How 3 Phase Transformers Work - why we need them 

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As a college grad in Electrical Engineering you guys won’t find anything better than this video. This is as good as it gets.

Just wanted to say I really appreciated how you re-orient some of the diagrams that position the schematic how it would be sitting in a physical transformer...as someone who is just curious "how stuff works" this is something I've never been able to wrap my head around you could have separate transformers doing 3 phase power even though I've seen the "triangle and Y" positioned diagrams countless times I just couldn't wrap my head around how it was possible until I saw your diagrams MOVE in the video and something finally clicked how the "real world position" would be vs the "diagrams" you see all the time! That was great!

I am an Electrical Engineer graduated in 2020 I find your videos very helpful for my MEP Construction Job and understanding the National Electrical Code and Electrical theory.

This RU-vid channel is gold-mine

As a retired Dutch engineer, working with single fase and three fase only, without any half tap at 120 Vac, this video finally explains how it works in the US. Thank you very much.

I’m showing all my substation interns this video to help them understand the madness behind electricity. ⚡️ As a PE working in substation engineering, I wish I had videos like this when I started 10 years ago. I truly appreciate your gift to teach. 🤝

Some interesting things about 3phase transformer connections. Delta - Y is usually preferred. Thats because 3rd harmonics don't get transmitted back into the incoming line. A zig-zag transformer can be used to create a central ground for delta connections, but that is only used for special industrial settings, at least to the best of my knowledge. In the US, Delta high leg and open delta are becoming obsolete. They were an out growth of the split phase systems used in residential power configurations. They are usually not installed in new service systems anymore. The vast majority of operating ones are legacy connections.

this channel is 100 times better than my professor......

I just want to say big Thank you for your videos. I am in an electrical apprenticeship and these videos are really helpful with understanding how these equipment and thoery works. Ever since i started watching your channel i have become better at trouble shooting and overall a better electrician! THANK YOU!!!

In 2005 when my mother remarried and moved to my stepfather's farm, we had an open delta 3 phsse, because we had a grain dryer, conveyer and large auger with 3 phase motors, with the majority of our loads being 120/240 single phase, transformers on the roadway, pole with meter and site disconnect in the middle of barnyard, single phase ran to house, 3 phase to barn, where there was a 3 phase panel dedicated for the motors, also feeding a single phase panel beside it for the other loads. Otherwise roughly 1/3 of the panel slots would be wasted because the B phase (high leg) is unsuitable for single phase loads, which is a major disadvantage of a 4 wire delta service and thus the 208Y/120 & 480Y/277 (or 600Y/347, if you happen to be in Canada or a few areas in the US) is a much more common and useful configuration. Open delta is still fairly common on some farms and small commercial buildings where the customer has mostly single phase loads, while also requiring limited amounts of 3 phase power, since it's cheaper to set up than a wye bank.

This might be a bit dense for a total newbie, but I'm finding it a wonderfully efficient, clear, and comprehensive refresher that really brings together the substance of multiple other longer sub-topic videos.

Ok. Ok. I understand that this might be more information than most people even care to know about how electricity (like the stuff that powers your home and, well, life) works, but I found this single video to be just about the best crash course on the subject that I've ever seen. He's managed to condense an entire college course of material into one video. Blew my mind at how well he did this. Also, don't let the British accent throw you. He's explaining the USA power grid.

I need to watch the rest of the video, just noting at the start the video shows peak voltage of 120v; 120 is the RMS voltage, peak is 169.7v.

Funny how different it is in various countries. In Poland, for instance, majority of households (at least not flats, but freestanding buildings) uses 3-phases split from 400V.

Thoroughly enjoyed. Even your sponsored ad was great. If I ever need a 3ph, MW transformer for my garage shop, I'll be sure to contact Maddox🙂

Thanks for the breakdown. As an electrician for 14 years, I've always wanted to know how the different configurations of delta/wye affect voltage/current output. The most intriguing thing is the ungrounded delta primary which gives uncommon voltages to ground. Very cool....

That was a GOD level explanation. Not even professor level...... But, GOD level ....... I bow down to you

THANK YOU! This is the best layman explanation I've ever seen.

Thank you for this video. So detailed and easy to understand. Goes step by step and doesn't go backwards, but rather it references what you learned earlier in the video and applies to the current topic.

The best explanation I have seen. Thank you!

Loved the video! Amazing work as always!

I use Maddox Step-Up/Boosting and Step Down/Bucking Transformers at work in both low and high KVA applications. I recently used a 208v Wye Secondary as a primary and stepped up to 480v Δ as secondary. I called the transformer company first to make sure this was allowable. It was and I have no issues. Maddox is a very knowledgeable company to work with and have great people on staff to answer any questions about their products and have many transformers in stock.

