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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 ` `
s ] Definitions ] Bus configurations ] Introduction to bus protection ] Relay input sources ] Bus protection methods ] Application of bus protection schemes ] Annexes
( ] new terms defined ] Bus protection and primary equipment ! " Temporary usage of a bus tie breaker in a multiple bus configuration to substitute for one of the network element͛s circuit breakers, typically for the maintenance of the latter; also known as È
# !$ " wonselective part of a multi-zone bus protection system measuring current flows around the entire station and supervising selective tripping from individual bus zones of protection
" Area of a bus or line that becomes isolated from the original zone of protection or an area that loses protection due to the loss of sensing to zone protection relays
% ] Continuity of service for the bus and essential 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
% ] Single bus ] Main and transfer bus ] Double-bus double-breaker ] Double-bus single-breaker ] Breaker-and-a-half ] Ring bus
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| ] Zones of protection ] Bus protection methods ] Scheme selection guidelines
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# ] 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
# ] Zone-interlocked schemes Simple blocking Directional blocking
] Time-coordinated relays overlapping the bus ] Protection (sensors) built into the gas isolated switchgear*
# ] Bus arrangement and flexibility Fixed vs. switchable buses
] Availability and characteristics of CTs ] For reconfigurable buses, availability of auxiliary contacts of disconnect switches ] Performance requirements Security, Selectivity, Speed, Sensitivity
] Cost and complexity
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] Current transformers Types Accuracy classes Equivalent circuit & time to saturation wo universal CT requirements
] Voltage Transformers Voltage trip supervision Directional blocking schemes
] Position of switches and breakers
( # ] Section 7 gives in-depth review of each method following a consistent pattern Theory of operation Setting considerations CT requirements Application considerations
( " ) %#* # 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 the secondary 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
( " ) %#* # CT requirements: ] CTs dedicated to bus protection (cannot be shared) ] Equal CT ratios* ] The accuracy class voltage rating of the CT with the lowest accuracy class above the selected voltage setting, with margin
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] 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
] Applications with paralleled CTs
Generally discouraged Guidelines included
] Application of auxiliary tripping relays Lockout relays won-lockout relays Ratings
] Automatic reclosing after bus faults ] Dynamic bus replica ] Check-zone ] Voltage trip supervision
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] Application of CT trouble detection Detection methods Fallback strategies
] Reliable, selective tripping at the differential zone boundary Line-side CT Bus-side CT Bus coupler considerations The role of Breaker Failure protection
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] CT column ground fault protection ] In-zone grounds Surge arresters Safety grounds and circulating current while testing In-zone grounding of out-of-service elements
] In-service transfer of network elements and breaker substitution
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] Stub bus considerations ] Breaker Failure considerations ] Backup protection Local backup ] Duplicated relays ] BF, batteries, wiring ] Reverse-looking distance relays ] Overcurrent relays
Remote backup
( ] Setting example for a high-impedance scheme (O O) ] Logic example for double-bus singlebreaker configuration (O ) 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 (O )
) %# %# ] Complex bus arrangements and switching ] Advanced bus protection topics (reconfigurable buses, RP relays) ] Balanced coverage of high- and lowimpedance schemes ] Protection scheme selection guidelines ] CT requirements given per scheme ] List of application considerations ] Detailed examples for most common schemes
