Low voltage secondary electrical networks supply the largest cities in the world. The cable in these systems was designed to be operated until it failed. This aging infrastructure can be actively managed by electric utilities to minimize cost, reduce risk and improve reliability by testing the cable using mobile detection technology.

1. Low Voltage Underground Cable
Developing an Asset Based Management Strategy
Stuart Hanebuth MEMBER
Vice President
Power Survey Company
25 Campus Drive
Kearny, NJ, 07032

2. Motivation & Outline
o Overview
o Voltage Class & Cable Insulation
o Low Voltage Cable Failure
o Causes of Cable Failure
o Impact of Cable Failure
o Asset Management
o Asset Management &Techniques
o Developing a Strategy
o Current Approach
o LV Cable Management Framework
o Summary & References
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

3. Overview
2 - 45 kV
Voltage Class
Low Voltage Medium Voltage High Voltage Extra High Voltage
120 – 600 V
Extruded Polymer Insulation
Extruded Polymer Insulation
46 - 160 kV
Paper Insulation
Paper Insulation
161 – 500 kV
Secondary Distribution Primary Distribution Subtransmission Transmission
Tan - δ
?
Tan - δ
Partial Discharge (PD)
Partial Discharge (PD)
Dielectric Strength
Dielectric Strength
Cable Diagnostic Method
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

4. Low Voltage Cable Failure
Low voltage cable failure affects capital expenditures, system outages and
interruptions as well as public safety.
• Reliability: 50% of underground
Miles of Cable
related failures are associated with
cable failure.1 H.V.
• Public Safety: NY utilities have Medium
reported more than 40,000 cases of Voltage
Contact Voltage, many of which are
cable failures.2
Low Voltage
• Cost: Utilities report up to 18% of Distribution
annual capital expenditures replace Cable
only 1% of cable 3
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

5. Low Voltage Cable Failure
Aging infrastructure
• Expected life – 30 years
•Thermal, chemical, mechanical failure
•Abrasion against metal support racks
In-situ Damage
•Construction dig-in
•Tampering by the public
•Duct collapse
Workmanship
• Unintentional damage
•Improper preparation
•Improper wiring (reversed polarity)
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

6. Asset Management
“Asset management means operating a group of assets over the whole
technical life-cycle guaranteeing a suitable return and ensuring defined
service and security standards.” 4
Asset Management Techniques
• Maintenance Strategies
• Condition vs. Importance
• Determine Component Condition
• Online – Offline Monitoring
• Simulate Asset over long term
• System dynamics
• Statistical approach
• Statistical Fault analysis
• Life management
• Optimizing remaining life
4 - “Asset Management Techniques “ Electrical Power & Energy Systems, J. Schneider et al. 2006, 28, 643-654
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

7. Developing a Strategy
LV-Cable Management: Our Current Approach
• Run to Failure: Corrective Maintenance (CM)
• System faults are designed to burn clear
• Condition of Cable is addressed following a system failure mode
• Smoking manhole
• Manhole fire and/or explosion
• Service interruption or outage
• Collateral damage to neighboring cable /equipment
• Contact voltage
• LV Cable Failure Data: Analysis
 Comprehensive database is largely nonexistent
 Scattered sources of cable failure data
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

8. Developing a Strategy
• Hybrid of Asset Management Techniques
•Visual detection of defects
• Repair data from CV programs 2
Maintenance •Proactive replacement
• Aged based cable replacement efforts
•Predictive modeling
• Machine learning techniques applied to
Condition Monitoring electric power grid 6
•CV detections
• Detection and Mitigation of CV
• Elevated voltage investigation 6
Asset Simulation
• Source determination: harmonic
measurement 7
•Unified system failure modes
• Contact Voltage & Manhole Events 8
Data & Analysis •Mechanisms of Aging and Degradation
• Diagnostics of cable systems 9
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

9. Summary
• LV Cable Characteristics: Voltage Class, insulation type and
distribution system configuration
• Types of cable failure: Age based deterioration, in-situ damage
and general workmanship issues
• Cable Failure Impact: Cost, reliability and public safety
• Asset Management Techniques: Maintenance strategies,
component condition, asset simulation and data analysis
• Current Approach to LV Cable Management: Not much exists,
corrective maintenance (run to failure)
• Developing the Framework for Management of LV Cable
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP

10. References
1 - Potomac Electric Power Company (PEPCO ) 2009-2011 Outage Reports
http://bit.ly/OFmEI9 FC 982
2 - New York State Public Service Commission Stray Voltage Report 2006-2011
http://www3.dps.ny.gov/W/PSCWeb.nsf/All/400E5FF8A07FEFC185257687006F38C8?OpenDocument
3 - Consolidated Edison 2011 Capital Expenditure Report
http://www3.dps.ny.gov/
4 - “Asset Management Techniques“ Electrical Power & Energy Systems, J. Schneider et al. 2006, 28, 643-
654
5 - Consolidated Edison 2011 Stray Voltage Report (p. 29-43)
http://documents.dps.ny.gov/public/Common/ViewDoc.aspx?DocRefId=%7B0D67AB70-0C8B-4DDB-A458-7EDD2978BB3C%7D
6 - “Processes for Investigating Elevated Voltage in the Urban Environment” D. Kalokitis et al. 2010
www.powersurveyco.com/?attachment_id=327
7 - “Using Harmonic Measurements to Aid in Source Determination during Elevated Voltage Investigations”, S.
Hanebuth et al. 2011
www.powersurveyco.com/?attachment_id=342
8 - “The Electro-Chemical Basis of Manhole Events”, L. Zhang et al. 2009, IEEE DEIS
http://www.ims.uconn.edu/~eprcable/manhole.pdf
9 - “Diagnostic testing of underground cable systems” National Electric Energy Testing Research and
Applications Center (NEETRAC)
www.neetrac.gatech.edu/publications/CDFI_Phase_1_Final-Report.pdf
GM12 – SUMMER 2012 PSPI 04 -- ASSET MANAGEMENT WORKING GROUP