Generator Stator Overload Protection In Accordance With Iec Or Ansi Standards - ABB REB670 Applications Manual

Section 10
Multipurpose protection
10.1.3.3
266
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
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
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
1MRK 505 337-UUS -
(Equation 84)
(Equation 85)
(Equation 86)
Application manual