Siemens siprotec 7SA522 - Direct Underreach Transfer Trip

2.6 Teleprotection for distance protection
131
7SA522 Manual
C53000-G1176-C155-3
The permissive transfer trip only functions for faults in the “forward” direction. Accord-
ingly, the first zone Z1 and the overreach zone Z1B of the distance protection must
definitely be set to )RUZDUG in addresses  2SPRGH= and 1351 2SPRGH
=%, refer also to Subsection 2.2.2 under the margin heading “Independent Zones Z1
up to Z5”.
On two terminal lines, the signal transmission may be phase segregated. Send and
receive circuits in this case are built up for each phase. On three terminal lines, the
transmit signal is sent to both opposite line ends. The receive signals are then com-
bined with an OR logic function. If the parameter 7HOHSURW'LVW (address )
is set to 6,*1$/Y3URW,QW and the parameter 180%(52)5(/$< (address )
is set to UHOD\V, the device is informed that it has two remote ends. The default
setting is UHOD\V, which corresponds to one remote end. If digital protection trans-
mission is applied and the protection data interface is used, signals will always be
transmitted phase-selectively.
If conventional transmission is used, the parameter 7\SHRI/LQH (address )
informs the device whether it has one or two opposite line ends.
During disturbance of the signal transmission path, the overreaching zone Z1B may
be activated by an automatic reclosure (internal or external) via the binary input
´!(QDEOH$5]RQHVµ.
If at one line end there is weak or zero infeed, so that the distance protection does not
pick up, the circuit breaker can still be tripped. This “Weak-infeed tripping” is referred
to in Section 2.9.1.
2.6.4 Direct Underreach Transfer Trip
The following scheme is suited for conventional transmission media.
Principle As is the case with PUTT (pickup) or PUTT with zone acceleration, a fault in the first
zone Z1 is transmitted to the opposite line end by means of a transfer trip signal. The
signal received there causes a trip without further queries after a short security margin
Tv (settable at address  7ULS7LPH'(/$<) (Figure 2-50). The transmit signal
can be prolonged by T
S
(settable at address  6HQG3URORQJ), to compensate
for possible differences in the pick-up time at the two line ends. The distance protec-
tion is set such that the first zone reaches up to approximately 85% of the line length.
On three terminal lines Z1 is also set to approximately 85% of the shorter line section,
but at least beyond the tee off point. The overreaching zone Z1B is not required here.
It may however be activated by internal automatic reclosure or external criteria via the
binary input ´!(QDEOH$5]RQHVµ.
The advantage compared to the permissive underreach transfer trip with zone accel-
eration lies in the fact that both line ends are tripped without the necessity for any
further measures, even if one line end has no infeed. There is however no further su-
pervision of the trip signal at the receiving end.
The direct underreach transfer trip application is not provided by its own selectable
teleprotection scheme setting, but implemented by setting the teleprotection supple-
ment to operate in the permissive underreach transfer trip scheme (address 
7HOHSURW'LVW = 3877=%), and using the binary inputs for direct external
trip at the receiving end. Correspondingly, the transmit circuit in Subsection “Permis-
sive Underreach Transfer Trip with Zone Acceleration Z1B (PUTT)” (Figure 2-49) ap-
plies. For the receive circuit the logic of the “external trip” as described in Section 2.10
applies.