Pilot Wire Monitoring (Optional), Transfer Tripping, Remote Tripping; Pilot Wire Monitoring - Siemens SIPROTEC 7SD600 System Manual

Numerical line differential protection SIPROTEC 7SD600 V3.0
4.4

Pilot wire monitoring (optional), transfer tripping, remote tripping

4.4.1

Pilot wire monitoring

The pilot wire connection is an integral part of the dif
ferential protection system and the system will only
operate properly if it is in perfect condition. Pilot wire
failure prevents the functional reliability of the protec
tion. Underground pilot wires laid over great distances
are just as prone to mechanical failure as power ca
bles. For this reason, it is important to monitor that
the pilot wires are healthy.
Pilot wire monitoring is fitted on a separate p.c.b.
(processor-aided pilot wire monitoring) that also con
tains the transfer tripping and remote tripping func
tions (version 7SD600K-KKKKK-2(3)KKK).
Pilot wire monitoring contains a transmitter and recei
ver in each of the coupled devices (Figure 4.8) and
operates with an impulse code modulated onto an
injected 2000 Hz current. The monitoring code is al
ternately transmitted from one device and received
by the other and vice versa. In order to ensure a defi
ned startup of this handshake operation, one device is
specified as the "master" (higher-level), the other as
the "slave" (subordinate) (parameter "11STATN").
The "master" device always starts the signal traffic,
the "slave" device responds.
A pilot wire fault is recognized at both ends of the
line. In the event of pilot wire interruption, the diffe
rential protection no longer trips as the differential
current can no longer flow.
Siemens AG January 1999
Method of operation
System manual Order no. E50417-G1176-C069-A1
In the event of a pilot wire short-circuit and through
fault current (external fault), tripping may occur. This
can be prevented by blocking the differential protec
tion once a pilot wire fault has been recognized (setta
ble) (parameter "11DIF.BL", "11T-Dibl")
Because pilot wire monitoring is a slow function, it
cannot prevent the differential protection responding
to a through fault current which occurs at the same
time as a pilot wire short-circuit; however, this is ra
ther unlikely as there is no connection between pilot
wire short-circuits and external line short-circuits.
The pilot wire monitoring function can be disabled
(parameter "11PW.MON") or externally blocked
(marshalling of binary input ">PWM bl" (Fno.
3363)). The alarms"PWM off" (Fno. 3371) or "PWM
blk" (Fno. 3372) are generated.
If pilot wire monitoring picks up, the alarm
"fault.WM" (Fno. 3376) is generated.
If the pilot wire monitoring function is not available
("11PW.MON" off), the transfer tripping and remote
tripping are also disabled.
During a fault, the pilot wire monitoring function is
idle as the line-frequency comparison current then
has priority. It is also not possible to monitor the pilot
wires during transmission of a remote trip signal (see
section 4.4.3) as only one pilot wire pair and one car
rier frequency are available.
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