Oil Removal from Redundant Cables

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Oil Removal from Redundant Cables

• Graham J Le Poidevin

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Current practice

• Maintain and monitor pressure
• Cut and cap sections of cable
• Purging of cables with nitrogen
• DISADVANTAGES
• Pure oil still remains within cable
• Oil can seep into the ducts after purging
• Oil accumulates at low points

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Detergent cleaning - requirements

• Suitable for all types of oil filled cable
• Removal of a prescribed amount of oil
• Detergent must be biodegradable
• Manageable volumes of waste
• Cost effective
• Safe to operate

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Typical equipment
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How is the process monitored?

• Inflow rate
• Outflow rate
• Sampling
• The above are essential for audit trail
  requirements

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Typical effluent samples
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Oil removal from 275 kV cable
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How effective is it?

• In theory
• Nearly 100 of oil can be removed by gas purging
  and detergent cleaning
• In practice
• 50 to 90 of oil can be removed in a sensible
  time scale
• Even with 50 to 90 oil removal the potential
  for damage to the environment is greatly reduced

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Lessons learned

• Remove as much oil by gas purging as possible -
  before detergent cleaning
• Carefully plan strategy
• Method statement
• Risk assessment
• Knowledge of circuit
• Water supply
• Vehicular access
• Be prepared to modify the plan!

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Improvements to the process

• Reduce cost by
• increasing section length (2 to 3 km)
• work on more than one section concurrently
• make the cleaning process part of decommissioning

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Conclusion

• The detergent cleaning process works
• It is believed to be cost effective
• Now provided as a service by EA Technology in the
  UK