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POWER Engineers, Inc.
Western Protective Relaying Conference
Wind PlantWind Plant
Collector Substation ProtectionCollector Substation Protection
Mr. John J. Kumm, P.E.POWER Engineers, Inc.
POWER Engineers, Inc.
Wind Generation Resources
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Renewable Portfolio Standard: 20% by 2030
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Introduction & Outline
Background & Objectives
Utility Interface
Transmission Line Protection
Transmission-Voltage Bus Protection
Collector Substation Transformer
Protection Collector-Voltage Bus Protection
Collector Protection
Capacitor Bank Protection
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The Wind Plant
Intertie
Switchyard
Collector
Substation
Collector System
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Background & Objectives
Wind plants now have planned build-outsto 1,000 MW, interconnect voltages to345 kV
Plants represent a large investment andappreciable production resource
Protection objectives of Dependability,Security, Selectivity, Speed, Simplicity,Economics all apply
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Typical Collector Substation Topology
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Wind Turbine Generator Types
Type A Simple Induction Machine
Type B Wound Rotor Induction withVariable Resistance
Type C Doubly-fed Induction
Type D Full Converter Interface
generator
full power
Plant
Feedersac
to
dc
dc
to
ac
generator
partial power
PlantFeeders
acto
dc
dcto
ac
generator
Slip power
as heat loss
PlantFeeders
PF controlcapacitors
ac
to
dc
generator
PlantFeeders
PF controlcapacitors
Type A Type B Type C Type D
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Utility Interface
Utility requirements for protection &control vary with location, voltage level
Determine protection scheme,communication, control, & datarequirements as early as possible
Consider protection signaling, breakerfailure transfer trip, remote metering &
control
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Transmission Line Protection
WTGs may not provide large or enduringcurrents for line faults
Frequently, the wind park is served by anew OPGW-equipped line
Dual, high-speed protection schemes are
typical and increasingly likely withincreasing line voltage and/or decreasingline length
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Transmission Line Protection
In POTT schemes, use weak-infeed logicat the wind plant terminal
DCB and line-current differential schemesare only impacted in sensitivity
In all cases, a time-stepped backupscheme should be provided for whencommunications are out
Many lines are initiallyor are likely tobecomethree-terminal lines.
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Three-Terminal Line Protection
DCB over fiber with channel-lossmonitoring is preferred
Several modern line-current differentialrelays support three-terminalapplications, consult with your vendor(s)
POTT performs acceptably but needsweak-infeed logic to improvedependability
Inter-tie utility will have the final word
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Transmission-Voltage Bus Protection
Frequently not required as a result ofstation topology and placement ofinstrument transformers to protect thebus in the line or transformer zones
When required, this protection needntbe exotic, high-impedance busdifferential will typically serve
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Collector Sub Transformer Protection
Transformer top ratings from 100 MVA to230 MVA
Usually the key single wind plant asset
Dual differential is typically desired andemployed
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Collector Sub Transformer Protection
Ground faults near the neutral ofgrounded wye windings may not drawsignificant phase current
Consider restricted earth fault protectionfor improved sensitivity to low-windingground faults
Monitor non-electrical trips (sudden
pressure, temperature) using thetransformer relay for SOE & reporting
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Collector-Voltage Bus Protection
34.5 kV buses may have very high faultduties (>40 kA)
Bus faults yield high arc flash hazard,particularly in indoor switchgearinstallations
Smaller installations may or may notinclude a bus main breaker
Fast bus fault clearing is desirable
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Collector-Voltage Bus Protection
High-speed bus protection through high-impedance differential or zone-interlockprotection is usually employed
Particularly in switchgear applications,match the CT ratio and C-rating of CTsemployed in high-impedance schemes.The C-rating should be at least C200
Backup bus time-overcurrent should be
employed in the bus main-breakerprotection set, or in the transformer relay
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Collector Protection (Phase Faults)
Coordinate with WTG step-uptransformer fuses
Coordination with other WTGprotection is not a concern
Cold-load pickup is not a concern,but transformer inrush may be
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Collector Protection (Phase Faults)
Directional supervision may permit moresensitive pickup settings
Fault duties may not offer discriminationneeded to employ an instantaneouselement
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Collector Protection (Phase Faults)
Skinny laterals near the substation cancause challenges
High available fault duties make itdifficult to protect lateral cable andcoordinate with WTG fuse.
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Collector Protection (Phase Faults)
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Collector Protection (Ground Faults)
Ground fault protection can be mademore sensitive than distribution feederprotection; no single-phase laterals andlittle natural unbalance
Be aware of cable neutral I2t rating
Account for the effects of the WTGs andtheir step-up transformers
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Collector Protection (Ground Faults)
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Collector Protection (Ground Faults)
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Capacitor Bank Protection
Overcurrent-based protection detectscatastrophic faults
Coordinate phase overcurrent elementswith capacitor fuses and trip thecapacitor breaker
Capacitor breaker must be rated forthis duty
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Capacitor Bank Protection
Voltage-balance-based protection detectsnon-catastrophic capacitor fuseoperations
Alarm/Trip before voltage on remaininghealthy capacitors exceeds 110% of
rating Refer to IEEE C37.99 Guide for Shunt
Capacitor Bank Protection
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Key Points
Negotiate transmission protection,signaling, and data exchangerequirements early in the project
Consider transmission relay selection andperformance for three-terminal lines
Analyze protection scheme for gaps dueto single-point failures
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Key Points
Confirm transformer and collector-voltage bus protection speed andadequacy
Examine collector cable and neutral faultwithstand capabilities when coordinating
collector elements