FUNCTION CHARACTERISTICS
227
NVA100X-D - Manual - 02 - 2016
Overfrequency - 81O
Preface
Two operation thresholds, independently adjustable with adjustable delay are provided.
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 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 overcomes the adjustable threshold (START);
after expiry of the associated operate time a trip command is issued; if instead the frequency drops
below 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).
Both 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) \ Overfrequency-81O \ f> Element (or f>> Element \ Defi nite time menu.
The overfrequency protection is enabled only when the maximum of the phase-to-neutral input volt-
ages 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 fi rst threshold trip (f>) may be inhibited by start of the second threshold (f >>) by setting ON the
f> Disabling by f>> start (f>disbyf>>) parameter available inside the Set \ Profi le A(or B) \ Overfre-
quency-81O \ f>> Element \ Setpoints menu.
Breaker failure (BF)
Both overfrequency elements (f>, f>>) can produce the Breaker Failure output if the f>BF and
f>>BF parameters are set to ON.
The parameters are available inside the Set \ Profi le A(or B) \ Overfrequency - 81O \ 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
t
f >>
def
f >
def
t
f
def>>
t
f
def>
General operation time characteristic for the overfrequency elements - 81O
TRIP
all-F81O.ai
Logic diagram concerning the overfrequency elements - 81O
ff
ON=inhibit
2nd Pickup Element 1st Pickup Element
Block1
Block1
Block1
BF
&
Block1
BF
State
f>disbyf>>
f
>
def
t
f>def
State
f
>>
def
t
f>>def
f> inhibition
f
> Start
f
> Trip
f
>> Start
f
>> Start
f
>> 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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