FUNCTION CHARACTERISTICS
229
NVA100X-D - Manual - 02 - 2016
Underfrequency - 81U
Preface
Four operation thresholds, independently adjustable with adjustable delay are provided.
Each threshold may be separately enabled or disabled.
Operation and settings
The frequency, acquired from U
12
,
U
23
,
U
31
phase-to-phase input voltages
[1]
is compared with the
setting values; a start is issued when the frequency goes down the adjustable threshold (START); af-
ter expiry of the associated operate time a trip command is issued; if instead the frequency exceeds
the threshold, the element is restored.
When the frequency value is out of the lock range, it is fi xed to the upper or lower limit
(20 Hz or 60 Hz).
All elements operate with defi nite time characteristic.
Each element can be enabled or disabled by setting ON or OFF the State parameter inside the Set \
Profi le A(or B) \ Underfrequency-81U \ f< Element (f<< Element, f<<< Element, f<<<< Element) \ Defi -
nite time menu.
The underfrequency protection is enabled only when the maximum of the phase-to-neutral input
voltages U
LMAX
=max(U
L1
, U
L2
, U
L3
) overcomes 0.2 U
n
for a tfEN adjustable time.
Setting of the tfEN value is available inside the Set \ Base menu with “level 1” session.
The trip of f< element may be inhibited by the start of the second, third and/or fourth element (f<<,
f<<<, f<<<<) by setting ON the Disable f< by start f<<, Disable f< by start f<<<, Disable f< by start
f<<<< (f<disbyf<<, f<disbyf<<<, f<disbyf<<<<) parameters available inside the Set \ Pro-
fi le A(or B) \ Underfrequency-81U \ f<< Element (f<<< Element,f<<<< Element) \ Setpoints menus.
Similarly the trip of the:
f<< element may be inhibited by start of the third and/or fourth element (f<<< and/or f<<<<) by setting
ON the Disable f<< by start f<<<, start f<<<< (f<<disbyf<<<, f<<disbyf<<<<) parameter avail-
able inside the Set \ Profi le A(or B) \ Underfrequency-81U \ f<<< Element, (f<<<< Element) \ Setpoints
menus.
f<<< element may be inhibited by start of the fourth element (f<<<<) by setting ON the Disable f<<<
by start f<<<< (f<<<disbyf<<<<) parameter available inside the Set \ Profi le A(or B) \ Under-
frequency-81U \ f<<<< Element \ Setpoints menu.
Breaker failure (BF)
All underfrequency elements can produce the Breaker Failure output if the f<BF, f<<BF, f<<<BF,
and f<<<<BF parameters are set to ON.
The parameters are available inside the et \ Profi le A(or B) \ Underfrequency-81U
\ f<< Element (f<<< Element,f<<<< Element) \ Setpoints menus.
[2]
Note 1 The frequency can also be measured on the three phase-to-phase voltages (calculated vectorially)
Note 2 The common settings concerning the Breaker failure protection are adjustable inside the Breaker Failure - BF menu.
—
•
•
f
f<<<<
def
f<<<
def
f
<<
def
f<
def
t
t
f
def
<<
t
f
def
<<<
t
f
def
<<<<
t
f
def
<
General operation time characteristic for the underfrequency elements - 81U
TRIP
Timers-F81.ai
t
fEN
81O-81U Enable
81O-81U disabled 81O-81U disabled81O-81U enabled
0.20 U
n
Max (U
L1
,U
L2
,U
L3
)
t
Overfrequency & underfrequency enable timer
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