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2.7 Definite-Time Overcurrent Protection (I>>, ANSI 50, 51, 67) with Direction Detection
Current Transform-
Example: Unit Connection
er in the Starpoint
(without direction
detection)
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 phenom-
ena, an additional safety factor of about 1.2 to 1.3 is recommended.
A value of T I>> = 0.1 s is recommended as tripping time delay, in order to enable
preferred tripping of the differential protection.
If at Address 113 O/C PROT. I>> was configured as directional, the Addresses
Current Transform-
1304 Phase Direction and 1305 LINE ANGLE are accessible. The inclination of
er on the Output
Side (with direction
the direction straight line representing the separating line between the tripping and the
blocking zone can be adapted to the network conditions by way of the LINE ANGLE
detection)
parameter. To do this, the line angle of the network is set. The direction straight line is
perpendicular to the set direction angle. Together with the parameter 1304 Phase
Direction = Forward or Reverse, this parameter covers the entire impedance
level. This is the reverse direction, provided that the protective relay has been con-
nected correctly according to one of the diagrams in the Appendix. A small zone is
located between the forward and the reverse zone. Due to phase displacement angles
of the transformers, a proper direction decision is not possible. There is no tripping in
the configured preferential direction in this zone.
7UM61 Manual
C53000-G1176-C127-3
Rated apparent power - generator
Rated voltage - generator
Direct-axis transient reactance
Transient synchronous generated voltage
(salient-pole generator)
Rated apparent power - transformer
Rated voltage, on the generator side
Transformer impedance
Current transformer
S
= 5.27 MVA
N, Mach
U
= 6.3 kV
N, Mach
x'
= 29 %
d
U'
= 1.2 · U
P
N,Mach
S
= 5.3 MVA
N, T
U
= 6.3 kV
N, VT prim
u
= 7 %
sc
I
= 500 A
N, CT, prim
I
= 1 A
N, sec
49
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