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Functions
2.8 Definite-Time Overcurrent Protection (I>, ANSI 50/51) with Undervoltage Seal-In
Figure 2-12
2.8.2
Setting Notes
General
Overcurrent protection is only effective and available if address 112 O/C PROT. I> is set to Side 1 or Side
2 during configuration. If the function is not needed it is set to Disabled.
Time Overcurrent Stage I>
Address 1201 O/C I> is used to switch the definite time-overcurrent stage I> ON and OFF, or to block only the
trip command (Block relay). The setting of the I> stage is mainly determined by the maximum operating
current. Pickup due to overload should never occur since the protection may trip if short command times are
set. For this reason, a setting between 20 % and 30 % over the expected peak load is recommended for gen-
erators, and a setting of about 40 % for transformers and motors.
The trip time delay (parameter 1203 T I>) must be coordinated with the time grading of the network in order
to ensure that the protective equipment closest to the corresponding fault location trips first (selectivity).
The selected time is only an additional time delay and does not include the operating time (measuring time,
dropout time). The delay can be set to ∞. If set to infinity, the pickup of this function will be indicated but the
stage will not trip after pickup. If the I> stage is not required at all, 1201 O/C I> = OFF is set. This setting
prevents tripping and the generation of a pickup message.
66
Logic Diagram of the Overcurrent Stage I> with Undervoltage Seal-In
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
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