Thịnh Đào - Academia.edu (original) (raw)

Papers by Thịnh Đào

IEEE Conference Proceedings, 2016

The effects of harmonic contamination on distribution transformer losses and temperature rise hav... more The effects of harmonic contamination on distribution transformer losses and temperature rise have become an increasing concern. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. The paper focuses on the particular effect of voltage harmonics on oil-filled distribution transformers losses. Laboratory experiments including short circuit and open circuit tests were conducted on two distribution transformers of different age. The results reveal significant increase in losses. Equations are proposed for correcting the calculation of the total transformer loss.

The effect of harmonic contamination on distribution transformer losses has become an increasing ... more The effect of harmonic contamination on distribution transformer losses has become an increasing concern over the last decade. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. In addition, many transformers have been in operation for years and service-aging also exacerbates the power losses. This paper presents a comparative study between two oil-filled distribution transformers of different age. Short circuit and open circuit tests were conducted under various voltage harmonic excitations to determine transformer electrical parameters. Results reveal sensitivity of the core load loss on voltage harmonics. Also observed is higher load loss in the aged transformer under harmonic pollution.

Ageing of transformer winding insulation is strongly temperature dependent and the problem of tem... more Ageing of transformer winding insulation is strongly temperature dependent and the problem of temperature rise in transformer during operation has been investigated. However, accurate temperature determination in transformer winding is still a challenge and the location of hottest-spot temperature in transformer also requires further studies. In this study, COMSOL Multiphysics simulation software was used to simulate an oil-filled distribution transformer, taken into account the temperature dependence of cooling fluid properties. The temperature rise in the transformer was investigated by solving the heat equations along with the equations for free convection flow. The proposed approach is able to predict the hottest-spot location as well as the hottest-spot temperature.

Iet Generation Transmission & Distribution, Nov 1, 2017

The effects of harmonic pollution in the power system on distribution transformer losses and temp... more The effects of harmonic pollution in the power system on distribution transformer losses and temperature rise have become an increasing concern. The pollution can be in the form of current and/or voltage harmonics present in the supply networks. Since the impact of voltage harmonics has hardly been investigated, this study examines the effects of distorted voltage excitation on oil-filled distribution transformers. Short-circuit and open-circuit tests were conducted on two distribution transformers. The results revealed significant increase in both losses and temperature. An equation is developed to quantify the power loss. This study also derives an equation to evaluate the resistance corresponding to the eddy-current loss.

Very low frequency (VLF) testing refers to AC testing in the frequency range of 0.01 Hz up to 1 H... more Very low frequency (VLF) testing refers to AC testing in the frequency range of 0.01 Hz up to 1 Hz. VLF testing is increasingly becoming popular as an alternative approach for test objects which require significant reactive power such as power cables. However, reliable diagnosis of partial discharge characteristics under VLF voltage excitation is still lacking. The paper presents a comparative study between testing at normal power frequency and at VLF. Corona and surface discharges were produced using a needle/bowl and a short section of 11kV XLPE cable. Experiments were conducted over a range of frequencies from 50 Hz down to 0.08 Hz and the results were analyzed. They showed some similarity of PD characteristics in terms of their phase-resolved patterns. The discrepancies of PD results are described in details.

The paper investigates the application of IEC Standard 60076-2 test procedure in determining the ... more The paper investigates the application of IEC Standard 60076-2 test procedure in determining the temperature rise in an ONAN oil-filled distribution transformer. The transformer was subjected to the heat-run tests under different voltage harmonic conditions in the laboratory. The harmonic distortion was generated by a programmable voltage source and the oil temperature was measured by distributed optical fiber sensors installed inside the transformer. The oil temperature rise and the cooling oil temperature were obtained then the hottest-spot winding temperature was determined by applying the standard. Test results showed an increase of the hottest-spot temperature when the transformer was injected with harmonic excitation. The thermal time constant was also determined and the results showed a smaller value of thermal time constant when the harmonic distortions were present. These effects will impact both the steady-state and transient thermal ratings of the transformer.

IEEE Conference Proceedings, 2016

The effect of harmonic contamination on distribution transformer losses has become an increasing ... more The effect of harmonic contamination on distribution transformer losses has become an increasing concern over the last decade. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. In this paper, an oil-filled distribution transformer was employed to run short circuit test and open circuit test. The electrical parameters of transformer were obtained and the effect of harmonics on these parameters was discussed. Also, the two-frequency method was applied to separate the no-load hysteresis loss and no-load eddy current loss.

