Instantaneous Overcurrent (50/50G/50N) - Siemens Reyrolle 7SR45 Argus Device Manual

Applications

5.5 Instantaneous Overcurrent (50/50G/50N)

5.5

Instantaneous Overcurrent (50/50G/50N)

Each instantaneous element has an independent setting for pickup current and a follower definite time lag
(DTL) which can be used to provide time grading margins, sequence coordination grading, or scheme logic.
The instantaneous description relates to the pickup of the element rather than its operation.
[dw_general-form_of_DTL-operate, 1, en_US]
Figure 5-6
Instantaneous elements can be used in current graded schemes where there is a significant difference
between the fault-current levels at different relay points. The instantaneous element is set to pick up at a
current level above the maximum fault current level at the next downstream relay location, and below its own
minimum fault current level. The protection is set to operate instantaneously and is often termed Highset
Overcurrent. A typical application is the protection of transformer HV connections – the impedance of the
transformer ensuring that the LV side has a much lower level of fault current.
The 50-n elements have a low transient overreach that is their accuracy is not appreciably affected by the
initial DC offset transient associated with fault inception.
98
General Form of DTL Operate Characteristic
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020