the current should point towards the PQF. Do not forget to remove the shorts on
the CT secondary (if present) before making the measurement.
Supply side
Figure 75: 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 76: Extrapolation of the fundamental component from a distorted waveform
From the fundamental component of both signals, the phase shift must then be
77).The time ∆T between zero crossing of the rising (falling) edge of
evaluated
(Figure
both traces must be measured and converted to a phase shift ϕ by the following formula:
L1
K
L
K
L2
L3
I
k
N
I
Positive direction
Manual Power Quality Filter PQFS Commissioning instructions 151
L
K
L
k
I
k
N
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
76).