The major practical service continuity risk for the transformer-feeder substation is when the substation supply cables are both laid in the same trench and suffer from simultaneous damage. Much of the substation cost savings would be lost if the supply cables were laid in separate trenches since the civil trench work, laying and reinstatement costs are typically between 33% and 40% of the total
supply and erection contract costs for 132 kV oil filled and 33 kV XLPE, respectively.
In congested inner city areas planning permission for separate trenches in road ways or along verges is, in any case, seldom granted. The civil works trenching and backfill costs for two separate trenches (one cable installation contract
without special remobilization) are typically 1.6 times the cost of a single trench for double circuit laying. The choice depends upon the degree of risk involved and the level of mechanical protection, route markers and warnings utilized.
supply and erection contract costs for 132 kV oil filled and 33 kV XLPE, respectively.
In congested inner city areas planning permission for separate trenches in road ways or along verges is, in any case, seldom granted. The civil works trenching and backfill costs for two separate trenches (one cable installation contract
without special remobilization) are typically 1.6 times the cost of a single trench for double circuit laying. The choice depends upon the degree of risk involved and the level of mechanical protection, route markers and warnings utilized.
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