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 NJ
Over 2 million customers
Combined electric and gas utility
Primary voltages 4, 13, & 26 kV
Secondary voltages 120/240 (radial),
120/208 (network), 277/480 (high-voltage
network)
7- Step Program
Realize there is a problem
Evaluate the problems and associated
costs
Search for a new technology?
Evaluate possible solutions
Adapting new technology
Field acceptance
Results of change
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,#2,2/0,350,500,750
All 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 months
Investigation results
> 1800 failures per year on secondary
> $1.5 million estimate in repair costs
Average $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 installer
No matter how well tape is applied it will
eventually leak and allow moisture in.
The Failure Process
Root Cause:
Moisture Ingress Into
Connection
Leakage current
accelerates corrosion
reaction
Al + H2O
Al2(OH)3 + H2
Aluminum hydroxide + Hydrogen
Eventually, cables corrodes
and has open failure.
Typical failure
Secondary Connection Failures
Salt water from rain and road salt corrode
connector rapidly
Mechanical connections come loose due to
water ingress
Impossible to seal connection with taping
Large 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 Considered
Heat Shrink Tubes
Cold Shrink Tubes
Pre-molded rubber boots
Gel sealing products
Evaluation
Heat shrink, cold shrink, and pre-molded
Advantages
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 technology
What is Gel?
Silicone oil embedded in a cross-linked silicone matrix
Combines the advantages of solid and liquid
insulating materials
9 Solid: Elastic memory
9 Liquid: Wetting, conforms to surfaces
Unique tackiness and thermal long-term
stability
Excellent aging properties
Extremely high elongation and elasticity
Excellent dielectric properties
Gel: Polymer Network with Embedded Fluid
How gel seals and prevents corrosion
Gel: 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 with
metal surface
Gel encapsulates connections
Gel Properties
Dielectric strength 40kV/cm minimum
Good chemical resistance
UV Resistance
Fungus resistant
Field Acceptance of Gel
Critical factors for Field
acceptance:
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 insulated
Totally sealed
Service Bus
350 2/0(2), #2(2)
4/0 - #2(4)
Multiple taps for
flexibility
Totally sealed
Connects to main bus
Eliminates the need
for vice-type
connectors
Results
After several years, gel products continue to
prove their value.
No new installation failures
Failures are NOT occurring on the gel
products.
New applications are still being introduced.
Gel Applications
Common Industry Uses
URD
Man Holes
Street Light Bases (Gel-Cap)
Taps
New Applications (PSE&G Leading)
500 and 750 MCM in-line limiters
Re-Jacketing URD Primary Cable
Gas 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?
