Technical library

While the share of installed cables without a jacket generally continues to decrease, the unjacketed cables that remain continue to age. As they do so, it is increasingly likely that a fault will develop on these cables. It can be particularly troublesome to locate faults on unjacketed cables as normal Time Domain Reflectometry, or radar, based fault location techniques often do not work, due to the corrosion of the neutral wires. While there is no guaranteed action that would result in locating the fault, this paper will outline some advanced methods, based on field experience, that can help when locating these types of faults. This paper was an article presented at NETA in 2017 and will discuss the Impulse Current method, which does not rely on the neutral wires being intact, in both a theoretical and practical light. 

Abstract-Switching operations and direct current applied during routine testing procedures of static winding resistance measurement leave residual magnetization in the core and/or fully saturate the core of the transformer.

Dielectric Frequency Response, DFR is the extension of power factor testing except that the measurement is performed from 1 kHz down to typically 1 mHz. It is a very useful tool for evaluating the moisture content in solid insulation of HV and EHV components such as power transformers, bushings, instrument transformers and PILC cables.

This paper will provide an insight into the factors that can go wrong during micro ohm measurements and how to prevent those using a proactive approach.

Diagnostics on both MV and HV cables is used as part of commissioning tests to check the quality of workmanship of newly installed cables and accessories. This paper goes into detail to all available excitation voltages for offline PD diagnostics.

The continuously increasing installation complexity for medium voltage power cables, results in many weak spots and therewith cable failures due to bad workmanship. This is mainly caused by the large variety of cable accessories as well as the reduction in insulation thickness and therewith in the margin of error throughout the entire cable installation process. The necessity for both commissioning testing of new cables as well as diagnostic measurements as part of a condition based maintenance is just a logical given fact. Nowadays cable testing as well as condition monitoring are well proven measurement methods for MV power cables which are guided by IEEE 400 [1] and IEC 60502-2 [2] standards.

Different partial discharge defects show a different distribution in the frequency spectrum. These typical characteristics could be used in combination with the appropriate phase resolved partial discharge pattern for the analysis of partial discharge defects. The classification of the partial discharges allows an assessment of the defects in terms of its criticality.

The value of insulation resistance (IR) is strongly affected by the temperature of the material. However, in most cases IR measurements are done at the operating temperature of the given device. For this reason temperature correction is required to ensure that meaningful conclusions can be drawn from the measured values of IR

Review of IEEE, CIGRE and IEC standards for power transformer testing including overview of various frequency response analysis (FRA) techniques.

During recent years a great deal of valuable research work has been done to increase our knowledge of the properties of insulating materials, yet notwithstanding the progress so made the natural laws governing insulation resistance are but little understood.