ABB REC670 Applications Manual page 268

Section 11
Multipurpose protection
262
Equation 96 can be re-written in the following way without changing the value for
the operate time of the negative sequence inverse overcurrent IED:
1
×
k
2
x
=
t
op
2
æ ö
I
NS
ç ÷
×
x I
è ø
r
EQUATION1374 V1 EN-US
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
æ ö
A
= × +
t k B
ç ÷
op
P -
è M C ø
EQUATION1375 V1 EN-US
where:
op
t 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 96 is compared with the equation
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:
1MRK 511 401-UEN A
(Equation 98)
(Equation 99)
98 for the inverse time
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Application manual