ABB Relion 670 Series Applications Manual page 194

Section 11
Multipurpose protection
step can be set in order to ensure proper function operation in case of repetitive unbalance
conditions.
Furthermore the other built-in protection elements can be used for other protection and alarming
purposes (for example, use OC2 for negative sequence overcurrent alarm and OV1 for negative
sequence overvoltage alarm).
11.1.3.3 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:
=
t
op
æ
I
ç
I
è
EQUATION1743-ANSI V1 EN-US
where:
t
op
TD
I
m
I
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%
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:
=
t
op
æ
ç
x I
è
EQUATION1744-ANSI V1 EN-US
188
TD
2
ö
-
m 1
÷
ø
r
is the operating time of the generator stator overload IED
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)
is the magnitude of the measured current
is the generator rated current
=
1.16 pu
1
×
TD
2
x
2
ö
I 1
-
m
÷
×
2
x
ø
r
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1MRK 511 407-UUS Rev. J
M13088-81 v3
(Equation 91)
(Equation 92)
(Equation 93)
Phasor measurement unit RES670
Application manual