Comments by "Ryrzard" (@Ryrzard) on "The Engineering Mindset" channel.

@Steve-sg3uz You can't make a comparison to a piston engine and expect all its properties to translate perfectly. This is not the case with electrical phases. Both 2 phase and 3 phase deliver constant power with no pulsation because of the sinusoidal voltage. For a 90 degree phase shift 2 phase system, the phase voltages are proportional to sine and cosine of the angle. Power is proportional to the square of the voltage. So the total power out of both phases is constant since sin²x + cos²x = 1.
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@Steve-sg3uz The sum of the squares of two sine waves offset by 90 degrees is a constant value, my man. Motors with more pole pairs have generally more torque because the flux lines are tighter.
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@Steve-sg3uz Why would you rectify them? We're talking about linear loads like motors. Just plot the power over time in some graphing calculator. Both 2 phase and 3 phase power (plus all symmetrical polyphase systems) output perfectly constant power. Again, electric motors are not combustion engines. Analogies only go so far and don't convey any nuance.
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@Steve-sg3uz He's plotting voltage, not power. Try plotting the power of each phase and summing them up.
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@Steve-sg3uz If you want a more detailed answer: P ∝ V^2 P ∝ sin(x + α)^2 In a 2-phase system: P ∝ sin(x + 0)^2 + sin(x + 90°)^2 sin(x + 90°) = cos(x) P ∝ sin(x)^2 + cos(x)^2 P ∝ 1 P is constant In a 3-phase system: P ∝ sin(x + 0)^2 + sin(x + 120°)^2 + sin(x - 120°)^2 sin(x + 120°)^2 = 3/4 cos(x)^2 + -1/2 sqrt(3) cos(x) sin(x) + 1/4 sin(x)^2 sin(x - 120°)^2 = 3/4 cos(x)^2 + 1/2 sqrt(3) cos(x) sin(x) + 1/4 sin(x)^2 sin(x)^2 + 3/4 cos(x)^2 + -1/2 sqrt(3) cos(x) sin(x) + 1/4 sin(x)^2 + 3/4 cos(x)^2 + 1/2 sqrt(3) cos(x) sin(x) + 1/4 sin(x)^2 = 3/2 P is constant This is high school math. You don't need to be an engineer to figure it out.
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If he understood the equations he'd know that both 2 and 3 phase systems deliver constant power.
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@therealpbristow Square of sines and cosines is commonly written with a superscript right after the sin/cos instead of the whole expression needing to be wrapped in brackets. Though it doesn't translate well to in-line text on a screen if you don't use the unicode superscript characters. sin²x + cos²x = 1
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@Steve-sg3uz Two phase only needs 3 wires though the neutral wire needs to be have roughly 40% larger cross-section than phase wires. It's not that specific systems provide more power per wire, it's more nuanced than that. A 3 wire 2 phase system with 90 degree offset is actually a hidden unbalanced 3 phase system. If each wire carries the same phase voltage and current then any number of wires will provide the exact same amount of power per wire. It also means that all single-phase systems are actually hidden two-phase systems and the reason they carry less power per wire than a 3 phase system is because their phase voltage is half of a 3 phase system. Also no, a 90 degree phase shift 2 phase system delivers constant power so no pulsation happens.
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@Steve-sg3uz Have you had trigonometry at school?
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@Steve-sg3uz Power peaks? Zero in either of them. The power is constant.
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@Trombonauta Pulsing heat can absolutely be picked up by sensitive equipment. It's not about EMF.
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@Trombonauta I'm not really understanding your objection with resistive heaters. They are a really simple example and there's a huge benefit to constant power for all loads (even if it doesn't matter for the device itself), regardless of their application. Resistive heating is just one example where you can omitt complex impedances and nonlinearities.
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@gsofgel You absolutely can
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@Steve-sg3uz 2 phase has rotation built-in as well and it uses just as many wires.
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@Steve-sg3uz If you were measuring power? 0.
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@Steve-sg3uz By rectifying to DC you lose sinusoidal current so that's a completely different scenario from powering a 3 phase load. There's zero ripple when powering a 3 phase load (or 2 phase in a 2 phase system).
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@Steve-sg3uz Why are you talking about rectification in the first place?
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@Steve-sg3uz Sure, but that's not relevant to the constant power property of polyphase systems. Also 3 phase power has a higher peak DC output because the DC is rectified line voltage, not phase voltage, so it's higher even if you smooth it with a capacitor.
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@erigabu1 You can't "smooth" AC voltage with a capacitor. That's not why they're used in single phase motors.
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@JustinLebo-d3t A 3 phase heater has at least 3 heating elements and while individual element will flicker, the sum of their heat outputs will be a constant without pulsation. That's assuming that they are purely resistive. Heaters, especially high temperature filaments, are not linear devices and their resistance changes with temperature and as a result, they produce some harmonics in the current, some of which would not be canceled out by 3 phase current. But generally speaking, 3 phase power provides constant power for linear loads ("dumb" devices).
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@Trombonauta While resistive heaters have their thermal inertia to smooth their output, the constant aspect is critical for big generators and inverters, as well as big industrial loads like motors. But even at a small home that has a 3 phase motors powering a heat pump or AC it's beneficial because the constant power and lack of pulsation decreases wear and noise.
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@Trombonauta Because the other guy mentioned them.
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@Trombonauta He asked whether resistive heaters would still flicker and the answer is yes. But they still operate at constant power because of 3 phase input. So that was the question and the answer. Not sure what your issue is.
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@Trombonauta Because it's a simple example without having to delve into the complex world of motors. And there are applications where a 100 Hz heat flicker may be undesirable since it can be picked up by sensitive semiconductor components.
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@Trombonauta Constant power is better whether the heater cares or not. A single phase grid would be very expensive and under terrible stress all the time due to the lack of constant power output. And no, it's not "more constant power thanks to more phases". Polyphase systems provide exactly constant power regardless of the number of phases.
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@Trombonauta If you're not pulling a constant power but instead a 100 Hz full power pulsation then rotating machines are pulsing at 100 Hz increasing cost and decreasing reliability.
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@Trombonauta This applies to all kinds of loads. Regardless if it's a heater or something else.
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@Trombonauta If you're pulling 100 Hz pulsating power then that pulsation occurs in the rotating machines that are powering that load, dude. Where do you think that power is coming from?
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@Trombonauta I'm really not seeing what the issue is. Constant power is always beneficial regardless of what the load is.
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@EngineeringMindset I'm not seeing you actually explaining that there's a constant power flow in a 3 phase system at any point in the video.
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@Trombonauta Well, the stability of the grid is a good thing and pulsing power is the enemy of that. So a constant power load is always beneficial regardless of the application of the load. The whole reason resistive heaters are even an example is because it's easy to show the constant power in them as was already explained.
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@Steve-sg3uz I think the whole problem is that you're confusing voltage with power. Believe it or not, they are not the same thing.
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@Zarinizarin You don't need integration for this. This is all just trigonometric identities.
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