7% 0, 07
x
pu
=
=
EQUATION1373 V1 EN-US
(Equation 77)
Equation
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 78)
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 79)
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
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.
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
k_OC1 = 20
Section 10
1MRK 505 370-UEN D
Multipurpose protection
232
Busbar protection REB670
Application manual
Summary of Contents for REB670 Series
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