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Generation Interconnection Short Circuit Analysis
PJM PlanningGeneration - PlanningNicole U. Segal
May 18, 2009
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Presentation Overview
I. Short Circuit Software and Case Conversion Options
II. Short Circuit Queue Case Creation
III. PJM Modeling Assumptions
IV. Short Circuit Results Breakdown
V. Differences Between Feasibility and Impact Studies
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ASPEN Short Circuit SoftwareOneLiner V3.1
• Short circuit and relay coordination program which PJM uses to model the transmission network and generation interconnection projects
Case Comparison V10.9
• Compares two cases and creates a difference file known as a CHF
Breaker Rating Module (BRM) V9.11
• Used to check the rating of circuit breakers against the short circuit fault currents
• Adheres to ANSI/IEEE for both total-current and symmetric-current rated breakers
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ASPEN Case Conversion Options
Table 1: 2009 Software Conversion Options and File Types
Software File TypeCAPE .DXT or .RAW, .SEQPTI PSS/E .RAW, .SEQANAFAS .ANAGE Short Circuit .SEQGE Power Flow (PSLF) .EPC
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ASPEN- CAPEResult Differences
Isolated Buses• CAPE recommends excluding isolated buses from the case
Phase Angle Inconsistencies• This problem can be fixed by going over each of the loops and
correcting the transformer implicit angle
XFMRs can be identified incorrectly as Y-Y instead of Y-Δ• For each loop check to see if any of the transformers have their
winding types incorrectly specified • Fixing one-loop will cause subsequent (multiple) loops to be fixed
ASPEN always includes XFMR Off-Nominal (fixed) Taps • This problem can be fixed in the initialization of the CAPE program
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Example of ASPEN-CAPE Discrepancies
Nominal Taps
Off-Nominal Taps
3LG 1LG 3LG 1LGASPEN n/a n/a 12784 A 14157 A
CAPE Converted from PSS/E
12428 A 13864 A 12786 A 14159 A
CAPE Convertedfrom ASPEN
12433 A 13876 A 12790 A 14171 A
Table 2: Comparison of Fault Results for a 69 kV Bus
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Short Circuit Queue Case Creation
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RTEP Base Case Model
• 5 year short circuit baseline
• Short circuit models from our T.O. and neighboring systems included
• Model should include all planned transmission system upgrades
• Model should include all planned generation projects that have proceeded past the Impact Study phase
• The system impacts of these projects have already been studied• Reinforcements for these projects are included in the case
• Beginning with the 2014 base case PJM will monitor all circuit breakers rated 100 kV and greater
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Generation Interconnection
• Model queue projects individually on the 5 year RTEP case• Study New Generation ≥ 30 MW• Verify data and case models for all upgrade projects• Projects connecting to ≤ 69 kV are not studied• Projects ≤ 10 MW are not modeled
• Each Queue is studied on a “Locked Case ” • Projects and upgrades for withdrawn projects are removed
until the case is locked
• If a circuit breaker is found to be overstressed, PJM communicates this to the transmission owner for them to verify the results and provide an upgrade plan.
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Short Circuit Modeling Assumptions
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Network Model Assumptions
1. Model Generators using X’’d(v)• Major sources of fault current• All Generators are online • Effects are localized (approx. 3 buses away)
2. Model lines & transformers using Z & Z0• Transformer winding connections
(e.g. delta, grounded wye)• Model zero sequence mutual coupling
3. Ignore loads, positive sequence shunts, & line charging
4. Flat-Start Voltage profile• Voltages at nominal
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X/R Modeling Assumptions
Assumed X/R Reference
Lines X/R = 10 Typical Value
Generators X/R = 120 Typical Value
Transformers X/R = 60 Highest Point on XR curve therefore conservative
All X/R ratios are taken from IEEE C37.010
Table 4: X/R Assumptions
Better than letting ASPEN assume R =0.0001 p.u.
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Zero Sequence Impedance Assumption
Table 5. Zero Sequence Impedance Assumptions
Assumed Zero Sequence
Lines Z0 = 3 * Z+
Underground Cable Z0 = 2 * Z+
Transformers Z0 = Z+
• Lines and Cables are unique this is a best guess estimate
• Most Transformers are Shell Type• Shell Z0 = Z+
• Core Z0 = 0.85 * Z+
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Zero Impedance Line Assumption
Zero Impedance Line Model
Z = 0.00001 + j 0.0001 p.u.
• Connects the new generation to the substation or to a tapped line
• Allows for the maximum amount of fault current to be transferred to the system
• Gives the most conservative result (worst case scenario) when running the breaker program
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Wind Turbine Model
Aggregate Generator
Aggregate Unit Transformer
Main GSU
Transmission Line or Cable
Zero Impedance Line
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Short Circuit Results
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New Over Duty Breaker
Breaker(s) with a maximum short circuit interrupting duty greater than 100%
Contribution to Previously Identified Over Duty Breaker
Breaker(s) with short circuit interrupting duties greater than 100% and with the addition of the queue project have an increase of 3%
Result Definitions
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Short Circuit Results
DutyPercent
With #023
DutyPercentWithout
#023
DutyPercent
DifferenceNote
117.30% 68.90% 48.40% New Overduty
105.60% 101.30% 4.30% Baseline- No Cost Allocation
104.70% 102.80% 1.90% Over 100%, < 3% contribution
100.00% 99.90% 0.10% -
138.20% 134.40% 3.80% Over 100%, > 3% contribution
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1. Identify all New Over Duty Breakers
2. Obtain Upgrade Plan for New Over Breakers from T.O.
• Includes new breaker rating(s) , cost and time estimate for
replacement/upgrade
3. Identify all Contributing Breakers
4. Verify all Lower kV (100 kV and below) Breakers
• Obtain Upgrade Plan from T.O. if necessary
Results
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Differences Between Feasibility and Impact Studies
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Feasibility Study:
• Approximate data from developer is used to create models• Cables for wind projects are not modeled• Lines are modeled as zero impedance line• Line, Transformer, and Generator X/R assumptions are used• LTAP are created at 50% on line between 2 substations
Impact Study:
• Final Data from developer is used to create models• Reinforcements for Queue project are included in models• Cable for Wind Projects are modeled if supplied• Lines are modeled using Z from T.O. or Developer• LTAP are created at the actual POI
Modeling Differences
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Resources
Breaker Interrupting Rating
• Total Current Rating (MVA) (IEEE C37.5)
• Symmetrical Rating (kA) (IEEE C37.010)
Planning Process Manuals
• Manual 14A ― Generation and Transmission Interconnection Process
• Manual 14C ― Generation and Transmission Interconnection Facility Construction
http://www.pjm.com/documents/manuals/rtep-process-manuals.aspx
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