C. Gonzalez-Garcia

Bio: C. Gonzalez-Garcia is an academic researcher from Carlos III Health Institute. The author has contributed to research in topics: Distribution transformer & Dielectric. The author has an hindex of 1, co-authored 1 publications receiving 96 citations.

Current Status and Future Trends in Frequency-Response Analysis With a Transformer in Service

Abstract: This paper presents the current status and future trends in the application of the frequency-response analysis (FRA) technique with the transformer in service (online) through bibliographic review and analysis. As a result, three basic stages of the online FRA test have been identified and defined: injection and excitation signal measurement; recording, filtering and processing of measured signals; and curve analysis and interpretation. This work presents an overview of the online FRA technique, useful for subsequent research in this area.

Dielectric Design of Ester-Filled Power Transformers: AC Stress Analysis

Abstract: In the last 20 years the use of ester fluids as an alternative to mineral oil for transformer insulation has been an active field of research and development. These liquids have a much lower environmental impact than mineral oils, besides reducing the transformer’s fire risk. Although the use of natural and synthetic esters is nowadays frequent for certain applications, as for distribution transformers in highly populated areas, railway transformers or off-shore windmill transformers, the experience on large and medium sized units is still reduced. One of the critical aspects that must be assessed to use esters as dielectric fluids for large size transformers is the dielectric design of the equipment. The permittivity of esters and ester-impregnated cellulose are different from those of mineral-oil-cellulose systems, what has an impact on the electric field distribution in the transformer. Additionally, in some cases, the dielectric strength of ester fluids differs from that of mineral oil. This paper presents a study about the dielectric design of ester-based power transformers. The insulation system of a 400/138 kV, 280 MVA transformer was modelled using a finite element tool and a comparison of the field distribution under 50 Hz AC power voltage of both insulation systems is provided.

Diagnostic Measurements for Power Transformers

Abstract: With the increasing age of the primary equipment of the electrical grids there exists also an increasing need to know its internal condition. For this purpose, off- and online diagnostic methods and systems for power transformers have been developed in recent years. Online monitoring is used continuously during operation and offers possibilities to record the relevant stresses which can affect the lifetime. The evaluation of these data offers the possibility of detecting oncoming faults early. In comparison to this, offline methods require disconnecting the transformer from the electrical grid and are used during planned inspections or when the transformer is already failure suspicious. This contribution presents the status and current trends of different diagnostic techniques of power transformers. It provides significant tutorial elements, backed up by case studies, results and some analysis. The broadness and improvements of the presented diagnostic techniques show that the power transformer is not anymore a black box that does not allow a view into its internal condition. Reliable and accurate condition assessment is possible leading to more efficient maintenance strategies.

Detection of Power Transformer Winding Deformation Using Improved FRA Based on Binary Morphology and Extreme Point Variation

Abstract: Frequency response analysis (FRA) has recently been developed as a widely accepted tool for power transformer winding mechanical deformation diagnosis, and has proven to be effective and powerful in many cases. However, there still exist problems regarding the application of FRA. FRA is a comparative method in which the measured FRA signature should be compared with its fingerprint. Small differences of FRA signatures in certain frequency bands might be produced by external disturbance, which hinders fault diagnosis. Additionally, the existing correlation coefficient indicator recommended by power industry standards cannot reflect key information of signatures, namely the extreme points. This paper proposes an improved FRA based on binary morphology and extreme point variation. Binary morphology is first introduced to extract the certain frequency bands of signatures with significant difference. A composite indicator of extreme point variation is adopted to realize the diagnosis of fault level. A ternary diagram is constructed by the area proportions of the binary image to identify winding faults, which has a potential to realize cluster analysis of fault types.

A Review of Frequency Response Analysis Methods for Power Transformer Diagnostics

Abstract: Power transformers play a critical role in electric power networks Such transformers can suffer failures due to multiple stresses and aging Thus, assessment of condition and diagnostic techniques are of great importance for improving power network reliability and service continuity Several techniques are available to diagnose the faults within the power transformer Frequency response analysis (FRA) method is a powerful technique for diagnosing transformer winding deformation and several other types of problems that are caused during manufacture, transportation, installation and/or service life This paper provides a comprehensive review on FRA methods and their applications in diagnostics and fault identification for power transformers The paper discusses theory and applications of FRA methods as well as various issues and challenges faced in the application of this method

Transformer winding deformation diagnostic system using online high frequency signal injection by capacitive coupling

Abstract: Transformer winding deformation is common among all sorts of transformer failures. Cumulative deformation can eventually burgeon into catastrophic faults and result in entire network outage. It is possible to detect the early signs of faults with continuous online monitoring transformer. However, frequency response analysis (FRA) is considered to be a useful and accurate tool for sufficient detection. This paper aims at proposing a novel diagnostic system for online monitoring power transformer winding deformation based on FRA. In order to realize online monitoring transformer winding, the system uses the capacitive coupling method to inject controllable nanosecond pulses, which function as the excitation signal of winding, and to obtain the response signal. This proposed method may extend frequency range for analysis and perhaps could early detect minor winding movement and looseness. Transformer experiments show great prospect in the application of the system.