0. Cable-in-Conduit (CIC) Challenges and Strategies
Name Seema Abraham
Title Senior Project Manager
Reliability & Infrastructure Replacement
Southern California Edison
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1. Southern California Edison
50,000 square miles
~ 76 billion kWh/year delivered
4.9 million customers
Over 400 cities & communities with a collective population of over 13 million people
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2. Distribution Assets 1,440,000 wood poles
50,000 cond-miles of UG primary conductor
106,000 cond-miles of OH primary conductor
715,000 distribution transformers
87,000 padmount/subsurface switches
2,800 substation transformers
10,500 substation circuit breakers
4,600 distribution circuits (mostly radial design vs. looped)
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3. SCE Org Structure SCE SVP of T&D Description
48_85
SCE Org Structure
SCE SVP of T&D
Distribution Business Line
Transmission, Substation, and Operations
Engineering & Tech Svc
Asset Management
Major Projects Organization
Description
Responsible for distribution network, vegetation management and field accounting
Responsible for grid operations, substation, and transmission activities
Oversee system planning, engineering, and design
Develop strategies for deployment, maintenance and replacement of T&D assets
Oversee the development of SCE’s major transmission and substation projects
Sub organizations
Distribution construction and maintenance by region
Design & Field Accounting
Pole assessments
Programs & strategies
Substation construction and maintenance by region
Transmission construction and maintenance by region
Grid operations
Edison Carrier Solutions
Engineering
System planning
Real properties
Advanced technology
Maintenance, performance, reliability
Contracts
Business planning
Business effectiveness
Project governance and admin
Major projects such as Tehachapi wind project
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4. How is Reliability Measured?
Momentary Outages:
Outages lasting 5 minutes or less
Sustained Outages:
Outages lasting longer than 5 minutes
MAIFI:
The number of times the average customer is interrupted by Momentary outages each year.
SAIFI:
The number of times the average customer is interrupted by Sustained outages each year.
SAIDI:
The cumulative amount of time the average customer is interrupted by Sustained outages each year.
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5. Problem = Aging Equipment
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6. 50,000 conductor-miles of Distribution UG primary cable
______________________________
37,000 miles in rigid duct (e.g., PVC, transite, soapstone, etc.)
most unjacketed
13,000 miles in polypropylene tubing
all unjacketed = > CIC
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7. Miles of CIC Expected to Wear-out Each Year
Cond-miles
Year
The current in-service failure volume of CIC ≈ 50 cond-miles.
Unaddressed, this will increase six-fold within 30 years.
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8. Cable-in-Conduit Example of 220mil XLP (#2xlp) and the 1.5” CIC Duct
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9. The Problems of CIC Installed as a radial system (no looped ties):
Limited operational flexibility
Increasing number of in-service failures:
Mean-time-to-failure = 41 years
20% of CIC population is older than MTTF
Significant impact on reliability:
Typical outage caused by CIC failure ~ 20 hours
Very high cost of replacement:
Historical replacement via trenching = $800,000 /mile
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10. 12,000 conductor-miles of CIC will exit the system before the year 2065
1. Wholesale replacement of entire radials based solely on failure history
2. Selective replacement of only cable segments determined “bad” via PD testing
Cable Rejuvenation
Rigid duct installed via trenching
Rigid duct via Directional Boring
Rigid duct via Directional Boring
Use existing duct via lube cart
Rigid duct installed via trenching
3. Run to failure
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11. 12,000 conductor-miles of CIC will exit the system before the year 2065
Wholesale replacement of entire radials based solely on failure history
Selective replacement of only cable segments determined “bad” via PD testing
Cable Rejuvenation
Rigid duct installed via trenching
Rigid duct via Directional Boring
Use existing duct via lube cart
Rigid duct via Directional Boring
Rigid duct installed via trenching
Run to failure
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12. Lack of Void Filler (e.g.:Grease)
Partial Discharge Testing – Why cable fails?