Great video, I like how you always go much more in depth than I expect while still keeping it simple to understand with some basic knowledge. Best channel in this niche IMO

Wow! Spectacularly concise info I've not seen elsewhere in one video, or 10.

Man your videos are nothing short of amazing! Thank you! This si very much appreciated. Please continue making these amazing videos! 🎉❤

Totally bought one of those mugs! Thank you!

Best video I have seen explaining the intricacies. Thanks

I use your videos to help train my technicians. They are very insightful, and well presented. Your channel is a valuable tool.

Excellent presentation. Thank you.

Top tier explanation as usual, can't thank you enough for all that you do!

Thank you for all you do! This is amazing! I'm currently an electrician in training and this kind of concise detailed content is what society needs.

Brilliant visuals as always!

I do not go into splitfase as we have 230/400, all our grid is 3 fase from producer to home. Most of our grid except a small part of 10kv and 60kv (60-150-400kv are airborn usually) is plowed down in the ground, and it will create less blackouts in adverse weather. All these different voltages and conversions, 120-208-240-277-480, 230/400 50hz is all we need in 90% of cases.

Thanks for this vedio. I was searching for this for so long. ❤️

I've been waiting for a video like this!

This explained so much to me that I probably should have already known. Thanks!

Fantastic video, nice work and worth downloading and saving.

Very professional video, thank you

Thanks and Thank you. best ever detailed explanation.

This is hands down the very best channel on RU-vid BY FAR. you have taught me and the rest of us so much. So very very grateful for the engineering mindset. You've turned me into a total nerd and I LOVE IT!!

Love your explanation!😊

Excellence (especially in knowledge sharing) is incredibly enjoyable as well as valuable. Many Thanks!

Just had my supply upgraded here in the UK, was a 4 property looped supply now 3 phase, nice bit of future proofing.

Fantastic video for Advanced Learners.

everything is very well explained and the graphics are great!

Thank you for your teaching.

Nicely done, very concise and comprehensive. Thank you for your time and expertise offered for our benefit in this production.

Another great video! Straightforward but detailed narration, killer animations and photos! Wish I had this back when I learned about transformers (beats static diagrams in a textbook!).

Fantastic video, but to explain the ground in the y configuration you could also explain the cases of simmetric and balanced where current and voltage have the same module and phase shift of 120 degrees therefore in the central node the sum of the 3 currents is 0 so as to obtain the return of the neutral

Awesome explanation!

Very well done.

Great video! Glad to see youre gaining enough momentum to pick up some commercial interest.

Thanks! Great videos and explanations. 😊

Great info!

Very good explanation.

Thank you for your sharing

Very good explain thanks for vedio ,

I finaly understand 3 phase. You made it easy to understand. Thank you!

Excellent! Thanks!

I really like your videos! There isn't another RU-vid channel that does explain electrical engineering as you do! CHEERS. Also, do you mind making videos about smart grids, dynamics and stability, or HVDC topics? I am currently doing an MSc in Power Engineering in ICL and I find those topics quite interesting to promote Electrical Engineering to fellow students.

such a great summary how the grid works

Great video thanks 😊

This is such a good explainer video - I wish this type of material was available back during my college days. Electrical engineering teachers need to be showing this vid in their classes (and the school then donating to the creator).

A thing or two that I noticed were missing - even if one of them is not necessarily germane to 3-phase specifically: "Corner-grounded delta" - this is a situation where one of the three legs of a delta secondary is connected to ground. This is ancient stuff at this point, but anyone working with electricity, or working at old industrial sites needs to know about it. You will have (in, say a 480V delta secondary) 480V from any leg to any other leg, but you'll get 480V to ground with only 2 of the three legs; the third leg will show 0V from hot to ground, even when the system is energized. This can cause deadly mistakes. Scott-T transformer: this is another ancient piece of tech that shouldn't be around any more, but sometimes things just stick. A Scott-T wound transformer can convert between 2-phase (not the split-phase system described in this video, the phases angles are separated by 90 degrees) and 3-phase systems.

Here in northern Europe, it's normal to have 3 220v/400v phases in apartments and houses.

Top explanations, thank-you. I was not familiar with "high leg delta", I have never come across it here in the UK. I was however aware of the 60hz USA vs 50Hz Europe. The centre tapped 120V domestic mains is a US thing too. In the UK we just get neutral and a 240V line.

Good video and explanation. You have some complicated transformer setups in the USA, in the UK we have single or three phase transformers opposed to your 3x single banks. 400v tpn and 230v spn.

Half semester of basic electrical theory in 24min. Where were you when I was graduating? 😂 Amazing.