2016 International Conference on Smart Green Technology in Electrical and Information Systems (ICSGTEIS), 2016

To investigate the effect of transformer energisation inrush, accurate modeling of the transforme... more To investigate the effect of transformer energisation inrush, accurate modeling of the transformer is vital where a mathematical model must be established for numerical calculations. This paper presents a detailed transformer modelling for the slow transients study. The PSCAD/EMTDC classical transformer combined with the Jiles-Atherton nonlinear hysteresis core model is used for modelling. The developed model enables determination of the B-H curve including consideration of the saturation effects in the magnetic material. For validation, laboratory work has been carried out. A 16kVA, 250V/11kV single phase distribution transformer is used in simulation and experimentation to obtain its magnetising inrush response. Both PSCAD simulation and experimental measurements show good agreement and thus demonstrates the capability of the model to accurately represent the energisation transient. The model shows it can generate the hysteresis loop representative of the magnetic core material. For further validation, MATLAB simulation is also developed for result comparison.

2016 IEEE International Conference on High Voltage Engineering and Application (ICHVE), 2016

This paper presents an improved transformer core modelling for slow-front transients caused by 50... more This paper presents an improved transformer core modelling for slow-front transients caused by 50 Hz line energization. Two single-phase 16 kVA, 11 kV/ 250 V oil-immersed distribution transformers with only basic nameplate data available are used for the study of magnetising and sympathetic inrush transients. Instead of using the classic Steinmetz Saturation Transformer Model as in previous study, the Jiles-Atherton model is applied which has the capability of representing minor loop operations and de-energization. Its parameters are evaluated by a series of differential evaluation algorithm with a few reasonable assumptions. Simulations of inrush current are carried out and the results compared with the experimental measurements. It is shown that improvement in accuracy is achieved with the use of the Jiles-Atherton model.

Measurement and Control, 2018

This paper deals with the eddy current technique for nondestructive evaluation of the crack depth... more This paper deals with the eddy current technique for nondestructive evaluation of the crack depth on a massive specimen used in aeronautical industry. A set of C-scan eddy current images is analyzed to reduce the noise and to select suitable features, which can be used to estimate the crack depth. Based on this study, a method relying on polynomial forward models of the relationship between crack depth and the maximum value of the sensor impedance is proposed. The least square and the non-negative least square techniques are applied to analyze the usability of proposed models. The error of obtained estimations is smaller than 10%, for almost used experimental data.

IEEE Conference Proceedings, 2016

The effects of harmonic contamination on distribution transformer losses and temperature rise hav... more The effects of harmonic contamination on distribution transformer losses and temperature rise have become an increasing concern. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. The paper focuses on the particular effect of voltage harmonics on oil-filled distribution transformers losses. Laboratory experiments including short circuit and open circuit tests were conducted on two distribution transformers of different age. The results reveal significant increase in losses. Equations are proposed for correcting the calculation of the total transformer loss.

The effect of harmonic contamination on distribution transformer losses has become an increasing ... more The effect of harmonic contamination on distribution transformer losses has become an increasing concern over the last decade. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. In addition, many transformers have been in operation for years and service-aging also exacerbates the power losses. This paper presents a comparative study between two oil-filled distribution transformers of different age. Short circuit and open circuit tests were conducted under various voltage harmonic excitations to determine transformer electrical parameters. Results reveal sensitivity of the core load loss on voltage harmonics. Also observed is higher load loss in the aged transformer under harmonic pollution.

Ageing of transformer winding insulation is strongly temperature dependent and the problem of tem... more Ageing of transformer winding insulation is strongly temperature dependent and the problem of temperature rise in transformer during operation has been investigated. However, accurate temperature determination in transformer winding is still a challenge and the location of hottest-spot temperature in transformer also requires further studies. In this study, COMSOL Multiphysics simulation software was used to simulate an oil-filled distribution transformer, taken into account the temperature dependence of cooling fluid properties. The temperature rise in the transformer was investigated by solving the heat equations along with the equations for free convection flow. The proposed approach is able to predict the hottest-spot location as well as the hottest-spot temperature.

Iet Generation Transmission & Distribution, Nov 1, 2017

The effects of harmonic pollution in the power system on distribution transformer losses and temp... more The effects of harmonic pollution in the power system on distribution transformer losses and temperature rise have become an increasing concern. The pollution can be in the form of current and/or voltage harmonics present in the supply networks. Since the impact of voltage harmonics has hardly been investigated, this study examines the effects of distorted voltage excitation on oil-filled distribution transformers. Short-circuit and open-circuit tests were conducted on two distribution transformers. The results revealed significant increase in both losses and temperature. An equation is developed to quantify the power loss. This study also derives an equation to evaluate the resistance corresponding to the eddy-current loss.

