 Good afternoon. This is Guillermo Salvatier, your host for Perspectives on Energy. And today we'll be talking about the second in a series of NERC exam preparation, where we'll be covering transmission. Hey, welcome back. And again, I'm Guillermo Salvatier, I'm Director of International Services for HSI. And I'm also your host tonight's episode of Perspectives on Energy. And on here, we're taking the time to go over different sections. Last episode, we went over balancing. And that part of the exam today, we'll talk about a few questions regarding transmission and transmission operations. Now, some of you may know that the NERC exam, usually what we cover is the RC, the reliability coordinator portion of the exam. So usually, these have a little bit of a challenging problem for some of these test takers. And a lot of cases is usually due to the fact that they may not have ever worked on the transmission system. Or other times we noticed it's usually a problem with our understanding principles. Either way, in our NERC exam prep program, and the course, and the online training as well, usually do a pretty good job of getting test takers ready to be able to meet that challenge of a NERC exam. At this time, it still has a pretty rough pass rate, like somewhere 65%. But usually with our program, they tend to score a lot higher and have a much higher success rate when they take the exam after going through our online training. And then on the four day instructor led course that we offer quarterly, I believe. And of course, we have a test prep Friday class every week where they get everybody on the class, which is part of the course page subscription to that program. So usually they get to answer questions, go over exam problems every Friday for a couple of hours. And if you're a test taker and you're in our program, I certainly encourage you, strongly encourage you to make sure you attend those Friday mentoring calls. All right, so without further ado, let's go ahead and talk about the first question we're going to cover today. There we go. So one of the questions you'll see in the exam, right? And a lot of them are basically more based on scenarios rather than memorization. The reason being is that memorization doesn't really challenge your understanding and knowledge, doesn't really test your understanding and knowledge of the actual workings of the power system. So in this case, we have something very simple, we got two buses, right? And one of those you're being shown a series of transmission lines connecting both, right? So of course, these are both 230 heavy buses, right? They got three lines, all the lines have the same impedance, right? And the question here reads that a simple power system is composed of three lines connecting generation and load. Each line has the same impedance and thermal limit of 500 megawatts. So each line cannot exceed 500 megawatts, right? The next part is each line is initially loaded at 300 megawatts. So here they give you the components of a formulation of a problem, right? So the question now reads, if one line trips, what will be the loading on the shortest remaining line? So the shortest remaining line, that shortest part is the detractor, right? Because basically all the lines here have the same impedance. So for all intents and purposes, electrically, they're all the same in this case, right? So in this case here, if all the lines are in service, when they are in service, right? Each line is loaded at 300 megawatts. That means there's three lines, 300 megawatts. That means there's a total of 900 megawatts flowing between the bus on the left to the bus on the right, right? And you're noticing the generation shows you 900 megawatts down there right below which says Gen 1000 MVA. Well, they show you 900 megawatts flowing, right? So the question here is if one line trips, what will be the loading the shortest remaining line? So now you're losing one of those options. So now you still have 900 megawatts flowing from one side to the other, but now you just have fewer lines. And since the lines are all the same, you're not going to divide those 900 megawatts. Instead of three, you're dividing it by two, which means the flow will flow equally on both of those lines, which 900 divided by two is 450 megawatts. And hence, that's why the answer in this case is delta D, 450 megawatts. And that that's distributed equally on both lines. Granted, this works if you have lines of the same impedance, right? If you have different impedance system, a whole different animal, right? So let's go ahead and go to the next question. There's going to be a slightly, this won't give you a bit of a twist, right? Very similar system, right? Same layout, but you're noticing now that there's different impedances, right? So what happened? A simple power system was composed of three lines connecting generations load. Each line has different impedances as shown in the diagram. So you have line one is 25 ohms, line two is 70 ohms, and line three is 30 ohms. So a lot of cases, most of these nerd exams, they're not going to test your mathematical or arithmetical skills, right? They, they're more concerned with concepts. So they're going to break things down rather soon. So the question says if line one trips, what is the loading on line three, right? So they're being very specific about which one trips and they're being very specific about which one is going to be, you're going to be measuring, right? So if you lose line one, that's 25 ohms, right? 25 ohms right now isn't that important. That piece of data is another detractor in this case, right? So right now, you know that you still had 900 megawatts flowing, right? From, from, from left to right, from generation to look right on that bus. So the question is if line one trips, what's the loading of line three? Well, in this case, you're doing a ratio, right? So 900 megawatts of that is going to be on, so dividing those 900 megawatts, it's basically doing a 70, 30 percentage in this case. So you'll be grabbing, that'll be the answer here will be 630 megawatts because of course, you're going to have a lot less impedance of line three and a lot more impedance of line two. So in this case, you're, you're dividing that and, and if you add them up, right? For example, you're looking at 900 megawatts and then you're getting like, for example, 30 percent of that in that case, maybe do a quick math on that, right? And that will work out to that amount, right? In other words, or 10 percent, right? Of 10 percent of 90, for example, 900 will be 90, right? In that case, you can do it in increments, right? In that case. So remember, it just, it's, it's the inverse because a lot of folks make the mistake of thinking 70 ohm, 70 percent. And it's not the case. It's, it's the inverse because the more impedance you have, the less power flow through there, right? So you're looking at it from like the inverse perspective. So if you have 30 ohms, right? On that line, it's likely going to be 70 percent of the flow will go through line three, 30 percent of the flow will go through line two. Hence, you do the math and you are doing, bringing this down proportionately based on