Time Delayed Derived Earth Fault Protection (51N); Figure 3.4.3-1 Logic Diagram: Derived Time Delayed Earth Fault Element - Siemens 7SR18 Solkor Manual

7SR18 Description Of Operation
3.4.3

Time Delayed Derived Earth Fault Protection (51N)

Up to four time-delayed derived earth fault elements are provided in the relay (depending upon variant): -
51N-n Setting sets the pick-up current level.
A number of shaped characteristics are provided. An inverse definite minimum time (IDMT) characteristic is
selected from IEC and ANSI curves using 51N-n Char. A time multiplier is applied to the characteristic curves
using the 51N-n Time Mult setting. Alternatively, a definite time lag delay (DTL) can be chosen using 51N-n
Char. When definite time lag (DTL) is selected the time multiplier is not applied and the 51N-n Delay (DTL)
setting is used instead.
The 51-n Reset setting can apply a definite time delayed reset, or when the operation is configured as an IEC or
ANSI or user characteristic if the reset is selected as IEC/ANSI (DECAYING) reset the associated reset curve will
be used. The reset mode is significant where the characteristic has reset before issuing a trip output – see
'Applications Guide'
A minimum operate time for the characteristic can be set using the 51N-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using the 51N-n Follower DTL setting.
Operation of the time delayed earth fault elements can be inhibited from: -
Inhibit 51N-n
50-n Inrush Action: Block

Figure 3.4.3-1 Logic Diagram: Derived Time Delayed Earth Fault Element

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51N-1, 51N-2, 51N-3 & 51N-4
A binary or virtual input.
Operation of the inrush current detector function.
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