Inner Conductor
Outer Conductor
Insulation
Basic Cable Design
Electrical Trees
Stress Enhancements
Foreign Objects
Cutback Issues
Contaminants
Water Trees
Voids
Insulation Cuts
Insulation Voids
Overheating
Semicon Damage
Lack of Void Filler (e.g.:Grease)
Incorrect Dimensions
Cable System
Failure
Operational Risk Factors
Over-voltage events
Breaker/Fuse reclosures
Fault locating
Lightning
Long out-of-service periods
Over-voltage protection
Placement in circuit
Sizing and Installation
Circuit Configuration
Accessory contamination
Open air terminations
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13. The Manufacturers’ Standards
Partial Discharge Testing – The Standards
The Manufacturers’ Standards
Testing Frequency
Component Standard
Sensitivity
Voltage
Terminations IEEE 48
Joints IEEE 404
Separable Connectors IEEE 386
MV Extruded Cable ANSIICEA S-97/94-682/649
HV / EHV Extruded Cable ANSIICEA S
50/60 Hz
5pC
3pC
≤ 1.5 Uo
≤ 1.3 Uo
≤ 4.0 Uo^
≤ 2.0 Uo
* No partial discharge should be observable above the sensitivity threshold up to the voltage threshold
^200 V/mil
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14. General Neutral Condition
Concentric Neutrals
Neutral Corrosion Assessment
Defect Specific Neutral Corrosion Diagnostic (HRTDR)
Time Domain Reflectometer
HRTDR Level
Wires Broken
Wires Remaining
SCE Priority
HRTDR Response 1
0% to 25%
75% to 100%
Good
<25% of the roundtrip reflection
No significant mid-span imped. inflect. 2
25% to 50%
50% to 75%
25% - 50% of round trip reflection
Smaller than a typical splice reflection 3
50% -100% of the round trip reflection
Larger than a typical splice reflection 4
Larger than the round trip reflection
Reference: IEEE 1617 Table 1 Corrosion Categories
Distributed Neutral Corrosion Assessment (BSIR)
BSIR Level
General Neutral Condition
BSIR Response A
No recognizable distributed neutral corrosion
Identifiable roundtrip of 20pC or better (smaller)
No significant signal attenuation B
Substantial distributed neutral corrosion
Identifiable roundtrip between 50 and 500pC
Substantial signal attenuation C
Severe distributed neutral corrosion
Identifiable roundtrip of 500pC or greater
Nearly complete or complete signal attenuation
Reference: IMCORP BSIR specification: Please consult IMCORP for more information.
Matrix Based on SCE Deteriorated Concentric Neutral Document - Phase to Ground
HRTDR Result
BSIR
Long Term Replacement
Short Term Replacement
Matrix Based on SCE Deteriorated Concentric Neutral Document - Phase to Phase
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15. SCE’s Pass Criteria Concentric neutrals must have a rating of 1A
No insulation PD at less than 2.5 times the operating voltage
No termination PD at less than 1.5 times the operating voltage
No splice (joint) PD at less than 1.5 times the operating voltage
No connection PD at less than 1.3 times the operating voltage
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16. Partial Discharge Testing @ SCE
2009 and 2011 – Limited scope pilot
September 2012 – Broader scope pilot
Q1/2013 – Initiated Partial Discharge Testing as a program
~7800 cable segments tested to-date
0.8% % 55.1%
Insulation Identified for No Replacement
Failure & Replacement Needed
Emergency
Replacement
40.2% Insulation
50.7% Concentrics
30.5% Splice/Termination
* Not Exclusive
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17. Partial Discharge Testing @ SCE
Pros & cons of Testing
Benefits:
Provides an assessment of the asset in the ground
Cost effective since testing allows replacement of only those segments that are known to be defective
Issues / Challenges:
Occasional testing induced failure (~1%)
Requires an outage
Time between completion of test and actual replacement of “bad” segment
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18. Cost-Effectiveness of Cable Testing
Cost of Replacement % Required to Pass to “Break Even”
$800,000 / cond-mi 5%
$500, %
$400, %
$300, %
$200, %
$150, %
Comparing the NPV of the revenue requirements for a) replacing all cable immediately without testing versus b) testing all cable, replacing immediately only the “bad” cable, and replacing the “good” cable exactly 10 years in the future, all assuming cost of testing program
Note: As the CIC ages, the “pass” rate will decline to the point where testing will no longer be cost-effective. At that time, we will simply replace all CIC.
