ABB RELION RET670 - Page 658

op
2
NS
r
TD
t
I
I
=
æ ö
ç ÷
è ø
EQUATION1740-ANSI V1 EN-US (Equation 485)
where:
t
op
is the operating time in seconds of the negative sequence overcurrent IED
TD is the generator capability constant in seconds
I
NS
is the measured negative sequence current
I
r
is the generator rated current
By defining parameter x equal to maximum continuous negative sequence rating of the
generator in accordance with the following formula
7% 0.07= =x pu
EQUATION1756-ANSI V1 EN-US (Equation 486)
Equation 485 can be re-written in the following way without changing the value for the
operate time of the negative sequence inverse overcurrent IED:
op
2
NS
r
2
TD
t
I
x I
1
x
×
=
×
æ ö
ç ÷
è ø
EQUATION1741-ANSI V1 EN-US (Equation 487)
In order to achieve such protection functionality with one CVGAPC functions the
following must be done:
1.
Connect three-phase generator currents to one CVGAPC instance (for example,
GF01)
2.
Set parameter CurrentInput to value NegSeq
3. Set base current value to the rated generator current in primary amperes
4. Enable one overcurrent step (for example, OC1)
5. Select parameter CurveType_OC1 to value Programmable
Section 12 1MRK 504 163-UUS A
Multipurpose protection
652 Transformer protection RET670 2.2 ANSI
Application manual