 Hi. I'm Zor. Welcome to Inezor Education. Excuse me. I would like to continue talking about distribution of electricity. Today we will talk about the grid. Well, basically the grid is something which we have come up with as a design idea to make sure that electricity power is delivered to consumers whoever needs the electricity in a reliable and uninterrupted fashion. Which is not easy, actually, as you will see during my short explanation. Nevertheless, it's a very necessary thing and people did come up with certain ideas, designs, etc. and implemented it. So basically, in all the developed countries, electricity is virtually uninterrupted except certain cases which I will talk about a little bit later. Okay, so this is about how to deliver electricity to consumer in a reliable and uninterrupted fashion. Now this lecture is part of the course called Physics for Teens presented in Unizor.com. I do suggest you to watch the lecture from the website because this lecture is part of the course and the website contains the course. Basically, it's not just one individual lecture. So there is a menu, there is a certain order. Also, every lecture has textual notes which basically can serve as a textbook. Also, there is a prerequisite course which is called mass routines which is absolutely necessary for studying physics. Maybe not for this lecture, but this is kind of a more explanatory thing without much mathematics. But in most of other aspects of learning physics, you need mass. Okay, so let's get to business. So again, we need a reliable supply of electricity. How can we achieve it? Well, let's take analogy. I live in the building in an apartment building. The water to our apartments is pumped to the tank on the roof and then from the tank it goes down to all the apartments. Just recently, our tank needed cleaning. So what has been done basically to do this? You can't really do the cleaning of the tank and use the water. So they shut down the water. So basically from this is the tank and this is the building. They shut the water here and then they did whatever is necessary and the building was without the water. It was an interruption. Now, what if instead of this design, we would have two tanks here and they are going into a common distribution pipe from which the water goes down to apartments. Now, if I want to clean this one, I'll just cut here but the water would still go from this tank to apartments and there is no interruption. If I want to clean this one, I do the other way around. Well, it's a good design. I don't think it's implemented in buildings because it's not such a big deal if the water is shut down for a couple of hours to clean the tank. But in case of electricity, I mean, it's a completely different story. With electricity, we do need uninterrupted supply. We have manufacturing facilities. We have hospitals. We have domestic consumers who need refrigerators and stuff like this. So, for electricity, we do think about something like this and, well, let's just gradually introduce the problems which really we have to overcome. You see, with water it's kind of easy, right? It's basically, you know, simple design and it works. With electricity, it's not as simple. Here is why. Let's consider you have a lamp which is supposed to be fed with direct current. So, let's start from direct current. And we have two batteries. Now, obviously, we can do this. So, these two batteries are connected in parallel. Each one gives the voltage required to this particular thing, to this particular lamp. So, for instance, the lamp needs, this is a small lamp, let's say, it needs three volts. So, we have each battery can supply three volts, but we would like the reliability, right? So, how do we have this reliability? Well, we just connect them in parallel. Even if one is not working, the other one would still supply three volts. Now, if we have three volts and three volts here, we will have still three volts on the lamp. But if both are working, it would just work twice as long, basically, because the amount of energy is twice as big in two batteries rather than one. Now, if we connect them in sequence, the voltage will be added together, so it will be six volts. That's not what we want. We need the same three volts, which is here. But we need it in a more reliable fashion. So, if one battery goes down, my three volts will still be there. The voltage will be the same. The lamp would still work. But if I have some sensor or whatever else, which gives me an indication which battery is already dead, we can put some kind of ampermeters here, whatever it is. So, I will know exactly which battery requires replacement. I will replace it, and we still have a reliable supply of electricity to this lamp. Okay. With direct current, we have actually solved the problem. What is important in this particular case? Important is that each battery is exactly what's needed to supply electricity to this guy. These three volts and these three volts. If I have different batteries, well, that's not exactly the good thing, because if this battery supplies three volts and this one supplies, let's say, five volts, then there is a difference between potential, between this and this point. And the electricity will not only flow here, but it will also flow in between these two things, because there is a difference in voltage, difference in potential. So, what's important in case of DC for a direct current? Equality of the voltage. And that's the only requirement, actually, which we need. So, if we have two different batteries supplying