Time-Delayed Earth Fault - Derived - Siemens Reyrolle 7SR46 Manual

Functions
3.5 51N Time-Delayed Earth Fault – Derived
3.5 51N Time-Delayed Earth Fault – Derived
Overview of the Function (51N)
The time-delayed earth fault protection is used to provide:
•
Detection of earth current in electrical equipment
•
Backup or emergency protection in addition to other protection functions or devices
•
Coordinated operation with other devices using time graded settings
Structure of the Function (51N)
The derived time‑delayed earth fault protection element has group-dependent settings. These settings can be
different in each settings group – group numbers (Gn) 1 and 2.
The function monitors the primary system earth current by calculating the sum of the 3-phase CT inputs for
example CT1/2/3.
The basic time‑delayed derived earth fault function (51N) is characterized by the following:
•
Current measurement is based on fundamental current.
•
A number of time versus current operate curves are selectable based on IEC and ANSI standards.
•
Alternatively, the 51N elements can operate with a definite time lag (DTL) characteristic.
•
LED operations are provided for earth fault. A general pickup and 51N‑n output are also provided.
Logic of the Function (51N-n)
[lo_7sr46_51N_TimeDelayedDerivedEFFn, 1, en_US]
Figure 3-5
50
Logic Diagram of Time-Delayed Derived Earth Fault Protection (51N)
Reyrolle, 7SR46 Device, Manual
C53000-G7040-C103-1, Edition 10.2022