ABB RELION RET670 - Page 670

FreqBandWidth 0.0
FilterLength 1.0 s
OverLap 75
Operation On
Now the settings for the multi-purpose overcurrent stage one shall be derived in order
to emulate the existing relay operating characteristic. To achieve exactly the same
inverse time characteristic the programmable IDMT characteristic is used which for
multi-purpose overcurrent stage one, which has the following equation (for more
information see Section “Inverse time characteristics” in the TRM).
[ ]
p
t
A
s B k
i
C
in
æ ö
ç ÷
ç ÷
= + ×
ç ÷
æ ö
-
ç ÷
ç ÷
>
è ø
è ø
EQUATION13000031 V1 EN-US (Equation 495)
In order to adapt to the previous relay characteristic the above equation can be re-
written in the following way:
[ ]
01
1
1
0
so
s
so
t
K
I
s T
I
I
æ ö
ç ÷
ç ÷
= + ×
ç ÷
æ ö
ç ÷
-
ç ÷
ç ÷
è ø
è ø
EQUATION13000032 V1 EN-US (Equation 496)
Thus if the following rules are followed when multi-purpose overcurrent stage one is
set:
•
in >
= I
S0
= 300A
•
35566
118.55
300
so
A
K
I
= = =
•
01
0.64B T= =
•
0.0C =
•
1.0p =
•
1.0k =
Section 13 1MRK 504 163-UUS A
System protection and control
664 Transformer protection RET670 2.2 ANSI
Application manual