ABB RET670 Applications Manual page 565

1MRK504116-UUS C
Application manual
then the OC1 step of the CVGAPC function can be used for generator negative
sequence inverse overcurrent protection.
For this particular example the following settings shall be entered to insure proper
function operation:
1. select negative sequence current as measuring quantity for this CVGAPC function
2. make sure that the base current value for the CVGAPC function is equal to the
generator rated current
3. set TD_OC1 = 20
4. 2
set A_OC1= 1/0.07
5. set B_OC1 = 0.0, C_OC1 = 0.0 and P_OC1 = 2.0
6. set PickupCurr_OC1 = 7%
Proper timing of the CVGAPC function made in this way can easily be verified by
secondary injection. All other settings can be left at the default values. If required
delayed time reset for OC1 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).
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
2
op
æ ö
I
-
1
m
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
= 204.0816
Section 3
IED application
(Equation 410)
559