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Voltage Sags and Swells
The power quality of electrical networks has become increasingly
important. The sophisticated loads (e.g. computers etc.) require
uninterruptible supply of "clean" electricity. Allen-Bradley
protection platform provides many power quality functions that can
be used to evaluate, monitor and alarm on the basis of the quality.
One of the most important power quality functions are voltage sag
and swell monitoring.
Allen-Bradley provides separate monitoring logs for sags and
swells. The voltage log is trigged, if any voltage input either
goes under the sag limit (U<) or exceeds the swell limit (U>).
There are four registers for both sags and swells in the fault log.
Each register will have start time, phase information, duration,
minimum, average, maximum voltage values of each sag and
swell event. Furthermore, there are total number of sags and
swells counters as well as total timers for sags and swells.
The voltage power quality functions are located under the
submenu "U".
Table 4.5 – Setting Parameters of Sags and Swells Monitoring
Parameter
Value
U>
20 ... 150
U<
10 ... 120
Delay
0.04 ... 1.00
SagOn
On; Off
SagOff
On; Off
SwelOn
On; Off
SwelOf
On; Off
Supporting Functions
Unit
Default
%
110
Setting value of swell limit
%
90
Setting value of sag limit
s
0.06
Delay for sag and swell detection
-
On
Sag on event
-
On
Sag off event
-
On
Swell on event
-
On
Swell off event
4-7
Description
857-UM001A-EN-P – July 2009
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