Satoru Miyazaki

Central Research Institute of Electric Power Industry | CRIEPI · Electric Power Engineering Research Laboratory

Space charge measurement accuracy is crucial when assessing the suitability of cables for high-voltage direct current (DC) systems. This study assembled state-of-the-art analysis technologies, including time-domain deconvolution, to mark electric field estimation accuracy, which the present techniques achieve. The pulse electroacoustic method was a...

Detection of the axial displacement of power-transformer winding is important to ensure its highly reliable operation. Frequency response analysis is a promising candidate in detecting the axial displacement. However, a method of detecting the axial displacement at an incipient stage without the need for fingerprint data has not been investigated y...

Long-term stabilities of shielded resistive voltage dividers for lightning and switching impulse, employed as the reference dividers of Japan High-voltage Impulse testing Laboratory Liaison (JHILL) are investigated. The DC scale factors and the step-response parameters have been annually measured for 20 years. Annual variations of impulse parameter...

It is recommended in IEC 60060-2:2010 that measuring systems employed in high-voltage impulse tests of electric apparatuses are calibrated directly or indirectly through comparison with a national standard. Japan High-voltage Impulse testing Laboratory Liaison has attempted to establish a calibration scheme of impulse-high-voltage measuring system...

A reference measuring system for lightning impulse high voltage maintained by Japan High Voltage Impulse Testing Laboratory Liaison (JHILL) is introduced. JHILL participated in the international comparison test of lightning-impulse-voltage measuring systems organized by the European Association of National Metrology Institutes (EURAMET). From the c...

The evaluation of the failure probability is essential in the reliability‐centered and risk‐based maintenance of power transformers. The breakage of the pressboard in disc‐type transformers is one of the critical factors determining the lifetimes of power transformers. In this paper, a hierarchical method for evaluating the probability of pressboar...

This study investigated mechanical faults in oil‐immersed power transformers with disc‐type windings. Short‐circuit tests were conducted on eight aged removed transformers. Before the short‐circuit tests, accelerated aging tests were conducted on all the transformers to discuss the life limit of transformers. Six out of eight transformers experienc...

Frequency response analysis (FRA) is a widely accepted diagnostic method to assess the mechanical integrity of the active parts within a power transformer. Recent studies in the field of FRA have led to the standardization of its measurement procedure as described in the IEC and IEEE standards. However, the interpretation of FRA results is still li...

Power transformers are one of the key apparatus in electric power networks. To ensure the reliability of power transformers, the diagnosis of mechanical faults, such as the deformation and displacement of windings, is important. Frequency response analysis (FRA) has attracted considerable attention as a diagnostic method for mechanical faults of po...

Lumps of snow shed from overhead ground wires occasionally damage plastic greenhouses, vehicles and so on. The overhead ground wires are wrapped with PTFE (Poly-tetra-fluoro-ethylene) tape to prevent the accretion of the snow lumps, however, it cannot be prevented completely. In this paper, an artificial snow accretion test was performed to study o...

Transfer functions of a transformer whose winding is axially displaced are measured in several connection schemes of frequency response analysis (FRA), and the sensitivities of the measured transfer functions in these connection schemes to the axial displacement are evaluated. For the objective evaluation, some numerical indices are employed, and i...

Good repeatability of measurements of frequency response analysis (FRA) on power transformers can only be secured when selecting the same connection method of the used measuring leads as that employed in the measurement of reference data.

Frequency response analysis (FRA) is a powerful technique to detect internal abnormalities within power transformers. However, diagnosis criteria of power transformers by FRA have not been fully established yet. In this paper, a new evaluation method of degree of identification between two transfer functions is proposed. In the proposed method, a f...

Soundness confirmation of internal windings of power transformers is important for reliable operation. In urgent situations such as invasions of lightning surge and external short-circuit faults, it is important to diagnose turn shorts and/or deformation of winding. In this paper, criteria in diagnosing turn shorts or heavy deformations of transfor...

Frequency Response Analysis (FRA) is a powerful technique to detect internal abnormalities within power transformers. However, diagnosis criteria of power transformers by FRA have not been fully established yet. In this paper, an indicator of identification degree of the two transfer functions is examined using data of real transformers and problem...

Soundness confirmation of internal windings of power transformers is important for reliable operation. In urgent situations such as invasions of lightning surge and external short-circuit faults, it is important to diagnose turns short and/or deformation of winding. In this paper, criteria in diagnosing turn shorts or heavy deformations of transfor...

Frequency Response Analysis (FRA) is a powerful technique to detect internal abnormalities within power transformers. However, diagnosis criteria of power transformers by FRA have not been fully established yet. In this paper, a new evaluation method of degree of identification between two transfer functions is proposed. In the proposed method, a f...

About 50% of the high-voltage (HV) static capacitors (SC) have been operating for more than 30 years by the beginning of the 2010s. Most of them are oil-immersed paper capacitors. For their efficient maintenance and management, it is necessary to establish an on-site partial-discharge (PD) diagnosis of the capacitors. In this paper, acoustic emissi...

In order to improve the signal to noise ratio for partial discharge (PD) detection using a resistance-temperature detector laid in the stator windings of a hydropower generator, the continuous wavelet transform (CWT) is applied as a kind of time-frequency analysis. Relying on the combination of frequency resolution and time resolution using an appl...

Comparison tests between Japanese national-standard-class measuring system for lightning-impulse high voltage and reference measuring system of 5 high-voltage laboratories are carried out. The evaluated uncertainties of the measurements by the reference measuring systems are less than the requirements of IEC60060-2:2010. Furthermore, it was confirm...

