FUNCTION CHARACTERISTICS
85
NVA100X-D - Manual - 02 - 2016
Undervoltage - 27
Preface
Two operation thresholds, independently adjustable with adjustable delay.
The fi rst one may be programmed with defi nite or inverse time, while the second threshold operates
with defi nite time characteristic.
Each threshold may be separately enabled or disabled.
The fi rst threshold trip may be inhibited by start of the second threshold.
Operation and settings
The fundamental frequency of a selectable voltages, phase to ground (
U
L1
,
U
L2
,
U
L3
) or phase-to-
phase voltages (
U
12
,
U
23
,
U
31
) are utilized:
Each of three voltages compared with the setting values. The start and trip logic may be selected
OR
or
AND
.
With
OR
selection, a start is issued when at least one of the three voltages goes down the adjust-
able threshold (START); with
AND
selection, a start is issued when all the three voltages go down
the adjustable threshold.
After expiry of the associated operate time a trip command is issued; if instead the voltages exceed
the threshold, the element is restored.
The fi rst threshold may be programmed with defi nite or inverse time according the following char-
acteristic curve:
t
=0.75
t
U<inv
/ [1-(
U
/
U
<
inv
)]
Where:
t
: operate
time
U
<
inv
: threshold
setting
t
U<inv
: operate
time
setting
For the inverse time characteristic, following data applies:
The operate time setting is referred to an input voltage equal to 1/4 of the pickup value.
Asymptotic reference value (minimum pickup value): 0.9
U
<
Minimum operate time:
0.1 s
Range where the equation is valid: 0 ≤
U
/
U
<
inv
≤ 0.9
The fi rst undervoltage element can be programmed with defi nite or inverse time characteristic by
setting the
U<Curve
parameter (
DEFINITE, INVERSE
) available inside the
Set \ Profi le A(or B) \
Undervoltage-27 \
U
< Element \ Setpoints
menu.
Each element can be enabled or disabled by setting
ON
or
OFF
the
U< Enable
parameter inside
the
Set \ Profi le A(or B) \ Undervoltage-27 \
U
< Element \ Setpoints
menu and/or the
State
parameter
inside the
Set\Profi le A(or B) \ Undervoltage-27 \
U
<< Element \ Defi nite time
.
The voltage measurement type (Phase-to-phase or phase-to-neutral) and the operating logic (AND
or OR), is adjustable inside the
Set \ Profi le A(or B) \ Undervoltage-27 \ Common confi guration
menu
by means the
Utype27
parameter
;
the allowed setting are
Uph-ph
(phase-to-phase) or
Uph-n
(phase-to-neutral).
The corresponding unit are p.u.
U
n
for
Uph-ph
setting and p.u.
E
n
for
Uph-n
setting.
—
•
•
•
•
U
12
=|
U
L1
-
U
L2
|
U
23
=|
U
L2
-
U
L3
|
U
31
=|
U
L2
-
U
L1
|
U
12
=|
U
L1
-
U
L2
|
U
23
=|
U
L2
-
U
L3
|
U
31
=|
U
L2
-
U
L1
|
General operation time characteristic curve for the undervoltage elements - 27
U
U
<<
U
<
0.9
U
<
t
U
<<
t
t
U
<
TRIP
General operation time characteristic curve for the undervoltage elements - 27
U
U
<<
U
<
0.9
U
<
t
U
<<
t
t
U
<
TRIP
