CHARACTERISTICS
45
NV10B - Manual - 04 - 2022
Undervoltage - 27
Preface
Two operation thresholds, independently adjustable (U<, U<<) with adjustable delay (t
U
<, t
U
<<).
The first one may be programmed with definite or inverse time, while the second threshold operates
with definite time characteristic.
Each threshold may be separately enabled or disabled.
The first threshold trip (U<) may be inhibited by start of the second threshold (U<<).
Operation and settings
The fundamental frequency of the input voltages (U
L1
, U
L2
, U
L3
) are employed.
Each of three voltages compared with the setting values (U<, U<<). 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 (t
U
<, t
U
<<) a trip command is issued; if instead the volt-
ages exceed the threshold, the element is restored.
The first threshold (U<) may be programmed with definite or inverse time according the following
characteristic 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 first undervoltage element can be programmed with definite or inverse time characteristic by
setting the U<Curve parameter (DEFINITE, INVERSE) available inside the Set \ Profile 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 \ Profile A(or B) \ Undervoltage-27 \ U< Element \ Setpoints menu and/or the State parameter
inside the Set \ Profile A(or B) \ Undervoltage-27 \ U<< Element \ Definite time.
The operating logic (AND or OR) is adjustable inside the Set \ Profile A(or B) \ Undervoltage-27 \ Com-
mon configuration menu by means the Logic27 parameter; the allowed settings are OR (at least
one voltage lower than threshold) or And (all three voltage must be lower than threshold).
The first threshold trip (U<) may be inhibited by start of the second threshold (U<<) by setting ON
the U< Disabling by U<< start (U<disbyU<<) parameter available inside the Set \ Profile A(or B) \
Undervoltage-27 \ U<< Element \ Setpoints menu.
t-int-F27.ai
U
U<< U<
0.9U<
t
U
<
t
t
U
<<
Caratteristica generale del tempo d’intervento relativa alla funzione di Minima tensione - 27
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