ABB RELION 670 Series Applications Manual page 504

Section 11
Multipurpose protection
This formula is applicable only when measured current (for example, positive sequence
current) exceeds a pre-set value (typically in the range from 105 to 125% of the generator rated
current).
By defining parameter x equal to the per unit value for the desired pickup for the overload IED
in accordance with the following formula:
x = 116% = 1.16 pu
EQUATION1377 V2 EN-US
formula 3.5can be re-written in the following way without changing the value for the operate
time of the generator stator overload IED:
=
t
op
æ
ç
è
EQUATION1378 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
3. Set base current value to the rated generator current in primary amperes
4. Enable one overcurrent step (for example OC1)
5. Select parameter
= ×
t k
op
EQUATION1375 V1 EN-US
where:
t
op
k
M
A, B, C and P are user settable coefficients which determine the curve used for Inverse Time Overcurrent
When the equation
of the OC1 step in it is obvious that if the following rules are followed:
1. set k equal to the IEC or ANSI standard generator capability value
2. set parameter
3. set parameter
4. set parameters
5. set
then the OC1 step of the CVGAPC function can be used for generator negative sequence
inverse overcurrent protection.
498
1
×
k
2
x
2
ö
I 1
-
m
÷
×
2
x I x
ø
r
CurrentInput to value PosSeq
CurveType_OC1 to value Programmable
æ A ö
+
B
ç ÷
-
P
è M C ø
is the operating time in seconds of the Inverse Time Overcurrent TOC/IDMT algorithm
is time multiplier (parameter setting)
is ratio between measured current magnitude and set pickup current level
TOC/IDMT calculation
504 is compared with the equation
A_OC1 equal to the value 1/x2
C_OC1 equal to the value 1/x2
B_OC1 = 0.0 and P_OC1 =2.0
StartCurr_OC1 equal to the value x
505 for the inverse time characteristic
1MRK 504 152-UEN B
(Equation 503)
(Equation 504)
(Equation 505)
Application manual