ABB REB670 Applications Manual page 273

1MRK 505 337-UUS -
Application manual
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,
GF01)
2. Set parameter CurrentInput to value PosSeq
3. Set base current value to the rated generator current in primary amperes
4. Enable one overcurrent step (for example OC1)
5. Select parameter CurveType_OC1 to value Programmable
æ ö
A
+
= × B
t TD
ç ÷
-
op P
è M C ø
EQUATION1745-ANSI V1 EN
where:
t is the operating time in seconds of the Inverse Time Overcurrent TOC/IDMT algorithm
op
TD is time multiplier (parameter setting)
M is ratio between measured current magnitude and set pickup current level
A, B, C and P are user settable coefficients which determine the curve used for Inverse Time Overcurrent
TOC/IDMT calculation
When the equation 86 is compared with the equation
of the OC1 step in it is obvious that if the following rules are followed:
1. set TD equal to the IEC or ANSI standard generator capability value
2. set parameter A_OC1 equal to the value 1/x2
3. set parameter C_OC1 equal to the value 1/x2
4. set parameters B_OC1 = 0.0 and P_OC1=2.0
5. set PickupCurr_OC1 equal to the value x
then the OC1 step of the CVGAPC function can be used for generator negative sequence
inverse overcurrent protection.
1. select positive sequence current as measuring quantity for this CVGAPC function
2. make sure that the base current value for CVGAPC function is equal to the generator
rated current
3. set TD = 37.5 for the IEC standard or TD = 41.4 for the ANSI standard
4. set A_OC1= 1/1.162 = 0.7432
5. set C_OC1= 1/1.162 = 0.7432
6. set B_OC1 = 0.0 and P_OC1 = 2.0
7. set PickupCurr_OC1 = 116%
Section 10
Multipurpose protection
87 for the inverse time characteristic
(Equation 87)
267