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Harmonics issues

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  • Harmonics issues

    I wanted to post this to see if anyone else has had this problem and if so, how did you overcome it?

    When I brought my system on line in March, I was watching the SolarEdge monitoring app pretty close just because it was new. I quickly started seeing that the inverter was sporadically shutting off. When I was able to be at the inverter when it happened, I see an error code about DC detected on the AC side. Before it tripped, it was making a noise like a Geiger counter. All I could get out of tech support was that it's "grid distortion" and I should contact my utility.

    Since I work in an engineering office, I talked with out power guys and found out that it was harmonics. Okay, now to find out where the harmonics were being generated. I knew that when we install VFDs at work, we use line reactors to control the harnonics generated from the VFD. So I picked up and added a 5% line reactor between the inverter and the breaker panel. This didn't help anything. The power guy in our office was able to get me a power quality recorder to monitor what was happening. I recorded for two days with the inverter off, two days with the inverter on between the inverter and the reactor, and two days with the inverter on between the panel and the reactor.

    When I looked at the recordings, the voltage harmonics indicated that it was caused by the inverter since they went away when the unit tripped. I finally was able to talk with an engineer at SolarEdge and he made a commom sense suggestion that I hadn't thought to try. He asked me to wait till it was making the noise and start turning off breakers to see if I could make it stop. So I tried this and found out that when I turned off the living room lights, the harmonics went away.

    Turns out that when I was looking for voltage harmonics I should have been looking for current harmonics. The problem was caused by several recessed lights with dimmable LED lamps. I changed the 8 LEDs back to incandescents and the problem stopped. The SolarEdge engineer suggested that this might be controlled by adding a motor run capacitor so I grabbed a 15 microfarad cap off the shelf and hooked it to a two pole breaker, removed the reactor that I didn't need anyway, and Was able to put the LEDs back in with no trips.

    LEDs, especially the dimmable kind, tend to chop up an AC wave form and cause harmonics problems.


  • #2
    Nature of LED's as the drivers are off the chart non-linear. Add dimmable and it gets worse. LED's are almost impossible to run on a battery Inverter if the Inverter is anywhere near operating at rated capacity. With utility power PF is not an issue, but hell on any Inverter and small generators

    Sadly it is easy for manufactures to fix, but very few actually do it as it drives the price way up and scares customers away. Secondly folks are learning LED's do not live up to their claimed service life claims because the drivers give out.

    Of course there is a easy fix, but again expensive, use low voltage DC LED's. Since LED's are Non-linear loads, there is no PF correction circuitry like capacitors or reactors that can work because it is not a phase shift between current and voltage. They generate pure garbage noise. Ham radi operators have to turn them off to operate because of the noise they generate.
    MSEE, PE


    • #3
      That was with the 150 watt electronic dimmer. I have the same dimmer in several rooms with no problem. I believe it was only a problem when there were more than one or two rooms lit. The living room has 8, the kitchen has 7, the master bedroom has 6, the office and daughter's bedroom have 4 each, all LEDs on dimmers. My wife is a stay at home Mom, so there are lights on quite a bit during the day.


      • #4
        Is there a dimming switch involved in this causal circuit? I know.....but sometimes the answer is simple.