ABB PQFM Instruction Manual page 169

Supply side
Figure 93: Connection of the scopemeter for checking the CT in phase L1
On the scopemeter screen, two waveforms should appear. The voltage waveform should
be approximately a sine wave and the current waveform would normally be a well-
distorted wave because of harmonic distortion. Usually, it is quite easy to extrapolate
the fundamental component as it is the most important one
Remark: If the earthing of the system is bad, the phase to ground voltage may appear
like a much distorted waveform. In this case, it is better to measure the phase-to-phase
voltage (move the black clamp to the phase L2) and subtract 30° on the measured phase
shift.
Figure 94: Extrapolation of the fundamental component from a distorted waveform
From the fundamental component of both signals, the phase shift must then be
evaluated (Figure 95).The time DT between zero crossing of the rising (falling) edge of
both traces must be measured and converted to a phase shift j by the following formula:
D
T
where T1 is the fundamental period duration.
j = * °
360
T 1
L1 K L
K
L2
L3
I k
I
Positive direction
Manual Power Quality Filter PQFM ç The PQF-Manager user interface 169
L
K L
k
I k
L1
X21.1
X21.2
X21.3
X21.4
X21.5
X21.6
X21.7
X21.8
X21.9
Ch1 Ch2
(Figure
I
I1
Load side
L2 L3
PQF
94).