126
FUNCTION CHARACTERISTICS
—
Negative sequence overcurrent for Line or Transformer protection - 46LT
Preface
Two operation thresholds, independently adjustable with adjustable delay.
The first one may be programmed with definite or inverse time according the IEC and ANSI/IEEE
standard, as well as with I
2
t or EM curve.
The second threshold has a definite time characteristic.
For each threshold a reset time can be set useful to reduce the clearing time for intermittent faults.
The first threshold trip may be inhibited by start of the second threshold.
Operation and settings
The negative sequence current is computed as:
I
2
=(
I
L1
+e-
j120°
·
I
L2
+e
+j120°
·
I
L3
)/3
where e
-j120°
=-1/2-j√3/2, e
j120°
=-1/2+j√3/2.
The negative sequence current is compared with the setting values. Currents above the associated
pickup value are detected and a start is issued. After expiry of the associated operate time (
t
2
>,
t
2
>>)
a trip command is issued; if instead the current drops below the threshold, the element is restored.
The first threshold (
I
2
>) may be programmed with definite or inverse time according the following
characteristic curves:
• Standard Inverse Time (IEC 255-3/BS142 type A or SIT):
t
= 0.14 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
)
0.02
- 1
• Very Inverse Time (IEC 255-3/BS142 type B or VIT):
t
= 13.5 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
) - 1]
• Extremely Inverse Time (IEC 255-3/BS142 type C or EIT):
t
= 80 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
)
2
- 1]
• Moderately Inverse (ANSI/IEEE type MI):
t
=
t
2
>
inv
· {0.01 / [(
I
2
/
I
2
>
inv
)
0.02
- 1] + 0.023}
• Very Inverse (ANSI/IEEE type VI):
t
=
t
2
>
inv
· {3.922 / [(
I
2
/
I
2
>
inv
)
2
- 1] + 0.098}
• Extremely Inverse (ANSI/IEEE type EI):
t
=
t
2
>
inv
· {5.64 / [(
I
2
/
I
2
>
inv
)
2
- 1] + 0.024}
• I-squared-t (
I
2
t = K):
t
= 16 ·
t
2
>
inv
/ (
I
2
/
I
2
>
inv
)
2
• Electromechanical (EM):
t
=
t
2
>
inv
· {0.28 / [-0236 · (
I
2
/
I
2
>
inv
)
-1
+ 0.339]}
Where:
t
:
operate time
I
2
>
inv
:
threshold setting
t
2
>
inv
:
operate time setting
The second threshold has a definite time characteristic
• Standard Inverse Time (IEC 255-3/BS142 type A or SIT):
t
= 0.14 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
)
0.02
- 1]
• Very Inverse Time (IEC 255-3/BS142 type B or VIT):
t
= 13.5 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
) - 1]
• Extremely Inverse Time (IEC 255-3/BS142 type C or EIT):
t
= 80 ·
t
2
>
inv
/ [(
I
2
/
I
2
>
inv
)
2
- 1]
• Moderately Inverse (ANSI/IEEE type MI):
t
=
t
2
>
inv
· {0.01 / [(
I
2
/
I
2
>
inv
)
0.02
- 1] + 0.023}
• Very Inverse (ANSI/IEEE type VI):
t
=
t
2
>
inv
· {3.922 / [(
I
2
/
I
2
>
inv
)
2
- 1] + 0.098}
• Extremely Inverse (ANSI/IEEE type EI):
t
=
t
2
>
inv
· {5.64 / [(
I
2
/
I
2
>
inv
)
2
- 1] + 0.024}
• I-squared-t (
I
2
t = K):
t
= 16 ·
t
2
>
inv
/ (
I
2
/
I
2
>
inv
)
2
• Electromechanical (EM):
t
=
t
2
>
inv
· {0.28 / [-0236 · (
I
2
/
I
2
>
inv
)
-1
+ 0.339]}
For all inverse time characteristics, following data applies:
• Asymptotic reference value (minimum pickup value): 1.1
I
2
>
inv
• Minimum operate time: 0.1
s
• Range where the equation is valid:
1
1.1 ≤
I
2
/
I
2
>
inv
≤ 20
For all definite time elements the upper limit for measuring is 50
I
n
(inductive CT versions) or 30
I
n
(ThySensor input versions).
All overcurrent elements can be enabled or disabled by setting
ON
or
OFF
the
I2> Enable
and/
or
I2>> Enable
parameters inside the
Set \ Profile A (or B) \ Negative sequence overcurrent - 46 \
I2> Element
(
I2>> Element) \ Setpoints
menus.
The first overcurrent element can be programmed with definite or inverse time characteristic by
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
I
2
I
2
>>
t
2
>
t
2
>>
I
2
>
t
General operation time characteristic curve for the negative sequence overcurrent element - 46
TRIP
XMR-D EQUIPMENT MANUAL
Ed. 2.9 - 02/2021
