Librairie technique Megger

The process of demagnetisation from the material viewpoint and its implications for transformer testing.

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.

The dielectric response of the overall transformer insulation is an invaluable source of information for those involved in the manufacture, operation and maintenance of power and distribution transformers. One of the greatest advances in the use of the transformer insulation dielectric response is without a doubt the possibility of performing advanced diagnostics of the oil-paper insulation to determine the moisture concentration of the solid insulation and the quality of the liquid insulation.

A cable replacement strategy and diagnosis method for water trees in XPLE cables has been developed at the Botkyrka 24 kV network. Measurement reports from 1996-2002 highlight improvements in age-analysis, overall effectiveness and cost.

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Times; color: #e12000} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Times; color: #797979} span.s1 {font: 12.0px Times; color: #797979} No electrical test is simpler...and few more commonly employed…than the continuity test. This simple test is a ubiquitous option on multimeters (DMMs) and insulation testers. It is simple to perform; connect two leads across opposite ends of the test item (IUT), press the test button, and within seconds you have the resistance reading. Low is good, high is bad. It’s so simple and easy that it is readily applied to testing situations that require a more rigorous performance from the test instrument. This article will examine the parameters that determine the separation between the types of instrumentation.

This paper will talk about a non-traditional method of field testing that utilises the superposition of two waveforms of dissimilar frequencies to achieve a power swing and out-of-step condition.

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.

Modern technology and developments in signal acquisition and analysis techniques have provided new tools for transformer diagnostics. Of particular interest are dielectric response measurements where insulation properties of oil-paper systems can be investigated.

Throughout this document, field experience is summarised when a three-winding transformer is removed from service and put to a series of testing procedures including DF, FDS and tip-up test on the high voltage bushings. Results of the analysis, experimental data and conclusions made based on the obtained results are presented herein.