# Transients-Intergrals



## jdd18vm (Aug 4, 2007)

Just a general question is an much as it can be. Ive posted (this board and the other) and read posts about "math" in general. Consensus always seemed to be not to get too caught up in it.

Starting Transients, and well as I am sure you are aware it appears very involved and complex. My question is do I need to go back to Calculus and understand all that and know how to rearrange and derive these expressions.

I just want to know what to focus on, and not waste time learning something I may not need to. Like if the problems are similar to NCEES 109, is there a certain approach that works.

Apologies if this is too vague.

John


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## Dark Knight (Aug 4, 2007)

jdd18vm said:


> Just a general question is an much as it can be. Ive posted (this board and the other) and read posts about "math" in general. Consensus always seemed to be not to get too caught up in it.
> Starting Transients, and well as I am sure you are aware it appears very involved and complex. My question is do I need to go back to Calculus and understand all that and know how to rearrange and derive these expressions.
> 
> I just want to know what to focus on, and not waste time learning something I may not need to. Like if the problems are similar to NCEES 109, is there a certain approach that works.
> ...


Math? Don't even bother.

Transients? I don't remember a single problem dealing with that.

Keep in mind that it took me three tries to pass so I might be wrong, but I don't think I am.


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## Flyer_PE (Aug 4, 2007)

I agree with Luis with a slight variation. Other than maybe a simple laplace transform and understanding that the derivative of sine is cosine, I wouldn't worry about it. There wasn't anything harder in this area than the problems in the NCEES sample problems.

Jim


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## jdd18vm (Aug 4, 2007)

Thanks Luis and Jim, just the sort of input I am looking for.

I admit i haven't a clue about Laplace and Fourier Transforms, how to apply them wtf they are even, just glancing at them scare the hell out of me. LOL

But I'll get there.

John


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## Dark Knight (Aug 4, 2007)

jdd18vm said:


> Thanks Luis and Jim, just the sort of input I am looking for.
> I admit i haven't a clue about Laplace and Fourier Transforms, how to apply them wtf they are even, just glancing at them scare the hell out of me. LOL
> 
> But I'll get there.
> ...


I would have a table with the *Laplace* and Fourier Transforms and keep it handy. What module are you going to do? If it is Power you will probably have to deal with it in the morning. If Electronic and Controls, well, you HAVE to go deep on it.

Not to scare you but I bet you will see something involving *Laplace*. These are the Bad News. The Good News is that for the morning it is so basic that I considered it a Low Fruit, you know, easy points(keep in mind that I am not Albert Einstein).

I might have a cheat sheet to recognize what *Laplace* and Fourier Transforms apply. I am afraid I gave it to a co-worker who was going to take the test. I will see if I still have it and let you know.

Jim, thanks for bringing this out( *Laplace* and Fourier ). You are a great asset to our small EE group here.

Hope you stay around.

*(Hope you get the message)*


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## jdd18vm (Aug 4, 2007)

Luis said:


> I would have a table with the *Laplace* and Fourier Transforms and keep it handy. What module are you going to do? If it is Power you will probably have to deal with it in the morning. If Electronic and Controls, well, you HAVE to go deep on it.
> Not to scare you but I bet you will see something involving *Laplace*. These are the Bad News. The Good News is that for the morning it is so basic that I considered it a Low Fruit, you know, easy points(keep in mind that I am not Albert Einstein).
> 
> I might have a cheat sheet to recognize what *Laplace* and Fourier Transforms apply. I am afraid I gave it to a co-worker who was going to take the test. I will see if I still have it and let you know.
> ...


I second what Luis says Jim, youve been a help thus far, and I have a long way to go. You too Luis, I know youve been around and posting a lot.

I see the tables in the EERM and have Schaums stuff. Hopefully I'll get it enough as needed.

Appreciate it, btw I'm taking the Power Depth. Out of school 24 years, its rough. I am determined though, so it wont be for lack of trying.

