Discrepancy on electrical theory between credible sources. Especially surge arrestors

[ggunn]

Usually text books have a disclaimer that says something like "because the resistance of the conductors are so low, we are not factoring it in in the calculations"
So voltage is essentially constant in a series circuit, but in reality copper is not a perfect conductor.

But disregarding the resistance of copper, voltage is constant in a series circuit at any specific point in time. Much the same way that the speed the wheels of a motorcycle are always spinning at the same speed to each other even if the motorcycle is traveling at variable speeds.

Do you mean in a parallel circuit? The voltage to the neutral or negative conductor is different at every other point in a series circuit.

 

[rambojoe]

The war on truth is a funny thing.
The big problem is texting something you read somewhere and screwing that up.
Its better to use that copy and paste thingy..
That way people can read from the person that actually learned something.
Too much info... i just work on being an electrician, thats fun enough.

 

[kwired]

Usually text books have a disclaimer that says something like "because the resistance of the conductors are so low, we are not factoring it in in the calculations"
So voltage is essentially constant in a series circuit, but in reality copper is not a perfect conductor.

But disregarding the resistance of copper, voltage is constant in a series circuit at any specific point in time. Much the same way that the speed the wheels of a motorcycle are always spinning at the same speed to each other even if the motorcycle is traveling at variable speeds.

presuming both wheels are on the ground and there is no traction slippage.

eta: and I have same question as ggunn, voltage is not same in series components, current is though.

 

[Sea Nile]

All I can say is LOL.

Do you mean in a parallel circuit? The voltage to the neutral or negative conductor is different at every other point in a series circuit.

Yes, if every load is connected to the source directly, such as the way receptacles in a house has the ungrounded conductor directly connected to an OCPD, if we ignore the fact that copper is not a perfect conductor, and we treat the electromagnetic spectrum as instantaneous instead of limited to the speed of light then everything plugged in will have the exact same voltage. If the voltage changes, such as with AC, then every load on the circuit will experience the changing in voltage at the exact same time, which means the voltage at the loads are still the same at each load as it's changing. I understand why @rambojoe doesn't like the term constant voltage. But if you consider nothing is constant it's ok.
It's a matter of perspective. I am not sitting still on my couch, I'm on a spinning planet rotating around a star that's spinning in a galaxy.

 

[Sea Nile]

To throw a monkey wrench into this whole argument one can argue that a 1000 v DC photovoltaic system could be considered AC if the reference voltage you are measuring to was a steady 500 volts, as the sun went high noon the voltage would be +500v to the reference point, and when night came it would be -500v to the reference point. So I could say it's alternating at a low frequency.

 

[kwired]

All I can say is LOL.



Yes, if every load is connected to the source directly, such as the way receptacles in a house has the ungrounded conductor directly connected to an OCPD, if we ignore the fact that copper is not a perfect conductor, and we treat the electromagnetic spectrum as instantaneous instead of limited to the speed of light then everything plugged in will have the exact same voltage. If the voltage changes, such as with AC, then every load on the circuit will experience the changing in voltage at the exact same time, which means the voltage at the loads are still the same at each load as it's changing. I understand why @rambojoe doesn't like the term constant voltage. But if you consider nothing is constant it's ok.
It's a matter of perspective. I am not sitting still on my couch, I'm on a spinning planet rotating around a star that's spinning in a galaxy.

What you described is parallel components and not series components that is why he asked if you meant parallel.

 

[Sea Nile]

What you described is parallel components and not series components that is why he asked if you meant parallel.

Oh, I see I wrote the wrong word. My mistake. I was thinking parallel, and I wrote series. Im sorry for the confusion

 

[rambojoe]

Oh, I see I wrote the wrong word. My mistake. I was thinking parallel, and I wrote series. Im sorry for the confusion

Its clear now.... Dude, work on being a better electrician... Theory is later.
And i didnt say "constant voltage", nor do i like or dislike it.
You said constant current, not constant voltage.. You are all over the place! Something tells me you are not old enough to be sea nile... No offense of course. But dont quote me please.

 

[rambojoe]

presuming both wheels are on the ground and there is no traction slippage.

eta: and I have same question as ggunn, voltage is not same in series components, current is though.

