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High 3rd harmonic on the neutral

MS01
Afternoon,

I was wondering if anyone has nay experiences of having issues with high 3rd harmonic currents on the neutral on high-rised residential schemes? I appreciate  non-linear single phase loads will impact the 3rd harmonic and even on a balanced system harmonics are an issue but we are measuring it at 300% but I can’t think why this may be the case on a residential building.

Does anyone have any ideas?



M
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  • 0
    So now we have 100 A in two of the line conductors and 150 A in the neutral.


     

    Exactly right,  but if you then look at a three phase installation you still have 100A in each phase but 200A in the neutral.

    And the problem is that a typical electronic power supply where the device starts by using the ac to charge a capacitor through a diode to give dc, there is zero current at the start of the cycle then, when the ac voltage gets above the voltage on the capacitor, the current is very high then it drops back to zero again long before the end of the half cycle, exactly what is required to produce lots of 3rd harmonics.
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  • 0
    So now we have 100 A in two of the line conductors and 150 A in the neutral.


     

    Exactly right,  but if you then look at a three phase installation you still have 100A in each phase but 200A in the neutral.

    And the problem is that a typical electronic power supply where the device starts by using the ac to charge a capacitor through a diode to give dc, there is zero current at the start of the cycle then, when the ac voltage gets above the voltage on the capacitor, the current is very high then it drops back to zero again long before the end of the half cycle, exactly what is required to produce lots of 3rd harmonics.
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