Dear Dr Zimmerman, Thanks for your reply. But I am still confusing about the second question of why line 14(branch 14) is all zero except column 8(bus 8) .
For the second question, I did the following experiment. I tried to increase the load on bus 2 (from 21.7 MW to 121.7 MW). Then I test the branch power flow of 14(bus7-bus8). I found the branch power flow of 14 did change from 11.7 MW to 48.145 MW. To calculate the branch power flow, I use branch_power_flow = sqrt( results.branch(14, PF) ^ 2 + results.branch(14, QF) ^2 ). Can you tell me why this result, branch power flow of 14(7-8) did change when I do a power injection on bus 2, is different from what PTDF matrix shows me? Thanks for your patience and help. On Sat, Aug 3, 2013 at 10:16 PM, Ray Zimmerman <[email protected]> wrote: > 1. Unfortunately, "branch power flow" is not a precisely defined term. > Your first expression is the apparent power flow at the "from" end of the > branch, whereas, mpc.branch(1, PF) is just the real or active power flow. > Keep in mind that the flow at the "to" end is likely different, so if you > are looking for a single number you may want to average them (you'll need > to flip the sign of one of them to that). > > 2. That row defines the sensitivities of the flow on line 7-8 with respect > to an increase in injection at the corresponding bus (with slack at bus 1 > decreasing the injection to compensate). Since bus 8 is connected radially > to the system at bus 7, increasing the injection at any bus except bus 8 > will have no impact on the flow in line 7-8. > > -- > Ray Zimmerman > Senior Research Associate > B30 Warren Hall, Cornell University, Ithaca, NY 14853 > phone: (607) 255-9645 > > > > > > On Aug 1, 2013, at 9:32 PM, Yahook K <[email protected]> wrote: > > Dear Dr Zimmerman > > I have 2 questions. > > First, in ac mode, if I want to calculate the branch power flow, take > branch 1 for example, should I use sqrt( mpc.branch(1,PF)^2 + > mpc.branch(1,QF)^2 ) ? Or simply mpc.branch(1,PF) is the branch power > flow we meant in the power system? > > Second, the following is the PTDF matrix for the case14.m(a 14 bus > example). I generate this use makePTDF(mpc.baseMVA,mpc.bus,mpc.branch,1). > But I don't understand why line 14(branch 14) is all zero except column > 7(bus 7) . What does this mean. And if I increase bus 1's power load by 1 > MW, when I runopf(mpc), the power flow of branch 14, is not zero (I use > sqrt( mpc.branch(1,PF)^2 + mpc.branch(1,QF)^2 ) ). > > 0 -0.8380 -0.7465 -0.6675 -0.6106 -0.6291 -0.6573 > -0.6573 -0.6518 -0.6477 > 0 -0.1620 -0.2535 -0.3325 -0.3894 -0.3709 -0.3427 > -0.3427 -0.3482 -0.3523 > 0 0.0273 -0.5320 -0.1513 -0.1031 -0.1188 -0.1427 > -0.1427 -0.1380 -0.1346 > 0 0.0572 -0.1434 -0.3167 -0.2158 -0.2487 -0.2986 > -0.2986 -0.2888 -0.2817 > 0 0.0774 -0.0711 -0.1994 -0.2917 -0.2616 -0.2160 > -0.2160 -0.2249 -0.2314 > 0 0.0273 0.4680 -0.1513 -0.1031 -0.1188 -0.1427 > -0.1427 -0.1380 -0.1346 > 0 0.0799 0.3067 0.5026 -0.3012 -0.0389 0.3584 > 0.3584 0.2808 0.2240 > 0 0.0030 0.0113 0.0186 -0.0111 -0.2075 -0.6338 > -0.6338 -0.4469 -0.4043 > 0 0.0017 0.0066 0.0108 -0.0065 -0.1211 -0.1658 > -0.1658 -0.2608 -0.2360 > 0 -0.0047 -0.0179 -0.0294 0.0176 -0.6714 -0.2004 > -0.2004 -0.2924 -0.3597 > 0 -0.0028 -0.0108 -0.0177 0.0106 0.1979 -0.1207 > -0.1207 -0.1760 -0.2873 > 0 -0.0004 -0.0016 -0.0026 0.0016 0.0291 -0.0177 > -0.0177 -0.0259 -0.0161 > 0 -0.0014 -0.0056 -0.0091 0.0055 0.1017 -0.0620 > -0.0620 -0.0904 -0.0563 > 0 0 0 0 0 0 0 > -1.0000 0 0 > 0 0.0030 0.0113 0.0186 -0.0111 -0.2075 0.3662 > 0.3662 -0.4469 -0.4043 > 0 0.0028 0.0108 0.0177 -0.0106 -0.1979 0.1207 > 0.1207 0.1760 -0.7127 > 0 0.0019 0.0071 0.0117 -0.0070 -0.1307 0.0797 > 0.0797 0.1163 0.0724 > 0 0.0028 0.0108 0.0177 -0.0106 -0.1979 0.1207 > 0.1207 0.1760 0.2873 > 0 -0.0004 -0.0016 -0.0026 0.0016 0.0291 -0.0177 > -0.0177 -0.0259 -0.0161 > 0 -0.0019 -0.0071 -0.0117 0.0070 0.1307 -0.0797 > -0.0797 -0.1163 -0.0724 > > Columns 11 through 14 > > -0.6386 -0.6309 -0.6323 -0.6433 > -0.3614 -0.3691 -0.3677 -0.3567 > -0.1269 -0.1204 -0.1215 -0.1308 > -0.2655 -0.2519 -0.2543 -0.2738 > -0.2463 -0.2587 -0.2564 -0.2387 > -0.1269 -0.1204 -0.1215 -0.1308 > 0.0948 -0.0137 0.0061 0.1607 > -0.3076 -0.2264 -0.2412 -0.3569 > -0.1795 -0.1321 -0.1408 -0.2083 > -0.5128 -0.6415 -0.6181 -0.4348 > -0.5402 0.1683 0.1452 -0.0356 > 0.0061 -0.5211 -0.1697 -0.0887 > 0.0213 -0.2886 -0.5936 -0.3104 > 0 0 0 0 > -0.3076 -0.2264 -0.2412 -0.3569 > -0.4598 -0.1683 -0.1452 0.0356 > -0.0274 -0.1902 -0.2367 -0.6008 > -0.4598 -0.1683 -0.1452 0.0356 > 0.0061 0.4789 -0.1697 -0.0887 > 0.0274 0.1902 0.2367 -0.3992 > > > Thank you very much for your patience. > > Sincerely, > > Yahook > > > > -- Sincerely, Sicong