exactly the same voltage, then we can arrange this type of thing. Uninterrupted power supply, everything is great. Okay, now, we have alternating current everywhere. It's good and it's bad. Now, why is it bad? Let me start from this. Well, because it's more complicated. The voltage is, in case of AC, the voltage is sinusoidal. So, what does it mean that we are equating the voltage of two different supplies? So, let's say you have one supply of electricity and another supply of electricity, and both are actually going to some kind of a motor. I have to basically do kind of similar thing to DC. I have to equate the voltage between these two sources of energy. And that's the trick. Why? Because the voltage is changing. It's a function of time. So, it's not two constants which I have to equalize. I have to equalize two functions. Well, so we have two sinusoidal things, one and another. So, why do we need to equalize them? Well, again, for the same reasons, because if this, at some moment at time, if at moment T equal T0, let's say, I have certain voltage here and certain voltage there. And these two voltages and these two generators are different than I will have current going into some other direction instead of here. What I need is the current to go from here and from here to here, or if it's an alternating the other way around. But I don't want the current to go in between here because that's a waste. Actually, I will just, you know, probably damage my generators. Not good. So, which components I have to equalize to make sure that these two are exactly the same as two functions of time, which means at any moment of time this function and this function should be equal to each other. Well, sinusoids have certain characteristics. Which ones? Well, amplitude. That's basically the height plus and minus over the middle line. It has frequency. That's basically how often I have these oscillations. It's exactly equivalent to the period. So, frequency is number of oscillations per second, let's say. It's the same as if I supply the period. So, if frequency f, then my period should be some kind of a function of f. Now, it's exactly equivalent to yet another characteristic, the length of the wave in time. So, the length of the wave is basically one over frequency, right? If I have a certain number of oscillations per second, then the length is one over f, something like this, right? Okay. So, there are certain equivalent characteristics. Periodicity, the frequency, and whatever else. Anyway, I will just concentrate on one particular characteristic because they're all the same frequency, number of oscillations per second. So, we have an amplitude, we have frequency. Now, is it sufficient? No. Because these two sinusoids can be the same amplitude and the same frequency, but shifted, let's say, this way. Against each other. So, they must be in sync. It's called phase. So, the phase should be exactly the same, which means at some moment in time, wherever this is equal to zero, this also should be equal to zero exactly at the same moment of time. So, three characteristics, amplitude, frequency, and phase must be the same. Otherwise, I cannot connect these two guys. So, let's think about how can we achieve it. I mean, these generators, our goal is to connect all the generators in whole, let's say, country, if not the world, into network, right, into grid. That's what grid actually is. Connection of all these generators into one basically massive uninterrupted power supply. So, these guys are different. Now, I was talking about DC direct current to batteries, and I was saying that batteries must be the same if you want to connect them. Now, with these, it's not practical. You have hydroelectric stations, and we have small, maybe wind turbine, which generates something. So, we need a lot of different things to be connected into one network, which means we have to really equalize something, whatever the raw output from the generator, we have to convert before we connect it to the grid. So, we have to change, but first of all, we have to have an AC, because something like certain sources of electricity, like, for instance, solar panels, they give you direct current, not alternating current. So, first, we have to make sure it's an alternating current because our grid is alternating. So, whatever the output from the solar panel or any other source of direct current electricity must be converted into AC. For this reason, we have certain devices. So, in this case, in the case of solar panels, we have inverters, which is supposed to convert into DC to AC. Okay, so we have solved one problem. So, all the sources of electricity now, using inverters, we convert DC into AC, so all the sources are AC. Now, hydroelectric station produces AC because there is a rotor which is rotating, and solar panels produce direct current and we use inverter to change DC into AC. Next thing, amplitude. How can we change amplitude to basically equalize certain standard which we need? Well, we do know how to do this. We have transformers, if you remember, and transformers can change the voltage. Okay, fine. So, we kind of know how to do this. Frequency. Well, with frequency, again, it's not easy, but basically, if frequency is determined by the rotation of the rotor in the turbine, then we have to be able to somehow change the rotation of the rotor. So, we are equalizing all the... mechanically, maybe even equalizing frequency to 50 or 60 hertz, 50 or 60 oscillations per second. In the United States, it's 60. In Europe, it's 50. Somewhere else, it's somewhere