[ ]
=
×
-
+
æ
ö
ç
÷
ç
÷
ç
÷
æ
ö
ç
÷
ç
÷
ç
÷
è
ø
è
ø
P
A
t
td
i
C
Pickupn
s
B
EQUATION1640 V1 EN
(Equation 195)
where:
p, A, B, C
are constants defined for each curve type,
Pickupn
is the set pickup current for step n,
td
is set time multiplier for step n and
i
is the measured current.
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 196)
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 197)
For the numerical protection the sum below must fulfil the equation for trip.
1MRK505222-UUS C
Section 22
Inverse time characteristics
1183
Technical reference manual
Summary of Contents for Relion 670 series
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