So why are 1st semester engineres taught about current sources and voltage sources?
So they would understand what current and voltage sources mean, if you were taught and paid attention, we wouldn't be having this discussion.
Did you ignore the Wikipedia citaon that demonstrates your mistake?
What mistake are you referring to?
Surge protection of appliances, like surge protection of buildings, means near zero voltages and extremely high amperes (ie 20,000 amps) Any device that could foolishly try to stop or block a surge (a current source) creates and suffers from a high voltage. That voltage only exists when a current source is blocked (see the formula V=IR). Direct lightning strikes without damage has always been about connecting a surge current harmlesslyl to earth so that a near zero voltage exists.
Another popular urban myth is surges created by power cycling major appliances. If those appliances create a surge, then they destoy themselves. If they create surges, the the protector is on the surge generating appliance - not on the victims. But those appoliances only create noise; not surges. Noise that may be as much as ten volts. Noise easily made irrelevant by protection already inside every appliance. Protection required by international design standards even decades before an IBM PC existed.
Since you seemed to have some faith in Schneider Electric, I thought you should know that they have the following to say about power disturbances in one of their TVSS literatue
"Lightning and fluctuations in utility power (caused by grid switching, for example) are often assumed to be the main sources of power disturbances. However, the overwhelming cause is actually equipment, such as motors and appliances, turning on and off. Even simply switching lights on and off will cause electrical surges.
In fact, 63% ofall transient voltage surges are generated from inside sources, while only 37% come from outside.
Key Causes of Internal Transients:
•Motors witching
•X-ray generators
•AC chillers
•Production machinery
•Robotics
•Welders
•Laser printers
•Copiers
•Capacitor bank switching
• Pumps"
And finally, if HVAC is creating surges daily, then MOVs in power strips are degraded (fail) in weeks or months. They are not designed for events that occur hourly. Their design specs are for events that occur maybe once every seven years. Just another reason why you know 120 volt appliances (ie HVAC) are not creating 330+ volt surges hourly or daily. Read the number on that protector box. It ignored any transiet (ie 10 volt noise) that does not exceed 330 volts. How often do your appliances suffer 330+ volt surges from the vacuum or HVAC? Never. But the myth is popular and easy to promote in a sound byte to consumers who ignore numbers.
I did not say most of those things, so don't be confused. In fact, in my initial responses I only cited lightning and switching as the main causes of surges. I only mentioned appliances because you yourself mentioned it in your post#92 and I even said surges resulted from them were far from being current sources.
Read numbers in that Wikipedia citation rather than assume all electricity comes from a voltage source.
Again you got it backward, you seem to think voltage source is created by a current source, no!! A voltage source, such as that from a generator, battery, charged capacitor, lightning clouds drives current through a load, governed by at least Ohm's law, among others. A voltage is then developed across the load, to the "source" (yes voltage), the voltage across the load is actually a form of voltage drop, but it is defintely not the source. The source is, I repeat, the "source" that causes the current to flow in the first place. Current source can be considered as a voltage source that has a high enough voltage and its internal impedance, or conversely output impedance is high enough such that the impedance of the load will not matter much. In reality, even the so called current sources, require a real voltage source, a generator capable of very high voltage and internal impedance is again, just one example. There are really not much point in debating the terms, it is more important to understand what they really mean. Norton and Thevinin, among others, used them as mathematical models for circuit analysis purposes. There is no need to get wrapped up in trying to address the OP's concerns.
Let me try to use an example that does not even need to call for Norton's and Thevinin's theorem.
A voltage source of say 100,000 volts to ground, and internal resistance or high output resistance (for simplicity, use pure resistance as example) of 10,000 ohms.
V=IR, so I=100,000/10,000=10A when connected to a load of zero impedance.
Now, insert a resistance of 1 ohm between the source's Live terminal and ground terminal and we get:
I=100,000/(1000+1)=9.999A
Or insert a resistance of 2 ohms, between the same two points and we get:
I=100,000/(1000+2)=9.998A,
Insert a resistance of 10 ohms, and you will get:
I=100,000/(1000+10)=9.99A.
So in this numerical example, increase the load impedance 10 times, the current remains practically constant and you get the idea how such one form of a current source works and that it still involves a voltage source of 100,000V. As I mentioned before, current sources are created by human, I cited current transformers as an easy to understand example and that's just one example in the non electronic world.
current source means that constant current must flow. Therefore from V=IR, voltage must increase if that current is blocked. That increased voltage is why protectors that must block a surge are easily destroyed - provide ineffective protection.
I am not going to say you are wrong, but may be just a little confused or inadvertently misled by Wiki. No offense, Googling is a great way to learn, but at some point you may want to read some text books too. I relied on Dr. Google as well, but I (I am sure jneutron too) also learnt things from textbooks and lecturers when in colleges and universities. As a matter of fact I happened to have had hands on experience with high end TVSS such as those used in municipal outdoor systems, industrial systems, and SA's up to 230,000 volts including those made by GE and ABB, and unfortunately had to replace some damaged ones over the years.
