GE T60 Instruction Manual page 629

CHAPTER 6: ACTUAL VALUES
is measured via software-implemented zero-crossing detection of an AC signal. The signal is either a
SOURCE FREQUENCY
Clarke transformation of three-phase voltages or currents, auxiliary voltage, or ground current as per source configuration
(see the
SYSTEM SETUP  POWER SYSTEM
frequency measurement is passed through a validation filter that eliminates false readings due to signal distortions and
transients.
6.4.3.10 Current harmonics and THD metering
ACTUAL VALUES  METERING  SOURCE SRC 1  CURRENT HARMONICS
 CURRENT HARMONICS
 SRC 1
This menu displays metered current harmonics values. The "SRC 1" text is replaced by the name was programmed for the
associated source (see
SETTINGS  SYSTEM SETUP  SIGNAL SOURCES
for the total harmonic distortion (THD) and 2nd to 25th harmonics per phase.
6.4.3.11 Voltage harmonics and THD metering
ACTUAL VALUES  METERING  SOURCE SRC 1  VOLTAGE HARMONICS
 VOLTAGE HARMONICS
 SRC 1
This menu displays metered voltage harmonics values. The "SRC 1" text is replaced by the programmed name for the
associated source (see the
SETTINGS  SYSTEM SETUP  SIGNAL SOURCES
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 cycle
ω = 2πf is the angular frequency based on the system frequency (50 or 60 Hz)
0
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 window
h = 1, 2,..., 25 is the harmonic number
The short-time Fourier transform is applied to the unfiltered signal:
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
settings). The signal used for frequency estimation is low-pass filtered. The final
SRC 1 THD Ia: 0.0

Ib: 0.0 Ic: 0.0%
SRC 1 2ND Ia: 0.0

Ib: 0.0 Ic: 0.0%
SRC 1 3RD Ia: 0.0

Ib: 0.0 Ic: 0.0%

SRC 1 25TH Ia: 0.0

Ib: 0.0 Ic: 0.0%
SRC 1 THD Va: 0.0

Vb: 0.0 Vc: 0.0%
SRC 1 2ND Va: 0.0

Vb: 0.0 Vc: 0.0%
SRC 1 3RD Va: 0.0

Vb: 0.0 Vc: 0.0%

SRC 1 25TH Va: 0.0

Vb: 0.0 Vc: 0.0%
). Current harmonics are measured for each source
menu).
METERING
6
Eq. 6-3
6-23