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 13)
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 14)
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
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:
Section 6
1MRK 511 423-UEN A
Multipurpose protection
82
Bay control REC650 2.2 IEC
Application manual