Or wheelies, or stoppies, or sliding, or losing the front....

 

[Sea Nile]

Its clear now.... Dude, work on being a better electrician... Theory is later.
And i didnt say "constant voltage", nor do i like or dislike it.
You said constant current, not constant voltage.. You are all over the place! Something tells me you are not old enough to be sea nile... No offense of course. But dont quote me please.

It's all good, sometimes what's in my head doesn't come out of my mouth the same way. I'm 48 years old with 25 years experience in the army as a military intelligence systems maintainer, troubleshooter, and systems integrator. Google 35T. I just officially retired from the army 4 days ago.

 

[gar]

In Mike Holts video regarding theory and operation of surge arrestors, it is stated by Mr. Holt that surge arrestors protect load devices downstream by clamping or limiting voltage potential level.

He states, these surge protectors contain a semiconductor in parallel path to the circuit being protected under cases of excessive voltage or lighting induction (mutual or direct contact). When exposed to high levels of voltage (300 volts or more?), the semiconductor in the surge protector connected in parallel to the circuit changes from an insulator to conductor and allows this excessive voltage to take this path and return on return path, neutral load leg.

Apparently, this causes such a high current that voltage is lowered or limited or “clamped” shunted on the circuit to loads to protect them.



However, in another credible source on electrical theory in the form of a text book (siting of source available upon request), it is stated that rules of parallel circuits follow that VOLTAGE IS CONSTANT, while amperes very per leg in parallel.

This I have also tested back in my old days as an ASE L1 Advanced level automotive electrician with a 94 Ford F-150 4.9L motor having 3 fuel injectors wired in parallel. When one injector went bad, the voltage remained constant BUT it’s individual AMPERE draw varied from the rest of the injectors.


Therefore, the old saying was that current travels ate the point of least resistance, but modern saying is that current takes ALL PATHS. Additionally, if we are following the rules of parallel circuits, how then can voltage be shunted or reduced to protect loads downstream from surge protectors since voltage remains constant in parallel circuits? Thanks

220905-1715 EDT

Jpflex:

Your confusion results from a lack of understanding of electrical circuit theory, and I will try to clarify this somewhat.

When we look at the relationship of voltage, current, and resistance we usually assume that resistance is unchanged ( constant ) meaning its value is unchanged with change of current or voltage. By resistance being unchanged in the following equation this also means that in the equation v = R * i is called a linear relationship.

So if I have a 100 ohm linear resistance, then for an applied voltage of 100 V across the resistor I will have 1 ampere of current flow thru the resistor, and for 200 V across the same resistor the current flow will be 2 A, and knowing the applied voltage across the resistor I can predict the current thru the resistor for any other value, or if I know the current thru the resistor I can predict the voltage across the resistor.

Think about this relationship. I will come back later and talk about a non-linear resistance where resistance changes as voltage across the resistor changes, or current thru the resistor changes.

.

 

[Fred B]

To throw a monkey wrench into this whole argument one can argue that a 1000 v DC photovoltaic system could be considered AC if the reference voltage you are measuring to was a steady 500 volts, as the sun went high noon the voltage would be +500v to the reference point, and when night came it would be -500v to the reference point. So I could say it's alternating at a low frequency.

How many Hz would that be? Relatively, if you are getting 1 cycle per 24 hours.

 

[ggunn]

How many Hz would that be? Relatively, if you are getting 1 cycle per 24 hours.

0.000012Hz, approximately.

 

[winnie]

0.000012Hz, approximately.

And such low frequencies can make it into the power grid, causing all sorts of havoc.

During a solar storm, the Earth's magnetic field gets pushed around as the particle flux from the Sun changes and the Earth rotates. This changing magnetic field coupled with transmission networks injecting very low frequency AC current.

A couple of volts of near DC can easily saturate transformers designed for hundreds of kilovolts at 60Hz.

Jon

 

[Fred B]

And such low frequencies can make it into the power grid, causing all sorts of havoc.

During a solar storm, the Earth's magnetic field gets pushed around as the particle flux from the Sun changes and the Earth rotates. This changing magnetic field coupled with transmission networks injecting very low frequency AC current.

