Time Delayed Derived Earth Fault Protection (51N); Figure 3-18 Logic Diagram: Derived Time Delayed Earth Fault Element - Siemens 7SR17 Rho Manual

3.5.3

Time Delayed Derived Earth Fault Protection (51N)

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, ANSI or user specific 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 full list of operating curves is given in Chapter 2 – 'Settings and
Instruments Guide'. Operating curve characteristics are illustrated in Chapter 3 – 'Performance Specification'.
The 51N-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 51N-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using 51N-n Follower DTL setting.
Where directional elements are present the direction of operation can be set using 51N-n Dir. Control setting.
Directional logic is provided independently for each 51N element.
Operation of the time delayed overcurrent elements can be inhibited from
Inhibit 51N-n
51N-n VTSAction: Inhibit
Gn 51N-n Element
Enabled
Inhibit 50-n
I
A
I
B
I
C
51N-n Dir Control
Non Dir
Forward
Reverse
67N Fwd
67N Rev
Figure 3-18
©2014 Siemens Protection Devices Limited
A binary or virtual input.
Operation of the VT Supervision function.
Gn 51N-n Setting
Gn 51N-n Charact
Gn 51N-n Time Mult
&
Gn 51N-n Delay (DTL)
Gn 51N-n Min. Op. Time
Gn 51N-n Follower DTL
Gn 51N-n Reset
En.
I
N
Dir En En.
Non Dir
Inhibit
&
1
&
Logic Diagram: Derived Time Delayed Earth Fault Element
Chapter 1) 7SR17 Rho Description Of Operation
Pickup General Pickup
trip 51N-n
51N-n VTS
Action
&
VT Fail
If directional elements are not present this
block is omitted and 'Dir En' signal is set TRUE.
&
51N-n Dir En
& 1
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