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When a power apparatus is put into operation, temperature difference always exists in its insulation. As to HVDC insulation system, this temperature gradient may play an important role on the space charge behavior and field distribution. This report summarized our attempts to understand the effects of temperature gradient on space charge and material lifetime. Modified pulsed electro-acoustic (PEA)...
In order to study the effect of space charge on oil flow electrification under DC voltage, an experimental model with plane electrode was designed. A closed oil circulating system was built to simulate the oil path between the windings inside a converter transformer. The results reveal that polarity of streaming current depends on the sample configuration. If the high voltage electrode was covered,...
Under high DC voltage, the space charge accumulation can largely alters the local field distribution in epoxy resin. And it has been revealed that nanoparticles have great influences on space charge distribution in epoxy resin. To reveal the mechanism of nanoparticles, the effects of nanoparticles on trap depth are investigated under different temperature. In this work, epoxy resin and its nano composite...
In this paper, in order to study the effect of temperature gradient on long-term reliability of high voltage direct current (HVDC) cross-linked polyethylene (XLPE) cable insulation during actual operation, an aging device under DC electrical stress companied with temperature gradient(the high temperature side is 60°C and the low temperature side is 20°C) for multi-group film specimen were designed...
In the coaxial cable space charge measurement system based on Pulsed Electro-Acoustic (PEA) method, the coupled mode of pulse is extremely important. The space charge measurement signal has a direct relationship with the coupled pulse. In this paper, based on the method that the pulse is injected into cable from outer semi-conducting layer, the space charge waveform of 10 kV cable has been measured...
In order to restrict the field distortion in the insulation of high voltage direct current (HVDC) cable under temperature gradient, this paper proposes a nano-filler, the addition of which can restrict the space charge accumulation of low density polyethylene (LDPE) under temperature gradient. To reveal the mechanism of the nannocomposite, the trap depth distribution of the pure LDPE and LDPE nannocomposites...
In the insulation of converter transformers for HVDC transmission, the effect of space charges on field distortion is an important factor. Multilayers of oil immersed papers and oil gaps that compose paper/paper and paper/oil interfaces are used in converter transformers. The interface charge behaviors may not follow traditional Maxwell-WagnarSillars polarization law. In this report, the measurement...
Our previous studies showed that the aging parameter, i.e. the n-value, of XLPE was quite different from that of XLPE nanocomposites. In order to investigate the effects of space charge on aging parameter under DC voltage, the n-values of XLPE and its nanocomposites were measured under AC voltage in this report, because few space charge exits in the sample under AC voltage. Step-stress tests were...
Space charge accumulation in the dielectrics can greatly distort the electric field, and then greatly influence the in-situ property, degradation and breakdown properties. It is affected by several factors like electrical field, temperature and fillers. The focus of this paper is the behavior of space charge in the unfilled/filled epoxy resin under temperature gradient. In this work, neat epoxy resin...
Space charge will accumulate within polyethylene when stressed under DC high voltage, and a temperature gradient will form throughout the insulation when a HVDC cable is in service. Previous research has revealed that temperature gradient can enhance hetero charge accumulation at the low temperature end, but the high temperature only helps a small quantity of homo charge accumulate, and the mechanism...
Under high DC voltages, the space charge distribution can greatly distort the electric field and may cause premature failure of the insulation material. The development of space charge in the material is affected by several factors like electrical field, temperature and electrode materials. In this work, the pulsed electroacoustic (PEA) technique was used to measure the space charge distribution in...
The study of production, transfer and accumulation of space charge in silicon rubber (SIR) under direct current (DC) is significant for the research of new high voltage (HV) DC cable accessories and the accessories' stable operation. In this paper, based on SIR materials used for cable accessories and the actual low working stress, the accumulation of space charges in SIR was measured under low DC...
It has been reported that a temperature gradient can have a major influence upon the space charge distribution in polyethylene (PE) and oil-impregnated paper however details of the mechanism by which these modifications are produced have not yet been clarified. The experimental results for PE under a temperature gradient show clear evidence of heterocharge next to the electrodes. This feature has...
According to our former investigation on space charge properties of two layers of oil-impregnated-paper and oil, the interface charge between oil and paper showed different properties with Maxwell-Wagner theory in which macroscopic conductivity and permittivity were only taken into consideration. It is assumed that the charge barrier existing at interface was responsible for the interfacial charge...
Polyethylene (PE) and oil impregnated paper are widely used as insulation materials in high voltage power equipment however, at high voltages the space charge inside the insulating material can distort the electric field distribution and thus greatly influence aging and degradation. Moreover, there is usually a temperature gradient across the insulation when the equipment is in service, and this can...
The effect of the introduction of nano-fillers into polyethylene on space charge accumulation is usually studied in electric fields reaching 100kV/mm using thin 100 μm samples, which is much thinner than the insulation in actual HVDC cables. Our previous work showed that space charge distributions in LDPE and its nanocomposites have different thickness dependences at isothermal temperature (20 °C...
As the temperature difference exists between the inner and outer conductors of high voltage DC cables in practice, it is important to study space charge behavior under temperature gradient. However, due to the effect of temperature on the acoustic propagation, it is necessary to study the waveform recovery method in pulsed electroacoustic (PEA) measurement. In our previous study, only the effects...
The introduction of nano-fillers into polyethylene can suppress space charge accumulation. The mechanism of this phenomenon hasn't been understood clearly, and has been explained in two different ways, i.e. an interface behavior that reduces charge injection and a bulk property that affects charge migration. In order to investigate which factor determines the space charge behavior in LDPE nano-composites,...
The temperature gradient, which occurs when HVDC cable is put into operation, can lead to space charge accumulation and distort the electrical field distribution in the insulation evidently. The addition of nano filler can dimish space charges in low density polyethylene (LDPE), therefore, the electrical strength of cable can be upgraded by replacing conventional insulation with nano composites. This...
The properties of space charge and breakdown in epoxy/paper composite were studied. The results show that the breakdown voltage of epoxy/paper composite is lower than epoxy under AC voltage, but is higher under DC voltage. In order to explain this phenomenon, space charge behaviors were investigated. In the epoxy/paper composites, space charges were easily gathered at the interface of epoxy and paper...
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