A couple of volts of near DC can easily saturate transformers designed for hundreds of kilovolts at 60Hz.

Jon

Would such present as an extra wave form intermixed with normal on a grid?

 

[junkhound]

Would such present as an extra wave form intermixed with normal on a grid?

Yes.
solar storms have caused megawatt xfmrs at substtions to saturate and burn up. An Ontario hdro event a few decades ago was one of the bigger events. Often termed 'electrohydrodyamic'. When we put long lines in MM sites in ND and Montana, we had a withstand 'dc' requirement of a few dozen volts 'dc' as a design requirement. A secondary effect of the EMP threat.

 

[gar]

220906-2140 EDT

Jpflex:

To continue from my last post.

Now I will create a theoretical circuit that will approximate an MOV as a transient limiter.

A typical real world MOV in an AC circuit will have clamping characteristics in both the + and - directions that are about equal. For my analysis I am going to just look at what happens for one polarity.

An electrical circuit that I am going to describe has an adjustable DC voltage source of v, and a linear internal impedance of X resistance.

If we consider this source to be adjustable from 0 to 500 V, and have a linear internal impedance of 0.1 ohms, then if my normal load is a 100 ohm linear resistance the load current is:

0 A when v = 0 V, and load voltage is 0 V,
0.5 A when v = 50 V, and load voltage is 50 - ( 0.5 * 0.1 ) = 49.95 V,
1.0 A when v = 100 V,
2.0 A when v = 200 V, and
5.0 A when v = 500 V, and load voltages 500 - ( 5.0 * 0.1 ) = 499.5 V

Next I place an MOV in parallel with the 100 ohm load resistor. For an approximation for the MOV I will a use a series equivalent circuit of a 200 V DC voltage source, a 1 ohm resistor, and an ideal diode. This equivalent shunt circuit draws no current when the applied voltage is less than +200 V.

When this series circuit has a voltage less than 200 V it draws 0 current. Above 200 V the current thru this combination is ( Vin -200 ) / 1. At 300 V across this combination the current is 300 A. Thus, the voltage drop across the internal impedance of the source is 300 * 0.1 = 30 V. This is an approximation, but sufficiently close for our purpose here. The clamped voltage across the load at 500 V input is about 470 V. Not much clamping for the values I chose. The current to the actual load is not much different from no transient limiter.

Does this help you understand a little about operation of a shunt transient MOV limiter? Different values will give you more likable values.

There are other considerations that are of major importance, such as series inductance.

 

[Strathead]

My first thought on this was that voltage is constant on a parallel circuit, however, the energy level of surges that a surge protector is effective on are not high, so when the semi-conductor breaks down the resistance of that path is extremely low, (we are supposed to keep the leads as short as possible. What I feel the OP failed to conceive is that the voltage of the energy available is clamped, the amperage is shunted, because each leg is subject to P=I*E and E=I*R. Is this correct?

 

[Jpflex]

220905-1715 EDT

Jpflex:

Your confusion results from a lack of understanding of electrical circuit theory, and I will try to clarify this somewhat.

When we look at the relationship of voltage, current, and resistance we usually assume that resistance is unchanged ( constant ) meaning its value is unchanged with change of current or voltage. By resistance being unchanged in the following equation this also means that in the equation v = R * i is called a linear relationship.

So if I have a 100 ohm linear resistance, then for an applied voltage of 100 V across the resistor I will have 1 ampere of current flow thru the resistor, and for 200 V across the same resistor the current flow will be 2 A, and knowing the applied voltage across the resistor I can predict the current thru the resistor for any other value, or if I know the current thru the resistor I can predict the voltage across the resistor.

Think about this relationship. I will come back later and talk about a non-linear resistance where resistance changes as voltage across the resistor changes, or current thru the resistor changes.

.

 

[Jpflex]

Gar what you are saying is basic and I would not have been licensed at 20 in central electronics association nor ASE electrical if I didn’t understand this primitive concept you state. I am discussing theory that has taken people a life time to discover and fully not understand. Lightning is said to not be fully understood, no one can know everything.