Lecture 4: Power Factor

[@donmoore7785]

This is an excellent course, and great instructor.

[@michaelandrews5499]

Great instructor. It's been many years since I graduated with my BSEE but I’m picking it up quickly thanks to the great instructor!

[@shahfenil08]

@10:19 This exactly happened to me. In my student dorm I had a crappy power strip. at some point, the fuse of the power trip blew off and I replaced it with a small part of a beer cane. Once I connected the inductance stove + oven on it. with the full power, insulator of the wire started melting (I saw smoke was coming out of the wire). So because of this lecture, I understood that fuses are actually for protecting the wires. :D :D great lectures!! I am just watching it without any particular reason. I grateful to the professor and MIT team to make available such great lectures!!

[@pyro-millie5533]

Omg glad you caught it quickly enough to be safe!! Yeah never replace a fuse with some random piece of metal. You need it to blow safely so your house doesn’t catch fire!

[@pyro-millie5533]

Yo I work in the lighting industry, and so many things mentioned in this lecture are things we work with every day! We have a whole characterization test we run on LED drivers (switch mode power supplies that are usually programmable) to determine if power factor and total harmonic distortion are within spec! I’d have to look at some standards to see what the minimum allowed PF is for approval, but I’ve seen it as high as 98-99% for most drivers running in their expected operating range. It gets ugly if you program the current really low and put small loads on them though. Which is really interesting to me. So cool to see where these calculations come from and get a better understanding of what they measure! Loving this lecture series so far!

[@stratfanstl]

In my EE curriculum, another 3 lectures would have been spent on exhaustively reproving the calculus behind the orthoganality of sinusoidal waveforms. And no student would have emerged with any intuition about how to use that fact in solving an actual design problem. Great material in this series.

[@PROShineKITO]

Dr. David Perreault at his best explaining a "complicated" concept such power factor in a magistral way!

[@erikev]

Great to see that MIT is doing trade school level teaching. Hope this is not only online but also in person. Good luck.

[@saurabhsorout203]

amazing teaching style and amazing storytelling to prove the point.

[@WeaselVaughn]

This camera man deserves a raise.

[@peternotarfrancesco2614]

And the sound person

[@jmbii9545]

and the professor

[@sporkeh90]

Great course, really amazing MIT puts this up for free. The power situation in the US amazes me though, 1.7kw on a breaker? in 2024? damn.. thats less than half of the average 16a 230v breaker in most other parts of the world.

[@lidarman2]

This is awesome. I got my undergrad in EE but never studied power electronics in much detail. This piqued my interest since at my job, we have a debate about how bad switching power supplies are for noise sensitive detectors but I feel this might put a new light on how great modern supplies work. Do I work with old school dogmatic people and this will show that we need to get with the new engineering ideas? Enjoying these lectures so far.

[@pyro-millie5533]

I work with switching power supplies a lot (LED drivers in my case), and there are actually limits imposed on how much noise the ones we work with are allowed to emit. (It might be a federal regulation actually). We do EMI tests on them. (I don’t for the life of me know how the EMI tester works yet, but that’s what its for). Some supplies have a fairly large ripple on the output you can see with a scope (and use to calculate the switching freq), but most I’ve looked at are pretty well-smoothed. Which is impressive for something switching hundreds of thousands of times per second tbh.

[@pratyushmundra861]

28:06 - Why would there be an offset in the half-wave rectifier line current? --- 27:47 - I was confused about the pink current waveform (AC line current) since there were sudden jumps in the current - and inductors wouldn't allow that. I mistook it for the load current, but under the assumptions of: - No line inductance or resistance (so current can change instantaneously and maintain a stable value as voltage changes) - Huge inductor on the load side (ensures current remains constant) - Ideal diode (instantaneous turn on & off) The line current pulse (square wave for half cycle) would make sense.

[@eduardotoloza4211]

Thanks for making this public. As an Electrical Engineer, it is a pretty beautiful class.

[@musicmakelightning]

Great class, great instructor. I wish David had been my power systems professor.

[@07sanjeewakaru]

Best power factor elaboration I've ever had..❤

[@jamescollier3]

Q: Is it too late to change my major to philosophy?

