GUIDELINE
DOCUMENT CLASSIFICATION
CONTROLLED DISCLOSURE
REFERENCE
REV
DISAGAAE3
2
DATE: AUGUST 2004
PAGE
OF
1
6
REVISION DATE:
AUGUST 2007
TITLE: SETTINGS PHILOSOPHY:
BUSCOUPLER PROTECTION
COMPILED BY
TESCOD APPROVED
FUNCTIONAL RESP APPROVED BY
AUTHORISED BY
Signed
Signed
Signed
Signed
.................................
G King
.................................
P A Gerber
SC Chairman
.................................
P R Groenewald
for TESCOD
.................................
MN Bailey
DTM for MD (D Div)
This document has been seen and accepted by:
P A Gerber
P R Groenewald
MN Bailey
Study Committee
for TESCOD
DTM
Contents
Page
Foreword ............................................................................................................................................ 2
1 Scope ............................................................................................................................................. 2
2 Normative References.................................................................................................................... 2
3 Definitions and Abbreviations......................................................................................................... 2
4 Guide .............................................................................................................................................. 2
4.1 Bus coupler modes of operation ................................................................................................. 2
4.2 Application aspects ..................................................................................................................... 3
4.3 Settings philosophies .................................................................................................................. 3
5 Revisions ........................................................................................................................................ 5
Annex
A Impact assessment ........................................................................................................................ 6
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Foreword
This guide was revised through the efforts and contributions of the following members:
P Gerber
Central Region
G Geddie
Southern Region
S van der Nest
North West Region
S van Zyl
North East Region
I van der Merwe
Western Region
1 Scope
This guide sets out the preferred protection setting practice to be applied to distribution buscouplers
and provides optimum solutions for the application of buscoupler protection for a distribution system
application (no transfer).
2 Normative Reference
The following document contains provisions that, through reference in the text, constitute
requirements of this guide. At the time of publication, the edition indicated was valid. All controlled
documents are subject to revision, and parties to agreements based on this guide are encouraged to
investigate the possibility of applying the most recent edition of the document listed below.
Information on currently valid national and international standards and specifications can be obtained
from the Information Centre and Eskom Documentation Centre at Megawatt Park.
Eskom SOG No. 0700-060.
3 Definitions and abbreviations
3.1 Abbreviations
3.1.1 CT: Current transformer
3.1.2 CTR: Current transformer ratio
3.1.3 E/F: Earthfault
3.1.4 IDMTL: Inverse definite minimum time lag
3.1.5 O/C: Overcurrent
4 Guide
4.1 Buscoupler modes of operation
The buscoupler protection is generally used in the following situations:
a) To provide the required protection functionality when new power plant is energized and
b) To provide protection functionality for a feeder on bypass.
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If it is not in one of these two modes, the buscoupler protection is normally disabled. Power may still
be transferred through the buscoupler from one bus-section/busbar to the next. In the extreme, an
energized busbar/bus-section may have all its incoming power channeled through the buscoupler if its
own incomers are disconnected.
4.2 Application aspects
4.2.1 General scheme philosophies
The buscoupler protection may be switched ON or OFF with a protection selector switch (PSS). In the
ON position the phase O/C and E/F functions (which may be either IDMTL, instantaneous, definite
time or a combination of them) shall be enabled, whilst they shall be disabled if the PSS is in the OFF
position. When switched to the OFF position, the relay shall not be powered down but shall be
blocked from operating so that alarming of O/C & E/F starters or other permanent alarms is prevented.
A timer function shall be energized on any close pulse issued to the buscoupler circuit-breaker close
coil. A contact of this timer shall bypass the PSS, irrespective of its position, and activate the
protection functions for the duration of the timer setting. The timer shall be set in excess of the
longest protection function operating time. This timer function shall enable remote energizing of plant.
The maximum available CT ratio shall be selected.
4.2.2 CTR selection
When energizing new plant through the buscoupler or providing protection functionality for feeders on
bypass, it shall be ensured that the sensitivity of the buscoupler protection is maximized without
compromising stability. The selected CTR shall allow E/F and O/C pick-up settings which shall be set
in accordance with the applicable protection philosophy for the specific item of plant. For example, the
suggested O/C pick-up setting for a distribution transformer is 150% of the transformer’s nominal rated
current. For overhead conductors a pick-up setting as close as possible to the emergency rating is
suggested.
On the other hand the CTR shall be selected to ensure that no more than 2A secondary current flows
to the protection relay when the buscoupler is the only incomer for a bus-section/busbar. This is the
extreme loading scenario as far as the buscoupler is concerned.
The required CTR is thus a trade-off between these two requirements.
4.3 Setting philosophies
4.3.1 Energizing new power plant
When energizing new power plant the buscoupler protection is not required to co-ordinate with any
other protection. The protection system dedicated to protecting the new item of plant becomes
operative when the plant is energized. However, when energized, sensitivity and speed of operation
are priorities rather than protection selectivity.
