In the paper a new partial discharge (PD) location technique based on acoustic emission and conventional partial discharge detection method is presented. Synergetic combination of two methods allows obtaining a high accuracy of the insulation fault location and reducing the time of measurement procedure. Several cases of practical application of the new technique for PD location in the power transformers tested in an HV laboratory and in a substation are discussed.

This article describes the design of UHF Hilbert curve fractal antenna (HCFA) specially adapted for the partial discharge monitoring system. The authors present the mathematical apparatus for calculating resonant frequencies of Hilbert fractal antenna and results of a computer simulation of the developed prototype. In the design process, the antenna’s working environment (mineral oil) and the mechanical construction of the transformer inspection window were taken into consideration as well. The article also shows the results of laboratory tests carried out in the transformer tank model with different type of partial discharge sources. Both simulations and partial discharge measurements showed that the HCFA, due to such properties as: multi-resonance, small size, low fabrication cost and high sensitivity, is an interesting alternative to other UHF probes installed in transformer inspection window

Continuous measurements of moisture content in transformer liquids open new diagnostic possibilities.

The current power cables IEC standards do not provide adequate recommendations for after-laying testing and diagnosis of offshore export and inter-array power cables. However the standards IEEE 400 and IEEE 400.4 recommend partial discharge monitored testing, e.g., by continuous or damped AC voltages (DAC). Based on the international experiences, as collected in more than 20 years at different power grids, this contribution focuses on the use of DAC for after-laying testing and diagnosis of submarine power cables both the export and inter-array cables. Higher risk of failure, long unavailability, higher repair costs, and maintenance costs imply that advanced quality control is becoming more important. The current state of the existing and drafting international standards are based on onshore experiences and not related to the actual serious problems experienced with failures on export up to 230 kV and inter-array cables up to 66 kV. The application of damped AC as a testing solution in this concern is specially discussed. The advantages of this testing technique, in combination with actual testing examples, show the findings on export and inter-array cables at offshore wind farms.

Failures of the insulation of HV power cables can occur during operation at normal voltage or as a result of a transient voltage spike due to lightning or switching. Failures may occur if localized electrical stresses exceed the dielectric strength of the insulation or if the insulation is degraded to the point that it cannot withstand the applied voltage.

By performing diagnostics on on-load tap changers by means of dynamic resistance measurements a condition diagnosis of high-speed resistor-type tap changers can result in pre-failure detection of contact degradation. It provides the measurement parameters that are most suitable for detecting these defects, such as the presence of a contact film, contact wear and pitting. The resistance curves of OLTCs are interpreted, to determine the occurring degradation mechanisms, which can be used to support strategic decisions about the maintenance or overhaul of the tap changer.