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The electrical degradation of cable insulation in distribution lines is due to the electrical stress caused by switching surges. During the operation, the insulation of power cables will be placed under high electrical stress, including overvoltages caused by switching. The status of power cable insulation aging is evaluated by the measurement of partial discharge level and AC breakdown voltage. The...
This paper presents results from laboratory experiments performed in order to evaluate different methods for quality control of polymeric insulated HVDC cables. In this work, we have investigated the effect of short term (24 h) DC stress followed by rapid grounding of the cable. This is comparable to a voltage step of -U0 at the point of grounding ,and depending upon the cable length, a step of up...
The differences between AC and DC aging are pointed out and are partly due to the different dissipated energy under the two types of field and partly due to the fatigue induced by the alternating stress. In addition to these effects, the sample size has also a considerable impact on both aging and breakdown. It is shown, from well known existing data, that the aging characteristics of polyethylene...
An atypical enhancement of both the dielectric properties and the static (dc) conductivity in polyimide (PI) films has been observed using isothermal dielectric relaxation spectroscopy at 300degC under air atmosphere during short-term thermal aging (up to 200h). Simultaneously, an increase of the dielectric strength of PI is observed. Despite a close similarity with the typical electrical signature...
We have shown elsewhere that the Eyring equation can describe the electrical aging of several polymers. This equation has two main activated parameters, namely the activated energy DeltaG and the activated volume DeltaV. In this paper, we confirm our previous supposition that DeltaG is related to the C-C bond strength by providing examples deduced from the electrical aging of polyethylene and polypropylene...
Utilities continue to experience electrically induced manhole events. Eighty-five percent of manhole events are caused by insulation breakdown, and 97% of the breakdowns occur on secondary cable insulation. The vast majority of manhole events involve only smoke, but a very small minority involve more serious phenomena. The restrictive conditions under which secondary cable insulation breakdown leads...
Because of its good physical properties (high ac dielectric strength and high thermal conductivity), the polycrystalline Al2O3 is used in IGBT power modules packaging as interface between the electronics device and the cooling system. The various constraints (electrical, thermal and mechanical) undergone by the Al2O3 substrates in service can lead to charge development in surface (surface discharges)...
In this report, we tried to simulate the behavior of space charge injection in low-density polyethylene (LDPE) under relatively low electric stress. In our previous paper, we found an interesting packet-like charge behavior in LDPE under high DC electric field of more than 100 kV/mm. It is thought that the huge packet-like charge must strongly affect to breakdown characteristics of LDPE. To analyze...
Presence of water droplets over the insulator surface enhances the electric field intensity and leads to electrical breakdown. This is important for outdoor insulation because the combination of moisture and contamination causes flashover at operating voltage; hence affects reliability of power delivery. Electric field has been calculated on insulating surfaces for different patterns of wetting. Simulations...
Dielectric properties of electrical insulation materials are needed for low temperature power applications. Performance of materials and their compatibility determine the size of the electrical insulation in power equipment. In this work we report the dielectric properties of some commercially available materials in sheet form. The selected materials are polypropylene laminated paper from Sumitomo...
This paper discusses the partial discharge (PD) resistant mechanism of nanocomposite enamel wires under repetitive surge voltage condition for inverter-fed motors. We focused on the reduction of deterioration depth and the surface condition of nanocomposite enamel wires after repetitive surge voltage application with successive PD. Experimental results revealed that the longer lifetime of breakdown...
Partial discharge (PD) in a void reflects degradation of insulating material and, therefore, is utilized for insulation diagnosis. Although it is well known that PD pattern changes with voltage application, it is not clear how the pattern change is related to material degradation or how it is related to final breakdown. We simultaneously observed PD characteristics and light emission from partial...
To achieve a safe operation of gas insulated switchgears (GISs), the reliability of electrical insulation is one of the fundamental importance. For this respect, there is an urgent need for better understanding of partial discharge (PD) mechanisms at different locations in GIS. In the current work, the PD inception characteristics at electrode/epoxy interface at insulating spacer in GIS, which represents...
6 to 60 kV class XLPE cables are widely used and playing important roles in power distribution and transmission systems in Japan. The aging degradation is dominated by water trees in these XLPE cables. Therefore, water tree diagnosis with high precision is quite important for operation, maintenance and replaces planning of these XLPE cables. The authors have been investigating the applicability of...
Partial discharges and corona are generally considered as unwanted processes in power systems as they are constant source of power loss and electrical noise (EMI). These effects can further develop into a major problem at the component level, causing insulation deterioration and component failure leading to possible electrical breakdown. The availability of switching power supplies operating at higher...
In this study, negative-polarity, standard lightning impulse voltages with different magnitudes were employed throughout the experiments. The percentage of SF6 in Ar was varied from 1% to 90% and from 1% to 75% at a total gas pressure of 50 kPa and 100 kPa, respectively. The breakdown voltage of each gas mixture was recorded at 50% breakdown probability. Similar to earlier studies under static electric...
Behaviors of composite insulation system are strongly affected by the performance of interface between dielectrics, which mostly correlates to the direction of applied electrical field and the frequency of applied voltage. In this paper, experiments were carried out to study the breakdown characteristics of solid composite insulation system, consisted of a polyethylene (PE) film (with a copper needle...
Electrical degradation of insulation in power cables can sometimes be associated with defects at the interface between the semiconductive shield and the dielectric insulation. The interfacial region between the semiconductive shield and insulation is a special region, which would be influenced by an evolution of the local morphological characteristics. In this study, we investigated the pre-breakdown...
To study the statistical behavior of dielectric breakdown of polymeric materials, experiments were conducted using a parallel plate electrode system for two polymeric insulating materials: low-density polyethylene (LDPE) and polyethylene terephthalate (PET). The results of the experiment were analyzed applying the Weibull distribution function. Values of median breakdown strength (BDS), shape and...
The addition of nanoscale metal oxide fillers to polymers has been shown, in many cases, to lead to an improvement in the dielectric breakdown strength and voltage endurance. In this paper, dielectric properties for silica- and alumina-filled polyamideimide (PAI) thin films are reported as a function of particle loading. The dispersion and thermal behavior are quantified. Experiments were also conducted...
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