Corrosion on Underground Power Transmission Cables

OUR SOLUTIONS

Underground power transmission cable systems are installed in congested
areas or locations where overhead electrical lines may not be feasible due
to construction, right-of-way (ROW), or regulatory constraints. There are
four main types of underground cable systems, each with its unique corrosion
challenges:

1. 1. High-pressure, fluid-filled pipe (HPFF)
2. 2. High-pressure, gas-filled pipe (HPGF)
3. 3. Self-contained, fluid-filled pipe (SCFF)
4. 4. Solid dielectric insulated cable

Pipe-type cables are enclosed in metallic pipes containing three copper or
aluminum conductors, each with insulation and metallic shielding. These
pipes are then filled with dielectric oil or gas to allow for heat
dissipation and additional electrical insulation. For fluid-filled pipes,
the dielectric oil is usually pumped by stations located within electrical
substations; they may also include heat exchangers for fluid circulation
systems.

Since the pipes are metallic, they are subject to external corrosion. This
corrosion can be due to changes in the soil or water environment due to
chemistry or changes in soil resistivity. They are also subject to stray
currents from nearby cathodically-protected infrastructures (DC currents) or
nearby electrical transmission infrastructure (AC currents). Prevention of
external corrosion involves coating applications or cathodic protection
systems.

Long-term corrosion of the metallic pipe will result in leaking dielectric
oil, reducing the heat and electrical insulation properties. If these are
not remedied, then the circuit is at increased risk of failure. Maintenance
programs often involve periodic surveys of the pipe-type cable itself and
the cathodic protection systems.

Cross-linked Polyethylene cable (XLPE) may have periodic splice pits or
vaults with their own localized grounding systems. These grounding systems
are also subject to stray DC and AC currents from nearby infrastructure,
which could result in external corrosion.

EN Consulting’s corrosion engineering group has extensive experience with
cathodic protection and interference studies for buried pipe-type cables and
grounding systems. We leverage our experience from the oil and gas industry
to provide solutions for the electric transmission and distribution groups
with their corrosion control and maintenance design.

SERVICES

• Soil resistivity measurements
• Close-interval survey (CIS)
• Coating surveys (ACVG, DCVG, PCM)
• AC and DC interference studies
• Site evaluations
• Periodic surveys and inspections
• Cathodic protection design
• Electrical grounding design
• Modeling services by SES CDEGS, ROW-Pro, and Multifields+ modules
• Evaluation against operator limits or regulatory controls
• Consulting services to modify designs as needed
• Professional Engineer (PE) review and seal