Reach Extension (Some Models Only) - Siemens 7SG164 Ohmega 400 Series Manual

1.3 Reach Extension (Some models only).

This scheme is only available in relays with built-in autoreclose.
1.3.1 Scheme Operation
The Reach Extension is designed to be used in conjunction with an autoreclose system.
The Zone 1 elements within the relay have two settings. The standard Zone 1 settings are set as for the time-
stepped distance scheme (i.e. 80% of the total line length). Zone 1 X settings are set to overreach the line length
(usually these are set to the same value as the zone 2 setting)
When the reach extension scheme is implemented, the relay will use the extended zone 1 reach for tripping. The
relay will trip and attempt to auto-reclose. After the CB has tripped and reclosed, the relay will use the standard
(underreaching) Zone 1 reach for tripping. Consider a transient fault (i.e. a fault which is removed by tripping and
auto-reclosing) in the last 20 % of the line, as shown in the diagram below. The overreaching Zone 1 will trip and
reclose for this fault, and since it is transient, it will be cleared. A permanent fault will be cleared after the Zone 2
time on the second trip. Since the majority of faults are transient in nature, this will allow transient faults to be
cleared more quickly.
Zone 1 reach used for first trip
Zone 1 reach used after reclosing
The disadvantage of this scheme is that since the extended Zone 1 reach is an overreaching Zone, it may
operate for faults in the next line section. However, when the relay has reclosed, the Zone 1 reach will be
reduced so the relay will trip after the Zone 2 time, allowing the correct relay to trip in Zone 1 after reclosing, if
the fault is permanent. Overall this will increase the amount of circuit breaker operations on the system, and thus
the amount of circuit breaker maintenance required, but it will improve clearance of transient faults. When a
status input assigned Block Reach Extension is energised will the relay will use the normal Zone 1 reach.
The extended zone 1 reach will be active regardless of whether the autorecloser is on or out of service. It is
advised that the Block Reach Extension status input is energised whenever the autorecloser is out of service. If
the relay features an internal autorecloser, a normally closed contact should be assigned to Autorecloser in
Service and connected back into the "Block Reach Extension" status input.
©2010 Siemens Protection Devices Limited
S/Stn 1
Relay
A
Relay A Zone 1 X
Relay A Zone 1
Relay A Zone 2
Relay A Zone 3
7SG16 Ohmega 402 60 Protection Schemes
S/Stn 2
Relay
B
Chapter 3 Page 5 of 13