Schemes Incorporating A Signalling Channel; Permissive Underreach - Siemens 7SG164 Ohmega 400 Series Manual

2 Schemes Incorporating a Signalling Channel

Where a signalling channel is available between ends, the coverage of the relays can be improved. When these
Protection Schemes are used, the Zone 1, 2 and 3 are arranged to trip as in the time stepped distance scheme.
In addition to this, the relay is also capable of carrying out what is known as a "Carrier Aided Trip", where the
time delay on one of the Zones is removed when the conditions at the remote end, as indicated by the signalling
channel meet certain criteria.
The distance protection signalling schemes use the relay outputs Signal Send 1 and status input Signal
Received 1 for the signalling channel. It is possible to configure these channels with delay using the settings SS
pickup, SS Dropoff and SR Dropoff.

2.1 Permissive Underreach.

2.1.1 Scheme Operation
Typically (as for the time stepped scheme) the Zone 1 is set to 80% of the line length, Zone 2 to 120% of the line
length and Zone 3 as delayed back up protection to cover at least the longest adjacent line.
The fault must be in the zone between the two relays (i.e. on the line section) if;
Zone 1 element operates, or
Remote end Zone 1 operates AND local Zone 2 element operates.
This is shown in the diagram below:
S/Stn 1
Relay
A
Relay A Zone 2
AND
Relay B Zone 1
The relay is arranged to send a signal when its Zone 1 picks up.
The relay will trip instantaneously for a Zone 1 fault. If a signal is received from the remote end, the time delay
will be removed from the Zone 2 element, allowing it to trip instantaneously. The name of the scheme comes
from the fact that a Permissive signal is being sent by the Underreaching Zone 1.
Where the signalling equipment has an output which indicates that the signalling channel is out of service, this
can be connected to a Status Input called Carrier Recv Guard. On energisation of this status input the relay will
revert to a time stepped distance scheme.
In this scheme, only a single signalling channel is required for two-way signalling, since if the zone 1 elements at
both operate, the permissive signal will not be required (since both ends will trip instantaneously in Zone 1). The
scheme also incorporates an Unstabilise Relay status input which can be used for intertripping. Energisation of
this status input will initiate a signal send
2.1.2 Settings.
Distance Scheme
SS Pickup
SS Dropoff
SR Dropoff
Status Inputs: UNSTABILISE RELAY, CARRIER RECV GUARD
©2010 Siemens Protection Devices Limited
Relay A Zone 1
Relay A Carrier Aided Trip
Relay A Zone 2
Relay A Zone 3
Relay B Zone 1
Relay B Carrier Aided Trip
Relay B Zone 2
Relay B Zone 3
PUR
0..60000 (0ms)
0..60000 (1ms)
0..60000 (1ms)
7SG16 Ohmega 402 60 Protection Schemes
S/Stn 2
Relay
B
Relay A Zone 2
AND
Relay B Zone 1
Chapter 3 Page 7 of 13