Lincoln Electric System (LES) has a network system in its downtown area of Lincoln, Nebraska, that consists of about 17 blocks of paper-insulated lead-covered (PILC) cable. In 1981, the utility installed six three-phase, 15-kV cross-linked polyethylene (XLPE) circuits in a duct system to connect the PILC network system to a new substation.
Over the 25-plus years that the XLPE cable has been in service, it has developed neutral corrosion and was identified to be a defective cable. To remediate the deteriorating cable before it becomes a problem, engineering and the network crew decided to replace the cable. This involves installing a transition splice. Central to the cable replacement discussion was the splice, which is crucial in maintaining the long-term reliability that the cable source has given us all these years. This particular type of splice is not an everyday occurrence at LES, so careful planning and evaluation of required skills and materials were important.
In preparing for the upcoming splice, it was important to include many departments and people in the planning and design process. Engineering will determine the type of replacement cable that is required. Planning will need to confirm the load and if the old cable is still large enough for the system or if an upgrade is necessary. The field personnel will be involved to determine if the manhole is adequate (size and congestion factor). The equipment procurement is involved along with the vendors in obtaining the specifications from engineering and converting this into a purchase order. And last but not least is training. The design of an oil-stop splice is different from a standard splice; therefore, the installers must understand how the new splice works and how it is installed.
The Skills Issue
Since the 1981 cable installation, LES has made many transition splices to add new network transformers to the system and to connect XLPE cable to existing PILC circuits. It is normal procedure on a more technical application, such as the downtown splice, to work closely with the vendor or manufacturer of the splice equipment. The vendors are familiar with the material specifications and know the latest advancements in both the products and methods for installation.
Raychem representative Fred Banta, the North Central Utility manager for Tyco Electronics/Energy Division, has been involved in the planning and design process, because LES has used the Raychem HVSY-1583D splice in the past for PILC to XLPE splices. Furthermore, Raychem is the only manufacturer LES knows of that makes this particular type of splice.
When Is It Time?
One of the first questions the review team had to answer was, “When do we need to replace this cable?” Cable replacement and the need for transition splicing is usually performed when a circuit is being upgraded, replaced or modified in some way.
The downtown XLPE cable was originally installed in a duct system. It was noted during an inspection of the network that the concentric neutrals were corroded. Other XLPE cable that is installed in duct systems is a vintage that is failing in other places in LES's system. The team decided to replace the cable before it fails in the network.
As with other cable replacement projects at LES, most existing bare neutral cables are being replaced with new jacketed solid dielectric cable.
If a PILC splice is leaking or corroding, the splice can be replaced. If the utility has trained lead splicers, the replacement of a lead sheath over a splice is a minor task; however, if the skilled resources have been lost, then other alternatives need to be found. One alternative is to remove all of the lead cable and replace it with solid dielectric cable.
Another choice is to remove only the bad section or accessory and replace it with a new heat-shrinkable splice. In this case, the LES review team decided to replace the cable. The project is scheduled for late 2005 or early 2006.
A splice can be installed in a manhole, direct buried or vertical on a pole. The location depends upon the failure and the method of replacement.
There are several different sizes of splices. The 1/C splice is about 2 ft long, whereas the 3/C splice is about 4 ft long. A short length of the old PILC cable is required to splice the new cable, but if the old cable is in a manhole and duct system, a long length of old cable may need to be removed in order to fix the damage if it is inside the duct.
Weather is not really a factor in making a heat-shrinkable-type splice. Transition splices have been installed in arctic conditions as well as desert conditions. Many of the splices are direct buried in wet locations and some are even installed under bodies of water such as the Great Lakes and bays/inlets where islands are being fed with under water PILC cable.
The main factor to consider in planning a splice is working conditions/available space. Some manholes are so crowded that making any splice is a real chore. If the manhole is adequate in the length and density of other circuits and still gives a crew room to work, then there should be no problem in making the splice under any weather conditions.
Changes in Splice Methods
The old method of installing a splice was to prepare the ends of the PILC cable and join the conductors together with a soldered connection. The conductors were insulated with oil-soaked varnish cambric cloth tape. The joint was shielded with copper mesh. A copper or lead sleeve was wrapped around the joint. It was made oil tight by wiping solder to adhere it to the lead sheath of the PILC cable. Last, but not least, the splice body was filled with hot oil or compound. The required time to perform this task was usually 8 to 12 hours or longer depending upon skill levels and working conditions.
The new method is to apply oil-blocking tubes and conductive breakout boots to the PILC cable using heat-shrinkable technology. After the PILC cable has been converted to a quasi-polymeric cable, the splice is completed using the same materials and tools used to apply a heat-shrinkable splice to a standard polymeric joint.
Installing a drilled connector is an important part of the splice to contain the oil in the PILC and out of the XLPE cable. A drilled connector contains a solid barrier between the two cables preventing the oil migration. It is also important to use the proper method to stop the oil. If you don't have the correct connector, the oil will migrate from the PILC cable into the XLPE cable. If enough oil is lost from the PILC cable, the paper will dry out and the cable will fail.
The time and cost of a splice varies depending upon the size of the cable and whether it is a single-phase transition or a 3/C PILC to 3-1/C POLY trifurcating transition. Materials for a normal splice range in price from $400 to $1400. The actual on-site installation is usually between four and six hours. The LES normal crew size is three: one ground man and two workers in the manhole. For a more complicated or unique splice, an engineer and a manufacturer's representative will be on-site. These hourly rates need to be factored into the cost as well.
A Good Splice
A good splice is made when the network crew follows the manufacturer's instructions. We do a test splice with the manufacturer's rep before we start the project to minimize installation time and problems. A high-voltage soak is usually placed on the cable overnight to detect any problems before the load is added. In an emergency repair situation, when the splice is completed and the safeties are removed, the splice is energized.
But the real test to know if you have a good splice is having good people doing the installation. This is something that hasn't changed over the years. You know you have a good splice when the installer feels good enough about his work to put his name on it. When he has taken pride in his work and placed his guarantee on the splice, you can take that to the bank for the next 30 years.
The successful installation of a new splice is a combination of proper design, selection of the latest technology and right product for the cable application, and training and expertise to see that the new splice is installed correctly.
Stan Wostrel is customer service supervisor at Lincoln Electric System, where he has been employed for 33 years. He is based in the company's service center in Lincoln, Nebraska. email@example.com