Generator Stator Overload Protection In Accordance With Iec Or Ansi Standards - ABB RELION RET670 Applications Manual

Section 12
Multipurpose protection
12.1.3.3
654
Generator stator overload protection in accordance with IEC or ANSI
standards
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:
TD
=
t
op 2
æ ö
I
-
m 1
ç ÷
I
è ø
r
EQUATION1743-ANSI V1 EN-US
where:
t is the operating time of the generator stator overload IED
op
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 is the magnitude of the measured current
m
I is the generator rated current
r
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:
= =
x 116% 1.16 pu
EQUATION1755-ANSI V1 EN-US
formula 3.5can be re-written in the following way without changing the value for the
operate time of the generator stator overload IED:
1
×
TD
2
x
=
t
op 2
æ ö
I 1
-
m
ç ÷
×
2
x I x
è ø
r
EQUATION1744-ANSI V1 EN-US
1MRK 504 163-UUS A
(Equation 489)
(Equation 490)
(Equation 491)
Transformer protection RET670 2.2 ANSI
Application manual
M13088-81 v3