0:22 In Europe the output is always a Y configuration. The voltage is 220 to 240 volts to ground. Or from phase to phase 380 to 420v. Often referred to as 230/400V...... 230* SQR(3)=400 V Rarely there is 230V from phase to phase (and 127V from phase to ground). The domestic sockets are connected to 220 to 240V 50Hz. Mostly 230V 50Hz

Finally a video i cannot watch in 2x. And need to rewatch at least once. Can someone explain why the resistance scales with amperage but not so much with voltage? Why do some countries build higher highvoltage cables than others? I forget the formulas

Not watching the video, saw the title and had to say very clever. I liked it

Excellent work. Most of these videos stop at kindergarten level. I remember being thoroughly confused the first time I encountered a high leg delta. Superficial knowledge of the theory without fundamentals is good for trivia night and useless in a dark sub-basement with a multimeter that's telling you that you don't know what you're doing. Thanks for going through the trig; the math is really straightforward once you actually start paying attention and working it out properly.

So what makes design engineers choose one transformer configuration over another? Type of equipment and demand on client side is all i can think of? Why would you want a delta vs a Y on secondary? If voltages are the same? Are there benefits/drawbacks to have Y as secondary for neutral safety?

Really good video, well put together as always and started really strong. Feel like it fell away at the end though and spent way too much time doing calculations at the end. Would’ve been much more interesting/relevant/beneficial to hear about some of the ancillary components to a transformer. Eg. their mechanical and electrical protection systems (buchholz, WTIs, duo bias). Earthing transformers, LERs/NERs. For all the talk on winding configurations, no mention of a Z winding which is much more common than an open Delta at least in my experience. Would love to see a part 2 to this video

I dont understand anything but I like it! Such delicate explanation

You’re awesome for this. Does your PDF you mentioned discuss corner grounded delta ?

Any chance you could follow this up with pros and cons of each system and give examples of why they are selected? And has the selection been changing because of the reduced need for 277V lighting (moving to 120V LED)? And include thoughts for other upcoming changes (maybe to accommodate energy storage systems}? Thanks, as always, for the excellent content!

Great video, now I know where to buy my substation. Wonder what I should do with it

That's actually one of the best video on tf

thanks the power company was telling me that I have a old "d" system in my building and never knew what they meant by it now I have a better understanding

Your video is very good and helpful! Thank you for taking so much time to put it up there. I am not electrician but have some electronics hardboard and circuits background. Now I want to use 110-120v device (Tv, laptop, fridge, and power drill …) in 220-240v source outlet; which normally will blow if I did! I wonder if I can use 2 or 3 three phase transformers to construct (as you did) & create a 110-120v for use with my devices? Is there an easier and better way to do this? Thank you!

Sweet dutch electricity. 400V 3 phase at modern homes. Serious juice 😄

Interesting, I didnt know there were so many single phase homes. I knew there were some but I dont recall the last time I saw one.

always wondered why they use laminated sheets of metal for transformer core rather than a single rod of metal. thanks for explaining why (eddie current suppression)!

The video mentions for residential connections that only one of the three phases connects to the transformer and the other connection is to the neutral side of the grid. While this is correct in some situations, this is called a Wye connection but it is not the only way to do this. As a matter of fact, another method is the single phase Delta connection and it is more widely used for residential connections in North America. The Delta connection uses two of the three phases, both of which feed into the H bushings of the single phase transformer. You can always tell if a transformer is connected as a Delta because the Delta connection is a phase to phase connection. When compared to a Wye connection which is a phase to neutral connection. If both bushings on top of the transformer (H bushings) are being fed from two of the primary high voltage lines, then that is a Delta connection. The secondary side of the single phase transformer are the X bushings and when going into a residence will provide 120/240 volts which is a single phase Delta connection that is referred to as Split phase. This connection on the transformer is known as a Delta Delta connection which is specifically, a Delta primary connection and a Delta secondary connection. While the above connection is the most widely used for residential in the USA, there are many other connection methods used in the USA and across the world all of which are either Delta or Wye connection or combinations of both utilizing one, two, or three transformers to achieve whatever the customer needs.

What crazy way of doing things but yet it still makes sense

This video is why in Europe we mainly just have one type of transformer. Everyone except heavy industry etc use 220 -240 VAC so none of the delta or wye nonsense. Just imagine, not just the less maths but the fewer spare parts to carry to fix the damages. Also, because of standardization hopefully cheaper products. Higher voltage finally means a greater margin to serve. As for safety, even 12vdc can kill you under the right conditions. Notice the term "right conditions" and avoid it at any cost.

Thank you for the thorough explanation, now I know that actually i know less about the power lines over my head

No, the sine waves exceed 120/240 volts. 120/240 volts are merely the average of one cycle.

