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

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AA

AA

257538100184205

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 ManagerSouthEastern IL Electric Co-opericjung@seiec.com