7SR11 & 7SR12 Applications Guide
Page 32 of 48 ©2017 Siemens Protection Devices Limited
An alternative type of load shedding scheme would be to set all underfrequency stages to about the same
frequency setting but to have different length time delays set on each stage. If after the first stage is shed the
frequency doesn’t recover then subsequent stages will shed after longer time delays have elapsed.
Generator
Network
Incomer
G59
300/5
STAGE 1: Least important
STAGE 2
STAGE 3
STAGE
4
Essential
Load
6
1
25 5 3 4
2
4
Figure 2.16-1 Load Shedding Scheme Using Under-Frequency Elements
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