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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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

ericjung@seiec.com