Get Longer Life from Primary Power Cables

by Greg Stano, Senior Standards Engineer, Wisconsin Public Service Corporation, USA

Do you specify, install or maintain primary solid dielectric power cables? Did you ever wonder what you could do before you purchase the cable and while you install and maintain it to get the longest service life out of your cables?

At Wisconsin Public Service Corporation (WPSC), solid primary dielectric cables installed in the 1960s are still in operation. With 7,000 miles of primary cable in operation, last year only 20 primary cable failures occurred due to cable insulation aging. That includes cables dating back to the 1960s. Here are some important guidelines that have served us well.

Before the cable is purchased

Refer to specifications. This is probably the most important place to start if you want to install long-life primary cables. Unless the cables are manufactured and tested under stringent parameters, you won’t know the quality of the cables you are installing. Refer to industry specifications, such as the Insulated Cable Engineers Association, Inc. (www.icea.net) and The Association of Edison Illuminating Companies, (www.aeic.org), to be sure you are purchasing the best cable available.

You also need to determine what is required for your particular situation when it comes to cable design and shipping, such as reel and conductor sizes, metallic shield types, etc. Some questions your specifications should answer are:

  • What size reels will work with the installation crew reel stands?
  • How much cable do you want on each reel?
  • How out-of-round will you tolerate the cable to be so that the terminating tools used will still work properly?
  • Do you want single cables on a reel or triplexed on one reel for three-phase installations?
  • Do you use a jacket on the cable? If so, do you want an insulating or semiconducting jacket?
  • What type and size of metallic shielding do you want?

If you have questions about what you need, contact the cable manufacturers or check out on-line information at the cable manufacturers’ web sites for ideas. Consider purchasing the AEIC has a “Guide for Developing Specifications for Extruded Power Cables Rated 5 through 46 KV”, CG10-2002 as well.

If you have questions about what you need, contact the cable manufacturers or check out on-line information at the cable manufacturers' web sites for ideas. Consider purchasing the AEIC has a "Guide for Developing Specifications for Extruded Power Cables Rated 5 through 46 KV", CG10-2002 as well.

To be certain the cable is meeting the specifications you require, incoming cable should be inspected. Testing can be contracted or done in house. WPSC has been inspecting incoming cable for the last 25 years. One reason we prefer TR-XLPE insulation is because it is easy to test. Other insulations make it difficult to adequately inspect a cable to be sure it was manufactured properly.

Why do we test incoming cable? Event though we find cables are made much better than in the past, we still find problems and reject some cables to avoid installing a shorter-life cable. What do we find?

Amber Contaminant Out-of-round Shield
Protrusion Deformed Conductor Shield Shrinkback
Conductor Shield Fall Through into Strands of Conductor


Use the best insulation available. We have used XLPE since the 1960’s. We prefer XLPE because it is easy to inspect for compliance to our specifications; the insulation is the same no matter who manufacturers it; we are experiencing long cable life (40 years on some cables); and we expect even better performance with TR-XLPE used here since 1985.

For a long-life cable, purchase high-quality materials only from companies you know. If possible, visit the manufacturing plants and check if dry-cure lines are used to make the cable; how good their quality assurance is; and do they have personnel involved with cable standard specifications in the industry?

If you need help understanding how to establish a quality assurance program to approve manufacturers, check out the AEIC “Guide for an Electric Utility Quality Assurance Program for Extruded Dielectric Power Cables” CG8-2003.

Installation

Your cable installers need training on the proper handling, installation and termination of the cables. They need to know the minimum bending radius allowed, proper terminating techniques, proper handling and storage of the reels and when to recognize a problem with the cable before installing it.

If the installation location is prone to lightning strikes, proper lightning protection is needed to maintain long cable life. Refer to lightning arrester manufacturer information for the proper voltage rating for your situation. Riser pole class arresters perform better under lightning surges than distribution class arresters.

Maintenance

When faults do occur, the personnel performing fault location testing should be properly trained to use the equipment. Otherwise, additional cable insulation damage may occur.

Studies have found in-service cable that is hi-potted will have a reduced life expectancy. Do not hi-pot cables that have been in service.

WPSC is a domestic energy delivery company that serves 425,000 electric and 300,000 gas customers. Greg Stano, Senior Standards Engineer for WPSC, has been responsible for the underground primary cable standards and specifications for 14 years.