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ACCC overload report issue

asked 2023-12-20 17:09:53 -0600

Ned P gravatar image


I'm currently looking at doing some ACCC. I have a loop that uses,




to loop through each contingency and check if the MVA flow is greater then the rating of the line. In my code this shows a line overloaded. But when I use,


showing the overload report it says there are no overloads. Any ideas why? Or which method is actually correct?


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answered 2023-12-21 06:22:28 -0600

perolofl gravatar image

In PSSE, the line (and transformer) rating can be expressed in MVA or as "current expressed as MVA". It is selected in Program Settings.

"Current expressed as MVA" is the best choice since the loading of the branch is then calculated as current load. The thermal stress of a line is determined by the current and not by the MVA load.

For example the transformer between bus 205 and 206 in savnw network is loaded to 927.1 MVA. The first rate is 900 MVA. The voltage at bus 205 is 0.949 pu.

When using MVA rate, the loading of the transformer is 927.1/900 = 103%

When using current expressed as MVA rate, the loading of the transformer is 927.1/900/0.949 = 108.5%

In the code you are using MVA rate while the saved case is most probably set to "current expressed as MVA" and the bus voltage is above 1 pu!

The rating is calculated as In * Ubase * sqrt(3), i.e. the nominal line current limit in kA is multiplied with bus base voltage in kV and the square root of 3.

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Thanks for the comment, I thought this might have been the case so I tried using psspy.non_trans_percent_units(0) to change what the branch was calculated with and I still have the same issue.

Ned P gravatar imageNed P ( 2023-12-21 16:06:30 -0600 )edit

Replicate your problem in savnw network and present the results.

perolofl gravatar imageperolofl ( 2023-12-21 16:15:42 -0600 )edit

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Asked: 2023-12-20 17:09:53 -0600

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Last updated: Dec 21 '23