tripping command when phase selection within the operating protection functions
is not possible, or when external conditions request three-pole tripping.
• Two-pole tripping for two-phase faults.
The three-pole trip for all faults offers a simple solution and is often sufficient in well
meshed transmission systems and in sub-transmission systems. Since most faults,
especially at the highest voltage levels, are single phase-to-ground faults, single-pole
tripping can be of great value. If only the faulty phase is tripped, power can still be
transferred on the line during the dead time that arises before reclosing. Single-pole
tripping during single-phase faults must be combined with single pole reclosing.
To meet the different double, breaker-and-a-half and other multiple circuit breaker
arrangements, two identical SMPPTRC (94) function blocks may be provided within
the IED.
One SMPPTRC (94) function block should be used for each breaker, if the line is
connected to the substation via more than one breaker. Assume that single-pole
tripping and autoreclosing is used on the line. Both breakers are then normally set up
for 1/3-pole tripping and 1/3-phase autoreclosing. As an alternative, the breaker chosen
as master can have single-pole tripping, while the slave breaker could have three-pole
tripping and autoreclosing. In the case of a permanent fault, only one of the breakers
has to be operated when the fault is energized a second time. In the event of a transient
fault the slave breaker performs a three-pole reclosing onto the non-faulted line.
The same philosophy can be used for two-pole tripping and autoreclosing.
To prevent closing of a circuit breaker after a trip the function can block the closing.
The two instances of the SMPPTRC (94) function are identical except, for the name of
the function block (SMPPTRC1 and SMPPTRC2). References will therefore only be
made to SMPPTRC1 in the following description, but they also apply to SMPPTRC2.
Three-pole tripping
A simple application with three-pole tripping from the logic block utilizes part of the
function block. Connect the inputs from the protection function blocks to the input
TRINP_3P. If necessary (normally the case) use a logic OR block to combine the
different function outputs to this input. Connect the output TRIP to the digital Output/s
on the IO board.
This signal can also be used for other purposes internally in the IED. An example could
be the starting of Breaker failure protection. The three outputs TR_A, TR_B, TR_C
will always be activated at every trip and can be utilized on individual trip outputs if
single-pole operating devices are available on the circuit breaker even when a three-
pole tripping scheme is selected.
Section 3 1MRK504116-UUS C
IED application
736
Application manual
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