AC power line spectrum

power line spectrum

Dear all.
I have some questions:
1- what is the ac power line(or plug in home users) frequency response?
the power is : 220 V-50 Hz

2- how we can measure the signal and all harmonics, till to existence frequency in spectrum.?

3-If I want to extract one of the line harmonics (like 100 Hz) which device or filter could be used??

4- can you introduce me good low freq Amplifiers or IC,s?

thanks alot.

powerline spectrum

Well, if you look directly at the voltage of the line, you should see the fundamental 50Hz as the only harmonic, at least in theory. However, depending on how clean the line connection is, you might see some higher harmonics.

The current drawn from your source also has harmonics and will depend on what you connect to the line. If you have a bridge rectifier, for instance, you will see the current being drawn in pulses instead of a pure sinewave, this will lead to much more harmonic content and you will see components other than the fundamental. This is the reason you will get low power factor for these kinds of system.

I suggest that you search the term "power factor correction" and "power line harmonics" and you will get lots of information about harmonics and ways to reduce harmonics (and increase power factor). I know you did not ask about power factor but I think this is a closely related topic.


Best regards,
v_c

Home plug has very close to 0Ω impedance to frequencies much higher than 50Hz, if that is what you have asked.

Harmonics can come through line itself from other users or from your equipment as well. As V_C explained, most common harmonics in households come from power supply rectifiers with poor power factor correction, where filter capacitors are charged discontinously during voltage peaks. Other in house sources could be triac/thyristor light controllers that are more like noise sources, brush motors,....

You can isolate low frequency harmonics with almoust any opamp in active filter configuration. National Semiconductor has free web based tool for active filter design called "webench" . I would recommend you to tackle some basics on opamps first. Search here "opamps fo everyone" or simmilar books.

Harmonics can be measured with spectral analyzer, but in absence of real one you could use PC's sound card and some of the spectral analyzer software.

Ammount of harmonics can be measured by comparing two measurements, one made with meter capable of "True RMS" measurement and second measuring only average value.

Harmonic Ratio (%) = [(Vrms - Vavg)/Vrms] x 100%

https://www.newark.com/pdfs/techarticles/mro/detectingHarmonicsInAC_Signals.pdf