FUNCTION CHARACTERISTICS
129
NVA100X-D - Manual - 02 - 2016
Phase overcurrent - 50/51 side H and side L
Preface
Three operation thresholds, independently adjustable with adjustable delay are provided on both the
H and L side of the protected device.
References used in this section are related to the protection of the H side: the elements on the L side
is similar (replace the H with L).
The fi rst one may be programmed with defi nite or inverse time according the IEC and ANSI/IEEE
standard, as well as with rectifi er, I
2
t or EM curve.
The second threshold may be programmable with independent or dependent time according to the
I
2
t curve and the third threshold with independent time.
For each threshold a reset time can be set useful to reduce the clearing time for intermittent faults.
The fi rst threshold trip may be inhibited by start of the second and/or third threshold.
Similarly the second threshold trip may be inhibited by start of the third threshold.
Operation and settings
Each phase fundamental frequency current is compared with the setting value. Currents above the
associated pickup value are 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 re-
stored.
The fi rst threshold (
I
>) 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
(H)
>
inv
/ [(
I
/
I
(H)
>
inv
)
0.02
- 1]
Very Inverse Time (IEC 255-3/BS142 type B or VIT):
t
= 13.5 ·
t
(H)
>
inv
/ [(
I
/
I
(H)
>
inv
) - 1]
Very Inverse Time (IEC 255-3/BS142 type B or LIT):
t
= 120 ·
t
(H)
>
inv
/ [(
I
/
I
(H)
>
inv
) - 1]
Extremely Inverse Time (IEC 255-3/BS142 type C or EIT):
t
= 80 ·
t
(H)
>
inv
/ [(
I
/
I
(H)
>
inv
)
2
- 1]
Moderately Inverse (ANSI/IEEE type MI):
t
=
t
(H)
>
inv
· {0.01 / [(
I
/
(H)
>
inv
)
0.02
- 1] + 0.023}
Very Inverse (ANSI/IEEE type VI):
t
=
t
(H)
>
inv
· {3.922 / [(
I
/
I
(H)
>
inv
)
2
- 1] + 0.098}
Extremely Inverse (ANSI/IEEE type EI):
t
=
t
(H)
>
inv
· {5.64 / [(
I
/
I
(H)
>
inv
)
2
- 1] + 0.024}
Rectifi er (RI):
t
= 2351 ·
t
(H)
>
inv
/ [(
I
/
I
(H)
>
inv
)
5.6
- 1]
I-squared-t (
I
2
t = K):
t
= 16 ·
t
(H)
>
inv
/ (
I
/
I
(H)
>
inv
)
2
Electromechanical (EM):
t
=
t
(H)
>
inv
· {0.28 / [-0236 · (
I
/
I
>
inv
)
-1
+ 0.339]}
where:
t
: operate
time
I
(H)
>
inv
: threshold
setting
t
(H)
>
inv
: operate
time
setting
The second threshold (
I
>>) may be programmable with defi nite or inverse time according to the I
2
t
curve:
t
= 16 ·
t
(H)
>
inv
/ (
I
/
I
>
inv
)
2
The third threshold is defi nite time.
For all inverse time characteristics, following data applies:
Asymptotic reference value (minimum pickup value): 1.1
I
(H)
>
inv
Minimum operate time:
0.1 s
Range where the equation is valid:
[1]
1.1 ≤
I
/
I
(H)
>
invv
≤ 20
If
I
>
inv
pickup ≥ 2.5
I
n
, the upper limit is 50
I
nH
For all defi nite time elements the upper limit for measuring is 50
I
nH
.
All overcurrent elements can be enabled or disabled by setting
ON
or
OFF
the
I(H)> Enable
,
I(H)>> Enable
and/or
II(H)>>> Enable
parameters inside the
Set \ Profi le A(or B) \ Phase
overcurrent-50/51 side H \
I(H)> Element
(
I(H)>> Element
,
I(H)>>> Element) \ Setpoints
menus.
The fi rst overcurrent element can be programmed with defi nite or inverse time characteristic by
setting the
I(H)>Curve
parameter (
DEFINITE, IEC/BS A, IEC/BS B, IEC/BS C, ANSI/IEE
MI, ANSI/IEE VI, ANSI/IEE EI, RECTIFIER, I2t, EM
) available inside the
Set \ Profi le A(or B) \
Phase overcurrent-50/51 side H \
I(H)> Element
(
I(H)>> Element
,
I(H)>>> Element) \ Setpoints
menu.
Note 1 When the input value is more than 20 times the set point , the operate time is limited to the value corresponding to 20 times the set point
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t-int-F50-51.ai
I
I
>>
I
>>>
t
>
t
>>
t
>>>
I
>
t
General operation time characteristic for the phase overcurrent elements - 50/51
TRIP
