Table of Contents
Advertisement
Protection and Automation Functions
5.20 51N Time-Delayed Earth Fault – Calculated
5.20
51N Time-Delayed Earth Fault – Calculated
Overview of Function
5.20.1
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
5.20.2
Structure of the Function
The calculated time‑delayed earth fault element has group dependent settings. These settings can be different
in each settings group – group numbers (Gn) 1 to 4.
This function corresponds to the logical node A51NPTOC* in IEC 61850.
The function monitors the primary system earth current by calculating the sum of the 3 phase CT inputs e.g.
CT1/2/3.
The basic instantaneous/time‑delayed calculated earth fault function (51N) is summarized below:
•
Measurement is based on either fundamental or RMS 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‑delayed (DTL) characteristic
•
Outputs are provided for general pickup and trip
The basic function is non-directional, it can be directionalized this requires 3 phase VT inputs e.g. VT1/2/3.
Each 51N element can be set to operate for forward current, reverse current or independently of current direc-
tion. Directionalized functionality uses the decision of the 67N element.
•
Provides information regarding flow direction of earth current for selective application of earth fault
protection
•
Ensures selective fault detection for parallel lines or transformers with infeed at one end
•
Ensures selective fault detection in cable runs with infeed at both ends or in lines connected to form ring
topologies
Where earth fault protection is directionalized correct operation is dependent on valid information being
received from the VT inputs, operation of each directionalized element will be affected if a VT fuse fails. When
a fuse failure is detected, 60VTS function, each element can be selected to either ignore the VT failure, switch
to non-directionalized operation (which does not require VT inputs) or be inhibited.
When installed in power transformer circuits earth currents may be measured by the function during switch in
of the transformer. Each element can be set to be inhibited when inrush current is detected, (see
sion Functions
, section 81HB2 Inrush Current Detection).
Elements can be mapped to start 79 Automatic Recloser by selection of the element as a 79 EF
Trigger within the 79 function element menus. For advanced autoreclose applications each element can be
selected to be inhibited during delayed autoreclose shots of a multi-shot sequence.
286
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual
C53000-G7040-C014-1, Edition 11.2019
6 Supervi-
Advertisement
Table of Contents
