Functions
2.9 Definite-Time Overcurrent Protection (I>>, ANSI 50, 51, 67) with Direction Detection
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
72
2.9.2 Setting Notes
General
The high-current stage I>> of the overcurrent protection is only effective and accessible if it has been assigned
within the framework of configuration at address 113 O/C PROT. I>> to either side 1 or side 2, i.e. if either
set = NonDirec. SIDE1, NonDirec.SIDE 2, Direc. SIDE1 or Direc. SIDE2. If the function is not
needed it is set to Disabled.
If direction acquisition is used, make sure that the CT and VT sets are consistent.
High-set Current Stage I>>
Address 1301 O/C I>> is used to switch the definite time I>> high-current stage for phase currents ON and
OFF, or to block only the trip command (Block relay). The high-current stage I>> (Parameter 1302 and its
associated delay time T I>>, 1303) is used for current grading with large impedances existing for example
with transformers, motors or generators. It is specified in a way ensuring that it picks up for faults up to this
impedance.
Current Trans-former in the Starpoint (without direction detection)
Example:
Unit Connection
a) Short-circuit calculation
Three-pole short circuit
b) Setting value:
The setting value is achieved by means of a conversion on the secondary side. In order to exclude an unwanted
operation caused by overvoltages or transient phenomena, an additional safety factor of about 1.2 to 1.3 is rec-
ommended.
A value of T I>> = 0.1 s is recommended as tripping time delay in order to enable preferred tripping of the
differential protection.
Rated apparent power - generator S
N, Gen
=5.27 MVA
Rated voltage - generator U
N Gen
=6.3kV
Direct-axis transient reactance x
d
’ = 29 %
Transient synchronous generated voltage
(Salient-pole generator)
U
P
’=1,2 · U
N,Gen
Rated apparent power - transformer S
N, T
= 5.3 MVA
Rated voltage, on the generator side U
N, VTprim
=6.3kV
Short-circuit voltage u
SC
= 7 %
Current transformer I
N, CT, prim
I
N, sec
=
=
500 A
1A
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