Underground Secondary Cable & Connections Timothy J. McLaughlin For ICC Educational Program Spring 2005 – St. Pete Beach, FL.
Underground Secondary Cable & Connections
Timothy J. McLaughlin For ICC Educational Program
Spring 2005 St. Pete Beach, FL.
Presentation adapted from article
How Reliable Are Your Secondary UG Circuits?published in
Transmission & Distribution World magazine August 2003
PSE&G Facts
2,600 mile service area running diagonally across NJOver 2 million customersCombined electric and gas utilityPrimary voltages 4, 13, & 26 kVSecondary voltages 120/240 (radial),
120/208 (network), 277/480 (high-voltage network)
Realize there is a problemEvaluate the problems and associated costs
Search for a new technology?Evaluate possible solutionsAdapting new technologyField acceptanceResults of change
7- Step Program
Scope PSE&G installs approx. average 1.5 million ft
(457km) of secondary cable per year.Engineering and field crews started taking note of
the significant number of failures on secondary system.
Primary failures are tracked very closely where, why, how it was repaired etc.
In contrast, secondary failures are numerous and not tracked in any way
Secondary Cable
UG sizes - #4,#2,2/0,350,500,750All Copper! (Since 1980)XPLE insulation on smaller sizes EPR insulation with a Hypolon jacket on
larger sizes (replaces EPR and Neoprene) = better mechanical protection
Engineering Studies Secondary Failures
Study trouble crew work orders - 12 monthsInvestigation results
> 1800 failures per year on secondary> $1.5 million estimate in repair costsAverage $700 per repair
Large % of failures occurred at connectors.Failed connections sealed/insulated with
tape.
Digging Into Cause
Existing hand taping process Apply mastic sealing tape Apply rubber and vinyl tape
Quality of installation HIGHLY dependent on installerNo matter how well tape is applied it will
eventually leak and allow moisture in.
The Failure ProcessRoot Cause: Moisture Ingress Into
Connection
Leakage current accelerates corrosion reaction
Al + H2O Al2(OH)3 + H2Aluminum hydroxide + Hydrogen
Eventually, cables corrodes and has open failure.
Typical failure
Secondary Connection Failures
Salt water from rain and road salt corrode connector rapidlyMechanical connections come loose due to
water ingressImpossible to seal connection with tapingLarge solder-type connections are short
term (solder is a poor conductor and has a low temp. rating)
Results of inferior sealing
High Failure Rates Short Service Life Span High Restoration Costs Negative Customer Satisfaction
Search for New Technology
Requirements for a new solution Seals extremely well with long lifetime Easily repeatable installation regardless of
installer or conditions. Can install with insulated gloves on for hot
installs. Solutions must be available for the wide variety
of connections
Alternatives ConsideredHeat Shrink Tubes
Cold Shrink Tubes
Pre-molded rubber boots
Gel sealing products
Evaluation
Heat shrink, cold shrink, and pre-moldedAdvantages
Seals well Multiple cable ranges
Disadvantages
Must be placed on cable prior to connector installation Require additional installation space due to parking on cable Require larger excavation in direct buried application
Evaluation
Gels Provided wrap-around installation Seemed easier to install with consistent performance
and minimal training Products available for the wide variety of applications Allows for easy and clean re-entry
Gels met all of our requirements and were adapted on a trial basis.
The gel technologyWhat is Gel?
Gel: Polymer Network with Embedded Fluid
Silicone oil embedded in a cross-linked silicone matrix
Combines the advantages of solid and liquid insulating materials
9 Solid: Elastic memory9 Liquid: Wetting, conforms to surfaces
Unique tackiness and thermal long-termstability
Excellent aging properties
Extremely high elongation and elasticity
Excellent dielectric properties
How gel seals and prevents corrosionGel: Moisture displacement
Displacement of possible moisture Gel wets the surface applying a thin
layer of silicone oil Corrosion cannot occur without
water & oxygen in contact withmetal surface
Gel encapsulates connections
Dielectric strength 40kV/cm minimumGood chemical resistance UV Resistance Fungus resistant
Gel Properties
Field Acceptance of Gel
Critical factors for Fieldacceptance: Belief in product Makes their job easier,
not more difficult Product performs as promised
The gels were readily accepted by the crews and continue to be after more than 3 years of use.
500 & 350 KCMIL CU Bus
Compression connection core
Rubber insulatedTotally sealed
Service Bus
350 2/0(2), #2(2) 4/0 - #2(4)Multiple taps for
flexibilityTotally sealedConnects to main busEliminates the need
for vice-type connectors
Results
After several years, gel products continue to prove their value. No new installation failuresFailures are NOT occurring on the gel
products.New applications are still being introduced.
Gel ApplicationsCommon Industry Uses
URDMan Holes Street Light Bases (Gel-Cap)Taps
New Applications (PSE&G Leading)
500 and 750 MCM in-line limitersRe-Jacketing URD Primary CableGas Application Service Entrance Seal Sealing submersible elbow installations
Gas Application Service meter
Conclusion
We are still convinced going to gel technology is the right move.
We continue to increase the number of applications which we seal with gel.
We are already seeing real benefit in time savings and reliability.
Cost avoidance of repair work Full benefits will be realized in the future due to
reduced secondary failures and greater customer satisfaction.
Questions?
Comments?