Power System Analysis for Overload?

[ha9981]

Need some guidance in a study I am trying to attempt as a EE in training.

Background: I work in the O&G industry and we have our own generation, transmission, and distribution. I have a distribution circuit that has high 13.8kV and low 120V. It consists of two substations both of which are 13.8kV. The first substation supplies a 4500HP compressor motor, feeds second substation, and two 120V loads. The second substation just feeds two 120v and two 480v. The circuit are setup for redundancy with normally open circuit breakers, I am not sure what this setup is called.


I am attempting to use ETAP to study this circuit under conditions which may result in equipment being overloaded. We want to know the conditions under which it will be operating above equipments nameplate rating. I am completely new to this and not sure what is the best method to approach this.

I am sure I am not even aware of what is needed to complete such a study. Let alone calling it a study. This is the only place I know to begin.

 

[Padlock01]

Hi Ha9981,
First I would suggest sketching a Single Line Diagram (SLD) from the top draw the 13.8kV input ( overhead power line / cable?)
connected to the first substation bus then add the 4500hp feeder circuit and 2 x 13.8kV /120v TX's (A)then draw a 13.8kV feeder to the next substaion bus
and add feeder circuits for 2 x 13.8kV /120v TX's and 2 x 13.8kV / 480v TX's.
I am not sure where the redundancy supplys comes in on a single 13,8KV ? however, should there be two 13.8kV incoming supplies then (A) is the redundancy.
ETAP Modelling
1.The first symbol ia a source symbol which will require info such as the Utility Fault level, X R values, Voltage etc.
2.Then choose acable or power line size to the substation
3. Choose a bus and fill in details
4. Incoming cct breaker symbol
5. Outgoing cct breakers on both subs
6. 4500hp load ( Motor Symbol)
7. TX's Symbols fill in details
8. Unless you know the loads ( put in lump loads)
9. Do the same for other sub.
Connect both substation via cct breakers.
Contact your nearest ETAP service dept for assistance.
I hope this assists you maybe other engineers can give input?

 

[desrod]

You might want to look at ETAP tutorials to get an idea of the required info.

Also, since you are an EIT, why not ask your supervising eng. for pointers? You can always ask questions, in fact that's the right way to do it and as a future professional your are expected to do so to expand your field of knowledge and expertise. The only thing is not to ask the same question over and over!

As suggested by PadlOck01, start with the SLD. You will then build it in ETAP and run a load flow study that will give you the current passing thru your conductors, transformers etc and help you flag potential overloads for various network configurations (like transfer on the alternate supply). You will also discover that you will need more info like load kVA & power factor, transformer impedance, equipment current carrying capacity etc.

Welcome to the EE job!
Desrod

 

[ha9981]

I actually have the circuit in ETAP model and load flow is easy. I will try to make a similar circuit as I don't think I should post the original. I have played with etap for load flow. What I think I need is a better understanding of the circuit to know what things I need to try to make it overload. Any suggestions from this perspective?

Also does ETAP alert on overload?

 

[LionelHutz]

There is such a broad range of possible equipment it's impossible to comment on what may cause components to be overloaded. There are also other ways to go over a components ratings besides just a higher then rated running current. You're meed to make your question much more specific if you expect any useful answers.

 

[juleselec]

From the sounds of it, you have a secondary selective system so the worst case loading conditions come about when you operate with one branch element (e.g. line/cable, transformer, etc) out of service and the bus-tie closed. This configuration is sometimes called an n-1 contingency scenario. So set up this configuration as a study case, re-run your load flow and check the % loading on your branch elements.

You should also confirm that the nominal ratings of your cables, transformers, generators, etc are site-rated (i.e. suitably derated or uprated for site conditions such as temperature).