Modeling Cold Load Pickup Eric Jung

1. Modeling Cold Load PickupEric Jung Good morning�. Cold load pickupGood morning�. Cold load pickup

2. Agenda Traditional methods of analysis Un-diversified load allocation Emergency capacity determinations Voltage drop analysis Examples Here�s what we�ll cover: Traditional methods of determining Cold load pickup currents How to load allocate to model CLPU Emergency capacity determinations Vdrop settings Some examples and results Lessons learned Here�s what we�ll cover: Traditional methods of determining Cold load pickup currents How to load allocate to model CLPU Emergency capacity determinations Vdrop settings Some examples and results Lessons learned

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. The definition of CLPU here does not include transient and sub transient portion of CLPU. These portions are due to transformer magnetization inrush and motor starting transients. IF THIS IS A PROBLEM NORMAL DIVERSIFICATION LOSS WILL BE A PROBLEM! These topics are well covered and typically do not present a problem to the distribution system due to they�re very short duration. Typical assumptions are that system load will decay exponentially to normal within some span of time. This span of time is controlled by the outside temperature and the length of the outage. This is however, rather immaterial as the initial lack of diversity is what we need to prepare for Thermostatically controlled loads make up the bulk of the normal load in residential applications. Residential load makes up the bulk of the load during CLPU scenarios. My interest in this has come about due to a busy couple of years�The definition of CLPU here does not include transient and sub transient portion of CLPU. These portions are due to transformer magnetization inrush and motor starting transients. IF THIS IS A PROBLEM NORMAL DIVERSIFICATION LOSS WILL BE A PROBLEM! These topics are well covered and typically do not present a problem to the distribution system due to they�re very short duration. Typical assumptions are that system load will decay exponentially to normal within some span of time. This span of time is controlled by the outside temperature and the length of the outage. This is however, rather immaterial as the initial lack of diversity is what we need to prepare for Thermostatically controlled loads make up the bulk of the normal load in residential applications. Residential load makes up the bulk of the load during CLPU scenarios. My interest in this has come about due to a busy couple of years�

4. 2008 Ice Storm 3/4� ice, worst ice storm in 25 years. �career� storm, won�t see another one of these in your career. Due to major transmission outages, I determined that it is important to look at CLPU for the entire substation; not just individual feeders. In other words, the whole sub is offline for 5 hours; when the transmission is restored, if all feeders and loads are still intact, the sub will experience an enormous loss of diversity. The magnitude of this diversity can be modeled using the methods outlined here.3/4� ice, worst ice storm in 25 years. �career� storm, won�t see another one of these in your career. Due to major transmission outages, I determined that it is important to look at CLPU for the entire substation; not just individual feeders. In other words, the whole sub is offline for 5 hours; when the transmission is restored, if all feeders and loads are still intact, the sub will experience an enormous loss of diversity. The magnitude of this diversity can be modeled using the methods outlined here.

5. 2009 Ice Storm 1� ice, worst storm southern IL has ever seen. Further reinforced the premise that we should be prepared for major transmission outages.1� ice, worst storm southern IL has ever seen. Further reinforced the premise that we should be prepared for major transmission outages.

6. Inland Hurricane�or Derecho? Worst damage many of the contract crews had ever seen�anywhere. Derecho defined: widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. Sustained winds of 86 MPH gusts to 100MPH Luckily this happened during a relatively mild May. Temps were in the 70�s and low 80�s the whole time. Cleanup took a week. >11000 outages from 23000 meters. I think that�s enough reinforcement�.Worst damage many of the contract crews had ever seen�anywhere. Derecho defined: widespread and long lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. Sustained winds of 86 MPH gusts to 100MPH Luckily this happened during a relatively mild May. Temps were in the 70�s and low 80�s the whole time. Cleanup took a week. >11000 outages from 23000 meters. I think that�s enough reinforcement�.

