EQUATION1373 V1 EN-US (Equation 516)
Equation 515 can be re-written in the following way without changing the value for
the operate time of the negative sequence inverse overcurrent IED:
2
2
1
op
NS
r
k
x
t
I
x I
×
=
æ ö
ç ÷
×
è ø
EQUATION1374 V1 EN-US (Equation 517)
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
A
t k B
M C
æ ö
= × +
ç ÷
-
è ø
EQUATION1375 V1 EN-US (Equation 518)
where:
t
op
is the operating time in seconds of the Inverse Time Overcurrent TOC/IDMT algorithm
k 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 515 is compared with the equation 517 for the inverse time
characteristic of the OC1 it is obvious that if the following rules are followed:
1. set k 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 StartCurr_OC1 equal to the value x
then the OC1 step of the CVGAPC function can be used for generator negative
sequence inverse overcurrent protection.
Section 12 1MRK 506 369-UEN B
Multipurpose protection
574 Line distance protection REL670 2.2 IEC
Application manual
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