Technical description
2 Protection functions
2.6 Undervoltage protection U1<
(27P)
VM55.EN005
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57
Figure 2.6-1 shows an example of low voltage self blocking.
A
The positive sequence voltage U
1
is below the block
limit. This is not regarded as an under voltage
situation.
B
The positive sequence voltage U
1
is above the block
limit but below the pick-up level. However, this is not
regarded as an under voltage situation, because the
voltage has never been above the pick-up level since
being below the block limit.
C
Voltage is OK, because it is above the pick-up limit.
D
This is an under voltage situation.
E
Voltage is OK.
F
This is an under voltage situation.
G
Voltage is under block limit and this is not regarded as
an under voltage situation.
H
Same as B.
I
Voltage is OK.
J
Same as G
K
Voltage is OK.
Figure 2.6-1 Positive sequence under voltage state and block limit.
Two independent stages
There are two separately adjustable stages: U
1
< and U
1
<<.
Both stages can be configured for definite time (DT) operation
characteristic.
