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Modeling Cold Load Pickup
Eric Jung
Agenda
• Traditional methods of analysis• Un-diversified load allocation• Emergency capacity determinations• Voltage drop analysis• Examples
What is Cold Load Pickup?
• Cold load pickup is a loss of diversity following an extended outage.
• “Cold” refers to the state of the load, not the ambient temperature.
• Problems stem from thermostatically controlled loads.
2008 Ice Storm
2009 Ice Storm
Inland Hurricane…or Derecho?
SouthEastern’sService Territory
“Rule of thumb” Methods & Shortcomings
• Assume 200%-300% of full load current– Only a 100% swing…Is that all?
• Fails to take nature of load into account
• Traditional methods require:– Normal peak data– Many assumptions
Requirements for modeling
• Billing file with 15-minute interval data– With AMR data, this is no problem.– Without AMR data, this must be calculated.
• Knowledge of operational characteristics of C&I customers– How will load ramp up after an outage?– What load will pick up immediately?
Un-diversified load allocation
1. Set sources to swing.
2. Set all load groups to “diversity fixed.”
3. CF % for residential should be 95%-100%.
4. C&I groups are variable.
5. Apply and Run
Emergency system capacity
• The following capacities must be determined:– Short time overload capacity of substation
transformer– Emergency conductor capacity– Overcurrent device capacity
• Emergency voltage standards must be established.
Emergency capacity of sub transformer
• FA 65˚C rating is 25%-40% above base
• Short time overload of < 30 min– 50% pre-outage loading = 168% overload– 70% pre-outage loading = 158% overload– 90% pre-outage loading = 145% overload
• Combined yield:– 181%-235% over base 55˚C rating
Determine capacity of conductor
• Emergency ampacity of overhead conductor:
• Emergency ampacity using 100˚C conductor temperature (no change in ambient)– 122% @ 25 C˚ Ambient– 131% @ 40 C˚ Ambient
old ambient,old cond,
new ambient,new cond,oldnew TT
TTII
Determine capacity of conductor example
• Emergency ampacity of 4/0 ACSR in 0˚C (32˚F) ambient
• Emergency ampacity of #2 ACSR in 38˚C (100˚F) ambient
%1413575052575
0100357505
AA
AA
2575
38100184205
AA
Determine capacity of system protection
• Electronic Reclosers– Minimum phase trip setting– Ground trip must account for downstream single
phase devices.– Windmill will base capacity on lowest Min Trip.
• Hydraulic Recloser– Cooper reclosers reference R280-90-4– Limit to 150% of series coil rating
Voltage drop setup: capacity
• Set capacity colors to match emergency capacities.
• Could use “Color by Custom.”– Allows further breakdown to
fuse, OCR…– Allows multiple colors based on
% over capacity
Voltage drop setup: voltage
• ANSI C84.1-2006• Range B standard
– 91.7%-105.8% nominal
• When is Range B tolerable?– Short term emergency conditions– Should be corrected as soon as
possible to Range A
Dixon Springs before
Normal peak current 68A
Dixon Springs updated
Three phase project
Carter south feed
Elizabethtown before
Closing this sectionalizer
Would open this recloser
Elizabethtown updated
Principle Lessons Learned
• System protection – Should be based on:
• Capacity• Fault current• Cold load pickup• Coordination
– Should not be based on:• Load current• Some arbitrary minimum fault impedance• The way we’ve “always done it.”
Contact info
Eric JungEngineering Manager
SouthEastern IL Electric Co-op