77
Definite and inverse time-delayed
residual overcurrent protection (TEF)
Chapter 11
Verifying settings by secondary
injection
Table 10: Operate time formulas
Also check the tMin (minimum operate time) and IMin (minimum
operate current) functions.
10. Activate the TEF--BC input to check the function of the
switch-onto-fault logic.
11. Check that the TEF--TRSOTF output is activated with a
300 ms time delay when injecting a current two times the set
IMin operate value in forward direction.
12. Set the phase angle of the polarising voltage to
ϕ
=245° and
check that the directional current function and the switch-
onto-fault logic gives no operation when the current is in the
reverse direction.
13. Connect the rated DC voltage to the TEF--BLOCK configured
binary input and switch on the fault current.
No TEF--TRIP nor TEF--START signal should appear.
14. Switch off the fault current.
Characteristics
Operate time (s)
Normal inverse
(Equation 1)
Very inverse
(Equation 2)
Extremely inverse
(Equation 3)
Logarithmic inverse
(Equation 4)
Where:
I
is a multiple of set current 3I
0
>
k
is a time multiplying factor, settable in the range of 0.05 to 1.10
t
0.14
I
0.02
1
–
--------------------
k
⋅
=
t
13.5
I
1
–
-----------
k
⋅
=
t
80
I
2
1
–
-------------
k
⋅
=
t
5.8
1.35
I
ln
⋅
(
)
–
=
