03/09/2012

Dow Electrical & Telecommunications

Improving wind-farm reliability with small cable materials and standards.

Wind power repairs and downtime are more
expensive than in conventional utility-grid
systems. This makes reliable equipment especially
important. Improving wind-power reliability is all about
planning. Each system component is considered in terms of
its total life-cycle cost–not just the price to buy and install.
This applies to power-cable selection where a life-cycle
cost model can assist in determining a wind farm’s return on
a cable investment.
Variables include:
• Wind farm specifics
• Cable length and cost
• Installation cost
• Predicted cable life and failures
• Cost per failure
• Dielectric losses
• Discount rate and tax rate
When comparing life-cycle costs, it’s important to
know that all cables are not created equal. For most
power transmission and distribution needs, high-voltage
or medium-voltage cables typically are specified. They are
often installed underground or underwater (submarine)
and connect the wind farm to the grid. Power cable
components usually consist of several different materials,
including cross-linked polyethylene (XLPE), ethylene
propylene rubber (EPR), and water tree-retardant XLPE (TRXLPE).
However, not all cable materials deliver the same
results. Hence, testing data and manufacturing standards
are needed to predict performance. It is critical that wind
developers are aware of how various materials perform in power-cable applications.
For instance, field studies over 30 years of
use show that TR-XLPE cables from Dow exhibit
little or no wear. This is due to jacketing and
insulation materials resistant to moisture intrusion.
Industry accepted tests estimate their lifespan at
more than 40 years. This kind of performance
is in line with wind-farm developers who are
targeting a similar lifespan. Lab and field testing
of cable components performed by independent
institutes such as Georgia Tech’s National Electric
Energy Testing Research and Applications Center
(NEETRAC) also should be considered. Specifically
recommended is the Cable Design Aging Test,
NEETRAC project 97-409.