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Assessing, Maintaining &
Replacing Fluid Filled Cable
Systems at PEPCO
April 2, 2014
Todd Goyette, P.E., POWER Engineers Mousa Hejazi, P.E., Pepco Holdings Inc.
Pepco Quick Facts
First incorporated in 1896
Service territory:
640 square miles
Customers served: 793,000
• Washington, D.C.: 260,000 • Montgomery County: 309,000• Prince George’s County: 225,000
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Purpose
Comprehensive review of PHI’s oil impregnated paper
insulated cable systems
•
Limited & decreasing number of manufacturers of
cable
•
Limited & decreasing number of manufacturers of
cable accessories (reservoirs, pumping plants,
etc.)
•
Decreasing numbers of qualified splicers to work
with these types of cables
Approach
Review separated into 3 tasks
• Task1: Industry Survey
– Determine current trend of industry with regards to maintaining or replacing these legacy cables systems
• Task 2: Cataloging Existing Systems
– Develop a complete list of the cable systems on PHI’s system
o Identify components and key drivers (type, voltage, length, age, etc.)
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Approach
•
Task 3: Risk & Condition Assessment
– Develop risk matrix to qualitatively and quantitatively identify areas of risk for these types of cable systems
Background: Self Contained Fluid Filled Cables (SCFF)
Developed in 1920s
Uses dielectric fluid under
pressure to maintain
insulation integrity
•
Pressure maintained by
reservoirs installed in
manholes and substations
Cable sheath acts as
pressure vessel & hermetic
seal
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Background: Self Contained Fluid Filled Cables
(SCFF)
Relies heavily on no air or moisture entrainment
Two subcategories
•
Low Pressure Fluid Filled (LPFF)
– Operating pressures 1-15 psig – Typically lead sheath
•
Medium Pressure Fluid Filled (MPFF)
– Operating pressures 5-70 psig
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PHI Self Contained Fluid Filled Cables
PHI has 32 SCFF systems and
Approximately 103 circuit miles of SCFF cable
# of Circuits 69kV 115kV 138kV 230kV Total
Low Pressure Fluid
Filled 14 0 2 0 16
Medium Pressure
Fluid Filled 16 0 0 0 16
Total 30 0 2 0 32
Mileage 69kV 115kV 138kV 230kV Total
Low Pressure Fluid
Filled 37.1 0 0.2 0 37.3
Medium Pressure
Fluid Filled 65.6 0 0 0 65.6
Background: High Pressure Pipe Type Cables (HPPT)
Historically most common type of
transmission cable installed in
the United States
•
Gained popularity after World
War II
Three cables installed in a
coated steel pipe
Requires pressurizing plants to
maintain a nominal pressure of
200 psig
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Background: High Pressure Pipe Type Cables (HPPT)
Requires active cathodic protection to
prevent pipe corrosion
Two subcategories
• High Pressure Fluid Filled (HPFF)
• High Pressure Gas Filled (HPGF)
PHI High Pressure Pipe Type Cables
PHI has 90 HPPT systems and
Approximately 322 circuit miles of HPPT cable
# of Circuits 69kV 115kV 138kV 230kV Total
High Pressure Gas
Filled 0 0 0 0 0
High Pressure Fluid
Filled 49 5 18 18 90
Total 49 5 18 18 90
Mileage 69kV 115kV 138kV 230kV Total
Low Pressure Fluid
Filled 0 0 0 0 0
Medium Pressure
Fluid Filled 170 11.6 74.1 66.1 321.7
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Industry Survey
Questionnaire sent to utilities across the United
States
• 29 questions covering a range of topics
– Existing Cable Systems
– New Cable Systems
– Proposed Cable Systems
– Replacement Cable Projects
– Electrical Failures
– Circuit Availability
– Maintenance Practices
– Contractor Usage
– Spare Material
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Industry Survey Results
PHI has one of the larger inventories of active SCFF & HPPT cable systems (both by number and mileage)
Utilities are actively seeking to reduce their self contained fluid filled cable inventory
• Age, reliability concerns, capacity
Utilities are not actively seeking to replace their high pressure pipe type circuits
High Voltage Extruded Dielectric (XLPE & EPR) is becoming more popular for new installations
• HPPT cable is still considered a viable option for certain conditions
There is a growing industry concern with the limited number of manufacturers & contractors for oil impregnated paper
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Risk Matrix Development
Cable systems evaluated on various criteria
•
Cable Construction
•
Installation Conditions
•
Planning Drivers
•
O&M Practices
•
Operation
•
Spare Material
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Physical Condition Assessment
Self Contained Fluid Filled Cables
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SCFF Condition Assessment
April 15 – 19, 2013
Visual inspection of cables and accessories
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Terminations
