EQUATION1756-ANSI V1 EN (Equation 407)
Equation 406 can be re-written in the following way without changing the value for the
operate time of the negative sequence inverse overcurrent IED:
op
2
NS
r
2
TD
t
I
x I
1
x
×
=
×
æ ö
ç ÷
è ø
EQUATION1741-ANSI V1 EN (Equation 408)
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 NegSeq
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
EQUATION1742-ANSI V1 EN (Equation 409)
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 406 is compared with the equation 408 for the inverse time
characteristic of the OC1 it is obvious that if the following rules are followed:
1. set TD equal to the generator negative sequence capability value
2. set A_OC1 equal to the value 1/x2
3. set B_OC1 = 0.0, C_OC1=0.0 and P_OC1=2.0
4. set PickupCurr_OC1 equal to the value x
Section 3 1MRK504116-UUS C
IED application
558
Application manual
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