching items in the system and any transients those create, or transients from further away lightning events that make it to your device location.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
True to a first approximation, but the takeoff points for a parallel circuit are in series with one another, so the first will see less of a voltage drop due to conductor impedance than will the last. It's probably not a measurable amount in this case, though.
kwired
Electron manager
- Location
- NE Nebraska
understand, I was disregarding conductor impedance, but it is something that can be a factor in some situations, schematically we do somewhat assume zero impedance of conductors until length or other situations begin to make a significant difference to what we are looking at.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Yeah, we had a voltage drop question a while back about widely separated parking lot lights all in parallel on a single circuit. Conductor impedance in that case was very much an issue.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
220911-1223 EDT
Jpflex:
Going back to your very first post I have some comments.
You have not experimented with the real world circuits you are describing, made measurements on the circuits you are describing, studied, and understand theoretical analysis of these circuits.
Start with a real world series circuit consisting of a battery as an energy source, an internal impedance in the battery, a switch, and a fixed load resistor. You can perform real world experiments on this circuit, and collect data. And the experiments will closely equal the theoretical results.
From a theoretical perspective at the moment we assume no other series impedance than that in the battery, that the battery internal voltage is absolutely constant, the wiring has zero impedance, the switch is either a perfect open circuit or a zero impedance closed circuit element, and the load resistance is perfectly constant at all current levels. These assumptions take us from the real world circuit to a theoretical circuit that we can mathematically analyze. This theoretical circuit is one that very closely describes a practical circuit you can assemble on a bench and experimentally test.
With the switch open you can measure the battery internal voltage at the battery output because there is no current thru the battery internal resistance, and that voltage at the battery terminals is the same as the internal battery voltage.
Close the switch and current now flows thru the total series circuit. that current will be the Internal Battery Voltage Source divided by the total series resistance in the total series loop which is ( R Internal Battery + R Load ).
When you run real world tests on this circuit, and compare the results with calculated results from the theoretical model, then you will find a close correlation between the two approaches.
To the extent that you can build a good theoretical model to your real world problem will determine how good your correlation is between the two methods.
Jpflex:
Going back to your very first post I have some comments.
You have not experimented with the real world circuits you are describing, made measurements on the circuits you are describing, studied, and understand theoretical analysis of these circuits.
Start with a real world series circuit consisting of a battery as an energy source, an internal impedance in the battery, a switch, and a fixed load resistor. You can perform real world experiments on this circuit, and collect data. And the experiments will closely equal the theoretical results.
From a theoretical perspective at the moment we assume no other series impedance than that in the battery, that the battery internal voltage is absolutely constant, the wiring has zero impedance, the switch is either a perfect open circuit or a zero impedance closed circuit element, and the load resistance is perfectly constant at all current levels. These assumptions take us from the real world circuit to a theoretical circuit that we can mathematically analyze. This theoretical circuit is one that very closely describes a practical circuit you can assemble on a bench and experimentally test.
With the switch open you can measure the battery internal voltage at the battery output because there is no current thru the battery internal resistance, and that voltage at the battery terminals is the same as the internal battery voltage.
Close the switch and current now flows thru the total series circuit. that current will be the Internal Battery Voltage Source divided by the total series resistance in the total series loop which is ( R Internal Battery + R Load ).
When you run real world tests on this circuit, and compare the results with calculated results from the theoretical model, then you will find a close correlation between the two approaches.
To the extent that you can build a good theoretical model to your real world problem will determine how good your correlation is between the two methods.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
Just a side note ... In the electronics field, they have what is called a "Crowbar" circuit to protect power supplies from drawing to much current.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
"Bypass" is a misleading term. Indeed the ignition switch of some (many?) cars disconnected (with series contacts) the majority of non-engine loads when turned to the start position. Both to conserve available battery current for the starter motor and ignition and to protect the other loads from the wild voltage present while the starter motor was connected.
That is not necessary, for the most part, with modern systems. And in addition, removing power completely from some of the electronics may erase their memory. Certain mechanical loads, like the A/C are prevented from running during the starting operation.
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