Field Performance History of UG Residential Distribution MV Cable

As presented by Mike Walker, CenterPoint Energy

CenterPoint Energy began installing 15 kV medium voltage (MV) underground residential distribution (URD) cable in 1963. Early cables were copper, high-molecular-weight polyethylene (HMWPE) with standard shield, full concentric neutral and unjacketed. We have also utilized 1/0 aluminum (Al) conductor and 1/0 Al TR HMWPE with standard shields, full neutral and PVC jacket with Mylar separator tape over the neutral.

In 1987, we moved to 1/0 Al strand-filled TR-XLPE with the neutral embedded in a linear low density polyethylene (LLDPE) jacket for both 15 kV and 35 kV URD cable. The 35kV URD cable is a 1/0 Al strand-filled TR-XLPE with supersmooth shields and the neutral embedded in a LLDPE jacket.

Since 1963, we've installed 2,405 miles of 15 kV URD cable and 3,185 miles of 35 kV URD cable. Failure rates have been carefully tracked and evaluated and we've learned that 98 percent of the dielectric failures that occur annually are on cable installed prior to 1981. The remaining two percent of the dielectric failures are on cable installed prior to 1986. There are no documented dielectric failures on cable installed after 1987.

As a result of the reliability of CenterPoint Energy's current URD cable construction, we have returned to direct burying our cable. However, since MV URD-type cable is a high- technology product sold as a commodity, we maintain an incoming cable inspection program to ensure that the cable we receive meets industry requirements and we actively monitor the system looking for any changes in reliability.

Dielectric Failure

CenterPoint Energy, Inc., headquartered in Houston, Texas, USA, is a domestic energy delivery company that includes electric transmission and distribution, natural gas distribution and sales, and interstate pipeline and gathering operations. The company serves nearly five million metered customers primarily in Arkansas, Louisiana, Minnesota, Mississippi, Oklahoma and Texas. Assets total approximately $16 billion. With more than 9,000 employees, CenterPoint Energy and its predecessor companies have been in business for more than 130 years.