5 Theory and internal operation
83
•
On single-phase systems, a voltage dip begins when the U
Rms(1/2)
voltage falls
below the dip threshold, and ends when the U
Rms(1/2)
voltage is equal to or above
the dip threshold plus the 2% of hysteresis voltage (see Figure 5.8)
•
On three-phase systems two different evaluation techniques can be used for
evaluation simultaneously:
o
a dip begins when the U
Rms(1/2)
voltage of one or more channels is below
the dip threshold and ends when the U
Rms(1/2)
voltage on all measured
channels is equal to or above the dip threshold plus the 2% of hysteresis
voltage.
o
a voltage dip begins when the U
Rms(1/2)
voltage of one channel falls below
the dip threshold, and ends when the U
Rms(1/2)
voltage is equal to or above
the dip threshold plus the 2% of hysteresis voltage, on the same phase.
A voltage dip is characterized by a pair of data: residual voltage U
Dip
and dip duration:
•
U
Dip
is the residual voltage, the lowest U
Rms(1/2)
value measured on any channel
during the dip
•
The start time of a dip is time stamped with the time of the start of the U
Rms(1/2)
of
the channel that initiated the event, and the end time of the dip is time stamped
with the time of the end of the U
Rms(1/2)
that ended the event, as defined by the
threshold.
•
The duration of a voltage dip is the time difference between the start time and the
end time of the voltage dip.
U nominal
Swell limit
Dip
duration
U
dip
U
swell
half cycle period
(10 ms @ 50 Hz)
U
t
Dip limit
Interruption
limit
U
rms(1/2)
[n] U
rms(1/2)
[n+1]
U
int
Interrupt
duration
Swell
duration
Figure 5.8 Voltage events definition
Voltage swell
Standard compliance: IEC 61000-4-30 Class S (Section 5.4.3)