•
Splices
•
Reservoirs
•
Pressure Gauges & Alarms
•
Exposed Cable
Fluid Leaks and other possible problems noted
Equipment & overall location condition given a
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SCFF Cable & Terminations Condition
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SCFF Reservoirs Condition
SCFF Overall Condition
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Conclusions / Recommendations
PHI SCFF cable systems are considered to be in fair to
good condition
PHI still encouraged to develop a system program to
replace these oil filled cable systems
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Current industry trend is to install extruded
dielectric at these lower voltages (69kV & 138kV)
•
Limited availability of manufacturers and qualified
workers
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Conclusions / Recommendations
• Increased costs of operation & maintenance
• Increase risk of circuit unavailability due to leaks & electrical failures
• Increased risk of environmental impacts cause by fluid leaks
• Increased risk of potential health impacts due to working with identified hazardous material (lead).
Replacement Strategy
Use Risk Matrix rankings to prioritize projects
• High Priority circuits should have projects initiated within 5 years
• Medium Priority circuits should have projects initiated within 10-15 years
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Replacement Options
Three Options Considered
• Option 1: Replace with HVED cable systems
– Eliminates ongoing environmental concerns with dielectric fluid – Reduces future O&M needs and costs
– Requires significant civil infrastructure improvements
o New manhole and duct system required
Replacement Options
• Option 2: Re-Conductor with SCFF cables
– Eliminates any concerns with existing age or condition of cables – Least cost solution
o Can Utilize existing manhole & duct system
– Does not eliminate environmental concerns with dielectric fluid – Does not reduce future O&M needs or costs
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Replacement Options Continued
• Option 3: Develop direct replacement HVED cable
– Partner with a high voltage cable manufacturer to develop a 3/C HVED cable that will fit in the existing manhole & duct system
– Combines the advantages of both Option 1 & Option 2
– Requires some engineering & developmental costs for cable & accessory design and testing
– Various cable manufacturers have expressed intent to
High Pressure Fluid Filled Cables
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HPFF Condition Assessment
May 13 – 16 & July 8 – 10, 2013
Visual inspection of cables and accessories
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Terminations
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Pressurizing Systems
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Cathodic Protection System
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Exposed Pipe
Fluid Leaks and other possible problems noted
Equipment given a ranking of good, fair or poor
based on observations
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HPFF Terminations Condition
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HPFF Terminations Condition
HPFF Terminations Condition
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HPFF Pressurizing Plants Condition
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Conclusions / Recommendations
PHI HPFF cable systems are considered to be in good
to very good condition
Small number of 69kV circuits are considered at a
medium risk
• Mostly attributable to condition of pressurizing plants
Continue with ongoing replacement program for
pressurizing plants
Conclusions / Recommendations
Continue with good maintain practices
• Active cathodic protection systems to prevent pipe corrosion
• Oil sampling and DGA analysis on periodic basis to identify incipient problems
Continue to monitor pipe type cable replacement options
for future consideration
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PHI’s Additional Replacement Factor Considerations
Replacement factor increase for SCFF
Cable failure Outage within past 5 years warrants
increase in replacement factor
Feeders with short lengths increase replacement factor
due to increased feasibility and lower cost
PHI Replacement Strategy
Coordinate risk matrix rankings with strategic plans from
other departments
• Transmission Planning
• Electric Construction & Maintenance
• System Operations
Look for synergy between circuits with common routes to
maximize efficiencies of design & construction
Questions
Thank you for your time!
This concludes the educational content of this activity
www.powereng.com Todd Goyette P.E. Senior Project Engineer
POWER Engineers
774.643.1833
todd.goyette@powereng.com
Mousa Hejazi, PE.
Senior Supervising Engineer Pepco Holdings Inc.
