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Partial discharges (PD) are very familiar in the electrical insulation world. A phenomenon able to reveal or cause incipient failure, as well as need of maintenance, of an electrical apparatus must play a fundamental role in the development of electrical asset diagnosis and design. [ABSTRACT FROM AUTHOR]

This paper focuses on the influence of repetitive square wave voltage rise time on partial discharge pulse characteristics in the ultra-high frequency range. Paerial Discharge (PD) tests on single-point contact crossed pairs were carried out using repetitive square wave voltages with a wide range of rise times, from 200 ns to 400 μs, including also 50 Hz sinusoidal voltage waveforms. Experimental results show that rise time has a significant influence on magnitude and frequency spectrum of PD pulses. Voltages of shorter rise times generate larger PD pulses with a predominance of high frequency components in the energy spectrum. Interpretations are presented for this phenomenon. [ABSTRACT FROM AUTHOR]

This paper focuses on the limits of partial discharge apparent charge estimation and calibration using an unified approach. The fundamental problems that prevent accurate apparent charge estimates (resonances, attenuation and partial discharge pulse splitting) are tackled through this approach, highlighting the physical limitations that prevent partial discharge charge to be measured properly. The feasibility of calibration of Ultra-Wide Bandwidth measurement systems, something that is not treated in the IEC 60270 standard, is also discussed. [ABSTRACT FROM AUTHOR]

A novel method for measurement and interpretation of PD phenomena in inverter-fed motors is discussed in this paper. The interpretation of PD measurements is carried out resorting to the direct-quadrature (dq) transform of the three voltages at motor terminals at the instant a PD event occurs. New tools (the dq loci, dq Hq and dq Hn patterns) are proposed to infer PD activity in a statistical way, similar to that used under AC supply. The method has been validated through tests on motorettes. In addition, measurements on low-voltage inverter-fed motors subjected to repetitive surges till breakdown are reported to support the capability of the method to infer onsetting faults. Measurements are performed through a reliable and lightweight (thus suitable for, e.g., automotive or avionics applications) antenna coupler characterized by excellent signal-to-nose ratio. [ABSTRACT FROM AUTHOR]

This paper deals with partial discharge (PD) measurements on inverter-fed motors. They are performed by means of a broadband sensor-filter system that allows PD signal to be recorded, damping the noise generated by the commutation interference of electronic power supply. In this way, online or offline measurements can be carried out with the purpose of evaluating the presence of PDs in adjustable speed drives, which often constitute the main cause of winding insulation degradation and premature breakdown. An offline testing technique is also proposed to offer an insight into PD activity and a more precise location of PD sources. These techniques can allow improved quality control and diagnostics on power-electronic-controlled motors. [ABSTRACT FROM AUTHOR]

The aim of this paper is to infer partial discharge (PD) detection limits in extruded cables as a function of the distance between PD source and detection point. The investigation is carried out for different types of detectors, from IEC 60270-compliant to ultra-wide bandwidth systems. For this purpose, a medium voltage cable has been modeled as a transmission line with frequency-dependent parameters accounting for skin effect, dielectric and semicon characteristics. Pulse propagation through the cable has been predicted for very tong distances. Different filters have been used to simulate different detectors, emphasizing the behavior of these systems, particularly the features of sensitivity, noise rejection, PD source separation and PD source localization. [ABSTRACT FROM AUTHOR]

An investigation on partial discharge (PD) propagation in power cables is carried out in this paper with the aim of inferring limits for PD detection as a function of the distance between PD source and detector. Although this problem has not an exact solution unless noise levels are not specified, useful information concerning detectability and error in estimates are provided in this paper for both medium and high voltage polymeric cables. The issue of calibrator characteristics with respect to sensitivity detection is also tackled. [ABSTRACT FROM AUTHOR]

A new technique for partial discharge (PD) source location in cable systems is presented in this paper. Such technique, here referred to as amplitude-frequency (AF) mapping, is based on the influence of attenuation and dispersion phenomena on PD pulse time and frequency characteristics. A comparative evaluation with other two well-known location techniques, i.e., time-domain reflectometry (TDR) and arrival time analysis (ATA) is presented through working cases. The results indicate that while TDR is appropriate for short cable systems, for longer cable systems, location by AF mapping can be obtained directly from PD testing, without additional efforts. The location thus achieved is, in most cases, accurate enough to allow maintenance practices to be carried out effectively. In some cases, ATA can be necessary to refine location and resolve ambiguities. [ABSTRACT FROM AUTHOR]

The article discusses the measurement and analysis of partial discharges (PD) as the main and the most effective tool in discovering local damage and flaws in cable systems. The methods of separation which is based on the deterioration of pulse frequency and identification resulted in improved reliability of PD assessment. Therefore, it offers information that can be used to develop maintenance procedure plans which is key in cutting operational costs in utility cable network.

An experimental investigation of the behavior of partial discharges occurring in insulation cavities as a function of light irradiation conditions is presented in this paper. Partial discharge inception voltage (PDIV) measurements were performed for different irradiation conditions of the test objects (visible light, of variable intensity, ultra violet (UV) light or absence of irradiation), defect geometry and conductivity of insulating material. It is shown that changes of such factors involve con siderable alteration of partial discharge inception features, in terms of both inception voltage and delay time. Depending on applied field, defect geometry, insulating material characteristics and irradiation condition, in fact, partial discharge inception voltage may be influenced prevailingly by background radiation, as generally stated in literature, or by field-assisted electron detrapping from material. cavity interface. [ABSTRACT FROM AUTHOR]

Applications of a new methodology, aimed at the identification of defects occurring in insulation systems of HV apparatus and based on partial discharge (PD) measurements, are presented in this paper. This methodology relies upon the digital acquisition of a large amount of PD pulses and separates the acquired pulses into homogeneous sub-classes. Signal processing tools recognize the presence of noise among the different classes. Identification of basic PD source typologies (i.e., internal, corona and surface discharges) is then achieved, resorting to fuzzy algorithms. The proposed procedure is applied to measurements performed on different HV apparatus, such as cables, transformers and rotating machines. The purpose of this paper is to show that the identification process is robust, regarding the measuring circuit, and flexible, so that it can constitute an advanced tool for condition based maintenance, guiding maintenance experts in making decisions on the condition of the insulation system under test. [ABSTRACT FROM AUTHOR]

In the framework of developing defect-based life models, in which breakdown is explicitly associated with partial discharge (PD)-induced damage growth from a defect, ageing tests and PD measurements were carried out in the laboratory on polyethylene (PE) layered specimens containing artificial cavities. PD activity was monitored continuously during aging. A quasi-deterministic series of stages can be observed in the behavior of the main PD parameters (i.e. discharge repetition rate and amplitude). The evolution of the parameters reflects the physicalchemical changes taking place at the dielectric/cavity interface during the aging process. PD activity shows similar time behavior under constant cavity gas volume and constant cavity gas pressure conditions, suggesting that the variation of PD parameters may not be attributed to the variation of the gas pressure. It is speculated that the change of PD activity is related to the composition of the cavity gas, as well as to the properties of dielectric/cavity interface. [ABSTRACT FROM AUTHOR]