7SR45 Description of Operation
© 2017 Siemens Protection Devices Limited Chapter 1 Page 17 of 34
3.2 Time Delayed Overcurrent Protection (51)
One time delayed overcurrent element is provided in the 7SR45 self powered overcurrent and earth fault relay.
51-1
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 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 51-n Reset setting can apply a definite time delayed reset, or when the operation is configured as an IEC
or ANSI and if the reset is selected as (IEC/ANSI) DECAY reset, the associated reset curve will be used.
A minimum operate time for the characteristic can be set using 51-n MinOperate setting.
A fixed additional operate time can be added to the characteristic using 51-n Follower setting.
Operation of the time delayed overcurrent elements can be inhibited by assigning binary inputs.
Inhibit 51-n A binary input.
Figure 3-2 Logic Diagram: Time Delayed Overcurrent Element
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