the impedances. So again, the answer here once is C, 630 megawatts will be flowing on line three. So a 230 to 115 kb transformer is rated at 100 mba and has 80 megawatts entering the primary site. Again, another tricky trick question here, right? So what would you expect the real power output to be on a secondary site? So here's an important thing to consider, right? On a transformer, power n equals power up, right? So you got to remember, what does a transformer do? It steps voltage up or down. So if a transformer stepping down voltage from 230 to 115, it is by property, it is stepping up current on the other side, right? So say it has, for example, 100 amps on the primary site and they'll quote me on the numbers that won't add up. It's just an example of proportions. So if it's cutting down by half, if it's 100 amps on the primary site, then it'll be like 200 mega amps on the low side, right? So the point is, when you do those calculations, power n always equals power out, right? So remember, if voltage doubles, current is cut in half. So that proportion holds true. So in this case, if you got 80 megawatts on one side of real power, you're going to have 80 megawatts on real side of the other power. So in this case, for example, they ask you that, what would you expect the real power output to be in the secondary side, right? So they're saying 80 megawatts entering the primary site, you're going to have 80 megawatts going on the other side. Granted, you're not accounting for losses. In some cases, you have very minimal losses in these transformers, but in this case, they're neglecting them. So it's another important thing to remember tonight. And why is voltage oftentimes from a plant, for example, stepped up? Well, ideally, the higher the voltage, if you're carrying the same amount of megawatts, the thinner the line can be. So you don't have to have such a thick conductor, especially out there in a high voltage transmission system. So that's another advantage of stepping up voltages. There's several others that are also easier to control voltage, easier to support power transfers with certain voltage levels over others. But one thing I always remember is that the transformer ratios, when you have a step up or a step down, power in always equals power out. Okay, let's do the next question. Radio transmission line. So a radio transmission line feeding a load is overload. The transmission operator must do which of the following to unload the line. So when they say the keyword here is radio, and radio means you've got only one way in or one way out. It's you got source on one side, load on the other, and it's not interconnected. So meaning that it's only being fed from one end. Problem with this is that there's nothing you can do. There's no generation on the other side. There's no re-dispatch. There's nothing you can do in this case. If you try and lower the out, lower the amount of power coming in, you're still going to cause other problems because you're going to depress voltage. So here the only solution here really is to shed load at the end of the line, which usually was something that's readily fed. That is usually the only solution unless you have generation that can be started and brought online at that radio lens. Other than that, there's no other solution, right? Lower the voltage at the receiving end that will help you at all. In fact, that will probably bring about a collapse, right? Raise voltage at the receiving end. That has very limited effect and really won't do much because the load is real when the load is still there, right? Raising voltage and ascending end is the same problem, right? You might actually aggravate such things because now you're going to send bars over to the load. So again, shedding load at the end of the line, it's the only solution in this case, right? Okay. Now we have one more question to go through, I think. All right. So question 24. Well, again, there were like 100 questions. I just paid four. Again, in our program, you get exposure to many more of these and there are test questions. And the other thing always that we really discourage people from memorizing test questions. What we do instead is we encourage you to understand what the concepts are. So in this case, a system operator identifies this transmission line that is operating at 100% of a system operating limit. What should be done? So in this case, in most cases, you're already at the limit. You haven't gone over the limit. You're at the limit in this case, right? So here you make an assumption, right? You want to immediately reduce loading? Well, how would you do that? Would you shed load? So you haven't really damaged the line. You haven't overloaded the line. You're just at the line's limit. Now, if you have something else happen, you may very easily overload this line or cause problems. But right now, nothing is nothing. Unless something changes in the wrong direction, nothing is really happening, right? In this case, you don't want to be there. And most utilities don't want you to be there, right? So for the most part, when a line is operating 100% of a system operating limit, right, you will monitor that in this case, right? And be ready to take action. A lot of those can involve redispatch. It could be involve shedding load. It could involve a sessionizing a line, right? Opening the line will probably be the worst thing you could do because now you will be in effect causing potentially a cascade, right in this case. So that's another example of something you don't want to be doing. So an important thing to understand, right? System operating limit means you're at 100%. Once you go to 101, now you're officially violating that hard limit on that line. Some places have a short-term and a long-term emergency ratings. Those vary. Now, again, this is probably post-contingency. This is already happening in real time, right? If you have a pre-contingency event, meaning that if you lose a certain element, you'll be at 100% or more, then that's a pre-contingency event. It hasn't happened yet, but you need to be really ready to take action right away if it happens. In this case, or something may have already happened where you're at 100% right on that edge and you haven't gone over that yet. If you were at 101%, then you would actually need to take some action at that point. All right, it looks like these are all the questions we have for today. I definitely encourage you to go ahead and visit our website for more information, HSI.com. In this case, we will go ahead and in a few weeks from now probably go do another section and a few more questions. But then again, I definitely encourage you to go ahead and go to HSI.com and look for NERC exam preparation. There's a lot of resources there that we can provide you to actually go ahead and do better on your exam. Once again, thanks for joining us in this case. Again, this is a short five-question refresher on what to expect or an intro. But again, there's a lot more available at HSI.com and our NERC exam prep programs. All right, thank you very much and have a lovely afternoon and evening. Thank you for looking at your exam. I'll see you in the next video.