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3
Operation
Theory
PCS-978 Transformer Relay
3-152
Date: 2013-01-16
NOTE!
If the minimum operating time [
x.
59G2
.tmin] is set to “0”, the maximum operating
voltage is valid, and the setting
[x.
59G2.K_3U0set] can be set according to requirements.
If the residual voltage is greater than [
x.
59G2.K_3U0set]x[
x.
59G2.3U0_Set], the
operating time of IDMT becomes flat, i.e. the operating time is equal to the operating
time
of
IDMT
at
the
point
residual
voltage
equal
to
[
x.
59G2.K_3U0set]x[
x.
59G2.3U0_Set]. If [
x.
59G2
.tmin] is not set to “0”, then maximum
operating voltage is not valid and users only can set the setting [
x.
59G2.tmin].
3.17 Undervoltage Protection (27)
3.17.1 Application
The increase of reactive power load leads to voltage decreasing, and voltage quality cannot be
satisfied only through AVR and OLTC voltage regulation. In this situation, undervoltage protection
should operate to shed part of loads to make voltage recovery to the normal level.
3.17.2 Function
Undervoltage protection has following functions:
Four-stage definite-time undervoltage protection with independent voltage and time delay
settings.
The rate of change of voltage blocking function is equipped.
3.17.3 Operation Principle
Three-phase undervoltage caused by the lack of system reactive power is almost symmetrical and
does not change suddenly, so the undervoltage protection adopts the positive-sequence voltage
for the protection calculation. If negative-sequence voltage is greater than 0.15Un or
positive-sequence voltage changes suddenly, the undervoltage protection is blocked.
Undervoltage load shedding protection has the unique capability of fault distinguishing, and its
operating time does not need to coordinate with that of other protections, so undervoltage
protection can operate quickly when system voltage is low.
When a short circuit occurs in the power system, bus voltage will decreases suddenly and
therefore undervoltage protection should be blocked simultaneously. After other protections
operate to clear the fault, the voltage at the relay location recovers quickly. If the voltage cannot
recover to the normal operation value, but greater than the value of setting [x.27.U_Recov],
blocking of undervoltage protection should be released at once, and the protection can operate to
shed corresponding loads to make voltage recovery (When system voltage collapses, disappears
or decreases, voltage recovery is the progress the system voltage recover to rated voltage.). A
time delay setting [x.27.t_Recov] should be set, which should be greater than the operating time of
backup protection generally. For example, if the longest operating time of backup protection is 4s,
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 ...