Provided are an envelope processor 103 , for obtaining an envelope for a detected signal; a FFT unit 104 , for converting the envelope into a frequency spectrum; a peak detector 105 , for smoothing the frequency spectrum by calculating a moving average, for further performing smoothing and differentiation for the spectrum, and detecting, as peaks, frequency points at which a sign of a differential coefficient is changed from positive to negative, for extracting peaks having a predetermined threshold value or greater, and for sorting the extracted peaks and detecting upper peaks; and a diagnosis processor T, for diagnosing an abnormality based on the detected peaks.

Abnormality diagnosing system for mechanical equipment

The suitable condition of an onload tap changer (OLTC) is essential for the operation of a power transformer. It is extremely desirable to have some indicators to assess the OLTC condition, especially if these indicators are capable of being used in an online monitoring system that does not affect the normal operation of the transformer. This paper describes a methodology by using envelope analysis based on the Hilbert transform and orthogonal decomposition of the wavelet to determine the main diagnostic parameters for power transformer OLTC condition assessment by means of vibration measurements during the tap changer operation.

Condition Assessment of Power OLTC by Vibration Analysis Using Wavelet Transform

This paper deals with the successful application of vibration analysis for circuit-breaker (CB) diagnostic testing with the aim of detecting mechanical anomalies in CB drive mechanisms and other moving parts in the interrupting chamber. An improved dynamic time warping algorithm was developed. Several case studies of defective mechanical components of SF6 power CBs equipped with hydraulic or spring-loaded drive mechanisms are presented. It is foreseen that vibration analysis can be used as a diagnostic tool for all CBs whenever mechanical anomalies are suspected.

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An Improved Vibration Analysis Algorithm as a Diagnostic Tool for Detecting Mechanical Anomalies on Power Circuit Breakers

An onload tap changer (OLTC) in suitable conditions is essential for the operation of a power transformer. It is extremely desirable to have indicators that help assess the conditions of the OLTC, especially if these indicators can be used in an on-line monitoring system that does not affect the normal operation of the transformer. This paper describes a method for detecting faults in the tap selector by means of vibration measurements during tap changer operation, using envelope analysis based on Hilbert transform and wavelet decomposition. Different failures at the tap selector can be distinguished in the vibration signature as they are reflected in different parts of that signature. The diagnosis parameters allowing the most selective failure classification are found.

Vibration Analysis Using Envelope Wavelet for Detecting Faults in the OLTC Tap Selector

It has been over two decades since the publication of pioneer works about the power transformer diagnostics based on monitoring of their acoustic fingerprints. Since then, there has been great progress in this field and the methods used are as complex as ever. Any unnecessary intervention on a power transformer implies its temporary disconnection from the power grid. The inability to supply electricity to the customer means not only financial loss for the utility but also generates a non-material loss, e.g., the loss of reputation to the customer. Faster, more accurate, more reliable, and less invasive diagnosis is the main reason behind development and improvement in this field. The main goal of this paper is to categorize and review state-of-the art of vibro-acoustic diagnostic methods for power transformers. This paper opens with a brief note about continuous condition monitoring, after which we overview the causes of transformer vibrations as well as the collection and preprocessing of diagnostic data. Then, we review and categorize works related to the acoustic condition assessment of power transformers considering both: feature extraction in the time, frequency, time-frequency domain, and mathematical modeling and system identification of dynamic systems.

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Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey

In the present method and apparatus for processing a vibro-acoustic signal (1) emitted by a high-voltage switching system, the vibro-acoustic signal (1) is converted into a digital signal (3). The digital signal (3) is rectified and the resulting rectified signal (5) is applied to a convolutional filter with a spectral window (6) to produce a smoothed signal (7). The smoothed signal (7) is decimated to produce a decimated signal (9) representing an envelope of the vibro-acoustic signal (1). A time realignment of the decimated signal (9) is carried out with respect to a reference signature (13A) to produce a realigned signal (11). Time deviation values generate an alarm if they exceed a limit threshold. The realigned signal (11) is added as a factor of means providing a reference signature (13A) and an actualized signature (13B). Variances (15A, 15B) of the realigned signal (11) are calculated with respect to the reference and actualized signatures (13A, 13B). The realigned signal (11) is compared with the actualized and reference signatures (13A, 13B) to detect a gradual behavior change or a sudden defect, taking the variances (15A, 15B) into consideration.

Vibro-acoustic signature treatment process in high-voltage electromechanical switching system

This paper presents an analysis method based on explicit dynamic analysis, enabling detailed and representative investigations of the mechanical effects of low-impedance faults in power equipment. To illustrate the effectiveness of the proposed method, a given transformer design having caused the projection of a heavy chimney/bushing assembly over a significant distance is used as a case study. A comparison about the observed projection distance of this assembly shows that the method provides representative results, thus offering the significant advantage of replacing costly and unpractical tests. The method is then used to study the retrofit measure proposed in this case to retain the chimney, further exemplifying its power to effectively study different design and retrofitting options.

Numerical Method for the Investigation of Fault Containment and Tank Rupture of Power Transformers

Vibro-acoustic diagnostic of on-load tap changers (OLTC) offer numerous advantages: applicable online, sensitive to mechanical as well as electrical malfunctions, retrofitable to old equipment, simple and low-cost. Over the last few years, Hydro-Quebec has spent considerable efforts in the development of a reliable acoustic methods for both monitoring and diagnostics, this paper describes the methodology proposed for periodic testing via a portable acoustic system. First, the process to extract the OLTC signatures from acoustic recordings is briefly discussed. Then, the measurement approach is described along with the diagnostic procedure. Finally, actual field cases of diagnostic are presented to demonstrate the capabilities and the sensitivity of the acoustic method.

On-line testing of on-load tap changers with a portable acoustic system

Vibro-acoustic signature comparison and time-warping correction with multi-scale correlation

A brief description of VIBEOL, a new computer model for the analysis of aeolian vibrations of bundled conductors, is given. Its main characteristics include the capability to treat, in the same span, different spacer-dampers, subconductors, and dampers and a calculation scheme based on the random behavior of aeolian vibrations. In addition, the model can take into account the flexural rigidity of the conductor, thus yielding more accurate estimates of conductor strains and allowing for the moments of inertia and angular stiffness of spacers, dampers and other special types of line equipment. The model has been used to investigate the effects of asymmetries of a twin ASCR conductor bundle equipped with Hydro-Quebec spacer-dampers. While differences in the rigidity of the spacer-damper articulation did not affect the control of aeolian vibration, tension differentials and bundle twist were shown to have a large influence on the reduction of vibration levels. >

Marc Foata

Papers

Vibro-acoustic signature treatment process in high-voltage electromechanical switching system

Numerical Method for the Investigation of Fault Containment and Tank Rupture of Power Transformers

On-line testing of on-load tap changers with a portable acoustic system

Vibro-acoustic signature comparison and time-warping correction with multi-scale correlation

Computer analysis of the effects of asymmetries of a two-conductor bundle upon its aeolian vibration