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IEEE C37.234 Guide for Protective
Relay Application to Power
System Buses
B.Kasztenny (Chairman), S.Conrad (Vice-Chairman),P.Beaumont, K.Behrendt, O.Bolado, J.Boyle, G.Brunello,
J.Burger, F.Calero, S.Chano, G.Dalke, A.Darlington, H.DoCarmo,
D.Fontana, Z.Gajic, J.Holbach, L.Kojovic, F.Lopez, D.Lukach,
D.McGinn, J.Miller, P.Mysore, J.O'Brien, B.Pickett,
S.Sambasivan, G.Sessler, V.Skendzic, J.Smith, D.Tholomier,
M.Thompson, J.Uchiyama, D.Ware, D.Weers, R.Whittaker,
R.Young, S.Zocholl
Presentation to the Main Committee of PSRC, January 14, 2010, Orlando, FL
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Table of Contents
Definitions
Bus configurations
Introduction to bus protection
Relay input sources
Bus protection methods
Application of bus protection schemes
Annexes
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Definitions
23new terms defined
Bus protection and primary equipment
breaker substitution Temporary usage of a bus tie breaker in a
multiple bus configuration to substitute for one of the networkelements circuit breakers, typically for the maintenance of the latter;
also known as breaker transfer
breaker substitution Temporary usage of a bus tie breaker in a
multiple bus configuration to substitute for one of the networkelements circuit breakers, typically for the maintenance of the latter;
also known as breaker transfer
check zone Nonselective part of a multi-zone bus protection
system measuring current flows around the entire station andsupervising selective tripping from individual bus zones of protection
check zone Nonselective part of a multi-zone bus protection
system measuring current flows around the entire station andsupervising selective tripping from individual bus zones of protection
stub bus Area of a bus or line that becomes isolated from theoriginal zone of protection or an area that loses protection due to the
loss of sensing to zone protection relays
stub bus Area of a bus or line that becomes isolated from theoriginal zone of protection or an area that loses protection due to the
loss of sensing to zone protection relays
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Bus design considerations
Continuity of service for the bus andessential network elements
Equipment maintainability and network
switching flexibility Economical and footprint constraints
Sectionalizing requirements to avoid
exceeding breaker fault duties
Ease of future bus expansion
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Bus arrangements
Single bus
Main and transfer bus
Double-bus double-breaker
Double-bus single-breaker
Breaker-and-a-half
Ring bus
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Main and transfer bus
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Main and transfer bus
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Introduction to bus protection
Zones of protection
Bus protection methods
Scheme selection guidelines
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Zones of protection
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Dynamic zones of protection
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Dynamic zones of protection
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Dynamic zones of protection
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Zones of protection
Over
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Bus protection methods
Differential Differentially-connected overcurrent
Instantaneous
Time-delayed
Percentage-restrained differential
Restrained
Advanced microprocessor based
High-impedance differential
Resistor-stabilized overcurrent
High-impedance
Partial differential overcurrent
Fault bus
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Bus protection methods
Zone-interlocked schemes
Simple blocking
Directional blocking
Time-coordinated relays overlapping the bus
Protection (sensors) built into the gas isolated
switchgear*
* Not covered in the Guide
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Scheme selection criteria
Bus arrangement and flexibility
Fixed vs. switchable buses
Availability and characteristics of CTs
For reconfigurable buses, availability ofauxiliary contacts of disconnect switches
Performance requirements
Security, Selectivity, Speed, Sensitivity
Cost and complexity
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Relay input sources
Current transformers Types
Accuracy classes
Equivalent circuit & time to saturation
No universal CT requirements
Voltage Transformers
Voltage trip supervision
Directional blocking schemes
Position of switches and breakers
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Detailed scheme review
Section 7 gives in-depth review of eachmethod following a consistent pattern
Theory of operation
Setting considerations
CT requirements
Application considerations
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Example High-impedance scheme
Voltage setting:
Above the maximum voltage for an
external fault assuming that one CT
saturates completely
High enough so that pickup current is
above the short circuit current on thesecondary of any PT or station service
transformer inside the bus zone
Below the accuracy class voltage
rating of the lowest accuracy class CT
in the differential circuit
Low enough so that pickup current is
below the minimum fault current for
the bus
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Example High-impedance scheme
CT requirements:
CTs dedicated to bus protection
(cannot be shared)
Equal CT ratios*
The accuracy class voltage rating ofthe CT with the lowest accuracy class
above the selected voltage setting,
with margin
* Ratio matching covered but discouraged
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Application of bus protection
Partial differential Loads
Capacitor banks
Application with overcurrent and distance relays
Combined bus and transformer zone
Buses with directly connected grounding
transformers
Application of auxiliary transformers
Generally discouraged
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Application of bus protection
Applications with paralleled CTs
Generally discouraged
Guidelines included
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Application of bus protection
Application of auxiliary tripping relays Lockout relays
Non-lockout relays
Ratings
Automatic reclosing after bus faults
Dynamic bus replica
Check-zone
Voltage trip supervision
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Dynamic bus replica
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Position of switches and breakers
Auxiliary contacts Scheme output89a 89b Declared position Discrepancy alarm
On Off Closed Normal
Off On Opened Normal
On On Closed Alarm
Off Off Closed Alarm
If not opened, then closed logic
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In-service transfer
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In-service transfer
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In-service transfer
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Check zoneCheck zone
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Application of bus protection
Application of CT trouble detection Detection methods
Fallback strategies
Reliable, selective tripping at thedifferential zone boundary
Line-side CT
Bus-side CT
Bus coupler considerations
The role of Breaker Failure protection
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Line-side CT
Bus
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Bus coupler considerations
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Bus coupler considerations
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Application of bus protection
CT column ground fault protection
In-zone grounds
Surge arresters
Safety grounds and circulating current whiletesting
In-zone grounding of out-of-service elements
In-service transfer of network elementsand breaker substitution
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Application of bus protection
Stub bus considerations
Breaker Failure considerations
Backup protection
Local backup
Duplicated relays
BF, batteries, wiring
Reverse-looking distance relays
Overcurrent relays
Remote backup
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Annexes
Setting example for a high-impedance
scheme (AnnexA)
Logic example for double-bus single-
breaker configuration (Annex B) Bus and Breaker Failure protection
Two zones, check zone and voltage supervision
In-service transfers and breaker substitution
Setting guidelines for differentially
connected OC schemes (Annex C)
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