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 Various papers in the IEEE database vary from 200% -500% multipliers of full load current. Variations are due to load mix, but 500% is extreme. Determining the nature of the load and thereby it�s load profile is very important to the accuracy of this process. Industrial loads typical peak based on industrial processes with HVAC being comparatively minor. During CLPU, industrial processes which are mainly controlled by magnetic contactors will not restart immediately. Questions to ask: Will these be turned on as soon as power is restored? If so how quickly? Is the starting procedure automatic? If the processes will not restart, CLPU will be based on HVAC, how does HVAC load relate to typical peak KW? If the processes will restart how does this relate to typical peak KW? (how quickly after restart is the system loaded) A system engineer must talk with their customers and determine their operational characteristics and needs. Using a power quality analyzer is a great way to see the load ramp up on a normal day, after outage should be a similar ramp up if immediate restart is in order. Large commercial loads (office buildings, warehouses etc) may follow industrial pattern, but probably will be more HVAC based and therefore closer to residential if they begin operations right away. Same questions need to be asked and addressed on an individual basis Small commercial loads likely to follow residential patterns. Residential loads: Likely that typical peak during peak month would be set when all thermostatically controlled loads are on, plus some portion of manual controlled loads. Residential loads will dominate the cold load pickup model!Various papers in the IEEE database vary from 200% -500% multipliers of full load current. Variations are due to load mix, but 500% is extreme. Determining the nature of the load and thereby it�s load profile is very important to the accuracy of this process. Industrial loads typical peak based on industrial processes with HVAC being comparatively minor. During CLPU, industrial processes which are mainly controlled by magnetic contactors will not restart immediately. Questions to ask: Will these be turned on as soon as power is restored? If so how quickly? Is the starting procedure automatic? If the processes will not restart, CLPU will be based on HVAC, how does HVAC load relate to typical peak KW? If the processes will restart how does this relate to typical peak KW? (how quickly after restart is the system loaded) A system engineer must talk with their customers and determine their operational characteristics and needs. Using a power quality analyzer is a great way to see the load ramp up on a normal day, after outage should be a similar ramp up if immediate restart is in order. Large commercial loads (office buildings, warehouses etc) may follow industrial pattern, but probably will be more HVAC based and therefore closer to residential if they begin operations right away. Same questions need to be asked and addressed on an individual basis Small commercial loads likely to follow residential patterns. Residential loads: Likely that typical peak during peak month would be set when all thermostatically controlled loads are on, plus some portion of manual controlled loads. Residential loads will dominate the cold load pickup model!

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? Concept: 15 min residential demand set during the peak month of a season is likely the undiversified demand of all the thermostatically controlled loads + some portion of the manually controlled loads. If we load allocate, without diversification (ie. All peaks at the same time) we will arrive at the approx CLPU load. C&I customers are a bit more difficult. They must be understood well enough to model how they will perform post outage. They are the lesser input however as residential loads will dominate.Concept: 15 min residential demand set during the peak month of a season is likely the undiversified demand of all the thermostatically controlled loads + some portion of the manually controlled loads. If we load allocate, without diversification (ie. All peaks at the same time) we will arrive at the approx CLPU load. C&I customers are a bit more difficult. They must be understood well enough to model how they will perform post outage. They are the lesser input however as residential loads will dominate.

9. Un-diversified load allocation Set sources to swing. Set all load groups to �diversity fixed.� CF % for residential should be 95%-100%. C&I groups are variable. Apply and Run Load allocation tab: check the box for �treat load control points as swing sources� Swing settings tab: set as shown in slide. C&I settings will vary depending on situation. The more accurate and preferable method of doing this would be to set this up at the individual LCP. This would result in greater accuracy as C&I setting for each LCP can be set to the individual situation. Once all is set, run load allocation. Load allocation tab: check the box for �treat load control points as swing sources� Swing settings tab: set as shown in slide. C&I settings will vary depending on situation. The more accurate and preferable method of doing this would be to set this up at the individual LCP. This would result in greater accuracy as C&I setting for each LCP can be set to the individual situation. Once all is set, run load allocation.