It is recommended that only phase and E/F instantaneous and definite time elements are used when a
new item of plant is to be energized for the first time.
4.3.1.1 Setting considerations
•
The instantaneous O/C and E/F functions shall be set so that they are insensitive to the
maximum energizing current of the plant that is being energized, for example, the line charging
current or the transformer inrush current), but they shall still be sensitive enough to detect worstcase three-phase or single-phase faults under minimum system configuration (maximum source
impedance) conditions.
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•
A definite time element with a settable time delay may be used to improve sensitivity. It may be
set below the transient inrush condition but a settable time delay shall be used to ensure stability.
For a transformer the definite time phase element may be set to 150% of the transformer rated
current.
•
If other stabilizing functions are available (eg. Harmonic restraint), which do not in any way
compromise the sensitivity and selectivity of the main protection function, then this can be
activated and used.
4.3.2 The protection of feeders on bypass
•
For feeder emergency protection purposes, for example, a feeder on bypass , the O/C and E/F
functions shall be set according to the unique power system scenario.
•
Here a combination of IDMTL, definite time and instantaneous O/C and E/F elements may be
employed.
•
In such a condition, it must be ensured that the settings applied are appropriate for the
configuration. Example of this is that if the initial application of the Bus Coupler scheme was to
energize new plant, then the sensitivity is maximized. With the feeder on bypass, the load
current needs to be taken into account to ensure that the pickup is not to low. If such conditions
occur regularly, it may be advisable to use different settings groups.
•
If different settings groups can be activated, then the relay logic or application needs to ensure
that the settings group can not be changed accidently.
4.3.3 Trip Coil Supervision
The logic for the trip coil supervision should be designed such that if the either the Main or Backup
TCS is asserted, then this condition should be alarmed both locally and remotely.
Furthermore, if both trip coils (Main and Backup) or in the case with only one trip coil the TCS is
asserted then the circuit breaker closing function should be blocked.
4.3.4 Breaker Fail Isolation
If the breaker fail isolation is achieved using a pushbutton or other binary input (i.e. not physical
disconnection of the breaker fail output contact), then within the relay logic the breaker fail output is to
be blocked as long as the breaker fail isolate is asserted.
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SETTING PHILOSOPHY:
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5 Revision Information
DATE
Nov 1995
Mar 2001
REV.
0
1
COMPILER
P Arendse
Aug 2004
1(A)
G King
NOTES
Original
! Foreword added
! 3 – Added CT, O/C and E/F
! 4.1.1 – Explanation of the Protection Selector Switch
reworded. Sentence added to state that in the OFF
position the relay must not be powered down but blocked.
Also added that the maximum available CT ratio shall be
selected.
! 4.2.1 - Two instantaneous phase overcurrent elements
changed to three instantaneous phase overcurrent
elements.
! 4.2.1.1 – Added transformer inrush current as an example
in addition to line charging current.
! 4.2.2 – Reworded the complete sentence.
! 4.2.2.1 – Added feeder on bypass as an example in first
bullet.
! Changed the Functional Responsible person
! Compiler changed (P Arendse)
! 4.3.1.1 Setting Considerations changed to include other
stabilizing functions.
! 4.3.2 Feeders on Bypass changed to include settings
groups if required.
! 4.3.3 Trip Coil Supervision added.
! 4.3.4 Breaker Fail Isolate added.
! Document Ref. Changed from SCS… to DIS…
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SETTING PHILOSOPHY:
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Annex A
(informative)
Impact Assessment
Impact assessment
Document title:
Document no:
SETTINGS PHILOSOPHY: BUSCOUPLER PROTECTION
DISAGAAE3
Revision no:
Activity
1.
2.
3.
4.
5.
6.
7.
8.
9.
9.
10.
11.
12.
13.
14.
15.
16.
1(A)
Detail
What training is required to implement this document?
(e.g. Awareness training, practical / on job, module.)
Who will require training? (State designations.)
What prerequisites are needed for students?
What equipment will be required for training? (Computers etc.)
What special tools will be required for training?
What special requirements are needed for the trainer?
Time period for training to be completed?
What special tools / equipment will be needed to be purchased by
the Region to effectively implement?
Are there stock numbers available for the new equipment?
Does the document affect the budget?
Time period for implementation of requirements after training is
completed?
Does the Buyers Guide or Buyers List need updating?
What Buyer’s Guides have been created?
Was Training & Development consulted w.r.t training requirements?
Were the critical points in the document determined?
Is any training material available on the subject in this document?
Was the document SCSPVABE0 adhered to?
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Yes
Total implementation period
Total training cost
Total cost of tools / equipment
Total cost involved
Comments:
Assessment Compiled by:
Recommended by (Functional Responsibility):
Name:
Gary King
Name:
Stuart van Zyl
Designation:
Senior Engineer
Designation:
Engineer
Dept:
EDNS
Dept:
DT CT
Date:
August 2004
Date:
25 August 2004