High-Current Switch-On-To-Fault Protection; Method Of Operation - Siemens siprotec 7SA6 User Manual

6.10

High-Current Switch-On-To-Fault Protection

6.10.1 Method of Operation

General
Pick-up
I
L1
I
L2
I
L3
SOTF-O/C Release L1
SOTF-O/C Release L2
SOTF-O/C Release L3
SOTF-O/C Release L123
L1
Figure 6-87 Logic diagram of the high current switch on to fault protection
7SA6 Manual
C53000-G1176-C133-1
The high-current switch-on-to-fault protection is intended to trip immediately and
instantaneously following energization of a feeder onto a fault with large fault current
magnitude. It is primarily used as fast protection in the event of energizing the feeder
while the earth switch is closed, but can also be used every time the feeder is
energized — in other words also following automatic reclosure — (selectable).
The energization of the feeder is reported to the protection by the circuit breaker state
recognition function. This is described in detail in Section 6.20.
The high-current pick-up function measures each phase current and compares it with
the set value ,!!! (address ). The currents are numerically filtered so that only
the fundamental frequency is evaluated. If the measured current is more than twice
the set value the protection automatically reverts to the unfiltered measured values,
thereby allowing extremely fast tripping. DC current components in the fault current
and in the CT secondary circuit following the switching off of large currents practically
have no influence on the high-current pick-up operation.
Figure 6-87 shows the logic diagram. The high-current switch-on-to-fault function can
be phase segregated or three-phase.
Following manual closure of the circuit breaker it always functions three-phase via the
release signal "627)2& 5HOHDVH /", which is derived from the central
information control in the device, assuming that the manual closure can be recognized
there (refer to Section 6.20).
If further criteria were determined during the configuration of the recognition of line
energization (address  /LQH &ORVXUH, refer to Section 6.1.3) the release signal
"627)2& 5HOHDVH /[" may be issued phase segregated. This only applies to
devices that can trip single-pole, and is then important in conjunction with single-pole
automatic reclosure.
Tripping is always three-pole. The phase selectivity only applies to the pick-up in that
the overcurrent criterion is coupled with the circuit breaker pole that has been closed.
D333
2404
I>>>
√2
2· ·I>>>
L2
L3
≥1
&
≥1
Functions
4282
SOF O/CpickupL1
4283 SOF O/CpickupL2
4284 SOF O/CpickupL3
≥1
4281 SOF O/C Pickup
4295 SOF O/CtripL123
6-157