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 FA capacity increase over OA rating is mainly dependent on the transformer size; smaller transformer = smaller increase. These ratings will be on the nameplate. Short time overload capacity from: �Electrical transmission and distribution reference book� Westinghouse electrical corporation East Pittsburgh PA copyright 1964 EG. If substation load prior to outage (normal peak) is 70% of FA rating, then transformer can be overloaded by 158% for up to 30 minutes. Combined yield: Combination of FA 65�C rating x short time overload rating. 181% corresponds to small (2.5MVA) station, with high (>=90%) initial loading. 235% corresponds to larger( >7.5MVA) station, with low (<=50%) initial loading. Note: Pre-outage loading is simply a method of determining the pre-outage temperature of the transformer. Since the transformer will cool during the outage this is slightly conservative. This cooling effect has been neglected due to the reality that load diversity is lost in much less time than transformer can appreciably cool. Therefore, cold load pickup loading could occur with minimal change in transformer temperature. Sub transformer capacity will vary depending on cooling type. Forced oil circulation and/or water cooling will result in higher overload percentages Standard curves for loss of life v. greater loading are available in referenced IEEE standard.FA capacity increase over OA rating is mainly dependent on the transformer size; smaller transformer = smaller increase. These ratings will be on the nameplate. Short time overload capacity from: �Electrical transmission and distribution reference book� Westinghouse electrical corporation East Pittsburgh PA copyright 1964 EG. If substation load prior to outage (normal peak) is 70% of FA rating, then transformer can be overloaded by 158% for up to 30 minutes. Combined yield: Combination of FA 65�C rating x short time overload rating. 181% corresponds to small (2.5MVA) station, with high (>=90%) initial loading. 235% corresponds to larger( >7.5MVA) station, with low (<=50%) initial loading. Note: Pre-outage loading is simply a method of determining the pre-outage temperature of the transformer. Since the transformer will cool during the outage this is slightly conservative. This cooling effect has been neglected due to the reality that load diversity is lost in much less time than transformer can appreciably cool. Therefore, cold load pickup loading could occur with minimal change in transformer temperature. Sub transformer capacity will vary depending on cooling type. Forced oil circulation and/or water cooling will result in higher overload percentages Standard curves for loss of life v. greater loading are available in referenced IEEE standard.

12. 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 Normal ampacity is calculated a conductor temp of 75 deg C and 25 deg C ambient. Emergency ampacity is normally calculated at 100 deg C. Ambient temperature can be adjusted based on time of year in model and is up to individual preference. Eg. Winter model, winter peak normally occurs at or near -18 deg C (0 deg F) in my system. Winter CLPU problems will likely arise during -18 deg C (or lower) days. Ampacity could be recalculated based on this, or something more conservative like 0 deg C. 100 deg C conductor and 0 deg C ambient results in 141% normal capacity. Note that clearance issues could be a problem due to increased conductor sag at higher temperatures and normal sag calculations are done at 75deg C (167 deg F)Normal ampacity is calculated a conductor temp of 75 deg C and 25 deg C ambient. Emergency ampacity is normally calculated at 100 deg C. Ambient temperature can be adjusted based on time of year in model and is up to individual preference. Eg. Winter model, winter peak normally occurs at or near -18 deg C (0 deg F) in my system. Winter CLPU problems will likely arise during -18 deg C (or lower) days. Ampacity could be recalculated based on this, or something more conservative like 0 deg C. 100 deg C conductor and 0 deg C ambient results in 141% normal capacity. Note that clearance issues could be a problem due to increased conductor sag at higher temperatures and normal sag calculations are done at 75deg C (167 deg F)

