Figure 3-14 Sensitivity For Single Phase Fault With Binary Output; Figure 3-15 Sensitivity For Single Phase Fault With Impulse Output - Siemens 7SR45 Argus User Manual

The following graphs show the sensitivity of the relay and corresponding operating time for different start up
currents.
Figure 3-14
Figure 3-15
NOTE:
The multi-phase current will improve the sensitivity.
3.15.1.2 Time Delayed Overcurrent Protection (51, 51G, 51N)
The operating time of the protection functions (51, 51G, 51N) are optimized at the lower current settings when the
relay is energized with short-circuit current or fault current.
The optimization of the operating time is done only in the start up condition for first 10 AC cycles if the fault
current persists.
The optimization is done as per the sensitivity characteristics of the binary output. However, the operating time of
the impulse output will also improve if the calculated operating time is less than the impulse output sensitivity
characteristics.
NOTE
The following conditions should be considered for the optimization algorithm:
1. If the calculated operating time is less than the boot up time as shown in the sensitivity graph, the
optimization is not effective.
2. If the battery is low, the calculated boot up time is increased, the optimization is not effective.
3. When the device is started with the load current and the fault current appears within 10 AC cycles, then the
operating time will be less than the calculated time.
4.
It is recommended to keep the Time Multiplier setting more than 0.1
© 2017 Siemens Protection Devices Limited
Sensitivity for Single Phase Fault with Binary Output
Sensitivity for Single Phase Fault with Impulse Output
7SR45 Description of Operation
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Chapter 1 Page 30 of 34