John


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## Flyer_PE (Aug 4, 2007)

jdd18vm said:


> I second what Luis says Jim, youve been a help thus far, and I have a long way to go. You too Luis, I know youve been around and posting a lot.
> I see the tables in the EERM and have Schaums stuff. Hopefully I'll get it enough as needed.
> 
> Appreciate it, btw I'm taking the Power Depth. Out of school 24 years, its rough. I am determined though, so it wont be for lack of trying.
> ...


Thanks fellas.

I plan to stick around. This board seems to be a pretty friendly place and I haven't seen much in the way of flame wars. I'm also convinced that if you really want to understand something, try explaining it to somebody else. Helping with problems where I can helps me keep those gears greased. I took the test 17 years after graduation and it was a real bite to blow out all those cobwebs.

One further note about working LaPlace transforms. Take a few minutes and re-learn how to do simple partial fraction expansion. The trick with the transforms is to take whatever they give you and make it match the pairs in the tables. The only other "gotcha" to remember is that the Laplace transform for the impulse (step) function is 1/s. If you're taking the power module, that's about as difficult as it gets. If there is one on the test, it will most likely be only one question but it doesn't take a lot of studying to make that one a gimme.

Jim


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## jdd18vm (Aug 4, 2007)

IFR_Pilot said:


> Thanks fellas.
> I plan to stick around. This board seems to be a pretty friendly place and I haven't seen much in the way of flame wars. I'm also convinced that if you really want to understand something, try explaining it to somebody else. Helping with problems where I can helps me keep those gears greased. I took the test 17 years after graduation and it was a real bite to blow out all those cobwebs.
> 
> One further note about working LaPlace transforms. Take a few minutes and re-learn how to do simple partial fraction expansion. The trick with the transforms is to take whatever they give you and make it match the pairs in the tables. The only other "gotcha" to remember is that the Laplace transform for the impulse (step) function is 1/s. If you're taking the power module, that's about as difficult as it gets. If there is one on the test, it will most likely be only one question but it doesn't take a lot of studying to make that one a gimme.
> ...


17...24 its all the same at some point so i hope i can do it. Thats some of my challenge, the BASICS, what seems second nature to many is like ...what the hell? So I'll relearning everything. Thanks again

John


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## benbo (Aug 5, 2007)

I don't think we can stress enough that for the AM make sure you know that NCEES exam. For the PM it is less helpful, because they can ask almost anything.

And don't forget to briefly review some qualitative things about Fourier series (as opposed to transform). You probably won't be asked to work out complicated coefficients in the AM. It takes too much time.


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## mudpuppy (Aug 5, 2007)

There's three ways to solve transients problems that I'm aware of. Keep in mind I'm in power as well, so I don't get too much into the complicated systems that the other areas might. This list below is, in my opinion, the hardest to easiest ways to solve these problems:

1. Diff-eq. Write out the equations for the circuit and solve. We were forced to do this in college, but I've never done things this way since--it's just seems pointless when there are easier ways.

2. Laplace. This way isn't too difficult if you keep in mind the things others have already said here. Also, don't forget about the initial conditions; I always tend to forget them.

3. By inspection. You know that simple systems will contain a response with something like 1-e-t/tau. There are tables in the EERM that tell you how to calculate tau for different systems (RC, RL), and you can usually tell by looking at the circuit what the forcing function is and generally what the circuit will do over time (i.e. a capacitor in series with a DC voltage source will charge toward the source voltage as time increases). For me, this method saved a lot of time; however it only works on simpler systems. For complicated circuits you'll have to resort to LaPlace. Of course, LaPlace will always give you the right answer and it is easy to overlook signs and such with the inspection method, so LaPlace may be a more surefire (though slower) method.


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## Art (Aug 5, 2007)

the EIT reference manual has good basic reference infomation on:

Laplace

Fourier

diff eq

etc.

shouldn't need anymore than this...

as far as motor starting transients, NEC tables/motor codes should do it..


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