7SR210 & 7SR220 Description of Operation
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3.1.2 Instantaneous Overcurrent Protection (50)
Two instantaneous overcurrent elements are provided in the 7SR21 relay. Four elements are provided in the
7SR22 e.g. giving the option of using two elements set to forward and two to reverse.
Each instantaneous element (50-n) has independent settings. 50-n Setting for pick-up current and 50-n Delay
follower time delay. The instantaneous elements have transient free operation.
Where directional elements are present the direction of operation can be set using 50-n Dir. Control setting.
Directional logic is provided independently for each 50-n element.
Operation of the instantaneous overcurrent elements can be inhibited from:
Inhibit 50-n A binary input, virtual input, function key or remote data Comms.
79 P/F Inst Trips: 50-n When ‘delayed’ trips only are allowed in the auto-reclose sequence
(79 P/F Prot’n Trip n = Delayed).
50-n Inrush Action: Inhibit Operation of the inrush current detector function.
50-n VTS Action: Inhibit Operation of the VT Supervision function (7SR22).
Figure 3.1.2-1 Logic Diagram: Instantaneous Over-current Element
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