IV.A.7. Three Phase Transformer Connections from Single Phase - NCEES Electrical Power PE Exam

[@dougrockwood1201]

The line you draw at 8:18, connecting C to A . Isn't that a direct short between the legs? Or am i missing something?

[@electricalpereview]

Hi Doug, technically speaking, yes, that is a short but not in a way that would cause a fault. That specific connection is what connects the final corner of the delta triangle between the first and third windings.

[@dougrockwood1201]

Thanks, for the response. I'm still confused though. Either you made a small mistake drawing it or I have failed to understand the concept completely. I just want to make sure either way, it could easily be the latter as i am not that experienced with transformers. It seems like the delta side of the delta to wye transformer is wired differently than all the other deltas and Im not sure why. For example the corner of the delta between the first and and second coil is not connected to anything, its just left isolated? and then Line A is wired directly to line in C in a way that isn't done on all the others, I dont understand why it wouldn't pull infinite current since there is no coil(s) between line A and C. Thanks for your time

[@electricalpereview]

I see you what you mean, the b and c tap connections need to be shifted upward, good catch, thank you. I'm going to mark this video to be edited.

[@TheMadMagician87]

@@electricalpereview Thanks for your videos, theyt're very good. Whenever you do get a chance though, please amend this (or at least the description) as whilst the video is very helpful, that particular mistake does throw some spanners in the works when one is learning (i.e. it's not necessarily clear to a beginner that 8:18 is a mistake and that it definitely should be analogous to the other deltas).

[@electricalpereview]

@@TheMadMagician87 Thanks! It appears that KZbin has officially removed all annotations from all videos in 2019 so the previous pop up that noted the mistake no longer appears on the video. I updated the description to point this out, along with where in the video to find the correction, and included time stamps to make it easier to spot them. Unfortunately, there is no way to replace this video without losing the view count so we are going to keep it "as is" for the now. However, the corresponding video in our review course at www.electricalpereview.com does have the most up to date version of this video with the correction. Thanks for the reminder, and I'm glad you've found our videos helpful. If you are taking the PE exam, then good luck! Don't forget there is a tremendous amount of free in-depth articles with step by step example problems on our website that you also may find helpful at www.electricalpereview.com/free-articles/

[@Amritadabbiru]

I was never comfortable with these transformer connections but your explanation made it really easy to understand. It is very well explained in this video.

[@prarthana9117]

This is one of the best explanations out there for transformer connections! Drawing the three phases separately really helped me grasp the required phase shifts for delta wye and wye delta.

[@electricalpereview]

Thanks for the kind words Prarthana. We enjoyed having you this semester as a student in our online program. Best of luck on the PE exam.

[@rjulian1]

Zach - Thank you for the easy to follow explanations of the different transformer connections. It is very helpful to see each connection side by side by side with the differences between them!

[@hc6775]

From phase shifts to the multipliers, this video will really help clarify a lot of confusion that surrounds transformers and different transformer connections. Would recommend to anyone.

[@danpaul1743]

Demystified a scary concept into simple terms. The diagrams and dialog are key to making the concepts click. I'm printing these off for my resources!

[@sheasuber6222]

These videos are the best help on the market.

[@EEzshepardVT]

Really breaks down the connections on each side of the transformer. A lot of sources seem to gloss over what is really happening on each side and seeing how you get the root 3 factor and phase shift for delta to wye/ wye to delta is very valuable

[@guilty96]

Great explanation for confusing 3-phase transformer connections

[@juliusraposa4747]

This was much easier to understand visually. Thanks for showing direction of current and voltage as well.

[@DB-iv6ks]

Thank you for another awesome video, this is a great all-in-one summary of most common xfmr configurations

[@justinobenchain93]

This was one of the most helpful videos I have watched on this topic! It really helped clear up transformer connections for me.

[@isaacmatute5325]

This video goes very in depth how to connect all the various transformer types and helped me understand where to use the square roof of 3 mistery

[@electricalpereview]

Thanks Isaac, glad to be of service.

[@assadcod5956]

Most Helpful video ever

[@electricalpereview]

Thanks Asad, glad it helped.

[@arashmoazami6658]

Great job Zach

[@miahamster333]

hi! I think on the wye-side of the delta wye you meant to write "V B-C" instead of "V B-A" around 10:15? Or, am I missing something?

[@joellumbala5684]

thank you for posting this video .... i have a question though how does the connections changes when using an additive polarity transformers ?

[@electricalpereview]

Hi Joel, the dot typically represents the positive voltage reference for the winding it is associated with. Shown above is additive polarity. Subtractive polarity would have the dot on either the primary or secondary winding moved to the other end of the winding. When this happens, current flow on the output is reversed compared to additive polarity since the positive/negative voltage reference has just been reversed. To better understand this, think of a single ac power source drawn on a circuit. Current always flows from the source in the direction of the negative to positive reference. The dot in transformer polarity is essentially showing where the positive "+" sign reference is for that specific winding.

[@kenrussel4670]

Well done.

[@SP-xm1gx]

key concepts easy to understand

[@axelrei96]

Hi Sir, i'm very glad have found your video. i have some questions may you can help me. 1. so, it is possible to build three phase transformer from single transformer? 2. like example, i wanna make 240V - 24V three phase transformer from single phase. how about the source of a, b, c, (primary windings) we just make a seri connection on a, b, c, and use single source or make different source for every single a, b ,c ? 3. how about the angle? it is automatically have a 120 degree if i follow your connection? GBU.

[@electricalpereview]

Hi Axel, I'm glad you enjoyed the video. 1. Yes, but to build a three phase transformer from a single phase transformer, you will need three total single-phase transformers. You may then connect the primary and secondary windings of all three single-phase transformers in either delta or wye depending on the connection type needed. This group of three single-phase transformers is what makes the three-phase transformer. 2. In order to make a 240V to 24V three phase step down transformer from three single-phase 240V to 24V transformers you would need to connect them in either delta-delta or wye-wye. Anytime you connect transformers in wye-delta, or delta-wye, you introduce both a 120 degree phase shift that will either lag or lead, and an additional √3 multiplier that will either make the magnitude larger by or smaller by the square root three depending on if it is wye-delta, or delta-wye. This is not a concern with delta-delta or wye-wye connected transformers.

[@axelrei96]

Electrical PE Review Ok. Thanks sir..