Very low frequency (VLF) testing refers to AC testing in the frequency range of 0.01 Hz up to 1 H... more Very low frequency (VLF) testing refers to AC testing in the frequency range of 0.01 Hz up to 1 Hz. VLF testing is increasingly becoming popular as an alternative approach for test objects which require significant reactive power such as power cables. However, reliable diagnosis of partial discharge characteristics under VLF voltage excitation is still lacking. The paper presents a comparative study between testing at normal power frequency and at VLF. Corona and surface discharges were produced using a needle/bowl and a short section of 11kV XLPE cable. Experiments were conducted over a range of frequencies from 50 Hz down to 0.08 Hz and the results were analyzed. They showed some similarity of PD characteristics in terms of their phase-resolved patterns. The discrepancies of PD results are described in details.

The paper investigates the application of IEC Standard 60076-2 test procedure in determining the ... more The paper investigates the application of IEC Standard 60076-2 test procedure in determining the temperature rise in an ONAN oil-filled distribution transformer. The transformer was subjected to the heat-run tests under different voltage harmonic conditions in the laboratory. The harmonic distortion was generated by a programmable voltage source and the oil temperature was measured by distributed optical fiber sensors installed inside the transformer. The oil temperature rise and the cooling oil temperature were obtained then the hottest-spot winding temperature was determined by applying the standard. Test results showed an increase of the hottest-spot temperature when the transformer was injected with harmonic excitation. The thermal time constant was also determined and the results showed a smaller value of thermal time constant when the harmonic distortions were present. These effects will impact both the steady-state and transient thermal ratings of the transformer.

IEEE Conference Proceedings, 2016

The effect of harmonic contamination on distribution transformer losses has become an increasing ... more The effect of harmonic contamination on distribution transformer losses has become an increasing concern over the last decade. This problem is caused by the widespread presence of non-linear loads and their ever-increasing proportion in the power system networks. In this paper, an oil-filled distribution transformer was employed to run short circuit test and open circuit test. The electrical parameters of transformer were obtained and the effect of harmonics on these parameters was discussed. Also, the two-frequency method was applied to separate the no-load hysteresis loss and no-load eddy current loss.

2016 International Conference on Smart Green Technology in Electrical and Information Systems (ICSGTEIS), 2016

To investigate the effect of transformer energisation inrush, accurate modeling of the transforme... more To investigate the effect of transformer energisation inrush, accurate modeling of the transformer is vital where a mathematical model must be established for numerical calculations. This paper presents a detailed transformer modelling for the slow transients study. The PSCAD/EMTDC classical transformer combined with the Jiles-Atherton nonlinear hysteresis core model is used for modelling. The developed model enables determination of the B-H curve including consideration of the saturation effects in the magnetic material. For validation, laboratory work has been carried out. A 16kVA, 250V/11kV single phase distribution transformer is used in simulation and experimentation to obtain its magnetising inrush response. Both PSCAD simulation and experimental measurements show good agreement and thus demonstrates the capability of the model to accurately represent the energisation transient. The model shows it can generate the hysteresis loop representative of the magnetic core material. For further validation, MATLAB simulation is also developed for result comparison.

2016 IEEE International Conference on High Voltage Engineering and Application (ICHVE), 2016

This paper presents an improved transformer core modelling for slow-front transients caused by 50... more This paper presents an improved transformer core modelling for slow-front transients caused by 50 Hz line energization. Two single-phase 16 kVA, 11 kV/ 250 V oil-immersed distribution transformers with only basic nameplate data available are used for the study of magnetising and sympathetic inrush transients. Instead of using the classic Steinmetz Saturation Transformer Model as in previous study, the Jiles-Atherton model is applied which has the capability of representing minor loop operations and de-energization. Its parameters are evaluated by a series of differential evaluation algorithm with a few reasonable assumptions. Simulations of inrush current are carried out and the results compared with the experimental measurements. It is shown that improvement in accuracy is achieved with the use of the Jiles-Atherton model.

Measurement and Control, 2018

This paper deals with the eddy current technique for nondestructive evaluation of the crack depth... more This paper deals with the eddy current technique for nondestructive evaluation of the crack depth on a massive specimen used in aeronautical industry. A set of C-scan eddy current images is analyzed to reduce the noise and to select suitable features, which can be used to estimate the crack depth. Based on this study, a method relying on polynomial forward models of the relationship between crack depth and the maximum value of the sensor impedance is proposed. The least square and the non-negative least square techniques are applied to analyze the usability of proposed models. The error of obtained estimations is smaller than 10%, for almost used experimental data.