Siemens 7SR18 Solkor - Time Delayed Overcurrent Protection (51)

7SR18 Description Of Operation
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3.3.3 Time Delayed Overcurrent Protection (51)
Up to four time-delayed overcurrent elements are provided in the relay (depending upon variant): -
51-1, 51-2, 51-3 & 51-4
51-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 51-n Char. A time
multiplier is applied to the characteristic curves using the 51-n Time Mult setting. Alternatively, a definite time lag
delay (DTL) can be chosen using 51-n Char. When Definite Time Lag (DTL) is selected the time multiplier is not
applied and the 51-n Delay (DTL) setting is used instead. The full list of operating curves is given in ‘Settings and
Instruments Guide’. Operating curve characteristics are illustrated in ‘Performance Specification’.
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 51-n Min. Operate Time setting.
A fixed additional operate time can be added to the characteristic using 51-n Follower DTL setting.
Where directional elements are present the direction of operation can be set using 51-n Dir. Control setting.
Directional logic is provided independently for each 51-n element
Operation of the time delayed overcurrent elements can be inhibited from e.g. giving the option of using two
elements set to forward and two to reverse.
Inhibit 51-n A binary or virtual input.
79 P/F Inst Trips: 51-n When ‘delayed’ trips only are allowed in the auto-reclose sequence
(79 P/F Prot’n Trip n = Delayed).
51c Activation of the cold load settings.
50-n Inrush Action: Block Operation of the inrush current detector function.
51-n VTSAction: Inhibit Operation of the VT Supervision function.