DC power cannot be transmitted over long distances. This is the original problem that caused AC to win out.
There are two forms of load, inductive and resistive, and two corresponding types of power, reactive and real. If we use a rowboat analogy, real power can be thought of as the oscillation of the oars back and forth, while reactive power becomes the force of the oar pushing the water. Of course, the oars only push the water in one direction, then they're lifted and repositioned to push again.
In DC power, real and reactive power are indistinguishable. Voltage and current push in one direction all the time. It's only AC power where the rowboat analogy comes into play. So, WHY DO WE USE AC?
Simply, current cannot be made to flow over vast distances. We learned early on that you cannot transmit DC power over much more than a few miles without starting to suffer unacceptable transmission losses (we're not talking a few percent here; trust me on this, there's no solving THIS problem without cheap hot superconductors).
Now, both AC and DC motors require a net current in one direction (inductive load, satisfied by reactive power). But current can't be sent very far. So the solution is capacitors. In areas too far from a spinning generator to receive reactive power from the generator, utility scale capacitors are used to create local reactive power loops, satisfying the inductive load.
Some rubes at this point suggest making all load resistive, by putting capacitors in all your appliances. This is not practical. The people who are opposed to it are the insurance companies and their associates like UL. Capacitors... explode. And big ones require a lot more care than the tiny ones that drive your computer fans.
Not forgetting that voltage switching using DC is a royal pain in the butt.
Historically, the easiest way to do so was actually to covert DC to AC and then convert that AC to the desired DC voltage.
And this is important, because one of the things that makes grid power practical is the high-tension power lines that carry the stuff from the power plant to your neighbourhood. If the grid is AC anyway, it's comparatively simple to run an AC-AC transformer to step the voltage up to transmission voltage and then back down again at the other end, without having to worry about who's going to babysit the M-G sets you would have needed floating around all over the shop for a DC backbone.
These days I hardly ever see their logo anymore. Especially on Amazon products the only certification I see is ETL, though I assume it's the same rules as UL?
(often on cheap Chinese crap there is no certification at all)
DC power cannot be transmitted over long distances. This is the original problem that caused AC to win out.
There are two forms of load, inductive and resistive, and two corresponding types of power, reactive and real. If we use a rowboat analogy, real power can be thought of as the oscillation of the oars back and forth, while reactive power becomes the force of the oar pushing the water. Of course, the oars only push the water in one direction, then they're lifted and repositioned to push again.
In DC power, real and reactive power are indistinguishable. Voltage and current push in one direction all the time. It's only AC power where the rowboat analogy comes into play. So, WHY DO WE USE AC?
Simply, current cannot be made to flow over vast distances. We learned early on that you cannot transmit DC power over much more than a few miles without starting to suffer unacceptable transmission losses (we're not talking a few percent here; trust me on this, there's no solving THIS problem without cheap hot superconductors).
Now, both AC and DC motors require a net current in one direction (inductive load, satisfied by reactive power). But current can't be sent very far. So the solution is capacitors. In areas too far from a spinning generator to receive reactive power from the generator, utility scale capacitors are used to create local reactive power loops, satisfying the inductive load.
Some rubes at this point suggest making all load resistive, by putting capacitors in all your appliances. This is not practical. The people who are opposed to it are the insurance companies and their associates like UL. Capacitors... explode. And big ones require a lot more care than the tiny ones that drive your computer fans.
Not forgetting that voltage switching using DC is a royal pain in the butt.
Historically, the easiest way to do so was actually to covert DC to AC and then convert that AC to the desired DC voltage.
And this is important, because one of the things that makes grid power practical is the high-tension power lines that carry the stuff from the power plant to your neighbourhood. If the grid is AC anyway, it's comparatively simple to run an AC-AC transformer to step the voltage up to transmission voltage and then back down again at the other end, without having to worry about who's going to babysit the M-G sets you would have needed floating around all over the shop for a DC backbone.
These days I hardly ever see their logo anymore. Especially on Amazon products the only certification I see is ETL, though I assume it's the same rules as UL?
(often on cheap Chinese crap there is no certification at all)
You sure about that, bro?
https://en.wikipedia.org/wiki/High-voltage_direct_current
Admittedly, HVDC Transmission was not possible in the early 20th century when electrification was taking place. It is possible now.
HVDC Transmission is not at all suitable for suburb or street level power transmission.
It's an edge case. It's easy to "move" enormous potential difference, even lightning can do that.
Yes, well, this is why I'm a certified EE dropout. I can only handle so much funny math.