Thanks for making this topic easy to understand. I have been frustrated by instructors who cannot speak English clearly and don’t know how to explain it.
The clearest , easiest to understand explanation of per-unit analysis I have experienced after 25 years of experience and learning and 2 degrees in EE .......well done mate !
This should have more likes. You do not rush through stuff and assume that the listener is with you. I like that you take the time and give a small example after each statement. It might be a slower pace for a lot of us impatient engineers, but if we actually listen, we can see that all nuances and bases are covered very well.
Great video but I thought you changed each zone to the new base... ah you covered it... but I also thought you have to be in same voltage base and consider turns ratio
My comment is a bit of a side-track, and doesn't involve the 3-phase example at the end of the video. But following along and practicing the technique presented, I'm wondering if some of the examples, if one saw them in the real world, would represent overloads (for the transformers, at least). At 6:39, the presenter explains that choice of S-base (Sb), the apparent power, can be anything, but good practice says you should choose a value that matches (as closely as possible) the apparent power base of your equipment. With that then in mind… In the example at 22:48, the math of course all works, but in that result, is it true that the apparent power is 23 MVA, noting the chosen Sb was only 10? Doesn't that mean we've blown out both of the transformers, one of which was rated 8 MVA and the other 12 MVA? If the example represented a real system, wouldn't you need to ensure the apparent power never exceeded 8 MVA, the (I'm assuming) apparent power handling rating of the lower of the two transformers? I was led to think about this from the prior example showing the nameplate ratings of a transformer at 17:20, which showed it was rated 50 kVA and 3.39%, and the statement following that the percent impedance only makes sense relative to the transformer's base values. Those base values influence your choice of system base (Sb). In the example at 21:15, both transformers were given as 3% and 5% on 10 MVA, and 10 MVA was chosen as the system base. Working the example, the Ipu came out to 2.31∠-17.1° p.u. (assuming I did it right). This is also 23+ MVA. But we chose 10 MVA as system base, because…somewhere this was a rated limit (came from one or both of the transformers, presumably). It seems like only the first example, at 13:13, had p.u. that were sensible for the apparent power capacity of the system (0.9901 p.u.). The video says that power system engineers recognize that values up to 1 p.u. are immediately recognized as a well behaved system. But in the examples presented in the middle of this video, we get p.u. currents around 2.3, suggesting (if the base values were chosen as the presenter recommends) our analysis has /also/ shown us that these example systems are fubar. Reaction?
wonderful video about pu in power systems i have many vids regarding this topic and let me tell you that your vid is the most beneficial vid thanks a lot
You have to follow the ratio of the transformers to get your voltage base in each zone. The 220kV/22kV transformer ratio is still 10:1, so 200 kV in the middle zone must still give you 20 kV in the load zone. We just need to be careful to adjust the impedance of the transformer so it matches the system base voltages because the 220/22 kV is on a different base.
