Siemens siprotec SJ62 User Manual page 498

Logarithmic inverse trip time characteristic
Logarithmic inverse trip time characteristic with knee point
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Figure 4-11 Trip time characteristics of inverse time ground fault protection with logarithmic
inverse characteristic
t =51Ns Tmax – 51Ns TIME DIAL ·ln(I/51Ns PICKUP)
Logarithmic inverse
Note: For I/51Ns PICKUP > 35 the time applies for I/51Ns PICKUP = 35; for t < 51Ns Tmin
the time 51Ns Tmin applies.
Figure 4-12 Trip-time characteristics of the inverse-time ground fault protection 51Ns with
logarithmic inverse characteristic with knee point (example for 51Ns = 0.004 A)
4.15 Ground Fault Detection 64, 50Ns, 51Ns, 67Ns
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