For inverse time characteristics a time will be initiated when the current reaches the
set start level. From the general expression of the characteristic the following can
be seen:
(
)
- × ×
-
= ×
>
æ
ö
æ
ö
ç
÷
ç
÷
è
ø
è
ø
p
op
i
t
B k
C
A k
in
EQUATION1190 V1 EN-US
(Equation 94)
where:
t
op
is the operating time of the protection
The time elapsed to the moment of trip is reached when the integral fulfils
according to equation
, in addition to the constant time delay:
0
-
×
³ ×
>
æ
ö
æ
ö
ç
÷
ç
÷
è
ø
è
ø
ò
p
t
i
C
dt
A k
in
EQUATION1191 V1 EN-US
(Equation 95)
For the numerical protection the sum below must fulfil the equation for trip.
1
( )
=
D ×
-
³ ×
>
æ
ö
æ
ö
ç
÷
ç
÷
è
ø
è
ø
å
p
n
j
i j
t
C
A k
in
EQUATION1192 V1 EN-US
(Equation 96)
where:
j = 1
is the first protection execution cycle when a fault has been
detected, that is, when
1
i
in
>
>
EQUATION1193 V1 EN-US
D
t
is the time interval between two consecutive executions of the
protection algorithm,
n
is the number of the execution of the algorithm when the trip
time equation is fulfilled, that is, when a trip is given and
i (j)
is the fault current at time j
For inverse time operation, the inverse time characteristic is selectable. Both the
IEC and ANSI/IEEE standardized inverse time characteristics are supported.
For the IEC curves there is also a setting of the minimum time-lag of operation, see
figure
.
1MRK 505 394-UEN A
Section 25
Inverse time characteristics
Line differential protection RED650 2.2 IEC
873
Technical manual
Summary of Contents for RED650
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