I am studying the RTS 96 test system for a power system simulation in Matlab. I have noticed that under the Branch Data file, there are some buses which have two lines connecting them. For example (from Table-12.txt) between buses 115 and 121
ID# = Branch identifier. Inter area branches are indicated by double letter ID. Circuits on a common tower have hyphenated ID#. Lam-p = Permanent Outage Rate (outages/year). Dur = Permanent Outage Duration (Hours). Lam-t = Transient Outage Rate (outages/year). Con = Continuous rating. LTE = Long-time emergency rating (24 hour). STE = Short-time emergency rating (15 minute). Tr = Transformer off-nominal ratio. Transformer branches are indicated by Tr <> 0. ID From To L - Perm. Tran. R X B Con LTE STE Tr # Bus Bus miles Lam-p Dur Lam-t pu pu pu MVA MVA MVA pu A25-1 115 121 34 .41 11 0.8 0.006 0.049 0.103 500 600 625 0 A25-2 115 121 34 .41 11 0.8 0.006 0.049 0.103 500 600 625 0
Is the reason purely physical, meaning, introducing redundancy to increase system security? When it comes to modeling, can I just combine these into one transmission line (with appropriately modified parameters)?