GE Multilin G60 Generator Protection System 6-21
6 ACTUAL VALUES 6.3 METERING
6
j) VOLTAGE HARMONICS AND THD METERING
PATH: ACTUAL VALUES METERING SOURCE SRC 1 VOLTAGE HARMONICS
The metered voltage harmonics values are displayed in this menu. The “SRC 1” text will be replaced by the programmed
name for the associated 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 cycle
ω
0
= 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 window
h = 1, 2,..., 25 is the harmonic number
The short-time Fourier transform is applied to the unfiltered signal:
(EQ 6.3)
The harmonics are a percentage of the fundamental signal obtained as a ratio of harmonic amplitude to fundamental ampli-
tude multiplied by 100%. The total harmonic distortion (THD) is the ratio of the total harmonic content to the fundamental:
(EQ 6.4)
Voltage harmonics are calculated only for Wye connected phase VTs. Ensure the SYSTEM SETUP AC INPUTS
VOLTAGE BANK F5 PHASE VT XX CONNECTION setting is “Wye” to enable voltage harmonics metering.
6.3.4 SYNCHROCHECK
PATH: ACTUAL VALUES METERING SYNCHROCHECK SYNCHROCHECK 1(4)
If a synchrocheck function setting is "Disabled", the corresponding actual values menu item is not displayed.
VOLTAGE HARMONICS
SRC 1
SRC 1 THD Va: 0.0
Vb: 0.0 Vc: 0.0%
MESSAGE
SRC 1 2ND Va: 0.0
Vb: 0.0 Vc: 0.0%
MESSAGE
SRC 1 3RD Va: 0.0
Vb: 0.0 Vc: 0.0%
↓
MESSAGE
SRC 1 25TH Va: 0.0
Vb: 0.0 Vc: 0.0%
SYNCHROCHECK 1
SYNCHROCHECK 1 DELTA
VOLT: 0.000 V
MESSAGE
SYNCHROCHECK 1 DELTA
PHASE: 0.0°
MESSAGE
SYNCHROCHECK 1 DELTA
FREQ: 0.00 Hz
F
real
mh,()
2
N
----
fm k–() h ω
0
tk()⋅⋅()cos⋅()
k
=
F
imag
mh,()
2
N
----
fm k–()h ω
0
tk()⋅⋅()sin⋅()
k
=
F
ampl
mh,() F
real
mh,()
2
F
imag
mh,()
2
+=
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