Method for the reduction of in‐service instrument transformer explosions

Abstract

SUMMARYThe methodology and test procedure for the reduction of possible in-service explosions of instrument transformers to negligibly low values is described. As the introduction, an interpretation of statistical results of a survey about different types of failure in instrument transformers is given, showing that about 90% of them develop gradually, taking from several hours to several months. The International Electrotechnical Commission (IEC) is about to adopt a standardised procedure requiring that instrument transformers should withstand the effect of an internal arc. The authors are taking a critical view of the proposal; explaining its main flaws. On the basis of calculations and experimental research on models and 123 kV current transformer it is shown that the mechanism causing explosions of instrument transformers cannot be simulated well enough in the way provided for in the draft of the new IEC standard. A new concept for the reduction of explosions of instrument transformers in service called 'explosion safe' is proposed. It includes additional routine and special tests, and usage of devices for the detection or measurement of oil pressure rise in transformers. The proposed tests are based on the investigation 'Volt-Time Relationships for PD Inception in Oil-Paper Insulation'.

Effect of Proximity, Burden, and Position on the Power Quality Accuracy Performance of Rogowski Coils

“…Pressure is another quantity that is used to assess ITs’ health. For example, in [ 33 ] and [ 34 ] new techniques were developed to measure the oil pressure inside high-voltage (HV) voltage transformers (VTs).…”

Validation of a Simplified Method for Estimating the Harmonic Response of Rogowski Coils with the Monte Carlo Method

“…[ 8 ] focuses on the design of ITs for railway applications. Predictive maintenance to prevent IT faults is studied in [ 10 , 11 ]. Finally, IT calibration and characterization are tackled by authors in [ 12 , 13 ].…”

Pushing the boundaries of inductive voltage transformer design

“…The main reason for this is the fact that it encompasses design features of transformer bushings and a conventional transformer winding outline in a single enclosure [1]. Insulation requirements for such units are strict in general, because it is expected for these units to function with no insulation breakdown for an approximate lifetime of 40 years, essentially without maintenance or any other user intervention during that period [2]. These requirements, as well as prescribed tests which accompany them, are more rigorous than tests required for their power transformer counterparts and vary from standard to standard [3] - [6].…”

“…However, as far as paper-oil insulated transformers are concerned, the open-core concept adds several advantages insulation and weight wise (and especially cost wise), when higher voltages are considered. This is explained in references [1], [2], [7] and [8].…”