TN-S Isolation Transformer Simulation


I am new to simulating transformers with LTspice, and I struggle getting the circuit to function as expected.

The source is a three phase TN-S (wye) connected. Then I wanted to add a 1:1 isolation transformer (wye/wye), but I cant get the output voltage to match 1:1 with the input voltage.

Played around with a lot of different values, but not getting any closer, so I dont know what I am missing...

Ignore "Rpe", the source was used in a previous model to simulate leakage current, and was used as a measuring point.

Help and pointers would be greatly appreciated.


Increase the inductance of your transformer windings to something like 1H. At 1µH and 10mOhm, the voltage drop across the ESR of the inductors will be huge because the small inductance of the windings leads to a large current through the inductor.

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  • \$\begingroup\$ Thanks! For some reason the simulation barely runs at 1H, but at 500m the voltage amplitude is fine! However, I have another problem, the output voltages are displaced (imgur.com/a/5PT9z). L1 = L1_out, but the others do not match. I tracked the error back to the "Phi" settings. If I change them all to 0, the input and outputs match. Any more tips to offer? Thanks again! \$\endgroup\$ – MemorX86 Nov 2 '17 at 18:46
  • \$\begingroup\$ @OleMartinBråtene Try lowering the transformer coupling to something realistic like 99% and simulate for a longer time. \$\endgroup\$ – Jonathan S. Nov 2 '17 at 18:59
  • \$\begingroup\$ Lowering the mutual coupling coefficient to 0.99 results in a simulation speed of 8.3 ns/s. Leaving it at 1 and increasing the simulation time shows the displacement clearing up (imgur.com/a/ULPOp). I tried starting the simulation at 50s instead, and now everything lines up (imgur.com/a/T9uI8). Thanks for all your help! \$\endgroup\$ – MemorX86 Nov 2 '17 at 21:48
  • \$\begingroup\$ @OleMartinBråtene This looks like LTSpice calculates a weird initial operating point... You could try skipping the initial operating point solution if you don't want to start the simulation at 50s or so. \$\endgroup\$ – Jonathan S. Nov 3 '17 at 14:32

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