Review of field acceptance hipot & PD testing of medium voltage underground cables
There are some well-defined guides and standards regarding factory testing of medium voltage shielded cables in laboratories provided by IEEE, IEC, ANSI/ICEA, and CSA. These guides cover AC withstand and PD testing of XLPE and EPR cables and accessories, such as 50/60Hz AC Hipot and PD tests which are routinely conducted on every reel of cable produced at the factory. All terminations, splices, and separable connectors are tested with more or less the same test method using different test levels and timing.
Approaches to the forensic failure investigation of medium voltage polymeric cables
Medium voltage (MV) polymeric cables are critical assets in modern power systems, since their introduction, approximately five decades ago. More recently, there has been a growing emphasis on the maintenance testing of polymeric cables, with some of them being prone to premature failures. This paper covers the various techniques available for the forensic failure investigation of polymeric cables through practical examples. Some of these include diagnostic electrical tests such as Insulation Resistance, AC Hipot & PD, and nonelectrical procedures such as visual inspection, optical microscopy, and differential scanning calorimetry (DSC). The recommended order of performing these techniques is also presented, based on the suspected failure mode. This serves as a practical guideline for utilities, towards identifying the type of cable failure sustained in the field. Diagnostic electrical testing (post-failure) helps establish the most probable cause of failure associated with polymeric cables and/or their accessories. A very useful, but less explored technique in polymer morphology is the DSC, which can be used to reveal the thermal history of a polymeric cable since its processing. In this regard, a detailed case study is presented to highlight the use of a DSC thermogram for determining the maximum temperature experienced by a polymeric cable and the potential source of heat.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.