M. M. Epstein

Analysis of Field Failure Data on HMWPE- and XLPE-Insulated High-Voltage Distribution Cable

The paper summarizes the results from Phase I of EPRI Research Project 1782-1 (EPRI Report EL-3501). Fifteen utilities supplied data on failures and operating parameters for more than 34,000 miles of HMWPE- insulated cables and 47,000 miles of XLPE-insulated cables. Data reduction and statistical analyses identified important predictors of high failure rates. For HMWPE, these are age, operating stress, and year of installation. Age and insulation wall thickness are the most important predictors of high failure rates for XLPE cable.

New technology for the 21st century

Summary form only given, as follows. The coming decade is expected to be a period of extensive advances in technology. This will have a profound impact on society as a whole but, in particular, on the electrical and electronics industries. The author provides an overview of some of the more interesting developments likely to reach the marketplace in some form before the end of the decade. Global subjects such as high-speed rail will be addressed along with more specialized subjects such as liquid crystal polymers and ferroelectrics.<<ETX>>

Morphology of thermoplastic and cross-linked polyethylene cable insulation

The following conclusions can be drawn: 1. The study of void population, size, and mobility will help define mechanisms of electrical failure in polyethylene cable insulation. Structural models explaining the origin of voids in terms of spherulitic domains must be expanded to include nonspherulitic morphologies. 2. Sample preparation for SEM investigations is extremely important. The actions of any etching procedure used in surface preparation must be carefully characterized. 3. Oxygen plasma etching reveals differences in strain as well as differences in aged and unaged morphology near and away from the burn hole. 4. Chlorosulfonic acid treated polyethylene can be thin sectioned to study void population by TEM.

Analysis of antioxidant in aged cables

Successful application of polyolefins as insulating materials for solid dielectric cable depends on their long-term stability against oxidation and electrochemical degradation. The usual method of stabilization is the addition of small quantities of antioxidants (AO), which act as radical scavengers in the oxidation process. The effectiveness of antioxidants depends not only on its capability for resonance stabilization but also on physical factors such as solubility, diffusivity, and volatility. The possibility of excess anti-oxidants accumulating and crystallizing in the voids and at interfaces of solid dielectric cable and acting as stress enhancers is important from service-life considerations.

Functional analysis of antioxidant in thermoplastic cable insulations

DSC and CL measurements are shown to be potential tools for monitoring functional antioxidant activity in LDPE cable insulation. Data from the two procedures are consistent for unaged polyethylene samples. The results suggest that either method could be used to determine quantitatively the amount of functioning AD in the dielectric if it has no aging history.

Considerations for valid accelerated life testing

For many situations, good estimates of the expected life of long-life materials, parts, or systems are essential. Practical considerations related to replacement costs, repair costs, maintenance costs, spare parts inventories, warranties, insurance, and safety all require good estimates of expected life. Unfortunately, such estimates are difficult to obtain. This is especially true for new systems when no field experience exists.

Dynamic mechanical spectroscopy and aging in high molecular weight and crosslinked polyethylene cable insulation

Considerations of the ordered, or crystalline, domains have long dominated research to characterize and explain the properties of polyethylene. This perspective has naturally influenced conceptions about the material, the nomenclature used to describe it, and the techniques used to measure its properties.

Computer integrated manufacturing systems and insulation analysis

Modern manufacturing entered a revolutionary phase approximately 10 years ago with the introduction of the computer to the workplace. The first state of this still-devolving process was labeled computer-aided design (CAD) and computer-aided manufacturing (CAM). This early technology is now strongly established in some industries, including segments of the plastics processing industry. CAD-CAM is now giving way to a more advanced concept, known as CIMS (Computer Integrated Manufacturing Systems), in which all operations within a manufacturing complex, from accounting to inventory control, are controlled to obtain the most efficiency from the system. These developments will inevitably influence the manufacture of electrical insulation systems.

Experience with miniature-cable terminations made from compounded materials and used under accelerated test conditions

Electrical termination is a critical issue in a large-scale accelerated-testing program with model extruded cables because economic forces dictate that the termination be low in cost and easily assembled. The termination must also be at least equal to the cable insulation in resisting the high stresses of accelerated testing. Achieving this result is difficult since the testing program included the continuous use of high overstresses: electrical field up to 350 V/mil or 13.8 kV/mm (seven times normal), frequency up to 600 Hz (ten times normal), and conductor temperature up to 90 C. Heat-shrinkable, resistive-capacitive electrical stress relief is a low-cost terminating technique because of easy assembly and flexibility with respect to cable diameters and constructions. The electrical losses in standard stress control material in normal usage produce a temperature rise of less than 1 C. However, under the unusual test conditions employed, excessive localized temperature rise was observed. These temperatures were reduced by using a specially formulated material with reduced loss. Reasonably successful terminations were obtained for XLPE and EPR cables with the modified material when the stresses were as noted above. Terminating LDPE cables at the higher stresses still poses a problem, although it is possible that a major part of the problem with this material was the high conductor temperature.

Accelerated life testing of solid dielectric cables

The achievement of an accelerated laboratory test capable of predicting the useful service life of products has been an elusive goal for most manufactures. This state of affairs applies to solid dielectric cables functioning in complex environments. The community of interests concerned with electrical power transmission and distribution has long been aware of the lack of a suitable test. It has devised a wide assortment of procedures for evaluating the performance of cable designs and materials, but they do not provide accurate validatable estimates of service life under normal operating conditions. In common with most tests that are loosely labeled “accelerated” they are upon close examination useful mostly for quality control and comparative purposes.