User manual 09/2009 - Schneider Electric

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User manual 09/2009 - Schneider Electric

The Metering FunctionRMS Currents and VoltagesMicrologic E trip units display the rms values of currents and voltages (see Real-Time Measurements,page 75).• The total rms current I rms is the square root of the sum of the square of the rms currents of eachharmonic:• The total rms voltage V rms is the square root of the sum of the square of the rms voltages of eachharmonic:Acceptable Harmonic LevelsThe acceptable harmonic levels are stipulated by various standards and statutory regulations:• Electromagnetic compatibility standard adapted to low voltage public networks: IEC 61000-2-2• Electromagnetic compatibility standards:• For loads below 16 A: IEC 61000-3-2• For loads higher than 16 A: IEC 61000-3-4• Recommendations from energy distribution companies applicable to the installationsThe results of international studies have revealed a consensus on the typical harmonic values that shouldideally not be exceeded.The table below lists the typical harmonic values for voltage as a % of the fundamental:Odd Harmonics That Are NotMultiples of 3Odd Harmonics That AreMultiples of 3Even HarmonicsOrder (n) Value as a % V 1 Order (n) Value as a % V 1 Order (n) Value as a % V 15 6% 3 5% 2 2%7 5% 9 1.5% 4 1%11 3.5% 15 0.3% 6 0.5%13 3% > 15 0.2% 8 0.5%17 2% — — 10 0.5%> 19 1.5% — — > 10 0.2%NOTE: Harmonics of a high order (n > 15) have very low rms values and can therefore be ignored.88 LV434104 09/2009

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