13. 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 If ambient temperature is adjusted to reflect a realistic value this is the effect on the ampacity of the wire. Assume that winter CLPU problems will occur when ambient temps are quite low, perhaps well below freezing. Assume summer CLPU problems will occur when ambient temps are quite high. Wind has a large effect on these values. I have neglected wind and left it constant in all calculations here. Typical ampacities are calculated using a wind of 2�/sec. If your area predominately has a different wind strength this should be adjusted. Looked at another way; Simply solve the temperature part of the equation to determine the percentage increase in capacity for all conductors.If ambient temperature is adjusted to reflect a realistic value this is the effect on the ampacity of the wire. Assume that winter CLPU problems will occur when ambient temps are quite low, perhaps well below freezing. Assume summer CLPU problems will occur when ambient temps are quite high. Wind has a large effect on these values. I have neglected wind and left it constant in all calculations here. Typical ampacities are calculated using a wind of 2�/sec. If your area predominately has a different wind strength this should be adjusted. Looked at another way; Simply solve the temperature part of the equation to determine the percentage increase in capacity for all conductors.

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 Note: Milsoft will show capacity according to the lower ground trip setting. This will mean electronic reclosers with ground trip settings will have to be looke at individually. It�s important to ensure that CLPU on a single phase hydraulic downstream will not trip the ground curve of an electronic recloser. Hydraulics can handle short term overloads of greater than 150%. Due to ambient temp differences and therefore oil viscosity differences + possible neglected maintenance I err on the side of caution with hydraulics.Note: Milsoft will show capacity according to the lower ground trip setting. This will mean electronic reclosers with ground trip settings will have to be looke at individually. It�s important to ensure that CLPU on a single phase hydraulic downstream will not trip the ground curve of an electronic recloser. Hydraulics can handle short term overloads of greater than 150%. Due to ambient temp differences and therefore oil viscosity differences + possible neglected maintenance I err on the side of caution with hydraulics.

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 OH capacity percentages calculated earlier URD capacity typically does not have an emergency rating as jacket degradation begins at 100% of capacity. Regulators also lack emergency ratings, ratings can be increased by limiting maximum regulation percentage however voltage drop problems may result. Transformers and sources are up to the individual�s discretion. My recommendations are given within however if loss of life can be tolerated capacity may be increased. Device capacity is a shortcoming of windmill, fuses, OCR�s, electronic reclosers etc all have different overload capacities and should be treated as such. I have settled on 150% as the point to review any device. After 150% I evaluate individually.OH capacity percentages calculated earlier URD capacity typically does not have an emergency rating as jacket degradation begins at 100% of capacity. Regulators also lack emergency ratings, ratings can be increased by limiting maximum regulation percentage however voltage drop problems may result. Transformers and sources are up to the individual�s discretion. My recommendations are given within however if loss of life can be tolerated capacity may be increased. Device capacity is a shortcoming of windmill, fuses, OCR�s, electronic reclosers etc all have different overload capacities and should be treated as such. I have settled on 150% as the point to review any device. After 150% I evaluate individually.

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 Range B is tolerable for short term, emergency condition. It should be corrected as soon as possible. Cold Load Pickup certainly falls into the emergency condition realm. Important to note: # 1 problem for me has typically been device capacity, otherwise� Hot weather CLPU scenario will likely be controlled by system ampacity or substation transformer capacity Cold weather CLPU scenario will likely be controlled by system voltage This is due to ambient temperature difference. In Cold weather transformer and conductor ampacity are greatly increased. This can be modeled, using a winter and summer CLPU model, adapt system capacities to the ambient temperature. If two peak system as I am, this leads to 4 models, summer and winter peak and summer and winter CLPU models.Range B is tolerable for short term, emergency condition. It should be corrected as soon as possible. Cold Load Pickup certainly falls into the emergency condition realm. Important to note: # 1 problem for me has typically been device capacity, otherwise� Hot weather CLPU scenario will likely be controlled by system ampacity or substation transformer capacity Cold weather CLPU scenario will likely be controlled by system voltage This is due to ambient temperature difference. In Cold weather transformer and conductor ampacity are greatly increased. This can be modeled, using a winter and summer CLPU model, adapt system capacities to the ambient temperature. If two peak system as I am, this leads to 4 models, summer and winter peak and summer and winter CLPU models.

