7SR45 Description of Operation
© 2017 Siemens Protection Devices Limited Chapter 1 Page 18 of 34
The following are the 51-n supported Curve Characteristic:
• DTL, IEC-NI, IEC-VI, IEC-EI, IEC-LTI, ANSI-MI, ANSI-VI, ANSI-EI
Table 3-2 Time Delayed Overcurrent Protection (51-n)
Parameters Description Default Value Min Max Step Change
51-n Element 51-1 Block Disabled - - -
51-n Setting Current Set point 1xIn 0.2xIn 2.0xIn 0.01
51-n Char Characteristics DTL - - -
51-n Time
Mult
Time Multiplier
(other than DTL)
1 0.01 s 10 0.01
51-n Delay
Delay
(Applicable only for
DTL)
5 s 0 s 15 s 0.01
51-n Min
Operate
Minimum Operate
Time
0 s 0 s 20 s 0.01
51-n Follower Follower DTL 0 s 0 s 20 s 0.01
51-n Reset Reset 0 s 0 s
60, IEC/
ANSI
DECAY
1
3.3 Instantaneous Derived Earth Fault Protection (50N)
Earth current is derived by calculating the sum of the measured line currents.
Two instantaneous derived earth fault elements are provided in the 7SR45 self powered overcurrent and earth
fault relay.
50N-1, 50N-2
Each instantaneous element has independent settings for pick-up current 50N-n Setting and a definite time delay
50N-n Delay.
Operation of the instantaneous derived earth fault elements can be inhibited from:
Inhibit 50N-n A binary input.
Figure 3-3 Logic Diagram: Derived Instantaneous Earth Fault Element
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