12.1.3.2 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:
2
op
NS
r
k
t
I
I
=
æ ö
ç ÷
è ø
EQUATION1372 V1 EN (Equation 249)
where:
t
op
is the operating time in seconds of the negative sequence overcurrent IED
k 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
EQUATION1373 V1 EN (Equation 250)
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:
2
2
1
op
NS
r
k
x
t
I
x I
×
=
æ ö
ç ÷
×
è ø
EQUATION1374 V1 EN (Equation 251)
In order to achieve such protection functionality with one CVGAPC functions the
following must be done:
1MRK 502 071-UEN - Section 12
Multipurpose protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 453
Application manual
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