This video has answered a question that's been bothering me for a long time: when I use a Public Level 2 EVSE to charge my car, I only get 208 volts/32 amps (6,600 watts), whereas when I use my own EVSE at home, I get 240 volts/32 amps (7,680 watts). Public chargers always take 45 minutes longer than my home EVSE to charge my car, and now I know why! Public EVSE's, typically in shopping center parking lots, are apparently being fed off of 3-phase, 480 volt Y or Delta transformers that only supply 208 volts per phase, whereas the NEMA 14-50 outlet in my garage at home is being fed from a center-tap 240/120 transformer that gives me a full 240 volts across the two hot lines. A 3-phase transformer with 480 volts per phase, is wired to give 120 volts on the secondaries, between any 1 of the output phases and the neutral. All well and good for supplying 120 volt ac wall outlets and lighting systems. If you tap any two of the phase coils, which are 120° apart in phase angle, you will see that when 1 phase is peaking at 120 volts, the other phase has 88 volts, and the combined voltage at that moment is 208. In a residential transformer, the magnetic field of the single phase 480 volt primary feeds a secondary coil wound 2:1, yielding 240 volts across the full coil, or 120 volts across either end of the coil and the center tap. This leaves me with just 1 question: why would commercial buildings be okay with 208 volts for running high power equipment, when standard residential service is 240 volts, for powering an electric cooking range, electric water heater, and heat pump or a/c compressor? Especially when you are powering an electric motor, like an a/c compressor motor, I would think that a motor designed for 240 volts would maybe overheat, or run at the wrong speed, if fed only 208 volts? Why isn't all power service 240 volts for everyone?

What a video !!

I'm in one of the few countries in the world where delta connections are used between the phases. 127/230 and it's the 230 we use residentially

Good video but I would like to clarify that split phase is not one phase split into 2 opposing phases 180 degrees apart. Split into 2 voltages yes (120/240), but not 2 phases with opposing voltages, that is a common misconception. If it was somehow 2 opposing voltages on the same circuit then overall voltage would be zero since they would subtract from one another. The reason we see 120 and -120 on the multimeter when attached from neutral to each hot is simply because people tend to flip the leads when testing the second hot

I liked your video, even if I'm not living in your USA, still it is valid information in regions where 240 volts and 50 Hz are common. Keep it up! 13:07 Why are there appliances with 208 volts and outlets of 120 volts? Why are there even appliances that deviate from logical calculations like 240 devided by 2 is 120 and so on. I don't understand why for instance a hairdryer needs 120 volts and an oven 208, is it not better to either let an oven be at 240 volts? I'm puzzled...

I've always wondered what those big green boxes were. Find it kind of funny that he is talking about 240 volts. I replaced a 240 line for a neighbor a couple hours ago

Phenomenal !!!

Now I understand how you can have a two transformer three phase. Also the explanation was wonderful explaining the stinger leg of three phase. Now if someone could explain why I shoot for 185 volts when we build three phase converters. 😂

it is a cool video. in germany it is a bit different wich transformer is used and where it is placed and also split phase is not a thing here but for the us this makes sense. you mentioned the taps, here in germany wie have 400v on the secondary and 10kv to 30kv on the primary. the villages have usually a closed loop 400v system wich goes over fuseboxes to homes in lines and on one line are 3 to 10 homes. on the closed loop of 400v are depending on the size of the village 2 or more main transformer each of them have a automated primary coil length system to hold the 230V of each phase. so there are not fixed like yours but can vary automatically. modern transformer changing this with a control system but older did this mechanically. i meam the winding change is still mechanically bit the control system is now with a computer. also be said if something is too off or the max/min winding is reached the transformer disconnect automatically. frequency can also change depending on the load but this is also controlled and can trigger a disconnect. this usually happen if a lightning strikes near by or you have a dead short on one of the fuseboxes or the loop it selfe. now this systems disconnect so fast that the 10kv to 30kv power line this barely notice. what i will say the frequency is not on every part in europa the same it is always a bit off but mostly by 0.001. it depends on the load and energy generation in that region. i think you have in the us a similar system to hold the voltages and protect the system if something bad happen, to prevent the system of collapsing. i work in a biomass powerplant and we se on the control panel a small part of the grid. we have 1 to 5 birds a day that shorting the power lines. normally this does not affect the grid because the bird explodes instantly and nothing is left that would keep a short. i speak from big birds like eagles. we dont see if someone sorts a outlet at home or shots his 63A main fuse box over all three phases. this load is way to small be be seen because the transformers in between dampening the effect. the powerplant i work in, we are hoked up to a 20kv power line and we make only 20MW of electrical power and burning about 800tonns of wood ships a day. i am a electrician by my self and always search for videos and materials to show the trainees so they can understand. this is a really good video i can show to refresh the basics and show them the difference between the america and europa power grid.

I want to mention one thing, the lines between a power source and a load are called line. Phase is a measured voltage between lines or neutral.