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
op
P
t TD
A
B
M C
= ×
æ ö
+
ç ÷
-
è ø
EQUATION1745-ANSI V1 EN-US (Equation 492)
where:
t
op
is the operating time in seconds of the Inverse Time Overcurrent TOC/IDMT algorithm
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
491 is compared with the equation 492 for the inverse time
characteristic 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%
1MRK 504 163-UUS A Section 12
Multipurpose protection
Transformer protection RET670 2.2 ANSI 655
Application manual
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