17. Dixon Springs before Results from substation that has not been re-sectionalized. Imbalance is magnified. Note that no conductor is colored for being over capacity Reclosers could not be expected to hold in this scenario This would require sectionalizing to pickup load The thru amps can be plotted into Light table to determine the likely operational sequence in this scenario 70L should lockout first, although multiple operations are likely since all reclosers are overloaded and the opening of any one recloser removes sufficeint current to drop below minimum trip of other two. The main load on this three phase feeder is a long single phase tap feeding a small community in the middle. The feeder is a 4/0 ACSR line that is often used to tie with two other subs to the west.Results from substation that has not been re-sectionalized. Imbalance is magnified. Note that no conductor is colored for being over capacity Reclosers could not be expected to hold in this scenario This would require sectionalizing to pickup load The thru amps can be plotted into Light table to determine the likely operational sequence in this scenario 70L should lockout first, although multiple operations are likely since all reclosers are overloaded and the opening of any one recloser removes sufficeint current to drop below minimum trip of other two. The main load on this three phase feeder is a long single phase tap feeding a small community in the middle. The feeder is a 4/0 ACSR line that is often used to tie with two other subs to the west.

18. Dixon Springs updated Proposed corrections: Three phase from dev# 0070994 south Rebalance Dev # 0072894 still overloaded We�ve begun converting the single phase to three phase as stage 1 Stage 2 will involve re-sectionalizing to accommodate not only the existing load but incorporate additional capacity in order to load shed from the west.Proposed corrections: Three phase from dev# 0070994 south Rebalance Dev # 0072894 still overloaded We�ve begun converting the single phase to three phase as stage 1 Stage 2 will involve re-sectionalizing to accommodate not only the existing load but incorporate additional capacity in order to load shed from the west.

19. Carter south feed Highlights one feed out of �Carter� substation. Re-sectionalized last year based on summer CLPU study, re-applied winter load. Take special note of devices 9S5 and 0072266. Both are three phase electronic reclosers. Windmill is calculating percent capacity from their ground trip settings not their phase trip settings. All protective devices within tolerance All conductor within ampacity All voltage within Range B limits Substation overload to 191.75% OA rating. Represents approx 14.4MVA of load if highest loaded phase is considered. 12.24 MVA total. (540A,496A,666A / A,B,C). Rebalance would help tremendously!Highlights one feed out of �Carter� substation. Re-sectionalized last year based on summer CLPU study, re-applied winter load. Take special note of devices 9S5 and 0072266. Both are three phase electronic reclosers. Windmill is calculating percent capacity from their ground trip settings not their phase trip settings. All protective devices within tolerance All conductor within ampacity All voltage within Range B limits Substation overload to 191.75% OA rating. Represents approx 14.4MVA of load if highest loaded phase is considered. 12.24 MVA total. (540A,496A,666A / A,B,C). Rebalance would help tremendously!

20. Elizabethtown before Note that not only are devices well beyond capacity, but voltage has dropped below 110V (pink lines) Device # 0074278 has voltage of 104V This substation has known CLPU issues. If load picked up @ dev # 0074278, dev 0071488 (50L) will operate to lockout. These two devices are 5 miles apartNote that not only are devices well beyond capacity, but voltage has dropped below 110V (pink lines) Device # 0074278 has voltage of 104V This substation has known CLPU issues. If load picked up @ dev # 0074278, dev 0071488 (50L) will operate to lockout. These two devices are 5 miles apart

21. Elizabethtown updated Moved dev# 71188 and changed to 70A-4H Changed 74278 to 35A H from 25A sectionalizer Removed 73678 and 71488Moved dev# 71188 and changed to 70A-4H Changed 74278 to 35A H from 25A sectionalizer Removed 73678 and 71488

22. 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.�

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