Generator Stator Overload Protection In Accordance With Ansi Or Ieee Standards - Hitachi Relion 670 Series Applications Manual

Section 11
Multipurpose protection
11.1.4.3 Generator stator overload protection in accordance with ANSI or IEEE
standards
Example will be given how to use one CVGAPC function to provide generator stator overload protection
in accordance with ANSI or IEEE standard if minimum-operating current shall be set to 115% of
generator rating.
The generator stator overload protection is defined by ANSI or IEEE standard for turbo generators in
accordance with the following formula:
=
t
op
æ
I
ç
I
è
EQUATION1743-ANSI V1 EN-US
where:
t is the operating time of the generator stator overload protection
op
TD is the generator capability constant in accordance with the relevant standard (TD = 37.5 for either the ANSI or IEEE
standards)
I is the magnitude of the measured current
m
I is the generator rated current
r
This formula is valid in the range of 10 s to 120 s, that is for stator current between 115% and 218% of
the generator rated current.
By defining parameter x equal to the per unit value for the desired pickup for the overload protection in
accordance with the following formula:
EQUATION1755-ANSI V2 EN-US
Equation 91
generator stator overload characteristic:
=
t
op
æ
ç
x I
è
EQUATION1744-ANSI V1 EN-US
In order to achieve such protection functionality with one CVGAPC functions the following must be done:
1. Connect three-phase generator currents to one CVGAPC instance (for example, CVGAPC:2)
2. Set parameter CurrentInput to value PosSeq
3. Set base current value to the rated generator current in primary amperes
(the correct Global Base values group shall be selected by the parameter GlobalBaseSel)
4. Enable one overcurrent step (for example OC1)
5. Select parameter CurveType_OC1 to value Programmable
178
TD
2
ö
-
1
m
÷
ø
r
can be re-written in the following way without changing the value for the operate time of the
1
×
TD
2
x
2
ö
I 1
-
m
÷
×
2
x
ø
r
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1MRK511407-UUS Rev. N
M13088-81 v4
(Equation 91)
(Equation 92)
(Equation 93)
Phasor measurement unit RES670
Application manual