Josh Perkel

Correlation between tan δ diagnostic measurements and breakdown performance at VLF for MV XLPE cables

The main contribution of this paper is to investigate the correlation between tan delta diagnostic measurements at 0.1 Hz (Very Low Frequency-VLF) and VLF breakdown performance for medium voltage (MV) cable samples through a laboratory test program. The cable samples used are a set of 15 kV, Cross-linked Polyethylene (XLPE), unjacketed cables removed from the field, the same service area, and having experienced similar operating conditions for almost four decades. The test program includes tan delta measurements at different voltage levels and a subsequent VLF extended step-withstand test. The VLF step test allows the evaluation of risk of failure during VLF tan delta testing and assessment of the ultimate performance of the cables. The tan delta diagnostic measurements are represented by the tan delta value and tip-up, which are considered the classical metrics. However, the paper also suggests the use of a new additional diagnostic feature that takes into account the scatter in the tan delta measurements for a particular test voltage level.

Underground Cable Systems

Underground cables have been used from the earliest time as integral parts of the power distribution and transmission system. Compared to their overhead analogues, they have been long regarded as the most critical of components due in part to their high total installed cost, their unique ampacity requirements, and the complexity of their installation. Thus, even from the very first technical papers, the sustainability, through reliability and longevity, has been of paramount importance. This contribution addresses the focus on sustainability today while maintaining a linkage to the lessons that have been already learned.

Determining routes for the analysis of partial discharge signals derived from the field

This paper discusses the experience of the National Electric Energy Testing Research and Applications Center (NEETRAC) with condition assessment of medium voltage power distribution cable systems using Partial Discharge (PD) measurements. Specifically, the main goal is to address the issue of selection of the appropriate PD diagnostic features. A large number of features for which a physical basis can be described are selected for analysis. The features are investigated using data obtained from field and laboratory tests. The investigation shows that two traditional diagnostic features are not enough to classify samples that are prone to fail in a four-year time window. Subsequently, cluster variable analysis is performed for a considerable number of PD diagnostic features. The analysis enables significant feature elimination and reveals that at least seven different types of PD diagnostic features are needed to achieve an acceptable level of dissimilarity between features. Future work, conclusions and remarks are also discussed.

Applying Diagnostics to Enhance Cable System Reliability (Cable Diagnostic Focused Initiative, Phase II)

The Cable Diagnostic Focused Initiative (CDFI) played a significant and powerful role in clarifying the concerns and understanding the benefits of performing diagnostic tests on underground power cable systems. This project focused on the medium and high voltage cable systems used in utility transmission and distribution (T&D) systems. While many of the analysis techniques and interpretations are applicable to diagnostics and cable systems outside of T&D, areas such as generating stations (nuclear, coal, wind, etc.) and other industrial environments were not the focus. Many large utilities in North America now deploy diagnostics or have changed their diagnostic testing approach as a result of this project. Previous to the CDFI, different diagnostic technology providers individually promoted their approach as the “the best” or “the only” means of detecting cable system defects.