Siemens siprotec 7SA6 User Manual page 275

7SA6
„Dis.T.SEND"
NC Contact
Pickup
&
Z1B
T1B
.
Direc
&
Q S
„>DisTel Rec.Ch1"
R
L–active
Station 1
Figure 6-56 Pilot wire protection — principle
7SA6 Manual
C53000-G1176-C133-1
For lines shorter than the shortest settable line please take into consideration that the
first distance zone is either set to "disabled" or that T1 is delayed for at least one
selective time interval.
If the line has single-end infeed an instantaneous trip for the whole line is possible.
Since no pick-up occurs on the non-feeding line end, the loop is not interrupted at that
point, but only on the feeding line end. After the fault is detected within Z1B, the loop
will be closed again and the trip command is executed.
To guarantee that the time period between pickup and tripping of the protection
function is sufficient to open and close the pilot wire loop, T1B must be delayed for a
short period. If the pilot wire comparison is used with two different types of devices at
both line ends (e.g. 7SA6 at one line end and a standard protection function at the
other end). Care must be taken that the difference in pick-up and trip delay of the two
devices, which may be considerable, does not lead to an unwanted release of the Z1B.
The quiescent state loop ensures a steady check of the pilot wire connections against
interruptions. Since the loop is interrupted during each fault, the signal for pilot wire
failure is delayed by 10 s. The pilot wire comparison supplement is then blocked. It
does not need to be blocked from external as the pilot wire failure is recognized
internally. The other stages of the distance protection continue operating according to
the normal grading coordination chart.
Due to the low current consumption of the binary inputs it may be necessary to
additionally burden the pilot wire loop with an external shunt connected resistor so that
the binary inputs are not blocked by the wire capacitance after an interruption of the
loop. Alternatively combinations of auxiliary relays (e.g. 7PA5210) can be connected.
L+1, L–1 Respective Tripping Voltage
L+2, L–2 Loop Voltage
L+2
Tripping
L+1
L–2
Please take note that both binary inputs are connected in series with each other and
the resistance of the pilot wires. Accordingly the loop voltage must be high or the
pickup voltage of the binary inputs must be low.
The isolation voltage of the pilot wires and the binary inputs and outputs must also be
taken into account.
In the event of an earth fault the induced longitudinal voltage must neither exceed
60 % of the isolation voltage of the pilot wires nor 60 % of the isolation of the device.
The pilot wire comparison is therefore only suited for short lines.
7SA6
„Dis.T.SEND"
NC Contact
&
&
Tripping
L+1
„>DisTel Rec.Ch1"
L–active
Station 2
Functions
Pickup
Z1B
T1B
.
Direc
Q S
R
6-93