3
Operation
Theory
PCS-978 Transformer Relay
3-126
Date: 2013-01-16
[
x.
50/51P4
.tmin] is not set to “0”, then maximum operating current is not valid and users
only can set the setting [
x.
50/51P4.tmin].
3.13 Ground Overcurrent Protection (50/51G)
3.13.1 Application
During normal operation of power system, there is trace residual current whereas a fault current
flows to earth will result in greater residual current. Therefore residual current is adopted for the
calculation of ground overcurrent protection.
In order to improve the selectivity of ground overcurrent protection in power grid with multiple
power sources, directional element can be selected to control ground overcurrent protection. For
application on transformer circuits, second harmonic also can be selected to block ground
overcurrent protection to avoid the effect of sympathetic current on the protection.
3.13.2 Function
Ground overcurrent protection has following functions:
Four-stage ground overcurrent protection with independent logic, current and time delay
settings.
Stage 1, stage 2 and stage 3 are definite-time characteristic, stage 4 can be selected as
definite-time or inverse-time characteristic. The inverse-time characteristic is selectable,
among IEC and ANSI/IEEE standard inverse-time characteristics and a user-defined
inverse-time curve.
Directional element can be selected to control each stage ground overcurrent protection with
three options: no direction, forward direction and reverse direction.
Second harmonic can be selected to block each stage ground overcurrent protection.
Measured neutral current or calculated residual current can be selected for the calculation of
ground overcurrent protection.
3.13.3 Protection Principle
3.13.3.1 Overview
Ground overcurrent protection consists of following three elements:
Ground overcurrent element: each stage equipped with one independent ground overcurrent
element.
Directional element: one directional element equipped shared by all ground overcurrent
elements, and each stage protection can select protection direction.
Harmonic blocking element: one harmonic blocking element shared by all ground
overcurrent elements.
Summary of Contents for PCS-978
Page 1: ...PCS 978 Transformer Relay Instruction Manual NR Electric Co Ltd ...
Page 2: ......
Page 6: ...Preface PCS 978 Transformer Relay IV Date 2013 01 16 ...
Page 10: ...Preface PCS 978 Transformer Relay VIII Date 2013 01 16 ...
Page 62: ...3 Operation Theory PCS 978 Transformer Relay 3 p Date 2013 01 16 ...
Page 250: ...4 Supervision PCS 978 Transformer Relay 4 b Date 2013 01 16 ...
Page 264: ...4 Supervision PCS 978 Transformer Relay 4 14 Date 2013 01 16 ...
Page 266: ...5 Management PCS 978 Transformer Relay 5 b Date 2013 01 16 ...
Page 272: ...5 Management PCS 978 Transformer Relay 5 6 Date 2013 01 16 ...
Page 334: ...6 Hardware Description PCS 978 Transformer Relay 6 60 Date 2013 01 16 ...
Page 370: ...8 Human Machine Interface PCS 978 Transformer Relay 8 d Date 2013 01 16 ...
Page 404: ...8 Human Machine Interface PCS 978 Transformer Relay 8 34 Date 2013 01 16 ...
Page 406: ...9 Configurable Function PCS 978 Transformer Relay 9 b Date 2013 01 16 ...
Page 446: ...10 Communication PCS 978 Transformer Relay 10 26 Date 2013 01 16 ...
Page 448: ...11 Installation PCS 978 Transformer Relay 11 b Date 2012 10 09 ...
Page 456: ...11 Installation PCS 978 Transformer Relay 11 8 Date 2012 10 09 ...
Page 458: ...12 Commissioning PCS 978 Transformer Relay 12 b Date 2012 12 07 ...
Page 468: ...12 Commissioning PCS 978 Transformer Relay 12 10 Date 2012 12 07 ...
Page 470: ...13 Maintenance PCS 978 Transformer Relay 13 b Date 2012 10 09 ...
Page 474: ...13 Maintenance PCS 978 Transformer Relay 13 4 Date 2012 10 09 ...
Page 476: ...14 Decommissioning and Disposal PCS 978 Transformer Relay 14 b Date 2012 10 09 ...
Page 478: ...14 Decommissioning and Disposal PCS 978 Transformer Relay 14 2 Date 2012 10 09 ...
Page 480: ...15 Manual Version History PCS 978 Transformer Relay 15 2 Date 2013 01 16 ...