ABB RELION REB670, Applications Manual

Page: 284 / 554

10.1.3.3 Generator stator overload protection in accordance with IEC or ANSI
standards
M13088-81 v3
Example will be given how to use one CVGAPC function to provide generator stator
overload protection in accordance with IEC or ANSI standard if minimum-operating
current shall be set to 116% of generator rating.
The generator stator overload protection is defined by IEC or ANSI standard for turbo
generators in accordance with the following formula:
op 2
m
r
t
TD
I
1
I
=
æ ö
-
ç ÷
è ø
EQUATION1743-ANSI V1 EN-US
(Equation 78)
where:
t
op
is the operating time of the generator stator overload IED
TD is the generator capability constant in accordance with the relevant standard (TD = 37.5 for the
IEC standard or TD = 41.4 for the ANSI standard)
I
m
is the magnitude of the measured current
I
r
is the generator rated current
This formula is applicable only when measured current (for example, positive sequence
current) exceeds a pre-set value (typically in the range from 105 to 125% of the
generator rated current).
By defining parameter x equal to the per unit value for the desired pickup for the
overload IED in accordance with the following formula:
116% 1.16
= =
x pu
EQUATION1755-ANSI V1 EN-US
(Equation 79)
formula 3.5can be re-written in the following way without changing the value for the
operate time of the generator stator overload IED:
op
2
2
m
2
r
t
1
TD
x
I 1
x I x
=
×
æ ö
-
ç ÷
×
è ø
EQUATION1744-ANSI V1 EN-US
(Equation 80)
Section 10
1MRK 505 370-UUS A
Multipurpose protection
278 Busbar protection REB670 2.2 ANSI
Application manual