else. I don't know. Okay, so we do this now. Can I adjust the frequency electronically somehow? Probably, I just don't know. But in any case, 50 or 60 hertz must be achieved somehow. So, that's the second thing. The third thing is phase. Well, so phase is probably even more difficult because, I mean, one thing, let's say you have two, more or less the same kind of turbines, and both of them produce the same oscillations with the same amplitude and the same frequency. How can I make sure that they are in sync? That's not easy, actually. Well, for this reason, again, there are certain devices and certain sensors which gives me the indication of whether they are in sync or not. There are certain videos on the Internet which I found how people do this. So, basically, they're slowing the rotation of one of these devices until the point where they are actually almost like in sync but a little bit behind or ahead. And then they just adjust the speed again to basically lock this particular phase for one of those oscillations. So, it's kind of almost manual. Well, it's manual but there are certain sensors and devices which people are using to adjust the phase. So, all this must be performed and believe me, it's not easy before you're connecting a new generator to the grid. So, the whole thing of connecting a new source of electricity, let's say a new power plant to the grid, is really a big deal. So, there are many different devices which are used. I was trying to indicate certain principles but to achieve whatever I was just talking about, we need special devices. It's electronic or whatever mechanical, different equipment we need and skills, by the way. So, it's not easy and it's supposed to be done by very, very highly qualified people who know what they're doing. Unfortunately, there are some cases when some people make mistakes or whatever else. Now, the whole thing must be monitored, obviously. So, if you have this network of thousands of sources of electricity, here it's only two, now we have thousands. They're basically the same. I mean, you can just connect more and more and more but you have to preserve the same principles. So, mistakes are made during monitoring of certain situations. Now, whenever something goes out of order for whatever reason, something must be adjusted and then it should be brought back to operation which means, again, we have to make sure that it's the same amplitude, the same frequency and the same phase before you're bringing back into grid. Not easy. So, mistakes were made sometimes and sometimes these mistakes are really very, very... Well, they have a lot of unpleasant consequences. I personally remember that in... I think it was 2003 when something was wrong, basically, somewhere in Ohio, in the United States, and there was a blackout. So, the whole grid, actually, in a very, very large area which basically included New York, New Jersey, Pennsylvania and even all the way up to Canada, certain areas, they just turned dark. So, I was in New York at the time. I mean, all the traffic lights are down, all the offices have lost electricity, all the homes were lost electricity and that lasted more than a day, actually. And that's a big deal, actually. I would consider the whole city of New York without lights at all for a day or something like this. Anyway, the funny case, I remember, well, it's not really funny, no traffic lights, but the cars, actually, have to move somehow. So, some volunteers, actually, were standing on every corner and directed the traffic, you go or you go, etc., like policemen, actually. You know, it was really a very, very difficult situation. In many offices we had some backup power generators, local, only for the building, but in many offices there are none and homes also not necessarily have this type of equipment. So, that was a difficult time. And, again, because it was in the grid so everything is interconnected, as small, maybe small, I don't know what kind of an error was made in the hire, actually kind of spread it around because certain safety functions, which were built into the grid, started working in a non-exactly designed fashion. For instance, if you have one of those generators going down, it means more electricity go to this particular consumer, not one consumer, many consumers, maybe to the city. So, consider this is the city of New York, let's say. So, if this generator goes down, then we need certain power. Before half of the power was from here and half of there. Now, if this goes down, all the power goes here, which means these lines become a little heavier load on these electric lines, which means that the current has increased and there are some safety mechanisms and the safety mechanism might actually do something like cut electricity if the current goes above certain amperage. So, it's difficult thing and it's supposed to be well balanced, etc. and some mistakes actually have lots of consequences like this. My point was to basically introduce you to this idea of how complex, complicated this grid actually is and even vulnerable because people, I know, are afraid of some kind of cyber attack, for instance, because obviously all these control devices are connected to certain computers internet, etc. and they're monitored and they are actually maybe somehow maintained using some computer interfaces. So, it's kind of vulnerable to cyber attack, etc. So, that's very important and it must be addressed all these issues. Complex issues require a lot of knowledge, a lot of skills. Well, that's it. Thank you very much and good luck.