Power and Voltage Quality Trainer
AD 2
– MI 3399
129
dip duration
retained voltage (u
ret
)
Dip threshold can be set by the user and represents part of nominal U
n
or declared U
c
voltage and can vary from 0.9 U
c
for troubleshooting to 0.65 U
c
for contractual
purposes.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
50
100
150
200
250
300
350
400
dip threshold
u
ret
=204 V
duration: 8 cycles
start time
end time
Figure 2-1: voltage dip attributes
The dip starts when U
rms(1/2)
drops below the dip threshold. The dip ends when U
rms(1/2)
rises above the dip threshold. The difference between end and start time is dip duration
and is reported in seconds or in cycles. Retained (residual) voltage u
ret
is the lowest
U
rms(1/2)
value recorded during a dip.
Origin
Voltage dips are caused by failures in the network or by excessively large inrush
currents.
Impact on customers’ equipment
Studies conducted over recent years have confirmed that voltage dips cause the
majority of malfunctions of equipment. Relays and contractors can drop out if a dip is
60% for longer that 1 cycle. Potential damage is dependent on the ability of the
equipment to sustain lower voltage for short periods. Information technology is
particular sensitive to a dip.
An asynchronous motor can draw a current higher than its starting current at dip
recover.
2.4 Supply voltage swells
Swells are instantaneous voltage increases (opposite to dips). The same attributes are
used for the classification of swells as are used for dips.
Origin
The origin of swells are single line ground failures (SLG), upstream failures, switching
off a large load or switching on a large capacitor.
Impact on customers’ equipment
Summary of Contents for MI 3399
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