63
NC20 - Manual - 01 - 2015
FUNCTION CHARACTERISTICS
Neutral unbalance current - 46N
Preface
One alarm and two operation thresholds, independently adjustable (
I
N>AL
,
I
N>
,
I
N>>
) with adjustable
operating times (
t
N>AL
,
t
N>
,
t
N>>
).
The fi rst one is based on defi nite time characteristic.
The
I
N
> operation threshold may be programmed with defi nite or inverse time according the IEC and
ANSI/IEEE standard; the second thresholds (
I
N
>>) is based on defi nite time characteristic.
The fi rst alarm threshold may be inhibited by start of the operation thresholds (
I
N
>,
I
N
>>); similarly
the fi rst threshold trip may be inhibited by start of the second threshold (
I
N
>>).
Operation and settings
The unbalance current
I
N
is used with:
Fundamental component of the neutral unbalance current measured on the double star connection
as module.
Displacement of the unbalance current
I
N
, positive for lagging current compared with
I
L1
current
φ
N
=(
∠
I
N
-
∠
I
L1
) as phase displacement.
To compensate the inherent unbalance in a un-faulted three phase capacitor bank, a suitable manual
or automatic adjustment is provided.
The user may adjust the compensation values (
I
C
,
φ
C
) by setting
I
C
=
I
N
and
φ
C
=
φ
N
, where the neutral
current when no fault are present on-duty bank capacitors (
I
N
,
φ
N
) are measured by relay.
The compensated imbalance current phasor is calculated by protection relay by the vector dif-
ference
I
NC
=
I
N
-
I
C
The user can check the current imbalance compensation by detecting the measures (
I
NC
module
and
φ
C
phase) for the current imbalance compensated phasor
I
NC
available inside the
Read \ Mea-
sures
menu.
The relay internally measures the real unbalanced current when fault are present:
I
NC
=
I
N
-
I
C
(module and phase displacement).
The compensation parameters are adjustable inside the
Set \ Compensation- 46N
menu.
The compensation may be performed:
Manually by means the
Manual compensation
command; the setting
I
C
and
Phi
C
parameter are
entered
Automatically by means the
Automatic compensation
command; the calculated
I
C
and
Phi
C
pa-
rameter are used. This command is active only with user level 1 when the measured currents are
inside the operating fi eld; the upshot of the command is shown by means the ACE fl ag. The used
parameters can be read inside the
Read \ Measures \ Calculated
menu.
If the unbalance current
I
NC
exceeds the setting threshold a start is issued. After expiry of the as-
sociated operate time a trip command is issued; if instead the current drops below the threshold, the
element is restored.
The fi rst threshold (
I
N>
) may be programmed with defi nite or inverse time according the following
characteristic curves:
Standard Inverse Time (IEC 255-3/BS142 type A or SIT):
t
= 0.14 ·
t
N
>
inv
/ [(
I
NC
/
I
N
>
inv
)
0.02
- 1]
Very Inverse Time (IEC 255-3/BS142 type B or VIT):
t
= 13.5 ·
t
N
>
inv
/ [(
I
NC
/
I
N
>
inv
) - 1]
Extremely Inverse Time (IEC 255-3/BS142 type C or EIT):
t
= 80 ·
t
N
>
inv
/ [(
I
NC
/
I
N
>
inv
)
2
- 1]
Moderately Inverse (ANSI/IEEE type MI):
t
=
t
N
>
inv
· {0.01 / [(
I
NC
/
I
N
>
inv
)
0.02
- 1] + 0.023}
Very Inverse (ANSI/IEEE type VI):
t
=
t
N
>
inv
· {3.922 / [(
I
NC
/
I
N
>
inv
)
2
- 1] + 0.098}
Extremely Inverse (ANSI/IEEE type EI):
t
=
t
N
>
inv
· {5.64 / [(
I
NC
/
I
N
>
inv
)
2
- 1] + 0.024}
Where:
t
: operate
time
I
NC
: compensated
unbalance
current
I
N
>
inv
: threshold
setting
t
>
inv
: operate
time
setting
The alarm threshold (
I
>
AL
) has defi nite time characteristic.
For all inverse time characteristics, following data applies:
Asymptotic reference value (minimum pickup value): 1.1
I
N
>
inv
•
•
•
•
•
•
•
•
•
•
•
t-int-F46N.ai
I
NC
I
N
>
I
N
>>
t
N
>
A L
t
N
>
t
N
>>
I
N
>
A L
t
TRIP
General operation time characteristic for the neutral unbalance elements - 46N
t-int-F46N.ai
I
NC
I
N
>
I
N
>>
t
N
>
A L
t
N
>
t
N
>>
I
N
>
A L
t
TRIP
TRIP
General operation time characteristic for the neutral unbalance elements - 46N
