Negative Sequence Overcurrent Protection - ABB REG670 Applications Manual

1MRK 502 071-UEN -
12.1.3.2
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual

Negative sequence overcurrent protection

Example will be given how to use one CVGAPC function to provide negative
sequence inverse time overcurrent protection for a generator with capability constant
of 20s, and maximum continuous negative sequence rating of 7% of the generator
rated current.
The capability curve for a generator negative sequence overcurrent protection, often
used world-wide, is defined by the ANSI standard in accordance with the following
formula:
k
=
t
op
2
æ ö
I
NS
ç ÷
I
è ø
r
EQUATION1372 V1 EN
where:
t is the operating time in seconds of the negative sequence overcurrent IED
op
k is the generator capability constant in seconds
I is the measured negative sequence current
NS
I is the generator rated current
r
By defining parameter x equal to maximum continuous negative sequence rating of
the generator in accordance with the following formula
= =
x 7% 0, 07 pu
EQUATION1373 V1 EN
Equation 249 can be re-written in the following way without changing the value for
the operate time of the negative sequence inverse overcurrent IED:
1
×
k
2
x
=
t
op
2
æ ö
I
NS
ç ÷
×
x I
è ø
r
EQUATION1374 V1 EN
In order to achieve such protection functionality with one CVGAPC functions the
following must be done:
Section 12
Multipurpose protection
(Equation 249)
(Equation 250)
(Equation 251)
453