Ryszard Malewski

Bio: Ryszard Malewski is an academic researcher from Hydro-Québec. The author has contributed to research in topics: High voltage & Transformer. The author has an hindex of 13, co-authored 31 publications receiving 535 citations.

Impulse testing of power transformers using the transfer function method

Abstract: The transfer function of a transformer winding is deconvoluted in the frequency domain from the digitally recorded neutral current and high voltage applied during impulse tests. The integrity of the winding insulation is determined by comparing the transfer function obtained at full and reduced test voltage. Differences between the transfer function plots reveal local breakdowns in the winding that can be dissociated from partial discharges. Thus the method permits unambiguous acceptance or rejection if the transformer and, since the transfer function is theoretically immune to changes in the applied impulse, also allows evaluation of the chopped-impulse test. Some 100 windings of large HV power transformers have been tested using the transfer function method, which on several occasions has revealed transformer faults as well a test setup problems that would have been missed or misinterpreted by conventional techniques. >

Measurement of switching transients in 735 kV substations and assessment of their severity for transformer insulation

Abstract: An automatic measuring system that digitally records transients generated by EHV-transmission-system switching operations and lightning strokes has been developed. The severity of these transients was assessed by comparing them with test voltages applied to the transformers during acceptance tests. In order to quantify in-service transients with respect to the impulse-test voltages, the frequency spectra of the time-domain records were calculated and expressed as a percentage of the test level. The presence of high-frequency winding oscillations was revealed by simultaneous measurements of the bushing voltage and neutral current. The results of these measurements are presented in the form of a transfer function, which can also be used to detect winding displacements in service. >

Comparative evaluation of computer methods for calculating the best-fit sinusoid to the digital record of a high-purity sine wave

Abstract: A comparative evaluation of programs used in the “equivalent bit” test is described. Four methods of determining the best-fit sine wave were tested using computer generated data contaminated to varying degrees with white noise. These data were supplemented with actual records of sine waves obtained using fast digitizers with 6- to 12-bit resolution and record lengths of between 512 to 16 000 words. The programs were evaluated for relative accuracy, absolute accuracy, and efficiency, both in terms of how often each method converged and also of how much computer time each method took to converge.

High voltage measuring circuit coupled to the capacitive grounding tap bushing of an HV device

Abstract: A high voltage measuring circuit for broadband measurement of transient signals occurring in high voltage apparatus The measuring circuit is housed in a shielded housing having an input sensing circuit for connection to a capacitive grounded tap of the high voltage apparatus The sensing circuit is connected to an output circuit through an electrical shielded connection The measuring circuit generates output signals which are replicas of the transient signals appearing on the bushing of the high voltage apparatus The broadband of the measuring circuit extends over a frequency range of from about 1 Hz to 1 MHz and has a signal level higher than background noise

Elimination of the Skin Effect Error in Heavy-Current Shunts

Abstract: A mathematical analysis of the transient skin effect in tubular and flat conductors has led to the development of a theory of ideal heavy-current shunts immune to the measuring error caused by this effect. A general expression was derived for calculating a profile of the measuring circuit laid inside the shunt wall that would give a step response undistorted by the skin effect. A model of the new shunt ws examined with a current step; the recorded response followed the applied pulse form.

Current Sensing Techniques: A Review

Abstract: This paper provides a thorough review of state-of-the-art current sensing techniques. It catalogues the current sensors according to the underlying physical principle in order to point out their strengths and weaknesses.

Partial discharges. Their mechanism, detection and measurement

Abstract: Different partial discharge (PD) detection and measurement procedures suitable for use on cables, capacitors, transformers and rotating machines are examined and compared. Both narrow and wide bandwidth PD detectors are considered; particular attention is given in regard to their suitability to different types of electrical apparatus and cable specimens under test as well as their applicability to discharge site location and their capability to detect different forms of PD. A rather substantial portion of the discussion is devoted to the use of intelligent machines as applied to PD pattern recognition in terms of either PD pulse-height/discharge epoch (phase) distributions or discharge pulse shape attributes.

A review of the charge simulation method and its applications

Abstract: The author provides a comprehensive review of the basic charge simulation method and its various modified versions reported in the literature. Applications of the charge simulation method, alone as well as in combination with other methods, are considered. Different aspects of this method are critically examined and its potentials and limitations are identified. Possible areas of future research are outlined in order to improve the overall effectiveness of computer-aided analysis and design of high-voltage insulation devices by using the charge simulation method. >

A high frequency transformer model for the EMTP

Abstract: A model to simulate the high-frequency behavior of a power transformer is presented This model is based on the frequency characteristics of the transformer admittance matrix between its terminals over a given range of frequencies The transformer admittance characteristics can be obtained from measurements or from detailed internal models based on the physical layout of the transformer The elements of the nodal admittance matrix are approximated with rational functions consisting of real as well as complex conjugate poles and zeroes These approximations are realized in the form of an RLC network in a format suitable for direct use with the ElectroMagnetics Transient Program (EMTP) The high-frequency transformer model can be used as a stand-alone linear model or as an add-on module of a more comprehensive model where iron core nonlinearities are represented in detail >

Distance Protection Based on Travelling Waves

Abstract: A technique is presented for rapid measurement of the distance to a fault using fault initiated travelling waves. The measurement uses the time it takes a given surge to travel from the relaying point to the fault and back. A correlation technique is used to recognise the surge returning from the fault and distinguish it from other surges present on the system. For a three phase transmission line, the modal components describing the incident wave are delayed and cross-correlated against the respective components reflected by the fault. Maximum output occurs when the delay corresponds to twice the fault distance.