Just another systems engineering and analysis presentation from Milsoft's 2009 User Conference. It was originally presented by Eric Jung. The Milsoft Electric Utility Solutions Users Conference is the premier event for our users and the vendors who provide interoperable utility management solutions or services that enhance Milsoft Smart Grid Solutions. If you’d like to be on our mailing list, just email: missy.brooks@milsoft.com.

1. Modeling Cold Load Pickup
Eric Jung

2. Agenda
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Traditional methods of analysis
Un-diversified load allocation
Emergency capacity determinations
Voltage drop analysis
Examples

3. 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.

4. 2008 Ice Storm

5. 2009 Ice Storm

6. Inland Hurricane…or Derecho?
SouthEastern’s
Service Territory

7. “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

8. 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?

9. 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

10. 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.

11. 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

12. Determine capacity of conductor
• Emergency ampacity of overhead conductor:
Inew  Iold 
Tcond, new  Tambient, new
Tcond, old  Tambient, old
• Emergency ampacity using 100˚C conductor
temperature (no change in ambient)
– 122% @ 25 C˚ Ambient
– 131% @ 40 C˚ Ambient

13. Determine capacity of conductor example
• Emergency ampacity of 4/0 ACSR in 0˚C (32˚F)
ambient
100  0
505 A  357 A
75  25
505 A  357 A 141%
• Emergency ampacity of #2 ACSR in 38˚C
(100˚F) ambient


100  38
205 A  184 A
75  25

14. 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

15. 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

16. 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

17. Dixon Springs before
Normal peak
current 68A

18. Dixon Springs updated
Three
phase
project

19. Carter south feed

20. Elizabethtown before
Closing this sectionalizer
Would open this recloser

21. Elizabethtown updated

22. Principle Lessons Learned
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System protection
–
Should be based on:
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•
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•
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Capacity
Fault current
Cold load pickup
Coordination
Should not be based on:
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Load current
Some arbitrary minimum fault impedance
The way we’ve “always done it.”

23. Contact info
Eric Jung
Engineering Manager
SouthEastern IL Electric Co-op
ericjung@seiec.com