K.J. Cornick

Bio: K.J. Cornick is an academic researcher from University of Manchester. The author has contributed to research in topics: Partial discharge & Transformer. The author has an hindex of 4, co-authored 4 publications receiving 106 citations.

Partial Discharge Location in Power Transformers

Abstract: In a power transformer, high levels of partial discharge activity may lead to an insulation failure. If a partial discharge (PD) could be detected and located before the insulation fails, the transformer could be repaired or replaced before any consumers connected to the transformer lose supply. A technique is described in the paper that can be used to locate a PD in a power transformer with a continuous disc type winding. The technique requires knowledge about the physical geometry and design parameters of the transformer and also information about the characteristics of how the pulse or pulses caused by the PD propagate through the winding. The latter is difficult to obtain and consequently numerous simulation studies with slightly different assumptions were necessary before the technique could be considered validated. This involved analysing the data available at the terminals when a PD occurred in the winding and trying to extract the features related to the PD location. An algorithm using feature template matching has been used to locate the PD source in a 110 kV continuous disc type winding. Experimental tests carried out on this type of winding were extremely important in verifying the validity of the PD location algorithm. Results indicate that a location accuracy of better than 5% of the winding length is normally achieved.

An algorithm for partial discharge location in distribution power transformers

Abstract: Partial discharges (PDs) are a major source of insulation failure in power transformers. Techniques for locating a PD source are of major importance in both the maintenance and repair of a transformer. A technique is described for locating a PD in a distribution power transformer. To study the propagation characteristics of a PD, a simulation model was developed for the transformer winding and the PD pulse. The terminal signals caused by PDs at different locations were analysed and the features related to the location extracted. An algorithm using feature template matching was developed for locating the PD source. Experimental tests carried out on a 110 kV continuous disc-type winding have verified the validity of the location algorithm. Results indicate that a location accuracy better than 5% of the winding length is normally achieved.

A simulation model for propagation of partial discharge pulses in transformers

Abstract: Partial discharge (PD) measurement is widely accepted as a quality control test for power transformers due to its ability to detect incipient insulation faults. For further development of PD testing as a diagnostic tool, it is important to study the propagation of PD pulses in transformers. A general simulation model is necessary which should include the different construction of transformer windings. In this paper, a simulation model is introduced which is constructed in the frequency domain and which takes account of the frequency dependent characteristics of transformer windings. A description of parameter calculation methods and system solutions is given. Some simulation results are presented. The promising application of this model in the simulation study of PD's in power transformers is outlined.

Partial discharge location in power transformers using the spectra of the terminal current signals

Abstract: Partial discharges (PDs) are a major source of insulation failure in a power transformer. The accurate location of the discharge is of crucial importance in on-site maintenance and repair. For power transformers operating at 132 kV and below and having a continuous disc type winding construction, a novel approach for PD location, based on a study of how PDs propagate in a transformer winding, is presented. Experimental tests are used to show that the PD source can be located using information available in the current signals measured at the transformer terminals.

Radiometric location of partial discharge sources on energized high-Voltage plant

Abstract: Partial discharges (PD) generate wideband radio frequency interference and, consequently, can be detected using radio receiving equipment. Due to the advances in ultra-high-speed sampling equipment, it is possible to accurately measure the propagation of the PD wavefront as it passes through a 4 element antenna array. From these measurements, the three-dimensional position of the PD source can be calculated using an iterative algorithm. The locating equipment is suitable for use within the vicinity of energized high-voltage plant and can locate sources up to 15 m from the array. Results are presented showing the location ability of the equipment under laboratory and field conditions. A significant advantage is the ability to detect PD sources in energized plant without the need for outages or electrical connections.

Winding movement in power transformers: a comparison of FRA measurement connection methods

Abstract: Frequency response analysis (FRA) is an effective diagnostic tool for detecting transformer winding movements. Various FRA traces can be measured from a set of transformer winding terminals each of which relate to a different test connection scheme. Practical considerations of test and analysis time dictate that only some of the connections are used, and currently there is no standard test connection. This paper presents a comparison of three FRA measurement connections widely employed in the industry today, namely: end-to-end voltage ratio, input admittance and transfer voltage ratio measurements. Using a simulation model of a 132/11 kV, 30 MVA transformer, FRA traces were generated under these connection schemes and their sensitivity towards three types of winding movement, namely: axial displacement, forced buckling and axial bending was studied. A correlation exists between the FRA measurement results of end-to-end voltage ratio, input admittance and transfer voltage ratio connection methods, provided that the HV neutral is grounded. Among the three connection methods assessed, the transfer voltage ratio connection method has the best sensitivity to axial displacement and forced buckling, whereas the end-to-end voltage ratio method has the best sensitivity towards axial bending

Simulation of a transformer winding for partial discharge propagation studies

Abstract: A simulation model of a continuous disc type 6.6 kV transformer winding was used to study the propagation behaviour of partial discharge (PD) pulses. The model based on multi-conductor transmission line theory uses a single turn as a circuit element with the capacitance, inductance, and losses calculated as distributed parameters. Transfer functions that describe how the location of the PD source affects the current signals measured at the terminals of the winding were calculated. The paper shows how the position of the zeros in the frequency response of the measured current signals can be used to locate the source of the discharge. Sensitivity studies on the parameters of the model were used to investigate the effect of inaccuracies in the model on the position of the zeros and hence the location of the discharge.

Partial Discharge Localization in Power Transformers Using Neuro-Fuzzy Technique

Abstract: Partial discharge (PD) is the most common sources of insulation failure in power transformers. The most important tools for quality assessment of power transformers are PD detection, measurement, and classification. As for the maintenance and repair of transformers, the major importance is the techniques for locating a PD source. The transfer function-based (TF) method for power transformers' winding in the high-frequency range is commonly used in power engineering applications, such as transient analysis, insulation coordination, and in transformer design. Although it is possible to localize PD in transformer winding using the transfer function (TF) method, this method cannot be used for transformers with no design data. Previous attempts toward finding a feature that localizes PD in transformers in general that lineate with PD location were found to be less successful. Therefore, in this paper, a neuro-fuzzy technique that uses unsupervised pattern recognition was proposed to localize PD source in power transformers. The proposed method was tested on a medium-voltage transformer winding in the laboratory. The results showed a significant improvement in localizing PD for major types of PD compared to currently available techniques, such as orthogonal transforms and the calibration line method.

Frequency domain correlation technique for PD location in transformer winding

Abstract: Partial discharge (PD) is one of the sources of insulation failures in Power transformers. Knowledge of the PD source locations are important for transformer maintenance and repair. Due to the complex structure of the transformer, it is very difficult to locate the PD accurately in transformer winding. Correlation methods are applied to locate the PD source across the winding. The PD across parts of the winding are simulated by applying voltage pulse across the sections. The winding response for a reference PD impulse across transformer sections are taken as base for correlation and correlated with winding response of PD impulse across any section with different PD pulse widths. In this paper the limitation of time domain correlation method in locating PD in transformer windings is found out. To overcome the limitation of time domain correlation method, frequency domain correlation with Gram Schmidt orthogonalization is proposed. Simulation and experiments are performed on layer, continuous disc and interleaved windings to prove the feasibility of the proposed method.