In order to improve S/N ratio for partial discharge (PD) detection using a resistance-temperature detector laid in stator windings of hydro-power generator, continuous wavelet transform (CWT) is applied as a kind of time-frequency analysis. Relying on the combination of frequency resolution and time resolution using an applied power voltage phase a...

Most of the aged high-voltage (HV) power capacitors are the oil-immersed paper capacitors in Japan. Hence, it is necessary to establish an on-site partial-discharge (PD) diagnosis of the oil-immersed paper capacitors. The capacitance of the capacitors is very large, so it is difficult to apply HVAC to the capacitors. Therefore, it is difficult to p...

Partial discharge (PD) phenomena are the major factors of insulation degradation to determine the life of high voltage power apparatus, and have been investigated from various viewpoints. In this paper, authors proposed an integral equation in order to explain the complex characteristics of partial discharge using very simple three-capacitance mode...

AbstractA national‐standard‐class impulse voltage measuring system in Japan was developed in the consignment research of the Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) from 1998 to 2006. The standard measuring system for the impulse voltage measurements is managed by the J...

A circuit model of a real transformer is established to reproduce the transfer functions of the transformer. This model is based on the configuration and dimensions of the real transformer. Using this circuit model, the sensitivities of the circuit elements to the resonant frequencies are analyzed. In frequency response analysis (FRA), this sensiti...

Partial discharge (PD) phenomena are the major factors of insulation degradation to determine the life of high voltage power apparatus, and have been investigated from various viewpoints. In this paper, authors proposed an integral equation in order to explain the complex characteristics of partial discharge using very simple three-capacitance mode...

The significance of on-site insulation diagnosis has been increasing year by year to deal with tremendous amount of aged high voltage power apparatus in utility companies. On-site diagnostic methods based on partial discharge (PD) measurement using resonant high-voltage supply are promising technique because resonant power supplies are smaller, lig...

Partial discharge (PD) phenomena are the major factors of insulation degradation to determine the life of high voltage power apparatus, and have been investigated from various viewpoints. In this paper, authors proposed an integral equation in order to explain the complex characteristics of partial discharge using very simple three-capacitance mode...

In evaluating the uncertainty of the standard measuring system for lightning-impulse high voltages, which is composed of a standard voltage divider, a digital recorder, and calibrators, step-response tests of the standard voltage divider may be useful. In this paper, a convolution algorithm is employed to calculate the output impulse voltage wavefo...

Deformation and/or displacement of transformer winding are hazardous because electromagnetic force generated by a short-circuit current may increase. Frequency Response Analysis (FRA) has the possibility to detect these abnormalities with high sensitivity. In this paper, fundamentals and diagnosis method of power transformers by FRA are introduced....

Displacement and/or deformation of a coil in oil-immersed transformers are hazardous. Frequency Response Analysis (FRA) has the possibility to detect these abnormalities with high sensitivity. However, a guideline for diagnosis of transformers by FRA is not yet firmly established. In this paper, FRA is applied to seven oil-immersed transformers ins...

The authors have been developing a simple partial discharge model to analyze phase-resolved partial discharge characteristics such as ! -n characteristics. The simple model is simply based on the Whitehead's three-capacitance equivalent circuit model for partial discharges. The authors proposed an integral equation based on the fluctuation of delay...

Long-term stability of step-response parameters of the standard voltage divider may be useful in evaluating the long-term stability of the standard measuring system for high voltage impulse, which influences the uncertainty of the system . Because dispersions of the step-response parameters have been large, they have not been considered in evaluati...

Frequency Response Analysis (FRA) is capable of detecting troubles of transformers, such as deformation of winding, displacement of winding and deformation of iron core, by detecting change of transfer function. However, interpretation of the change with reference to the trouble is not clear. In this paper, an identification method of the troubles...

The influence of elevated objects, when they are hit by lightning, on the measured lightning currents and associated fields is studied. For the present study, an electromagnetic model of return strokes with the help of NEC-4 is employed. Cases of strokes to ground, to independent towers, and to a transmission line are compared and the validity of c...

Induced magnetic fields inside of a directly stricken building by lightning may cause faults, malfunctions, or data loss in electronic systems. In IEC 62305-4, the space to be protected is divided into several levels of lightning protection zones (LPZs). Steel frames of a building form a lightning protection system (LPS), and the space inside of it...

The time derivatives of the magnetic flux density and the electric field intensity associated with two rocket-triggered lightning return strokes are reproduced in the submicrosecond range by using a transmission line type model. The proposed model is based on the detailed optical observation of the attachment process. In the proposed model, return...

A lightning return stroke model is indispensable in calculating electromagnetic field associated with a return stroke. A lot of return stroke models have been proposed, however, no model has ever succeeded in reproducing all the features of typical electromagnetic field waveforms at various distances. In this paper, two return stroke models are pro...

Lightning current distribution in a directly hit building is studied by using a simple equivalent circuit and an electromagnetic model. Numerical Electromagnetic Code (NEC-4) is employed for numerical electromagnetic analysis. Error in portion of lightning current into wiring, which is calculate by the electromagnetic model, is estimated to be less...

In this short paper, a new "engineering" model of subsequent return stroke has been proposed. In the model, the propagation characteristic of a channel current follows the Diendorfer and Uman (DU) model in the bottom region but a current pulse attenuates further in the upper region. This model has succeeded in reproducing all the features of report...