Principles of Symmetrical Components Part 1 This is the first part of the series of the introduction to the principles and theories of symmetrical components used in the power system. Now understanding symmetrical components is not difficult. It's actually quite easy to learn, but it's sometimes presented in the most confusing and impractical manner.
Our goal is to get an intuitive understanding of symmetrical components. This introductory series will go step by step and explain what symmetrical components are. components are, the value of symmetrical components, how do we use them in setting circuit breakers and relays. We'll look at some of the examples of symmetrical components as well.
Remember our principal goal is to get an intuitive understanding. Now if you find this video tutorial useful, please subscribe to the GeneralPAC channel by clicking on the subscribe button on the bottom right corner of the screen. In this part, let's try to answer our first fundamental question. What are symmetrical components?
The short answer to that question is, well, symmetrical components simply transform an unbalanced set of phasors into a balanced set of symmetrical components which are called positive sequence component, negative sequence component, and zero sequence component. Now, if this is the first time that you've been exposed to symmetrical components, this explanation means nothing to you. And that's just the nature of learning something new. So let's get a better picture of this definition by asking another question.
Why are symmetrical components so valuable? Now the best way to understand the value of symmetrical components, which is the language of some power system engineers, is to give an example without symmetrical components available to us. In the early 1900s, before the discovery of symmetrical components, we still had generators, transformers, transmission lines, and most importantly, fault and short circuits. Let's start this example by drawing a simple 3 line dart.
We'll draw our 3 phase generators. The generators are connected to a short transmission line. Then we have a step down power transformer connected Y grounded, Y grounded.
We have an AC 3 phase circuit breaker on the secondary side of the transformer. Some distribution line and a dedicated 3 phase line. As a power systems engineer, we are asked to set the circuit breaker so it trips for all types of faults on the distribution line feeding our load. We are given all system parameters like line impedance. Now the question comes up, right?
What are all types of faults mean? In the power system, there can exist a line to ground fault, a two line to ground fault, a line to line fault, and lastly a three phase fault. We'll explain this in more detail later. So we arrogantly tell ourselves, yup, this can be done.
We can easily calculate the magnitude of all of the fault types, no problem. Remember, this is the early 1900s before symmetrical components were discovered. To determine the fault current, we begin by drawing an equivalent single phase diagram.
And like a simple circuit problem, we expect to calculate the short circuit current. So we draw our voltage source, which represents our generator, impedances of the transmission line, impedance of the transformer, impedance of the distribution line, and impedance of our load. Now if we had a fault at the terminal of our load, which means that we have a short circuit here, we should expect a huge short circuit current that comes from our generator and feeds our fault.
To calculate this current, We take the voltage at the terminal of our load and divide by the equivalent impedance seen at the point of the fault, right? This is Ohm's law, plain and simple. Current equals voltage over impedance. And that makes total sense.
And suppose we get 5000 amps of 3 phase fault current. Wow, that was pretty easy. But my friends, we have simply calculated a perfectly balanced 3 phase fault. Now how do we calculate an unbalanced fault?
such as a line to ground, a two line to ground, and a line to line fault with the same methodology. And that is the point. That is the defining point. Without symmetrical components, we can only calculate balanced three-phase fault types. Without symmetrical components, it would be extremely difficult for us to even attempt to calculate unbalanced faults like the line to ground fault, the two line to ground fault, and the line to ground fault.
So in this example, what is the value of symmetrical components? Well with it, we can easily calculate both balanced and unbalanced faults. And we are able to properly set the breaker for all expected fault types on our distribution line.
And that my friends is extremely critical for the reliability, security, and integrity of the power system. But that was just one brief conceptual introduction to symmetrical components. In this series, we'll go step by step and explain how it all works in the most intuitive manner possible. In the next part, in part 1B, we'll take a step back and describe the balanced set of phasors and review basic phasor operations.
This video was brought to you by GeneralPak.com. Making power system protection, automation and controls intuitive.