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For inverse time characteristics a time will be initiated when the current reaches the set
pickup level. From the general expression of the characteristic the following can be seen:
(
)
- ×
-
×
æ
ö
æ
ö
× ç
÷ =
ç
÷
ç
÷
è
ø
è
ø
P
op
i
t
B td
C
A td
Pickupn
EQUATION1642 V1 EN
(Equation 76)
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:
-
×
³
×
æ
ö
æ
ö
ç
÷
ç
÷
ç
÷
è
ø
è
ø
ò
0
P
t
i
C
dt
A td
Pickupn
EQUATION1643 V1 EN
(Equation 77)
For the numerical protection the sum below must fulfil the equation for trip.
( )
=
D ×
-
³
×
æ
ö
æ
ö
ç
÷
ç
÷
ç
÷
è
ø
è
ø
å
1
P
n
j
i j
t
C
A td
Pickupn
EQUATION1644 V1 EN
(Equation 78)
where:
j = 1
is the first protection execution cycle when a fault has been detected,
that is, when
>
1
i
Pickupn
EQUATION1646 V1 EN
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.
1MRK 511 287-UUS A
Section 19
Time inverse characteristics
659
Technical manual
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