6-20 L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALMETERING CHAPTER 6: ACTUAL VALUES66.4.3.9 Voltage harmonics and THD meteringACTUAL VALUES METERING SOURCE SRC 1 VOLTAGE HARMONICSThis menu displays metered voltage harmonics values. The “SRC 1” text is replaced by the programmed name for theassociated source (see the SETTINGS SYSTEM SETUP SIGNAL SOURCES menu).To extract the 2nd to 25th voltage harmonics, each harmonic is computed on a per-phase basis, where:N = 64 is the number of samples per cycleω0 = 2πf is the angular frequency based on the system frequency (50 or 60 Hz)k = 1, 2,..., N – 1 is the index over one cycle for the Fast Fourier Transform (FFT)m is the last sample number for the sliding windowh = 1, 2,..., 25 is the harmonic numberThe short-time Fourier transform is applied to the unfiltered signal:Eq. 6-3The harmonics are a percentage of the fundamental signal obtained as a ratio of harmonic amplitude to fundamentalamplitude multiplied by 100%. The total harmonic distortion (THD) is the ratio of the total harmonic content to thefundamental:Eq. 6-46.4.4 SynchrocheckACTUAL VALUES METERING SYNCHROCHECK SYNCHROCHECK 1(4) VOLTAGE HARMONICS SRC 1 SRC 1 THD Va: 0.0Vb: 0.0 Vc: 0.0% SRC 1 2ND Va: 0.0Vb: 0.0 Vc: 0.0% SRC 1 3RD Va: 0.0Vb: 0.0 Vc: 0.0% SRC 1 25TH Va: 0.0Vb: 0.0 Vc: 0.0%Voltage harmonics are calculated only for Wye connected phase VTs. Ensure that the SYSTEM SETUP AC INPUTS VOLTAGE BANK F5 PHASE VT XX CONNECTION setting is “Wye” to enable voltage harmonics metering. SYNCHROCHECK 1 SYNCHROCHECK 1 DELTAVOLT: 0.000 kV SYNCHROCHECK 1 DELTAFREQ: 0.00 Hz SYNCHROCHECK 1DELTA PHASE: 0.0° SYNCHROCHECK 1SYNSCP D_PH: 0.0°
