7SG16 Ohmega 402 60 Protection Schemes
©2010 Siemens Protection Devices Limited
Chapter 3 Page 3 of 13
1 Basic Schemes
1.1 Time Stepped Distance.
1.1.1 Scheme Operation
A TIME-STEPPED DISTANCE scheme is normally applied when there is no signalling available between relays.
Generally, the Zone 1 elements are set to operate for faults up to 80% of the line length. The Zone 2 elements
operate up to 120% of the line length after a time delay. The Zone 3 elements are set with a longer reach than
the Zone 2 elements, and often have a degree of reverse reach (i.e. an offset characteristic) to provide a further
level of back up protection. The Zone 3 time delay is set to be longer than the Zone 2 time delay.
The disadvantage of such a scheme is that faults in the last 20% of the line are cleared after the Zone 2 time
delay. This may be acceptable for lower voltage distribution systems, but for important circuits or higher voltage
systems additional schemes are available to improve the tripping of the relay.
1.1.2 Settings
Distance Scheme:
Distance Scheme
TIME-STEPPED
Status Inputs:
N/A
Relay Outputs:
N/A
S/Stn 1
S/Stn 2
Relay A Zone 2
Relay
A
Relay
B
Relay
C
Relay A Zone 1
Relay A Zone 3
Relay B Zone 2
Relay B Zone 1
Relay B Zone 3
Relay A Zone 2
Relay A Zone 1
Relay A Zone 3
Relay A Zone 1
Relay A Zone 2
Relay A Zone 3
Time
