ABB Relion 670 Series Applications Manual page 247

1MRK 511 358-UUS A
The subsynchronous current frequency is calculated as follows:
=
50
f
s
EQUATION13000030 V1 EN-US
In order to properly extract the weak subsynchronous signal in presence of the dominating 50Hz
signal the SMAI HPAC filter shall be set as given in the following table:
Table 25:
I_HPAC_31_5Hz: SMAIHPAC:1
ConnectionType
SetFrequency
FreqBandWidth
FilterLength
OverLap
Operation
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).
æ
ç
[ ]
ç
=
s
t
ç
ç
è
EQUATION13000031 V1 EN-US
In order to adapt to the previous relay characteristic the above equation can be re-written in the
following way:
æ
ç
ç
[ ]
=
s
t
ç
ç
ç
è
EQUATION13000032 V1 EN-US
Thus if the following rules are followed when multi-purpose overcurrent stage one is set:
Application manual
- =
Hz 18.5 Hz 31.5 Hz
Proposed settings for SMAIHPAC
ö
÷
A
÷
+ ×
B k
p ÷
æ i ö
-
C
÷
ç ÷
>
è in ø
ø
ö
K
÷
I ÷
+ ×
so T 1
÷
1 01
æ ö
I
÷
-
0
s
ç ÷
÷
I
è ø
ø
so
Ph — N
31.5
0.0
1.0 s
75
On
Section 11
System protection and control
(Equation 109)
(Equation 110)
(Equation 111)
241