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How to relate power flow solution to a subsequent contingency analysis process?

asked 2014-07-18 15:43:45 -0500

ypwang gravatar image

Dear everyone,

First, I want to apologize for any misused power system terms in my question because I am not a power system major.

My question might seem silly to you as professional power system engineer. Anyway, let me try to describe my question in a simple way.

What I have: I have a hourly RAW data file for a real power system.

What I want: I want to simply test all N-1 contingency on this system. My current method: I simply use "readrawversion" module to load the RAW hourly data, and generate my .sub, .mon, .con and .dfax files in PSSE GUI (I import the same RAW data in PSSE), then I call "acccwithdsp_2" module to run all the contingency analysis

Where I am stuck: The problem is that I got an error saying "largest mismatch exceeds mismatch tolerance". I am using 0.6MW as the mismatch tolerance. So I eventually have to increase this tolerance until 200MW to get my AC contingency run properly.

Suggested Solution from some power system engineer: Some expert told me that the problem is that I didn't run power flow (I use FNSL(i.e.Full Newton-Raphson method) ) first on the data before I run contingency analysis.

Now comes the question: I kind of understand what he meant-- contingency analysis step needs to use the solution of power flow as a starting point. But as far as I know, the AC contingency analysis only requires input including mismatch tolerance, a bunch of parameters/options and fours files (i.e. .sub, .mon, .con, and .dfax) as necessary arguments. On the other side, module "FNSL" dosen't return solution in any form. So how ACCCWITHDSP_2 module gonna benefit from running a power flow?

My guess: I will just simply run FNSL before ACCCWITHDSP_2 with a small desired mismatch tolerance of 0.6 to see what happens. If problem solved, then I guess PSSE just somehow knows that a power flow has been run for that contingency analysis process.

Could anyone explain to me the underlying mechanism for this to work? Thanks very much for your generous help and time!

Best regards,


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answered 2014-07-19 00:19:59 -0500

jconto gravatar image

You can review concepts of power flow and then contingency analysis (on the net or from books on power systems.)

The power flow run will check if the electric network reaches or not a secure, operable state. Typical mismatch tolerance is 0.1 MW and could be as large as 2 MW for contingency studies but never 200 MW. If the load flow does not converged to the mismatch tolerance during pre-contingency or post-contingency, then it is an indication that the total generation of P & Q does not match total consumption of P & Q and it is recommended to resolve such issues. On the extreme, non-convergence of the network could mean a voltage collapse condition.

Before a contingency is applied, a load flow is performed and only if it converges then overloads and voltage violations are checked to assure an acceptable operable state ("base case"). In post-contingency, the effect of a contingency on the network is checked with a load flow solution.

ACCC is a tool to allow processing many contingencies in an automated way that include an internal step in "solving the load flow" in post-contingency. In the API manual, there are additional python functions (pssarrays) to process the results.

In your case, it seems your base case is not good enough to perform contingency analysis.

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Appreciate it, Jconto! I like your explanation.I agree that ACCC must internally solve a post-contingency load flow, but not sure if it does also solve the pre-contingency load flow (i.e. run the base case before applying contingency). My test of running FNSL before ACCC actually solved my problem.

ypwang gravatar imageypwang ( 2014-07-19 15:47:01 -0500 )edit

ACCC would not perform a load flow run pre-contingency. That is the task of the user, to assure a good base case that converged before running ACCC or any other tool (N-1-1, PV, QV, etc.)

jconto gravatar imagejconto ( 2014-07-19 19:08:45 -0500 )edit

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Asked: 2014-07-18 15:43:45 -0500

Seen: 1,557 times

Last updated: Jul 19 '14