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19. Cable Rejuvenation What is Cable Rejuvenation? Methods of Rejuvenation
Cable Rejuvenation is technology that injects an engineered, silicone-based fluid into spaces between the cable strands of underground medium-voltage cable under low to moderate pressure. The fluid then migrates into the conductor shield and insulation to restore the cable to better-than-new performance.
Methods of Rejuvenation
Sustained Pressure Rejuvenation (SPR)
Used when no splices are present. All accessories are replaced and cable is injected under moderate pressure to return the cable to its full dielectric strength. Extends cable life up to 40 years.
Un-sustained Pressure Rejuvenation (UPR)
Used when the segment of cable has one or more splices. An airflow test is performed to confirm fluid will flow. Uses low pressure to flow fluid through splices when cable is energized. Extends cable life up to 25 years.
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21. Cable Rejuvenation @ SCE
2013 – Limited scope pilot
October 2014 – Second pilot
May 2015 – Broadened pilot scope to rejuvenate complete circuit(s)
2014 – Targeted rejuvenation of ~45,000’
0.0% % % %
Failure Successfully Identified as Identified for
& Rejuvenated newer strand Replacement
Emergency filled cable
Replacement
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22. Pros & Cons of Rejuvenation
Wholesale replacement of entire radials based solely on failure history
Run to failure
Rigid duct via Directional Boring
Use existing duct via lube cart
Rigid duct installed via trenching
Cable Rejuvenation
Selective replacement of cable segments determined “bad” via PD testing
Benefits:
Promises to extend cable life by up to 40 years
All terminations are replaced
Issues / Challenges:
Cannot be performed on segments with splices between BURD’s
Uncertainty over effectiveness
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23. CIC SCE
Replacement of cable in existing polypropylene tubing
Installing rigid duct using Directional Boring
Traditional method of installing duct using trenching
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24. Replacement in existing duct using new methods
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25. Pros & Cons of using existing duct
Wholesale replacement of entire radials based solely on failure history
Run to failure
Rigid duct via Directional Boring
Use existing duct via lube cart
Rigid duct installed via trenching
Cable Rejuvenation
Selective replacement of cable segments determined “bad” via PD testing
Benefits:
Least expensive of all options (when it works)
No need for easements
New “Flat-Strap” cable should have a MTTF of 46 years
Issues / Challenges:
Requires a second (after testing) outage
Does not always work
Operations perception that this is a “band-aid” and not a long term solution (vs installation of rigid duct)
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26. Pros & Cons of replacement using Directional Boring
Wholesale replacement of entire radials based solely on failure history
Run to failure
Rigid duct via Directional Boring
Use existing duct via lube cart
Rigid duct installed via trenching
Cable Rejuvenation
Selective replacement of cable segments determined “bad” via PD testing
Benefits:
Potentially faster and much less expensive than trenching
Limited noise and surface disruption with construction activity mostly at access points
Widely used by utilities across the U.S.
Results in installation of rigid duct
Issues / Challenges:
Not applicable in all scenarios
Reluctance within SCE
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27. Pros & Cons of Traditional Replacement
Wholesale replacement of entire radials based solely on failure history
Run to failure
Rigid duct via Directional Boring
Use existing duct via lube cart.
Rigid duct installed via trenching
Cable Rejuvenation
Selective replacement of cable segments determined “bad” via PD testing
Benefits:
Minimal outage since new circuit is built in parallel with existing circuit
Issues / Challenges:
Easements, HOA Approvals and Permits
Expensive. Historically ~$800,000/mile
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28. Seema Abraham Senior Project Manager Reliability and Infrastructure Replacement
CONFIDENTIAL – Use subject to terms of utilities Confidentiality Agreements