2.15 Undervoltage protection U< (27)
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For details of setting ranges see chapter 9.3.
Set = An editable parameter (password needed)
C = Can be cleared to zero
F = Editable when force flag is on
Recorded values of the latest eight faults
There are detailed information available of the eight latest
faults: Time stamp, fault voltage, elapsed delay and setting
group.
Recorded values of the overvoltage stages (8 latest faults)
U>, U>>, U>>> (59)
Time stamp of the recording, date
Elapsed time of the operating time
setting. 100% = trip
Active setting group during fault
2.15. Undervoltage protection U< (27)
This is a basic undervoltage protection. The function measures
the three line-to-line voltages and whenever the smallest of
them drops below the user's pick-up setting of a particular
stage, this stage picks up and a start signal is issued. If the
fault situation remains on longer than the user's operation time
delay setting, a trip signal is issued.
Blocking during VT fuse failure
As all the protection stages the undervoltage function can be
blocked with any internal or external signal using the block
matrix. For example if the secondary voltage of one of the
measuring transformers disappears because of a fuse failure
(See VT supervision function in chapter 3.7). The blocking
signal can also be a signal from the user's logic (see chapter
5.8).
Self blocking at very low voltage
The stages can be blocked with a separate low limit setting.
With this setting, the particular stage will be blocked, when the
biggest of the three line-to-line voltages drops below the given
limit. The idea is to avoid purposeless tripping, when voltage is
switched off. If the operating time is less than 0.08 s, the
blocking level setting should not be less than 15 % to the
blocking action to be enough fast. The self blocking can be
disabled by setting the low voltage block limit equal to zero.
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