[@_soupnazi]

this is a graduate level course, so yeah sorta

[@jcolonna12]

This class is inline with my undergraduate class

[@DungPhan-rs1dt]

Quy luật của vũ trụ là cho cái này nhưng lại lấy cái kia. Dòng điện đi từ cực dương, (+) thêm giá trị đến cực âm (-) bớt giá trị thì mới làm đèn sáng tạo ra công suất, hiệu suất , năng suất, hiệu quả làm việc cao ( thiết bị điện hoạt động có hiệu quả ,phục vụ nhu cầu của con người ). Vậy bạn không nên buồn khi cuộc sống đầy gian nan và thử thách vì vũ trụ cho cái này nhưng lại lấy cái kia. Muốn có thêm giá trị mình phải bớt đi một giá trị tương đương. The law of the universe is to give this but take that. The current flows from the positive pole, (+) adding value to the negative pole (-) subtracting value, to make the light produce high power, efficiency, productivity, and working efficiency (electrical equipment operates with high efficiency). effectively, serving human needs). So you shouldn't be sad when life is full of hardships and challenges because the universe gives this but takes that. If you want more value, you have to subtract an equivalent value. Nhận dạy kèm Anh Văn địa chỉ Thầy Dũng 91/2 đường 15, khu phố 4, phường Tân Thuận Tây Quận 7 ĐT [phone]

[@brucetenet6140]

Great course! Amazing professor and camera man. And the subtitles helps a lot! Thank you very much for uploading this playlist.

[@beeman1885]

Reminds me of my undergrad EE classes (not at MIT). For real life practicality, I would have preferred much less math and much more emphasis on circuit design, component selection, part reliability, consumer safety, practical EMI/EMC effects, etc. All the stuff you have to do in the real world.

[@SuperMnunez]

We have trade schools for that sort of stuff

[@beeman1885]

@@SuperMnunez Trade school grads might install and repair but they don’t design for production.

[@CutoutClips]

I think a lot of that is discussed at some point in the course, as the final project involves using real components to design a buck converter circuit with a closed-loop feedback system. The assignment provides a list of specifications such as input voltage range, output voltage, output ripple, minimum efficiency, etc that all must be met. It seems like a fairly good blend of theory and practical application.

[@luisjalabert8366]

I think what he says at around minute 6 can only be true if m and n are integers, and it's not true for just "different frequencies" like he mentions.

[@duhnboa5447]

EDIT: This isn't completely correct, see my following posts I think if you integrate over 2pi * a common multiple of m and n, it's still zero, even for fractional numbers. Not sure if that still fulfills the definition of orthogonality. Harmonics are always at integer multiples anyway.

[@luisjalabert8366]

@@duhnboa5447 no, it's not zero for any arbitrary fractional pair of numbers. Just think about one of the sine functions having a very low frequency, so that in the interval where the other one does one cycle, the low frequency one is equivalent to ~kt (since its argument is close to zero). Then you would clearly have a non-zero integral. Like I said, this can only be true for integer values.

[@duhnboa5447]

@@luisjalabert8366 now integrate over a period of k*T where k is a common multiple of 1/m and 1/n (assuming m, n rational numbers), and T = 2pi/omega I wrote 2pi* common multiple of m and n above, but on closer inspection, that doesn't make sense. Whoops, at least I'm not alone in that, Prof. Perrault's interval of 2pi doesn't make perfect sense either so let's say: integral 0 to k*T of sin(n*omega*t)sin(m*omega*t) = 0 e.g. for n = 5/6 and m = 2/3 we could look at k=6T. 5 full periods of the n term = 4 periods of the m term. Voilà, the integral is zero. While all this might be an interesting question to nitpick about, it's irrelevant to the lecture because, as I said, harmonics are *integer* multiples of a base frequency

[@jw106]

@@luisjalabert8366 The instructor mentioned that the two sines must commensurate over the integration interval. In that case, also for non-integer m and/or n, they are indeed orthogonal and the integral of their product will evaluate to 0.

[@duhnboa5447]

@@jw106 Thanks for your answer. It seems like KZbin deleted my post for some reason. You said it better anyway!

[@manfredinotarangelo5525]

I’m doing the 6.622 assessment. I Don’t understand why in the solution the period is pi and not 2*pi. Can anyone help me please?

[@hassegreiner9675]

Evene worse - the meter is running wild even if you don't receive any power

[@jasonpfeilsticker5692]

love the lectures but this guy's "(t)" looks more like "/A"

[@davidwilkie9551]

A reiteration of this essential practical experience in Circuitry in parallel with 3BLUE 1BROWN graphics of Musical Measure Theory, and Math-Physics of Euler's e-Pi-i Superposition-point at the instantaneous Origin of the Unit Circle Quantum-fields Mechanism is left to the imagination.., all the aptitude inherent in beginning students to detect correlations in temporal thermodynamical correspondence. (I'm "too old" by way of compounding combinations of relevant information that take long-term analysis to reorganize and reorientate) This topic is global in scale, because it's Universal. What does "division by zero-infinity actually mean => recognition of coherence-cohesion objectives.., and the illusion of separation delusion.

[@caleb7799]

Mr. Smacky over here. lol