-1
\$\begingroup\$

At recent days, I was studying on load affect of transformers. I realized, capacitor changes frequency of voltage at some conditions.

Here the circuit that I used

If we run the simulation, we see everything is normal, frequency is 60 Hz and stable. But if we change the resistances with capacitors, and disconnect the ground, it behaves so different as below:

enter image description here

If we connect ground to primary one, simulation runs for so little time and crash. The frequency is not stable as well...

If I load the system unbalanced, the circuit works but not stable again.

enter image description here

Primary frequency is also so different than secondary.

enter image description here

The all simulations is ran at least 4-5 seconds, so these are stable conditions.

What happens to this circuits? What is difference? Why does capacitor affect the frequency? We generally use capacitors as filters to fix frequency distortion in AC systems, but this distorted the frequency.

\$\endgroup\$
7
  • 3
    \$\begingroup\$ Some type of simulation error or computational rounding error or something. Inductors capacitors and resistors cannot change the frequency of an input signal. \$\endgroup\$
    – mkeith
    Jan 1 at 8:22
  • \$\begingroup\$ youtube.com/watch?v=vrZ_fMqd8k8 \$\endgroup\$
    – mkeith
    Jan 1 at 8:25
  • 1
    \$\begingroup\$ Don't trust pop-up boxes to calculate your frequency, you don't know how they handle limited time records. Post plots of what the output does, so we can see the waveforms. Ls and Cs do not change the frequency in the steady state, that's as fundamental as energy conservation or thermodynamics, it just does not happen. But they do ring on transients, which can confuse 'frequency calculating' pop-up boxes in simulators that maybe work by just counting zero crossings unintelligently. \$\endgroup\$
    – Neil_UK
    Jan 1 at 8:47
  • \$\begingroup\$ See your transformers model. If the coupling coefficient is not exactly 1, you will see logically starting oscillations in your simulation. When this coefficient decrease, the frequency of starting oscillation will change also. \$\endgroup\$
    – Antonio51
    Jan 1 at 9:07
  • 1
    \$\begingroup\$ It looks like you have a floating ground in your first picture. Some simulators don't handle that -- which, rightfully, should be the user's job. I don't know how the transformer is modelled, or how Multisim handles these cases, but you need a ground in order for the matrix (circuit) to be solved. If you really intend on having a "floating ground", then add a high valued resistance to ground from a node (e.g. 1meg), to provide a DC path for the solver. \$\endgroup\$ Jan 1 at 9:41
0
\$\begingroup\$

Coefficient K of coupling is very important.

enter image description here

enter image description here

enter image description here

\$\endgroup\$
5
  • \$\begingroup\$ I thnik your results are for not-steady conditions. But the issue what I mentioned occurs even in steady conditions. But thanks for sharing your experiemen results. \$\endgroup\$
    – Wtow
    Jan 1 at 13:19
  • \$\begingroup\$ And all these occur when I just play with ground and loads. \$\endgroup\$
    – Wtow
    Jan 1 at 13:21
  • \$\begingroup\$ Sorry. Even in steady-state conditions and output ground was forgotten, nothing happens, some results. What is the model in Multisim ? \$\endgroup\$
    – Antonio51
    Jan 1 at 15:24
  • \$\begingroup\$ What do you mean by >What is the model in Multisim ?< \$\endgroup\$
    – Wtow
    Jan 1 at 17:37
  • \$\begingroup\$ I see that it is a very simplified model and one must add some components ... Google search " multisim transformer model" multisim.com/help/components/configurable-transformer/… and this ni.com/fr-be/support/documentation/supplemental/12/… \$\endgroup\$
    – Antonio51
    Jan 1 at 17:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.