FUNCTION CHARACTERISTICS
42
NC020 - Manual - 05 - 2022
—
Residual overcurrent - 50N/51N
Preface
The residual current is calculated by the vector sum of the three phase currents.
Two operation thresholds, independently adjustable with adjustable delay.
For each threshold a reset time can be set useful to reduce the clearing time for intermittent faults.
Operation and settings
The residual fundamental frequency current is compared with the setting value. Current above the
associated pickup value is detected and a start is issued. After expiry of the associated operate time
a trip command is issued; if instead the current drops below the threshold, the element is restored.
For all elements the upper limit for measuring is 40
I
n
.
All elements can be enabled or disabled by setting the relative start and/or trip output to a selectable
relay inside the
Set \ Relays
menu.
An adjustable reset time delay is provided for every threshold
t
IE>RES
,
t
IE>>RES
).
Breaker failure (BF)
The elements (
I
E
>,
I
E
>>) can produce the Breaker Failure output if the
Trip IE>
and/or
Trip IE>
outputs are set for
BF Enable.
The outputs are available inside the
Set \ Breaker failure
menu.
[1]
Cold load pickup
If the CLP function (Cold Load Pick-up) is enabled for element blocking, the selected threshold may
be blocked for an adjustable time interval, starting from the circuit breaker closure.
This operating mode may be select by setting
ON-Blocking
the
IECLP>
and/or
IECLP>>
param-
eters inside the
Set \ 50N-51N \
IE>Element (IE>>Element) \ IE>Setpoints (IE>> Setpoints)
menus.
If the CLP function (Cold Load Pick-up) is enabled for threshold change, the selected threshold may
be changed for an adjustable time interval, starting from the circuit breaker closure.
This operating mode may be select by setting
ON-Changing
the
IECLP>
and/or
IECLP>>
parameters inside the
Set \ 50N-51N \
IE>Element (IE>>Element) \ IE>Setpoints (IE>> Setpoints)
menus, whereas the operating thresholds within the CLP may be adjusted inside the
Set \ 50N-51N
\
IE>Element (IE>>Element) \ IE>Definite ( IE>>Definite )
menus.
For both operating modes the CLP Activation time parameters (
tIECLP, tIECLP>>
) may be ad-
justed inside the
Set \ 50N-51N \
IE>Element (IE>>Element ) \ IE>Setpoints (IE>> Setpoints)
menus.
Note 1 The common settings concerning the Breaker failure protection are adjustable inside the
Breaker Failure - BF
menu.
I
EC
t
E
>
def
I
E
>
def
I
E
>>
def
t
E
>>
def
t
TRIP
General operation time characteristic for the residual overcurrent elements - 50N/51N
Timers-F50N-51N.ai
IE> element - 50N/51N - residual overcurrent timers
IE> Start
IE> Trip
t
IE>def
t
IE>def
I
EC
≥ threshold
t
IE>RES
t
IE>RES
t
IE>RES
t
