Covered Conductor Systems

Recent developments in the field of connector technology used with covered conductor systems aim to improe the level of service and reliability of electric power delivery.

Sep 1st, 2018
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Insulation piercing connectors offer logical next step toward enhancing grid reliability

By Brian Trager

Utilities worldwide, in an effort to improve the level of service and reliability of electric power delivery, have been investing in medium voltage construction practices that have proven those aims are achievable. Two that have been used in North America since 1951 are the Aerial Spacer Cable System, originally designed by Bill Hendrix; and the Tree Wire configuration, which utilizes covered conductor in open construction on cross arms with polyethylene insulators. Rather than discuss the features and benefits of either of these systems, this article will present recent developments in the field of connector technology used with these covered conductor systems.

European installation of an IPC, using a hot stick.

The Fundamentals

In order to connect transformers to a covered conductor line, the utility is required to strip the covering to install the connector. In most situations, the tap is left bare and a protective covering is placed over the messenger above the tap to prevent temporary outages that might occur from tree or animal contact. As an added standard precaution, an arrester is also used to avoid possible problems in the event of lightning strikes.

Perceived Challenges with Covered Wire Systems

One of the challenges expressed by utilities in adopting spacer cable and covered wire systems is the difficulty in adequately and safely stripping the conductor covering prior to making a tap. When utilities have needed to make a tap for a transformer, the requirement has always been to strip the cable. This is a relatively simple process with the correct stripping tools. However, tools are not always available or in good working condition. In some cases, line workers have taken to using knives to strip the insulation. This creates safety hazards at the jobsite, and also introduces the possibility of damaging the insulation and/or the cable, impacting the long-term reliability and integrity of the cable. Other safety concerns with stripping, like being too close to adjacent phases, the awkwardness of stripping tools, or the difficulty of stripping with temperature, inherently cause reluctance on the part of some utilities to adopt covered conductor usage in a significant way.

Historically, covered conductors need to be stripped to tap in transformer connectors. Taps are typically left bare.

Insulation Piercing Connectors

Technological advancements and the development of Insulation Piercing Connectors (IPCs) have eliminated the need for insulation stripping — which leaves the system fully insulated and water-sealed. The technology goes a long way toward achieving goals the industry has had for years, including avoiding stripping altogether, increasing the safety of line workers, avoiding damage to the cable, and maintaining the reliability/integrity of the grid.

European vs. North American Adoption

IPCs actually have a long history of usage worldwide for low-voltage systems and have been used with medium voltage (MV) applications in Europe for over a decade. Adoption of IPC technology in the U.S. has been slower, but that is about to change as new IPCs go a long way toward addressing industry concerns.

European standards for covered conductors1 are quite different than those used in the U.S. and which are codified in international standards.2 The standards adopted in North America require much thicker insulation for covered aerial cables than what are utilized in Europe. While IPCs passed the EU standard type tests ages ago, there was concern regarding use of the IPCs at the thicker insulation levels. This was overcome with the IPCs passing ANSI C119.4.3

To address the challenges around IPCs, a rigorous and comprehensive type test program was designed (see Table 1), focusing on all of the concerns of ANSI C119.4 while also including type tests from EN-50397-2 (when the ANSI standard did not address a particular concern included in the European standard).

Industry Concerns and Early Adopters

Utilities across North America continue to be skeptical (as they are with any “new” technology) about improper installation of IPCs and potential resulting system failures. Further research has shown that failures result from improper stripping and tapping without IPCs, and that failures resulting from poor workmanship are an unfortunate industry reality. Installation of IPCs are by no means foolproof, and formal installation procedures should be followed. But industry goals are to reduce failures and accidents to zero, and proponents of IPCs in the covered conductor marketplace hope the newly adopted IPC technology will help in that regard.

Early adopters of IPC technology see its widespread introduction and adoption as the logical next step toward enhancing grid reliability. Utilizing covered conductors such as Hendrix Aerial Cable as part of grid-hardening initiatives is a start. With proper installation techniques, the implementation of covered conductors can be a great success. And the use of IPCs simplifies installation tremendously, saving a significant amount of time (and money) and increasing the reliability of the cable (since the IPCs nearly eliminate cable damage).

IPCs essentially create a piercing of the insulation with controlled force and with a high-grade copper alloy blade, engineered to offer low contact resistance and high conductivity. The miniscule contact points are supported by a seal made of insulation material, which acts as a second skin and recreates the cable insulation. Pressure is applied evenly by tightening of the bolts, providing protection of the connection points from corrosion and water infiltration for decades. Image courtesy of SICAME Corp.

IPC = Increased Grid Reliability

Now that IPC technology has been given the green light after years of field-proven experience and, most recently, backed by type tests to meet ANSI specs with thick-jacketed ICEA standards, utilities across North America have one less obstacle to implementing covered conductors across their networks and advancing their grid-hardening programs.

Implementing covered conductors across a network is now easier than ever, and utilities gain the added benefits of improving the safety and well-being of their crews in the field, decreasing installation costs, decreasing long-term grid-hardening costs, improving grid reliability, and increasing customer satisfaction. Whether in the Black Forest of Europe or the back roads of North America, these are goals that any utility should hope to attain. And IPC technology, used in conjunction with covered conductors, provides a proven method for achieving these goals. UP

the Author: Brian Trager is the director of technology and international sales at Hendrix Aerial Cable Systems in Milford, N.H. He can be reached at btrager@marmonutility.com.

References

1. EN-50397-2. Covered conductors for overhead lines and the related accessories for rated voltages above 1 kV AC and not exceeding 36 kV – Part 2: Accessories for covered conductors: Tests and Acceptance criteria. European Committee for Electrotechnical Standardization. 2009.

2. ANSI/ICEA S-121-733. Standard for Tree Wire and Messenger Supported Spacer Cable. Insulated Cable Engineers Association. 2016.

3. ANSI C119.4. Connectors for Use between Aluminum-to-Aluminum and Aluminum-to-Copper Conductors Designed for Normal Operation at or Below 93°C and Copper-to-Copper Conductors Designed for Normal Operation at or Below 100°C. American National Standards Institute. 2016.

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