How Can I Build a Low Cost Harmonics Generator for 120v 60hz Power Lines?

[boss987]

Low Cost "Harmonics Generator"

Hi,

Thanks in advance. I noticed how good is this forum so I decided to share my thoughts with you about the following. If possible, I need some ideas from you guys to build a low cost circuit to generate only 2nd an 3rd harmonics for a 120v 60hz sinewave input voltage...Now, I know that it could be easily done with a PC software and a DAC card...but, I have a limited budget. Below is a description of what I'm looking for:

1- two outputs:
a- First o/p is the 2nd harmonic of the original sinewave (ie. 33% amplitude of the input waveform and 120hz)

b- Second o/p is thethird harmonic of the same original sinewave

2- Taking those 2 o/p's and either add them to the original input waveform or subtract them from it.

The reason for my little project is to simulate a real life issue with power lines harmonics...and then feed the distorted signal to a relay to see how the relay would behave

Thanks a lot guys...please let me know if anything is ambigious

 

[berkeman]

Hi,

Thanks in advance. I noticed how good is this forum so I decided to share my thoughts with you about the following. If possible, I need some ideas from you guys to build a low cost circuit to generate only 2nd an 3rd harmonics for a 120v 60hz sinewave input voltage...Now, I know that it could be easily done with a PC software and a DAC card...but, I have a limited budget. Below is a description of what I'm looking for:

1- two outputs:
a- First o/p is the first harmonic of the original sinewave (ie. 33% amplitude of the input waveform and 180hz)

b- Second o/p is the second harmonic of the same original sinewave

2- Taking those 2 o/p's and either add them to the original input waveform or subtract them from it.

The reason for my little project is to simulate a real life issue with power lines harmonics...and then feed the distorted signal to a relay to see how the relay would behave

Thanks a lot guys...please let me know if anything is ambigious

Welcome to the PF!

The 180Hz signal you refer to above is the 3rd harmonic, not the "first harmonic".

I'm not sure that the level of harmonic distortion that you are trying to add to the AC mains signal is realistic. What is the source of your information on powerline harmonics? There are also powerline dropouts that you may want to consider in your testing.

What does this relay do?

 

[boss987]

Thanks Berkeman,

Yes Berkeman you are right about the harmonics. The relay(SEL-751) is capable of measuring the rms voltage (including the fundamental frequency and higher order harmonics in the signal). Anyways, the relay is not really important at this stage. I have a basic knowledge about this subject because I do more of programming. let's also forget about the power line dropouts for this step. I just want to have some general thoughts of what components should I use in my design...should I use class C amplifier or...Thanks for the help

 

[schip666!]

Some kind of chopper or diode clipper might do it. A cheap inverter that makes square waves would have all the odd harmonics. Perhaps an SCR dimmer to add a "square" onset. But if you really need exact harmonic content those will be too dirty.

 

[boss987]

Great, schip666...Feeding a square wave to a Low pass filter would do the trick...Depending on the filter cutoff frequency I can decide what harmonics should pass...

Thanks