High Losses with Parallel Transformers

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Kyle Ingraham
Kyle Ingraham on 16 Sep 2011
Answered: Joel Van Sickel on 18 Aug 2021
Hi. I'm using SimPowerSystems to simulate a large AC power system. One of the issues I'm running into is very high losses being reported after performing load flow analysis. The losses seem to come solely from transformers that I have connected in parallel at various buses. This even occurs for transformers that are identical and have no impedance, turns ratio, and MVA rating mismatches. Is there a way to get rid of these losses? Here is an example from the load flow report:
13 : BUS_27 V= 0.940 pu/7.2kV -45.44 deg Generation : P= 0.00 MW Q= 0.00 Mvar PQ_load : P= 5.29 MW Q= 3.37 Mvar Z_shunt : P= -422.82 MW Q=-4681.02 Mvar --> 2 : P= 417.53 MW Q= 4677.65 Mvar
50 : 2 V= 0.957 pu/33kV -43.69 deg Generation : P= 0.00 MW Q= 0.00 Mvar PQ_load : P= 0.00 MW Q= 0.00 Mvar Z_shunt : P= 21.01 MW Q= 230.81 Mvar --> 18 : P= -7.71 MW Q= -3.65 Mvar --> BUS_27 : P= -13.30 MW Q= -227.16 Mvar
BUS_27 is the PQ load and 2 is one of the transformers connected to the load. Notice the high Z_shunt load value on BUS_27. The SimPowerSystems manual says Z_shunt load comes from Z type RLC loads and magnetizing branches of transformers. There is a Z type RLC load at that bus but it is only 2.31 MW. Are these losses something that I need to worry about? Below are the total system results:
Total generation : P= 218.21 MW Q= 136.77 Mvar
Total PQ load : P= 146.27 MW Q= 92.99 Mvar
Total Zshunt load : P= -4672.34 MW Q= -53404.10 Mvar
Total ASM load : P= 0.00 MW Q= 0.00 Mvar
Total losses : P= 4744.28 MW Q= 53447.88 Mvar

Answers (1)

Joel Van Sickel
Joel Van Sickel on 18 Aug 2021
I realize it is too late to for this answer to be useful for the asker, but as part of a Matlab Answers cleanup effort, here is a response:
If the only z-load is pulling 2 MW, and the rest is truly from the transformer magnetization reactance, this is definitely problematic. I expect something is going wrong with the transformers in parallel. I would try with an equivlanet transformer that is the circuit equivalent of them being merged.

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